Ferenc Horkay, National Institutes of Health
Jun Fu, Chinese Academy of Sciences
Marc In het Panhuis, University of Wollongong
Jie Zheng, University of Akron
MilliporeSigma (Sigma-Aldrich Materials Science)
Multifunctional Materials | IOP Publishing
BM05.01: 3D Printing of Hydrogels
Marc In het Panhuis
Monday PM, November 27, 2017
Sheraton, 2nd Floor, Back Bay C
8:15 AM - BM05.01.00
Reprogrammable Transformations of Anisotropic Hydrogels with Modulated Internal Stress
Guorong Gao 1 2 , Zuxiang Xu 1 2 , Jun Fu 1 2 Show Abstract
1 Polymers and Composites Division, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo China, 2 Cixi Institute of Biomedical Engineering, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo China
Smart polymer hydrogels have been widely recognized as the materials for devices through numerous fabrication methods including 3D/4D printing. Essentially, the actuation, transformation, or motions of the hydrogel devices are driven by the internal of external stresses upon exposure to external stimuli. Therefore, it is critical to design and fabricate well-defined structures of hydrogels. Conventional methods based on multi-step synthesis enable integration of hydrogels with different properties into single devices. Recently, 3D or 4D printing of hydrogels with different responsiveness has been demonstrated powerful to create devices with delicate structures and programmable actuation behaviors. It remains challenging to convert isotropic hydrogels into anistropic or heterogeneous hydrogels in facile, versatile, and convenient methods.
Here we demonstrate two methods to generate hydrogel devices with well-defined structures that undergo predictable 3D transformations/actuations upon external stimuli.
First, by modulating the internal electrostatic attractions in a controlled manner, single hydrogels were reprogrammed to show a vast number of 2D, 3D, and 4D transformations. The hydrogels are chemically crosslinked, and reinforced through the integration of two physical interactions, i.e., host-guest association between beta-cyclodextran and adamantane moieties, and electrostatic attraction between the methylacrylate groups (COO-) and the quaternized ammonium moieties. By carefully modulating the protonation, deprotonation, evolution of salt concentration in the hydrogels, they underwent well controlled swelling/deswelling. We demonstrated a successful control of the spatial distribution and evolution of these processes. As a result, the isotropic hydrogels were converted into smart devices with well designed and controlled anisotropy. The anisotropic internal swelling drove a series of predictable and sophisticated actuations and transformations. Such properties were utilized to fabricate bio-inspired or biomimetic devices.
Second, we demonstrated a rapid fabrication of structures with local changes in crosslink density, stiffness, and responsiveness through well controlled local coordination with metal ions. By contacting iron electrodes with hydrogels with COO- groups, for example, the contact zones were further crosslinked by the released Fe3+ through COO-/Fe3+ coordination. Our studies showed that Fe3+ coordination/crosslinking significantly enhanced the crosslink density and modulus of the gels. Moreover, with the presence of NIPAM moieties in the gels, the LCST became lower than that of PNIPAM due to Fe3+ crosslinking. The changes in these important properties, when regularly localized in the gels, were utilized to create novel hydrogel devices with internal undulations in properties. Upon exposure to external stimuli, the gels experienced a series predictable 3D transformations and actuations. Manipulators were easily fabricated and demonstrated.
8:30 AM - *BM05.01.01
3D Printing of Transparent and Conductive Heterogeneous Hydrogel-Elastomer Systems
Joost Vlassak 1 Show Abstract
1 , Harvard University, Cambridge, Massachusetts, United States
Interest in stretchable electronics has grown significantly in recent years, driving a need for soft and stretchable materials that can sustain high strains and still fulfill their function in applications such as wearable sensors for health monitoring or feedback sensors in soft robotics. Many stretchable conductors exist including liquid metals, nanowires, and micro-cracked metals. Conventional strategies of incorporating hard components with soft elastomers to attain stretchability often lead to failure of the hard-soft material interface and limited stretchability. The use of gels as soft conductors, where ions are the charge carriers instead of electrons, represents an entirely different approach that has gained popularity recently. Their high stretchability, when combined with recent improvements in toughness and stiffness, enable their use as stretchable electrical conductors, capacitive strain sensors, and chemical/pH sensors. Gel-based ionic circuits thus represent a unique class of devices within stretchable electronics. Fabrication of stretchable electronics using hydrogels requires integrating hydrogels with stretchable dielectrics such as dielectric elastomers; a process thus far achieved primarily via the combination of several different manufacturing techniques. We have developed an extrusion printing technique capable of fabricating an entire ionic circuit that integrates a LiCl-doped poly(acrylamide) (PAAm) hydrogel with a poly(dimethylsiloxane) (PDMS) dielectric elastomer. By incorporating hygroscopic salts such as LiCl into the hydrogel, we are able to prepare an ionically conductive hydrogel with excellent water-retaining properties. For printing reliability, we have optimized the rheological properties of a high ionic-strength hydrogel precursor and the interfacial adhesion between PDMS and hydrogel. Printed ionic devices that consist of PAAm and PDMS exhibit outstanding mechanical and electrical stability when tested with up to 1000 cycles of uniaxial tension. We demonstrate functionality in terms of signal transmission and as a soft sensor by fabricating and characterizing an ionic cable and several strain gauges. We describe a simple method for measuring the adhesion between printed hydrogel and elastomer and present data on the stability of the PDMS/PAAm hydrogel interface.
9:00 AM - *BM05.01.02
Softer is Harder: What Differentiates Soft Robotics from Hard Robotics?
Gursel Alici 1 Show Abstract
1 , University of Wollongong, Wollongong, New South Wales, Australia
As a continuously growing field of robotics, soft robotics is the science and engineering of the robots primarily made of soft materials, components and monolithic active structures such that the soft robots can safely interact with and adapt to their environment better than the robots made of hard components. Soft robotics offers unprecedented solutions for applications involving safe interaction with humans and objects, manipulating and grasping fragile objects, crops and similar agricultural products. The progress in soft robotics will have a significant impact especially on medical applications including prosthetic limbs or devices, wearable robots, assistive devices, and rehabilitation devices. Soft materials with programmable mechanical, electrical and rheological properties, and conformable to additive manufacturing based on 3D printing are essential to realize soft robots.
In this talk, we will present on what characteristics or features differentiate the field of soft robotics from the conventional hard robotics and outline the significance of soft materials in establishing soft robotic systems. These features include built-in actuation, sensing, motion transmission and conversion mechanism, embodied intelligence, morphological computation, and compliance (i.e. softness) matching and tuning. The features should ideally be integrated into the monolithic morphology of a soft robot which should be fabricated from soft and hard materials or from a strategic combination of them. We will try to answer the challenging question of what should be the characteristics of “dream soft materials” to especially establish new actuation concepts. We expect to create a medium of discussion and interaction among the delegates attending conference and hence contribute to the establishment or consolidation of an effectual bridge between materials research and robotics research in order to deliver the expected outcomes of soft robotics in a timely manner.
10:00 AM - BM05.01.03
Investigation of Interfacial Properties in Stereolithographic 3D Printed Systems
Matthew Lampe 1 , Alan Lesser 1 , Paul van der Schaaf 2 , Andre Fuchs 2 Show Abstract
1 , University of Massachusetts Amherst, Amherst, Massachusetts, United States, 2 , BASF Schweiz AG, Basel Switzerland
The layer-by-layer nature of 3D printing processes leads to materials that have many inherent internal interfaces. These interfaces can create a real challenge for the scientific community to produce components with isotropic mechanical properties. This is especially difficult when components are loaded in a direction perpendicular to a given internal interface. Results are presented from a systematic investigation which evaluates how the interfaces resulting from stereolithographic deposition affect the fracture toughness and behavior of these materials. Controlled displacement fracture studies are conducted on samples with crack surfaces perpendicular, parallel, and orthogonal to the deposition interfaces using a specially designed test method that allows for observations of the fracture process at the deposition interface length scale. The method utilizes a Single Edge Notched Bend (SENB) test geometry combined with a loading device that applies and measures a controlled displacement along the load line of the SENB test sample. Results highlighting the anisotropic nature of the fracture process, which stems from manufacturing, will be presented. These results will also be correlated with the measured elongation at break of these materials. Additionally, the nature of the interfaces, including the thickness and relative covalent bond density, will be examined through a combination of chemical and mechanical methods and results will be discussed. A commercially available acrylic stereolithography resin, Formlab’s Clear V2, printed in the Form 2 printer with its 405nm laser, was selected for study due to its commercial relevance.
10:15 AM - BM05.01.04
3D Printing of Living Materials and Devices
Xinyue Liu 1 , Hyunwoo Yuk 1 , Shaoting Lin 1 , German Parada 1 , Xuanhe Zhao 1 Show Abstract
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Nature creates living systems (for example, biofilms, biological tissues and organs) by integrating living cells with polymeric matrices, and water. Synthetic living materials and devices have been recently developed to harness the power of living cells as active components in engineering materials and devices. Existing fabrication methods of living materials and devices usually give relatively simple structures with low spatial resolutions. Here, we demonstrate that 3D printing of multiple types of programmed bacterial cells and chemicals in hydrogel inks represents a versatile method to fabricate living materials and devices with high spatial resolution (~30 μm), complex structures, and a wide range of sizes (30 μm- 30 mm). The ink system we develop can be 3D-printed with high reproducibility and cell viability. After photocrosslinking, the functionality of 3D-printed living materials is maintained by the nutritious and robust hydrogel matrices. In addition, the design of the living materials and devices can be rationally guided by models that account for the responses of cells and matrices. We further demonstrate a functional living tattoo with printed cell-laden circuits, which can sense chemicals and deliver drugs on skin. This procedure of cell programing, structure design and 3D printing provides a simple yet powerful method for the design and fabrication of future living materials and devices.
10:30 AM - BM05.01.05
Developing Supramolecular 3D Printing Materials
Chenfeng Ke 1 Show Abstract
1 , Dartmouth College, Hanover, New Hampshire, United States
Transforming nanoscopic molecular functions, such as controlled self-assembly and stimuli-responsive behaviors, into the macroscopic scale in a predictable manner is of great interest for the development of smart materials. Developing functional materials by integrating mechanically interlocked molecules and supramolecular building blocks into a defined three-dimensional architecture will allow a rapid and effective amplification of molecular functions into macroscopic scale. This property, in turn, will allow the investigations of their macroscopic behavior and the design, synthesis, and fabrication of complex smart devices that are currently beyond our grasp as well as unleashing the great potentials of the 3D printing technology.
There is no precedent design rule, however, to facilitate the 3D printability of mechanically interlocked molecules and supramolecular building blocks. Here, we report the design and synthesis of printable polypseudorotaxane-based hydrogels that are composed of α-CD rings and Pluronic F127 axles for 3D printing. Photo-crosslinking the F127 axles after direct-writing affords polyrotaxane-based monoliths with good 3D structural integrity and mechanical stability. Disrupting such interactions by a solvent exchange enables the α-CD rings to shuttle dynamically along the axles of the polyrotaxanes, which weakens the mechanical strength of the PM and, in turn, leads to a 3D structural deformation. Re-establishing the inter-ring hydrogen bonding interactions reconstitutes the 3D structure of the PM, therefore allowing the amplification of the molecular shuttling motions of molecularly interlocked architectures into the macroscopic motion of the monolith through the conversion of chemical energy input into mechanical work.
1. (a) J.-P. Sauvage, C. Dietrich-Buchecker, Molecular catenanes, rotaxanes and knots: a journey through the world of molecular topology, John Wiley & Sons, 2008; (b) C. J. Bruns, J. F. Stoddart, The nature of the mechanical bond: from molecules to machines, John Wiley & Sons, Hoboken, New Jersey, 2017.
2. Q. Lin, X. Hou, and C. Ke, Angew. Chem. Int. Ed. 2017, 56, 4452 – 4457.
10:45 AM - BM05.01.06
Micro-Reactive Inkjet Printing of Three-Dimensional Hydrogel Structures
Mei Ying Teo 1 , Kean Aw 1 , Jonathan Stringer 1 Show Abstract
1 , University of Auckland, Auckland New Zealand
Inkjet printing, of the researched techniques for printing of hydrogels, gives perhaps the best potential control over the shape and composition of the final hydrogel. It is, however, fundamentally limited by the low viscosity of the printed ink, which means that crosslinking of the hydrogel must take place after printing. This can be particularly problematic for hydrogels as the slow diffusion of the crosslinking species through the gel results in very slow vertical printing speeds, leading to dehydration of the gel and (if simultaneously deposited) cell death. Previous attempts to overcome this limitation have involved the sequential printing of alternating layers to reduce the diffusion distance of reactive species. In this work we demonstrate an alternative approach where the crosslinker and gelator are printed so that they collide with eachother before impinging upon the substrate, thereby facilitating hydrogel synthesis and patterning in a single step. Using a model system based upon sodium alginate and calcium chloride a series of 3D structures are demonstrated, with vertical printing speeds significantly faster than previous work. The droplet collision is shown to increase advective mixing before impact, reducing the time taken for gelation to occur, and improving definition of printed patterns. With the facile addition of more printing inks, this approach also enables spatially varied composition of the hydrogel, and work towards this will be discussed.
11:00 AM - BM05.01.07
3D-Printable Hydrogel-Elastomer Device for Sensing Simulated Peripheral Nerve Signals
Charles Hamilton 1 2 , Kevin Tian 3 , Jinhye Bae 3 , Canhui Yang 3 4 , Gursel Alici 5 2 , Geoffrey Spinks 5 2 , Marc In het Panhuis 1 2 , Zhigang Suo 3 6 , Joost Vlassak 3 Show Abstract
1 Soft Materials Group, School of Chemistry, University of Wollongong, Wollongong, New South Wales, Australia, 2 ARC Centre of Excellence for Electromaterials Science, University of Wollongong, Wollongong, New South Wales, Australia, 3 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 4 State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi’an Jiaotong University, Xi'an China, 5 School of Mechanical, Materials, Mechatronic, and Biomedical Engineering, University of Wollongong, Wollongong, New South Wales, Australia, 6 Kavli Institute for Bionano Science and Technology, Harvard University, Cambridge, Massachusetts, United States
The detection of neuronal signals from humans has remained an area of importance for decades and numerous methods for detecting peripheral nerve signals have been reported in the past. Many previously reported devices to detect peripheral nerve signals rely on the use of expensive materials. Additionally, they often result in a device that is not mechanically compatible with the biological tissue and could potentially harm the organism over long periods of time . We propose a 3D-printable soft, stretchable, and transparent hydrogel-elastomer device, based on previous work , that is able to detect simulated ‘nerve’ signals. The signal is passed to a conductive hydrogel electrode through a non-contact method of capacitive coupling through polydimethylsiloxane (PDMS). We demonstrate that the device is able to detect sinusoidal waveforms passed through a simulated ‘nerve’ made from conductive hydrogel over a range of frequencies (1 kHz – 1 MHz). Analysis of signal detection showed a correlation to the electrode contact area and a Vin/Vout of larger than 10%. This provides the framework for the future development of a soft, 3D-printable, capacitive coupling device that can be used as a cuff electrode for detecting peripheral nerve signals.
 Lacour S. P., Courtine G., and Guck J., Nature Reviews Materials, 2016, 1, 1-14, DOI: 10.1038/natrevmats.2016.63
 Tian K., Bae J., Bakarich S. E., Yang C., Gately R. D., Spinks G. M., in het Panhuis M., Suo Z., and Vlassak J. J., Advanced Materials, 2017, 29, 1604827, DOI: 10.1002/adma.201604827
11:15 AM - BM05.01.08
3D Printed White Light-Emitting Diodes
Bingfeng Fan 1 2 , Yingxue Wang 4 , Yunhao Li 3 , Jun Li 3 , Yunfei Ge 3 , Gang Wang 3 Show Abstract
1 Institute of Advanced Technology, Sun Yat-sen University, Guangzhou, Guangdong, China, 2 Device and Equipment Research and Development Department, Foshan Institute of Sun Yat-sen University, Foshan China, 4 , The Pennsylvania State University, University Park, Pennsylvania, United States, 3 School of Electronics and Information Technology, Sun Yat-sen University, Guangzhou, Guangdong, China
With the development of lighting technology, white LEDs as an energy-saving light source, has a huge market and bright prospects. The improvement of white LEDs has become a hot research direction among the scientists. Meanwhile, as a new type rapid manufacturing technology, 3D printing possesses the merits of digitization and personalization. DLP (Digital Light Processing) UV curing 3D printing technology, one of the 3D printing technology, with its high precision and high-speed molding is increasingly the focus of international attention. This paper applied 3D printing to the phosphor coating of white LEDs, trying to develop a new manufacturing technique. In this letter, firstly, we described the basic theories of 3D printing and white LEDs, and the use of 3D printing in the field of electronic devices fabrication were investigated. We demonstrated the light-emitting mechanism of white LEDs and the existing coating process. The transmission model of light in the white LEDs is also established based on Mie scattering theory, which describes the absorption, excitation and scattering process of light in the phosphor layer. The possible problems in the printing of the phosphor layer were analyzed. Moreover, a model was designed to measure the dimensional resolution and distance resolution of the printing model under different parameters. To optimize the printing system, we added a one-way transmission film, reducing the effect of edge-curing. Experiments showed that with the increase in the exposure time or decrease in print layer thickness, the dimensional resolution would rise while the distance resolution would reduce, causing the augment of edge-curing effect. At last, we applied 3D printing technology to print the phosphor layer on a blue LED chip. The optical properties of two samples with different layer thickness were measured. As a result, with the increase in layer thickness, the luminous efficiency of LED increased while the optical power decreased, and the yellow light components in the spectrum increased, making the emergent light closer to white light.
11:30 AM - BM05.01.09
Microfluidic Formation, Processing and Assembly of Planar Biomaterials
Shashi Malladi 1 , Axel Guenther 1 Show Abstract
1 , University of Toronto, Toronto, Ontario, Canada
Extrusion-based approaches play a significant role in 3D printing of hard and soft materials. They often involve the deposition of a fiber-like filament via a printhead that is translated in three dimensions.
Here, we present a microfluidic approach for the one-step preparation of planar biopolymeric materials with control over composition, dimensions and tensile properties. The approach is enabled by a multilayered microfluidic printhead that is controllably translated relative to a moving surface. The printhead co-delivers biopolymer and cross-linker solutions at well-defined flow rates onto a conveyor belt. We demonstrate the compatibility of this strategy with a variety of natural and synthetic biopolymers, micro and nanoparticle payloads, as well as ionic, thermal and pH –induced gelation mechanisms. We produce homogeneous hydrogel sheets with tunable thicknesses and elastic moduli that are in good agreement with theoretical model predictions. We demonstrate the formation of stripe-patterned multimaterial sheets. Case studies serve to illustrate roll-to-roll processing of homogeneous and architected biomaterial sheets and sheet assemblies with functional characteristics.
11:45 AM - BM05.01.10
Exploitation of Electrostatic Interactions between Anionic Biopolymers and Cationic Nanoparticles for Enhanced Properties of Bioprinted Tissue Constructs
Mihyun Lee 1 , Jin Chang 1 , Marcy Zenobi-Wong 1 Show Abstract
1 , ETH Zürich, ZURICH Switzerland
Bioprinting is a promising technique which allows the fabrication of patient-customized tissue grafts as well as natural biomimetic complex tissue constructs. To print mechanically robust tissues such as cartilage, heart and skin, development of bioink materials and crosslinking strategies that facilitate high structural fidelity, mechanical strength, and biocompatibility is highly desirable. Here we present a novel strategy to enhance both printability and mechanical strength of bioinks using nanoparticle (NP)-polymer interactions. We hypothesized that cationic NPs would effectively and reversibly crosslink anionic biopolymer chains via electrostatic interactions. Commercially available amine-functionalized silica NP dispersion (NH2-NP, +33 mV, 33 nm) was utilized as cationic NPs. Ludox silica NP dispersion (Si-NP, -28 mV, 28 nm) was also tested because Si-NPs are known to improve mechanical properties of various hydrogels via non-specific interactions. Each NP dispersion was added to an established bioink comprising two clinically approved anionic polysaccharides, alginate (3 wt%) and gellan gum (3 wt%), at a final concentration of 6 wt%. Addition of either NH2-NP or Si-NP resulted in increased viscosity (both ~3 times higher than the non-added bioink (plain ink)) and enhanced shear thinning properties. Interestingly, the NH2-NP-ink exhibited much higher storage modulus (2,500 Pa) compared with the Si-NP-ink (790 Pa) or plain ink (580 Pa). Furthermore, after second crosslinking in a CaCl2 solution (100 mM, 30 min), the storage modulus of the NH2-NP-ink was enhanced by 220 % (550 kPa), whereas that of the Si-NP-ink (110 kPa) was slightly reduced compared with the plain ink (170 kPa). Poly(ethyleneimine)-functionalized Si-NP (P-NP)(+38 mV, 40 nm) was prepared as another cationic NPs and added to the bioink. Similar to the NH2-NP, addition of P-NP increased storage modulus both before (10,000 Pa) and after (190 % increase) calcium ion crosslinking, which implies the possibility of using various functional cationic nanoparticles as a crosslinker. Next, printability of the NH2-NP-ink was assessed using an extrusion-based 3D printer. Maximum printing speed increased by ~40% (20 mm/s) compared with the plain ink. Furthermore, high structural fidelity was achieved using NH2-NP-ink. Distinct individual lines were evident with no line-merging between printed layers and the swelling and shrinkage of edges were greatly suppressed during ionic crosslinking, which were attributed to high mechanical strength of the NH2-NP-ink and crosslinked construct. Finally, bovine chondrocytes were encapsulated in the NH2-NP-ink and cultured for 3 weeks. The viabilities of encapsulated cells were 94 % at day 0 and 95 % at day 21. We expect this new type of bioink formulation involving cationic NPs would contribute to applications of bioprinted tissues where enhanced mechanical properties and high structural fidelity are required.
BM05.02: Charged Polymer Systems
Monday PM, November 27, 2017
Sheraton, 2nd Floor, Back Bay C
1:30 PM - *BM05.02.01
Polyelectrolyte Association, Ion Dissociation and Solvation
Jack Douglas 1 , Alexandros Chremos 1 Show Abstract
1 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
The dynamic clustering of charged particles and polymers in solution is a ubiquitous, but poorly understood phenomenon that underpins many biological and manufacturiung processes. For highly charged particles and polyelectrolytes, the counter-ions become dissolved into the solvent but continue to associate with the polyelectrolyte, leading to the formation of a diffuse “polarizable” cloud of counter-ions around the polymers. This effect has significant implications for the function of proteins and other natural occurring polyelectrolytes, as emphasized by Kirkwood and coworkers. To probe this general phenomenon, we perform molecular dynamics simulations of a model of polyelectrolyte solutions that includes an explicit solvent and counter-ions, where the relative affinity of the counter-ions and the polymer for the solvent is tunable. We find that the dispersion energies between the solvent and the ionic species greatly influences the nature of the association between the polyelectrolyte chains. In particular, we identify conditions in which three distinct types polyelectrolyte association emerge. We rationalize these types of polyelectrolyte association based on the competitive association of the counter-ions with the solvent and the influence ion redistribution on the effective interactions between the polyelectrolytes. We calculate static and dynamic correlation functions to quantify the equilibrium structure and dynamics of these complex liquids.
2:00 PM - *BM05.02.02
Non-Linear Elasticity and Relaxation in Cells, Tissues and Biopolymer Networks
Paul Janmey 1 Show Abstract
1 , University of Pennsylvania, Philadelphia, Pennsylvania, United States
The stiffness of tissues in which cells are embedded has effects on cell structure and function that can act independently of or override chemical stimuli. Most measurements of tissue stiffness report elastic moduli measured at a single frequency and at a low strain, but tissues and the cells within them are subjected to strains that often exceed the range of linear viscoelasticity. Rheologic measurements of liver, brain, and adipose tissues over a range of shear, compressive, and elongational strains show that the viscoelastic response of these tissues differs from that of synthetic hydrogels that have similar elastic moduli when measured in the linear range. The shear moduli of soft tissues generally decrease with increasing shear or elongational strain, but they strongly increase under uniaxial compression. In contrast, networks of crosslinked collagen or fibrin soften under compression, but strongly increase shear modulus when deformed in extension. The mechanisms leading to the unusual strain-dependent rheology of soft tissues and fibrous networks do not appear to be explained by current models of polymer mechanics, but appear to relate to local and global volume conservation within the networks and tissues.
3:00 PM - BM05.02.03
Engineering Hydrophobicity of Polyelectrolyte Complexes as a Route to Fundamental Insights and New Applications
Kazi Sadman 1 , Kenneth Shull 1 Show Abstract
1 , Northwestern University, Evanston, Illinois, United States
The associative behavior of oppositely charged polyanions and polycations is a phenomenon relevant to many biological processes as well as many synthetic applications. In complex biomacromolecules, the details of the charge distribution, hydrophobic moieties and steric effects dictate the shape, conformation and ultimately the function of those molecules. In synthetic applications, the polyelectrolyte complexes can be engineered to form micelles, gels, and coatings. In all of these contexts, the dynamic ionic bonds formed between oppositely charged ions help dictate the responsiveness and properties of the final material. These dynamic bonds impart a continuum of properties to polyelectrolyte complexes (PECs), which can be accessed by controlling the extent of electrostatic association in the system. While the effects of pH and salt on the responsiveness of PECs are well known, the effects of hydrophobicity and chain architecture have not been explored in detail. Furthermore, no work has yet attempted to build a unifying mechanical picture of PECs spanning the entire spectrum of their phase behavior, from solid-like complexes to low viscosity coacervates. The present work demonstrates that by making simple amendments to the chain architecture it is possible to affect the salt responsiveness of PECs in a systematic manner. This is achieved by quaternizing poly(4-vinylpyridine) with methyl, ethyl and propyl substituents– thereby increasing the hydrophobicity with increasing side chain length– and complexing them with a common anionic polyelectrolyte, poly(styrene sulfonate). The mechanical behavior of these complexes are compared to the more hydrophilic system of poly(styrene sulfonate) and poly(diallyldimethylammonium) by quantifying the swelling behavior in response to salt stimuli. More hydrophobic complexes are found to be more resistant to doping by salt, yet the mechanical properties of the complex remain contingent on the overall swelling ratio of the complex itself, following universal swelling-modulus master curves that are quantified in this work. We demosntrate for the first time that fractional rheological models ("Spring-pots") offer a natural rheological description of polyelectrolyte coacervates, yielding new insigths behind their dynamic response and relaxation behavior, resulting in a complete mechanical picture of PECs in the process. Lastly, we extend the concepts and insights gleaned from this work for developing adanced filtration membranes capable of nano/ultra filtration of water, organic solvents, and oil water mixtures. The concept of a PEC membrane platform is introduced, which may be engineered toward a variety of filtration applications, while maintaining an environmentally benign processing method.
3:15 PM - BM05.02.04
Photo-Responsive Polyelectrolyte Multilayer Free-Standing Films with Tunable Modulus
Matthew Feeney 1 , Samuel Thomas 1 Show Abstract
1 , Tufts University, Medford, Massachusetts, United States
Layer-by-layer (LbL) self-assembly is a method of material fabrication capable of producing structurally ordered films with thicknesses in the nanometer range. Electrostatic LbL, typified by the repeated deposition of polycationic and polyanionic materials, affords films containing bilayers of oppositely charged polymeric species termed polyelectrolyte multilayers (PEMs). Films based on ion-pairing, and other relevant non-covalent interactions, have poor mechanical stability and are subject to degradation in high ionic strength or hydrolytic environments. Covalent crosslinking is a means for providing physical and chemical stability to these films. PEMs with controllable modulus through crosslinking are of interest for various applications, such as directed cell adhesion, controlled stem cell differentiation, and antifouling coatings.
This presentation will introduce photo-crosslinking PEM films based on the well-known reversible [2+2] photodimerization of coumarin moieties. A coumarin functionalized with a methacrylate pendant, prepared in two steps from 7-hydroxycoumarin, was copolymerized with 2-(dimethylamino)ethyl methacrylate via AIBN initiated free-radical polymerization. Protonation of the amine side-chains in acid provided a positive charge to the polymer, necessary to drive self-assembly with the commercial polyanion poly(acrylic acid). Coumarin incorporation was dictated by utilizing monomer feed ratios of 0%, 5%, 10%, and 25%. Interestingly, 0 and 5 % incorporation polycations did not assemble into films with PAA, highlighting the important role of hydrophobic interactions for film assembly.
Preparation of free-standing PEM films was possible through delamination of the crosslinked films from quartz substrates upon which they were deposited. Specifically, the bottom layers anchoring a film to the substrate were degraded, also by photochemical means. Dissolution of the anchoring layers through exposure to UV light, while simultaneously crosslinking the top film, led to detachment of the film from the substrate after 10 minutes of rinsing in 0.1 M sodium bicarbonate. Transfer of free-standing films to a more hydrophobic medium, such as isopropyl alcohol, afforded rigid thin films capable of measurement by dynamic mechanical analysis (DMA).
Our preliminary results suggest that increasing coumarin feed ratio and increasing UV light irradiation time have a positive correlation with the elastic moduli of the free-standing films. Additionally, the reversibility of the coumarin dimerization will allow for tunable modulus through exposure of the film to different wavelengths of light. The ability to reversibly prepare a gradient of modulus across a film would provide, for example, a reversible ability to pattern cells. Additionally, the known two-photon absorbance efficiency of coumarins opens the possibility of using lower energy photons to drive this reversible chemistry, providing conditions more suited for cell studies.
3:30 PM - BM05.02.05
Stimuli Responsive Materials—From Hydrogel to Ionogel
Xiao 'Matthew' Hu 1 2 3 Show Abstract
1 School of Materials Science and Engineering, Nanyang Technological University, Singapore Singapore, 2 Environment Chemistry and Materials Centre, NEWRI, Nanyang Technological University, Singapore Singapore, 3 Temasek Laboratories@NTU, Nanyang Technological University, Singapore Singapore
The presentation focuses on our recent and latest work concerning both fundamental and practical aspects of stimuli responsive soft matters including those responsive to multiple stimuli. A number of different but related materials to be highlighted may include (i) IPNs/semi-IPNs hydrogels of PNIPAM and their nanocomposites, (ii) CO2-responsive linear and star-shaped polymers, (iii) responsive aqueous ionic liquids, and (iv) responsive polyionic hydrogels. Last but not least, discussion will be carried out on the design, preparation and properties of thermally responsive non-aqueous polymeric ionogels. The origin of the responsive behavior of the ionogels and selection criteria of the ionic liquids and polymer are now clearly understood through systematic experimental investigation with the aid molecular dymanics simulation. Such in-depth understanding is essential becasue it may serve as a useful guide to design not only the molecular structures but also the targeted functions of these smart soft matters. Potential applications of these materials are also demonstrated.
3:45 PM - BM05.02.06
Capacitive Pressure Sensors with Micropatterned Pyramidal Ionic Gels
Sung Hwan Cho 1 , Ihn Hwang 1 , Yujeong Lee 1 , Han Sol Kang 1 , Cheolmin Park 1 Show Abstract
1 , Yonsei University, Seoul Korea (the Republic of)
The development of pressure sensor over a broad range of pressures is crucial for a future electronic skin to broaden the applicability in sensitive pressure detection from acoustic wave to dynamic human-motion. The capacitive sensors based on the capacitance change upon pressure are advantageous due to their low power consumption resulting from vertically stacked device architecture. In addition, the electrically insulating pressure sensitive materials can avoid the possible electrical leakage of a device. The capacitive sensors, however, suffer from low sensitivity because most of pressure responsive materials such as elastomers and gels have low dielectric constants which are negligibly varied upon small pressure. Here we present flexible capacitive pressure sensors incorporating micropatterned pyramidal ionic gels (MPIGs) to enable ultra-sensitive pressure detection. Our devices show superior pressure sensing performance with broad pressure sensing range from a few Pa up to 50 kPa with a fast response time of < 20 ms and a low operating voltage of 0.25 V. Since high-dielectric-constant ionic gel was employed as constituent sensing materials, an unprecedented sensitivity of 40 kPa−1 in low-pressure regime of < 400 Pa and 13 kPa−1 at the pressure range between 0.5 kPa and 5 kPa could be realized in the context of metal-dielectric-metal platform. The fast capacitance response to applied pressure and consistent device operation over multiple pressure cycles, are attributed to the elastic properties of our MPIG that results from its low modulus, surface attraction, and adhesion properties. This broad-range capacitive pressure sensor allows for efficient detection of various pressure sources from a few Pa to tens of kPa including sound wave, light weight object, jugular venous pulse (JVP), radial artery pulse, and finger touch without using any signal amplification component. We argue that our pressure sensor platform offers a simple, but robust approach to low-cost and scalable device design that enables the implementation of electronic skin in practical application such as diagnosis of cardiac and vascular disease.
4:00 PM - BM05.02.07
Multivalent Ion and Solvophobic Contributions to Polyelectrolyte Collapse
Blair Brettmann 1 Show Abstract
1 , Georgia Tech, Atlanta, Georgia, United States
Polyelectrolytes are essential materials for many biological and industrial applications, including as rheology modifiers in manufacturing, dispersants when in a brush configuration, drug delivery agents in many forms and as ion conducting layers when present as a gel. The conformation of the polyelectrolyte and the manner in which it interacts with its environment are essential to understand for successful application of these materials. It has been shown that, in the presence of multivalent ions, a polyelectrolyte undergoes a sharp collapse to a dense phase, but the interactions leading to this collapse are poorly understood. Here we use a model system, the polyelectrolyte brush, to examine the dual effects on collapse of polyelectrolytes in multivalent ionic media: solvophobic effects from the polymer backbone and electrostatic ion bridging attractions. Previous surface force experiments on opposing polyelectrolyte brushes in the presence of multivalent counterions have shown an attractive force between the brushes as they are pulled apart. Both the sharp collapse and the attractive forces indicate that there is an attractive interaction between separate polyelectrolyte chains, which is expected to be the bridging of polyelectrolyte chains by the multiple charges of multivalent ions. However, due to high levels of counterion condensation for multivalent ions, which can effectively neutralize the polyelectrolyte, solvophobic effects from the polyelectrolyte backbone must also be considered. Using a combination of theory, simulations and experiments, we demonstrate that both electrostatic bridging and solvophobic effects lead to the significant shrinkage and phase separation that occurs. This fundamental understanding of competing molecular interactions leads to better prediction of collapse transitions of polyelectrolytes in solutions, on surfaces and as gels and extends capabilities for rational design of new, stimuli-responsive materials.
4:15 PM - BM05.02.08
Using Graphene to Control Rheological Characteristics of Gels
Radha Perumal Ramasamy 2 , Miriam Rafailovich 1 Show Abstract
2 Department of Applied Science and Technology, Anna University Chennai, Chennai, Tamil Nadu, India, 1 Materials Science and Engineering, Stony Brook University, Stony Brook, New York, United States
Gels are important class of materials and have wide applications. Gel polymer electrolytes is an interesting field and has gained much scientific attention in recent years. Controlling the rheological properties of gels can benefit its applications in fields such as batteries. In this research the effect of incorporation of graphene upon the rheological properties of chitosan-gold gels is explored. The chitosan solution was prepared by adding 1% (w/v) of chitosan powder of and 1.5% (w/v) of acetic acid to double distilled water. The solution was stirred and heated at 60°C until a semitransparent thick chitosan solution was obtained. The solution was cooled to room temperature. To this solution, appropriate amounts of 1 M HAuCl4.3H2O were added to have 5 mM Au. Also graphene (grade H5 – XG Sciences) was incorporated in the gels to have 0, 10 and 20% of graphene (by weight compared to that of chitosan). The rheological and SEM measurements were made on these gels. The rheological measurements were made one day after the formation of the gels. The complex modulus for chitosan-5mM gold gels showed an increase from 100 Pa to 620 Pa as temperature increased from 25°C to 85°C. It then rapidly decreased to 36 Pa as temperature increased to 100°C. Chitosan-5Mm Au-20% graphene had a peak at 95°C. The viscosity has maximum values at 85, 90 and 95°C for graphene concentrations of 0, 10 and 20% in chitosan-5mM Au gels. Between 25 to 70°C the viscosity of chitosan- 5mM Au-10% graphene > chitosan- 5mM Au > chitosan- 5mM Au-20% graphene. Between 70 to 85°C the viscosity of chitosan- 5mM Au > chitosan- 5mM Au-10% graphene > chitosan- 5mM Au-20% graphene. Phase angle measurements showed that chitosan- 5mM Au, chitosan- 5mM Au-10% graphene and chitosan- 5mM Au-20% graphene gels had lowest values at 80, 85 and 95°C respectively. These results indicate that the rheological properties are influenced by the graphene incorporated in it. Interestingly, as graphene concentration increases to 20%, chitosan-5mM Au-20% graphene remains as a gel even at 100°C (as it has high viscosity) though chitosan-5mM Au and chitosan-5mM Au-10% graphene gels collapse at 100°C (as they have low viscosity). This indicates that graphene can be incorporated in gels to increase the temperature at which it can be operated. TEM images for graphene added to 5Mm Au solution (in room temperature) showed very less presence of gold nanoparticles. TEM images for chitosan-5Mm Au-10% graphene in room temperature (incubated for 10 days) showed presence of several sub-micron sized gold particles. Spherical, triangular and hexagonal shaped particles were observed. Some particles were as large as 500 nm. The particles were heterogeneous in sizes. TEM images for chitosan-5Mm Au-10% graphene heated to 90°C for 60 min (until the solution turned red in color) showed that uniform gold nanoparticles formed. Also gold nanoparticles attached to graphene indicating that graphene acts as nucleation site.
4:30 PM - BM05.02.09
A New Synthesis Road for Belousov Zhabotinsky Hydrogel
Baptiste Blanc 3 , Ning Zhou 1 , Bing Xu 1 , Hyunmin Yi 2 , Seth Fraden 3 Show Abstract
3 Physics, Brandeis University, Waltham, Massachusetts, United States, 1 Chemistry, Brandeis University, Waltham, Massachusetts, United States, 2 Chemical and Biological Engineering, Tufts University, Medford, Massachusetts, United States
Yoshida developed a gel in the late nineties that experiences cyclic swelling and deswelling changes without external stimuli. This self oscillating gel contains a catalyst involved in the Belousov Zhabotinsky (BZ) reaction, an oxydation-reduction cyclic reaction, leading to a cyclic change of solubility of the gel. Recently, our group reported that the amplitude of the oscillation could be enhanced by flowing the BZ reactants with the exception of the catalyst, around the gel. Our goal is now to explore in detail the consequences of advection on the oscillating behavior of this gel, by varying the size, the composition of both the gel and the surrounding media, and the flow rate. We envision this system as the building block for soft matter robots directly converting chemical energy into mechanical energy.
We focus our talk on a different synthesis method of producing the BZ gel. While our first experiment consisted of using a one step technique where the ruthenium was directly included into the gel during the polymerisation, we now use a two step process, creating the gel matrix first, then functionalizing it with the ruthenium. We use two experimental set-ups to make the gel matrix: (1) a home-made photolithographic printer with which we shine UV light with controlled size and intensity on a microfluidic chip containing solutions of the gel monomers, and (2) a molding technique which enables us to synthetize micrometer sized spherical monodisperse gel beads.
The synthesis of various BZ catalysts, as well as their incorporation into the the gel, have been explored.
4:45 PM - BM05.02.10
Hydrogel Electrolytes for Thermal Energy Harvesting
Madeleine Dupont 1 , Matthew Russo 1 , Douglas MacFarlane 2 , Jennifer Pringle 1 Show Abstract
1 ARC Centre of Excellence for Electromaterials Science, Institute for Frontier Materials, Deakin University, Melbourne, Victoria, Australia, 2 ARC Centre of Excellence for Electromaterials Science, School of Chemistry, Monash University, Melbourne, Victoria, Australia
Thermo-electrochemical cells are promising devices for converting waste heat into electricity. Low grade waste heat (<200 ○C) such as that generated via industrial processes, vehicles or the human body, is a large source of potential energy. Thermo-electrochemical cells (thermocells) can utilize this thermal energy to generate a continuous current output without producing any emissions, consuming any materials or needing to be re-charged.
Thermocells generate electrical energy via the formation of a temperature gradient between two identical electrodes which are immersed in an electrolyte solution containing both halves of a redox couple. The temperature dependence of the redox reaction gives rise to a potential difference between the electrodes, causing oxidation to occur at one electrode and reduction at the other. In these devices, the current output is continuous because the redox species which are oxidised at one electrode are then transported across the cell to the other electrode where they are reduced (and vice versa).
One promising application for thermocells is to utilise the temperature difference between the human body and the outside temperature to generate energy, which could be used to power low-power devices, such as medical devices, sensors and trackers. It is essential for such wearable thermocells to be flexible, leak-free and have low toxicity. Most current research into thermocells focusses on aqueous electrolytes, however these systems have significant limitations for wearable applications due to their liquid electrolyte being prone to leakage. Hence, the development of solidified electrolytes for thermocells is necessary to fabricate safe, wearable devices.
The most significant limitation of solid electrolytes for thermocells is their poor mass transport properties. Mass transport in thermocells, which occurs via a combination of convection, diffusion and migration, is one of the most significant factors influencing the power output. However recent developments in hydrogel electrolytes have demonstrated that power outputs approaching that of aqueous electrolytes can be achieved .
Hydrogels have already shown promising characteristics for use as an electrolyte in thermocells. However, further development and optimisation is required before they are viable for use in commercial devices. In this work, the fabrication and characterisation of a range of hydrogels for use in thermocells is reported.
1. L. Jin, G. W. Greene, D. R. MacFarlane and J. M. Pringle, ACS Energy Letters, 2016, 1, 654-658
BM05.03: Poster Session I
Tuesday AM, November 28, 2017
Hynes, Level 1, Hall B
8:00 PM - BM05.03.01
Modulating Functional Pendant Groups of Poly(ethylene glycol) Hydrogels for Refined Control of Drug Release
Mirae Kim 1 , Chaenyung Cha 1 Show Abstract
1 , Ulsan National Institute of Science and Technology, Ulsan Korea (the Republic of)
Hydrogels are highly attractive delivery vehicles for therapeutic proteins. Their innate biocompatibility, hydrophilicity and aqueous permeability allow stable encapsulation and release of proteins. The release rates also can be controlled simply by altering the crosslinking density of the polymeric network. However, the crosslinking density also influences the mechanical properties of hydrogels, generally opposite to the permeability. In addition, the release of larger proteins may be hindered below critically diminished porosity determined by the crosslinking density. Herein, the physical properties of the hydrogels are tuned independent of crosslinking density by presenting functional pendant chains. Heterobifunctional poly(ethylene glycol) monoacrylate (PEGMA) with various end functional groups is synthesized and copolymerized with PEG diacrylate (PEGDA) to engineer PEG hydrogels with pendant PEG chains. The release rates of proteins with different isoelectric points could be effectively controlled by the type and the density of functional pendant chains of the PEG hydrogels; sulfonate (negative charge), trimethylammonium chloride (positive charge), and phenyl (hydrophobic). The therapeutic potential of this hydrogel system was also validated with in vitro studies, further demonstrating its potential as refined protein delivery.
8:00 PM - BM05.03.02
Amplification of Ring Motions into Macroscale in a 3D-Printed Polyrotaxane Monolith
Qianming Lin 1 , Xisen Hou 1 , Chenfeng Ke 1 Show Abstract
1 Department of Chemistry, Dartmouth College, Hanover, New Hampshire, United States
Amplifying molecular motions to the macroscopic scale will enable the development of mechanically interlocked molecules(MIMs)-based smart devices. In solution, MIMs, more often than not, counterbalance each other’s mechanical work as a result of their random orientations, leading to no useful work macroscopically. The keys to overcome this obstacle as suggested by Stoddart et al. are controlling the spatial assembly of MIMs and synchronize their molecular motions. In addition, three-dimensional (3D) printing methods have been reported to maximize materials property difference under different states by taking advantage of their 3D geometries. Hence, integrating 3D printability into MIMs will allow effective amplification of molecular motions to macroscopic scale events. In this presentation, we report the design and synthesis of 3D printable polypseudorotaxane hydrogels (PRHs), which are composed of α-cyclodextrins (α-CDs) and Pluronic F127. The hydrogen-bonding interactions between the CDs and formed crystalline domains allow PRHs to possess appropriate shear-thinning and self-healing properties to facilitate their 3D printability. The PRHs are fabricated into woodpile-lattice cubes, and photo-crosslinked to afford polyrotaxane monoliths (PMs). Through solvent exchange-induced hydrogen-bonding deformation/formation, the CD rings on the polymer axles switch between the shuttling and stationary states. Since the 3D structural integrity is stabilized by the hydrogen-bonding network, disrupting or re-establishing such ring interaction will dynamically control the shape deformation and reconstitution of PMs in three dimensions. In addition, PMs are capable of lifting objects vertically against gravity, thus converting the chemical energy input into mechanical work. Our work demonstrates a general approach to control the macroscopic motions through molecular motions in MIMs and to perform useful mechanical work at macroscale.
8:00 PM - BM05.03.03
Cytokines Profiles of the Protein Corona Formed by Chitosan Nanoparticles
Majed Majrashi 1 Show Abstract
1 , King Abdulaziz City for Science and Technology (KACST), Riyadh Saudi Arabia
Targeting immune cells and their products may open new avenues for treating inflammatory diseases such as septic shock. The Immune response modulators decorating the surfaces of chitosan nanoparticles (CS-NPs) were investigated using RAW 264.7 macrophages as a model cell line.
All prepared NPs were characterized via dynamic light scattering (DLS). Proteome-mapping techniques that include one-dimensional gel electrophoresis, liquid chromatography, and tandem mass spectrometry.
Our proteome-mapping analysis identified 3 unique proteins involved in immune modulation. Indeed, chemisorption of the identified proteins can be controlled when coating CS NPs with a layer of hyaluronic acid (HA-CS NPs). Our strategy was able to differentially chemisorb proteins for the successful synthesis of either immune activating- or immune suppressing-surfaces. We have observed small or negligible production of inflammatory cytokines (TNF-α, IL-1β) and NO (measured as nitrite) upon treating cells with the immune suppressing-surfaces relative to controls.
8:00 PM - BM05.03.04
Facile Access to Robust Self-Healing Hydrogels
Cai-Feng Wang 1 , Qing Li 1 , Feng-Xiang Wang 1 , Chao Yu 1 , Yuan Fang 1 , Guan Wu 1 , Su Chen 1 Show Abstract
1 State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemical Engineering, Nanjing Tech University, Nanjing China
Self-healing conception has aroused global scientific and industrial interests. This property can furnish a range of structural and functional materials with the capability to repair themselves after damage, which prolongs the lifespan of materials and reduces replacement costs. However, the input of external stimuli is required in most current available routes to self-healing materials, and the challenge still remains to fabricate hydrogels with autonomic healing ability as well as good performance. To this end, our recent efforts have been devoted to the fast preparation, self-healing capacity and multifunction of hydrogels. We have developed the fast syntheses of hydrogels within 15 minutes via frontal polymerization. We have thoroughly investigated the experimental parameters on the morphology and properties of hygrogels, yielding series of poly(vinylimidazole)-, polyacrylate- and poly(vinylpyrrolidinone)-based hydrogels with good performance. Specifically, we have quickly fabricated supramolecular hydrogels β-cyclodextrin/poly(N-vinylimidazole-co-2-hydroxypropyl acrylate) within 5 minutes via magnetically induced frontal polymerization. Such hydrogels have autonomic healing capacity and good mechanical strength, to show 95% of healing efficiency, 1.25 × 105 Pa of stress intensity, and the elongation at break over 967 %, respectively. Moreover, with combination of some functional groups in polymer chains, series of multi-responsive and auto-healing hydrogels have been achieved. We have also studied the potential applications of the as-prepared hydrogels. These works may bring a new insight into fabricating versatile smart materials with self-healing ability and desired performance.
8:00 PM - BM05.03.05
Static and Stimuli Responsive Polymer Nanogels Derived from Hyperbranched Polyglycerols (HPG)—A Simple Approach for Material Encapsulation and Delivery
James Iocozzia 1 , Zhiqun Lin 1 Show Abstract
1 , Georgia Institute of Technology, Atlanta, Georgia, United States
Hyperbranched polyglycerols (HPG) are an attractive class of water soluble nonlinear highly branched polymers composed of many ether linkages and hydroxyl groups possessing a high degree of functionality. These properties make it an attractive material for soft polymeric nanogels. Unlike perfect dendrimers, which are tedious to produce in large quantities at larger generation sizes (sequential protection-deprotection chemistry), HPG possesses several advantages. First, it can be made in a one-pot reaction with fairly well-controlled molecular weights and polydispersities now obtainable. Second, the inner ether-rich core of HPG can be used to coordinate various compounds and precursors with varying degrees of binding affinity. Lastly, HPG possesses biocompatibility analogous to poly(ethylene glycol) (PEG). In this work, HPG is esterified with primary and tertiary bromides to produce HPG-based macroelectrophiles and ATRP macroinitiators with high degrees of functionality. The HPG macroelectrophile is functionalized with azide to produce HPG-N3 which can undergo UV-induced intramolecular coupling to produce static crosslinked unimolecular HPG nanogels which can coordinate metallic precursors as well as various organic molecules. The HPG macroelectrophile can also be crosslinked with bipyridine derivatives to produce nanogels with sizes of several tens of nanometers that are responsive to light, pH, and the local chemical environment. The ATRP HPG macroinitiator (HPG-Br) is used to grow various star-like polymers including polystyrene (PS), poly[(oligoethylene)9 methyl ether methacrylate) (PEOMEM), and poly(chloromethyl styrene) with added functional crosslinker molecules. These HPG-based star polymers can also be used to developed nanogels with crosslinked shells with the potential for encapsulating drug analogues. The work presented herein suggests the great potential of HPG-based nanomaterials (i.e. nanogels, networks and coatings) whereby simple chemical treatments allow for a diverse range of applications in areas including hard and soft nanomaterials, surface antifouling, biocompatible carriers and chelation chemistry.
8:00 PM - BM05.03.06
Microstructure and Load Bearing Properties of Cartilage
Ferenc Horkay 1 , Emilios Dimitriadis 2 , Iren Horkayne-Szakaly 1 , Peter J. Basser 1 Show Abstract
1 , National Institutes of Health, Bethesda, Maryland, United States, 2 NIBIB, National Institutes of Health, Bethesda, Maryland, United States
Cartilage is a load-bearing tissue located at joint surfaces. It can be viewed as a fiber-reinforced, highly permeable composite gel filled with physiological salt solution. The unique properties of cartilage originate from the architecture and organization of its extracellular matrix (ECM). Cartilage ECM consists of a fibrous collagen network, which is prestressed by the osmotic swelling pressure exerted by negatively charged proteoglycan (PG) assemblies embedded in the collagen network. The major PG is the bottlebrush-shaped aggrecan, which, interacting with linear hyaluronic acid (HA) chains and a link protein form large aggregates (size > 1 mm) imbedded in the fibrous collagen network. The charged groups in the PG molecules favor hydration. Tissue swelling is constrained by the collagen network. At equilibrium the osmotic swelling pressure of the aggrecan–HA complexes is balanced by the elastic stress developed in the collagen matrix. The load-bearing ability of cartilage is governed by the swelling pressure that depends on the concentration of the main macromolecular components (aggrecan-HA complex and collagen) of the ECM and the interactions between them.
There is a fundamental need for characterization of the morphology and mechanical properties of biological tissues. This is essential not only for a better understanding of tissue behavior, but also to provide a framework for the design of novel biomaterials with well-defined end properties for specific biomedical applications. We investigate the mechanical and thermodynamic properties of cartilage. We determine the interactions between the main macromolecular components of cartilage ECM using an array of experimental techniques (osmotic swelling pressure measurements, small-angle X-ray scattering, small-angle neutron scattering, and dynamic light scattering). We map the elastic modulus of cartilage at the nanoscale using the Atomic Force Microscope (AFM). AFM based elastic modulus mapping allows us to determine surface stiffness and to characterize tissue heterogeneity. This knowledge is critically important to understand biological function and develop successful tissue engineering strategies for cartilage repair.
8:00 PM - BM05.03.07
Osmotic Muscle—Development of a Innovative Soft Actuator Based on Fast Swelling Gels
Vincent Mansard 1 Show Abstract
1 , CNRS LAAS, Toulouse France
we present the development of a bio-inspired soft actuator that we call the osmotic muscle. The study of innovative actuators – often called artificial muscles- is an emergent field. This actuator will replace electrical motors that are currently poorly adapted for robotics or for medical prostheses.
This artificial muscle is based on the synthesis of a new mechanically active material: a swelling macroporous gel. We use gels, which can reversibly swell. This swelling is driven by the osmotic pressure and is controlled by the pH. Up to now, long swelling times limited the development of gel actuators. Swelling is due to diffusion - a slow process - of solvent in gel. To reduce the swelling time below 1s, we give the gel a porous structure with pores size about 1 to 10µm. The swelling macroporous gel is a new material, which offer a new approach to convert chemical energy to mechanical energy. We then realize an actuator based on this material by developing a mechanical structure -inspired by pneumatic muscle- converting the 3D swelling into a directed actuation.
8:00 PM - BM05.03.08
Development of a Freshness-Retaining Package System with Hydrogels for Japanese Brand Fruits Using 3D Printer
Yoshihiro Deguchi 1 , Jin Gong 1 , Masato Makino 2 , Tomoya Higashihara 1 Show Abstract
1 Graduate School of Organic Materials Science, Yamagata University, Yonezawa, Yamagata, Japan, 2 Graduate School of Science and Engineering, Yamagata University, Yonezawa, Yamagata, Japan
Yamagata prefecture in Japan is very famous for agricultural productions of some brand Yamagata cherries (“Sato-nishiki”, “Benishuhou”, etc.) and grapes (Muscat). They may become popular products even in the emerging online retailers, covering worldwide markets day by day. Unfortunately, there is a technical limitation in overseas transportation because they are easily damaged from various stresses (e.g., impact, frequency, high temperature and low humidity) during the exportation. In the previous work, a new package system called Fulltector® (KOBAYASHI, co., ltd.) has been developed for freshness-preservation of cherries. The system showed impact/vibration-resistances derived from the presence of a hole tray to fix the position of cherries and stretchable polyethylene (PE) films to gently sandwich them. Indeed, the system reduced the rate of damaged cherries by 15% in the exporting test from Yamagata, Japan to Hong Kong. In order to establish the package system displaying the reliable freshness-retaining functions, alternative new approach should be demanded.
In this work, a novel freshness-retaining package system for Japanese brand fruits has been developed using a 3-D printer and hydrogel materials to realize the ability of impact/vibration-resistances, cooling effect and humidity control. The proposed package for Yamagata cherries consists of a synthesized hydrogel seat and a silicone seat with some certain holes. The hydrogel material plays an important role for controlling the high humidity and low temperature inside. On the other hand, the soft silicone material is for impact/vibration-resistance. In practice, the test export has been performed of Yamagata cherries (“Benishuhou”, 2L (mean diameters: 25 mm), 32 kg, cool chains of tracks and airplane transportation (<10 °C), 7 days (July, 2016)) from Yamagata, Japan to Taipei, Taiwan. The freshness of exported cherries was evaluated for new and conventional packages using typical freshness-indices established. They include damages from impact/vibration and from temperature/humidity. The former is related to the occurrence of peduncle come off, bruise and water core. The latter is related to the wilted peduncle and brightness. As a result of the test export, the proposed packages recorded much better freshness-retaining function than the conventional one in almost all freshness-indices. Especially, it was found the size matching of cherries with the 3D shape of the silicon sheet was important to fix the cherries during the export, improving the freshness-retaining functions. Furthermore, it was revealed that the proposed package suppressed the spoiled cherries to almost 0% even after the 7 days test export (normally limit times are 3-4 days for Yamagata cherries).
8:00 PM - BM05.03.09
Developing Polypseudorotaxane-Based Slide-Ring 3D Printing Materials
Haoyi Wang 1 , Chenfeng Ke 1 Show Abstract
1 , Dartmouth College, Hanover, New Hampshire, United States
Mechanically interlocked molecules (MIMs) possessing interesting molecular motions such as ring spinning, switching and etc., have inspired the development of MIM-based functional materials. In early 2000, Ito et al.  crosslinked the ring components of cyclodextrin(CD) based polyrotaxanes and synthesized the so-called ‘slide-ring’ materials. Upon solvent swelling or mechanical stretching, the threaded rings can translocate in response to the external stimuli via sliding motions, hence exhibiting outstanding mechanical properties with high toughness and stretchability. Incorporating slide-ring architectures to 3D printing materials will further promote its performance by taking advantag of designed 3D geometries. However, current design of synthesizing slide-ring material is not compatible with the rheological requirement of direct-write 3D printing technique, since the slide-ring material is still a densely covalent cross-linked hydrogel, where the stoppers of the polyrotaxanes restrict the ring translocation to a certain extend.
Presented in this poster, we plan to fundamentally redesign the polymer network in order to overcome this obstacle by introducing multiple kinetic barriers to facilitate the 3D printability. Hydrogels possessing three-dimensional network are formed by threading the ring components of a β-CD-co-dimethylacrylamide polymer onto a pluronic block copolymer. Upon shearing, the ring shuttling as well as the dethreading/rethreading motions enable the network deformation without breaking a covalent bond, therefore providing suitable rheological properties for direct-write 3D printing. The fabricated material is post-synthetically modified to introduce kinetic barriers. In contrast to the as-printed monolith which is soluble in DMSO, the post-modified material is stable after soaking in DMSO for 2 weeks. By using multiple kinetic barriers as “speed bumps”, the extend psedorotaxane structure can be partially deformed but recover after the removal of external force. Our preliminary results have demonstrated a new strategy to incorporate slide-ring architecture into 3D printing materials, more investigations are currently ongoing in the lab.
 C. J. Bruns, J. F. Stoddart, Wiley, The Nature of the Mechanical Bond: From Molecules to Machines, 2016, ISBN: 978-1-119-04400-0
 K. Ito, K. Kato, K. Mayumi, Royal Society of Chemistry, Polyrotaxane and Slide-Ring Materials, 2015, ISBN: 9781849739337.
Q. Lin, X. Hou, C. Ke, Angew. Chem., Int. Ed. 2017, 56, 4452-4457.
 P. R. Ashton, I. Baxter, M. C. T. Fyfe, F. M. Raymo, N. Spencer, J. F. Stoddart, A. J. P. White, D. J. Williams, J. Am. Chem. Soc. 1998. 120, 2297 - 2307.
8:00 PM - BM05.03.10
Graphene-Nanoplatelet-Doped Biodegradable Polymer Composite for 3D Printing Multidrug-Eluting Coronary Stent
Santosh Misra 1 2 , Fatemeh Ostadhossein 1 2 , Ramya Babu 1 , Joseph Kus 1 , Divya Tankasala 1 , Andre Sutrisno 1 , Kathy Walsh 1 , Corinne Bromfield 1 , Dipanjan Pan 1 2 Show Abstract
1 , University of Illinois at Urbana Champaign, Urbana, Illinois, United States, 2 Mills breast cancer Institute, Biomedical Research Center, Urbana, Illinois, United States
A biodegradable polymer–carbon composite is prepared doped with graphene nanoplatelets to achieve controlled release of combinatorics as anticoagulation and antirestenosis agents. Patients with percutaneous coronary intervention generally receive either bare metal stents or drug-eluting stents to restore the normal blood flow. However, due to the lack of stent production with an individual patient in mind, the same level of effectiveness may not be possible in treating two different clinical scenarios. This study introduces for the first time the feasibility of a patient-specific stenting process constructed from direct 3D segmentation of medical images using direct 3D printing of biodegradable polymer–graphene composite with dual drug incorporation. This study develops a technology prototyped for personalized stenting. An in silico analysis is performed to optimize the stent design for printing and its prediction of sustainability under force exerted by coronary artery or blood flow. A holistic approach covering in silico to in situ–in vivo establishes the structural integrity of the polymer composite, its mechanical properties, drug loading and release control, prototyping, functional activity, safety, and feasibility of placement in coronary artery of swine.
Ferenc Horkay, National Institutes of Health
Jun Fu, Chinese Academy of Sciences
Marc In het Panhuis, University of Wollongong
Jie Zheng, University of Akron
MilliporeSigma (Sigma-Aldrich Materials Science)
Multifunctional Materials | IOP Publishing
BM05.04: Printing of Polymers
Tuesday AM, November 28, 2017
Sheraton, 2nd Floor, Back Bay C
8:00 AM - BM05.04.01
Stereolithographic 3D Printing of Alginate-Graphene Oxide Microstructures
Thomas Valentin 1 2 , Po-Yen Chen 3 , Luke Morales 1 , Eric DuBois 1 , Lauren Stephens 1 , Ian Wong 1 2 Show Abstract
1 Center for Biomedical Engineering, Brown University, Providence, Rhode Island, United States, 2 Institute for Molecular and Nanoscale Innovation, Brown University, Providence, Rhode Island, United States, 3 Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore Singapore
Additive manufacturing of composite polymer-nanomaterial hydrogels may enable designer mesoscale architectures with enhanced physicochemical functionality. For instance, graphene oxide is a 2D material with exceptional tensile strength that behaves as a soft material “building block” with the optoelectronic properties of hard materials. An intriguing 3D printing approach is stereolithography-based photopatterning, which can enable complex structural geometries and do not require optimization of material rheology. Here, we show that composite alginate-graphene oxide microstructures can be printed on demand by ionic crosslinking. Our approach is based on the selective illumination of photoacid generators (PAG) in the presence of insoluble cationic salts. Remarkably, both alginate and graphene oxide can be crosslinked by ions alone, resulting in composite hydrogels with enhanced mechanical stiffness. We further show that these alginate-graphene oxide microstructures can be controllably degraded by ion chelation, enabling the templating of macroporous architectures using a second encapsulating material. We systematically explore the use of these composite microstructures as stretchable electronic materials and actuators. Ultimately, we envision this approach will be broadly applicable for a variety of polyelectrolytes and nanomaterials, enabling the digital prototying of chemomechanically responsive structures, soft robots, and other biologically inspired microdevices.
8:15 AM - BM05.04.02
3D Fabrication of Degradable Polymer Scaffolds with Self-Stiffening and Shape Memory Capacity for Guided Bone Regeneration
Ben Zhang 1 , Jordan Skelly 1 , Jacob Maalouf 1 , David Ayers 1 , Jie Song 1 Show Abstract
1 , Univ of Massachusetts-Medical School, Worcester, Massachusetts, United States
Regenerative reconstruction of traumatic long bone defects requires the use of suitable bone grafts, often in combination with an effective dose of osteogenic protein therapeutics. At present, allografts and autografts are clinically most utilized to treat critical sized bone defects. However, these treatments have inherent shortcomings such as high failure rates due to poor graft fixation/tissue integration (allografts) and limited supplies (autografts). Synthetic bone grafts, if properly engineered with physical properties enabling stable graft fixation, robust osteoconductive and osteoinductive properties encouraging new bone growth, and safe degradation, could help address these challenges.
We developed a series of triblock amphiphilic degradable poly(lactic-co-glycolic acid)-b-poly(ethylene glycol)-b-poly(lactic-co-glycolic acid) (PELGA) with different degradation rates that exhibit high-efficiency shape recovery around body temperature and unusual stiffening upon hydration. Additionally, composites of these polymers and bone mineral hydroxyapatite (HA) were shown to support the attachment, proliferation and osteogenesis of osteoprogenitor cells in vitro. Here we report the fabrication of PELGA/HA composite scaffolds with staggered interconnected macroporosity by 3D rapid prototyping. Sacrificial poly(vinyl alcohol) (PVA) was used during the rapid prototyping to generate dense composites that were more readily cut post-printing and was washed away in water to recapture the design macroporosity prior to in vivo implantation. The shape memory and hydration-induced stiffening properties enabled these 3-D scaffolds stably fixed into critical femoral segmental defects in rat femurs, resulting in 100% long-term fixation success. These osteoconductive scaffolds resulted in substantial new bone formation as early as 4 weeks in the absence of any osteogenic growth factors. With a single dose of preabsorbed recombinant human bone morphogenetic protein-2/7 heterodimer (rhBMP-2/ 7), both the quantity and quality of the bone regeneration was further enhanced as supported by longitudinal microCT and histological analyses.
8:30 AM - *BM05.04.03
Recent Advances in Theory and Applications of Stimuli-Responsive and Recognitive Gels
Nicholas Peppas 1 , David Spencer 1 , Angela Wagner 1 , Matthew Miller 1 Show Abstract
1 , The University of Texas at Austin, Austin, Texas, United States
Over the past century, gels have emerged as effective materials for an immense variety of applications. The unique network structure of gels enables very high levels of hydrophilicity and biocompatibility, while at the same time exhibiting the soft physical properties associated with living tissue, making them ideal biomaterials. Stimuli-responsive hydrogels have been especially impactful, allowing for unprecedented levels of control over material properties in response to external cues. This enhanced control has enabled groundbreaking advances in healthcare, allowing for more effective treatment of a vast array of diseases and improved approaches for tissue engineering and wound healing. Here, we identify and discuss the multitude of response modalities that have been developed, including temperature, pH, chemical, light, electro, and shear-sensitive hydrogels. We discuss recent modeling efforts of gel swelling in gels with Gausssian or non-Gaussian chain desitribution, cationic or anionic behavior, presence of larger tie-junctions, multifunctionality, etc. We summarize ionic gel properties and the mechanisms used to create these responses, highlighting both the pioneering and most recent work in all of these fields. Finally, we address current and proposed applications of these hydrogels in medicine and industrial settings.
9:00 AM - *BM05.04.04
Lessons Learned in a Decade of Printing Cartilage
Lawrence Bonassar 1 Show Abstract
1 Meinig School of Biomedical Engineering and Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca, New York, United States
In all of its forms and locations in the body, cartilage is an ideal target tissue for bioprinting, due to its complex anatomic shapes and the spatial heterogeneities that comprise its microstructure. These factors combined with its minimal capacity for intrinsic healing and suitability to in vitro culture, make printed cartilage a prime candidate for clinical deployment.
A significant challenge in cartilage bioprinting is the formulation of suitable bioinks for delivery of chondrocytes. In addition to considerations inherent to all cell-based bioprinting, inks for cartilage printing must achieve a sufficient level of mechanical function to enable culture and ultimately implantation. While such properties need not match the native tissue, achieving compressive moduli of 10-100 kPa is likely needed to enable manipulation both during culture and surgery.
Recent work has focused on collagen bioinks, which utilizes both chemical and thermal transitions to achieve printability. The complex rheology of collagen inks adds to the considerable challenge of achieving high cell viability and shape fidelity. Alterations in gel concentration, the pH at which gels are neutralized, and addition of photocrosslinkers enables precise tuning of geometry while maintaining cell viability and biosynthetic activity. Monitoring rheology of inks prior to, during, and immediately after gelation enables a more detailed understanding of how the properties of these materials relate to their printability. In our work, shear modulus immediately prior to printing is the most reliable predictor of print accuracy. Notably, properties of collagen gels can be tuned across a range of properties while maintaining high cell viability for printing. Additionally, such tuning also enables the generation of gradients in cell type, composition, and properties that enable more precise recapitulation of the heterogeneities that exist in native cartilaginous tissues.
10:00 AM - BM05.04.05
Bioinspired 4D Printing of Edible Materials for Food Engineering and Beyond
Wen Wang 1 , Lining Yao 1 2 , Hiroshi Ishii 1 Show Abstract
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Human Computer Interaction Institute, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Inspired by how nature creates hygromorphic composite materials that are hierarchical and transformative, we study the water gradient-driven actuation of a group of biomacromolecule- based gel materials, including starch, gelatin and agar. We developed a unique material composition structures in order to realize sequential folding under a single and global stimulus-dependent water gradient. This shape changing matrix composite includes a matrix phase made of a thin film that has a density distribution and differentiated water intake capacity and the dispersion phase made of non-soluble cellulose fibers. Multiple dynamic and transformative structures are presented, with different transitional states of shapes trying to reach an energy balance.
To demonstrate the unique application areas of the edible composite, we developed a concept of transformative appetite, where edible 2D films made of common food materials (protein, cellulose or starch) can transform into 3D food during cooking . This transformation process is triggered by water adsorption, and it is strongly compatible with the ‘flat packaging’ concept for substantially reducing shipping costs and storage space. To develop these transformable foods, we performed material-based design, established a hybrid fabrication strategy, and conducted performance simulation. Users can customize food shape transformations through a pre-defined simulation platform, and then fabricate these designed patterns using additive manufacturing. Three application techniques are provided - 2D-to-3D folding, hydration-induced wrapping, and temperature-induced self-fragmentation, to present the shape, texture, and interaction with food materials. Based on this concept, several dishes were created in the kitchen, to demonstrate the futuristic dining experience through materials-based interaction design.
For the diversity of the transformation the system can achieve, the fast response (within seconds) and the biocompatibility, we will also introduce a few applications in drug deliveries and packaging.
 Wen Wang, Lining Yao, Teng Zhang, Chin-Yi Cheng, Daniel Levine, and Hiroshi Ishii. 2017. Transformative Appetite: Shape-Changing Food Transforms from 2D to 3D by Water Interaction through Cooking. In Proceedings of the 2017 CHI Conference on Human Factors in Computing Systems (CHI '17). ACM, New York, NY, USA, 6123-6132. DOI: https://doi.org/10.1145/3025453.3026019
10:15 AM - BM05.04.06
3D Printing Dielectric Elastomer Actuators for Soft Robotic Applications
Ghazaleh Haghiashtiani 1 , Frank Gardea 2 , Ed Habtour 2 , Michael McAlpine 1 Show Abstract
1 , University of Minnesota, Minneapolis, Minnesota, United States, 2 , U.S. Army Research Laboratory, RDRL-DE, Aberdeen Proving Ground, Maryland, United States
Soft robotics is a nascent field empowered by the development of advanced soft materials with properties commensurate to their biological counterparts, and with the purpose of reproducing locomotion and other distinctive capabilities of active biological organisms. Despite several promising examples in this field, the performance of soft robots has been limited by the availability of materials and manufacturing techniques. Recent advances in extrusion-based, multi-material 3D printing allows for the direct incorporation of functional materials into the fabrication process to produce 3D structures at multiple length scales and with a wide variety of applications, ranging from complex electronics to bionic devices. The development of functional soft actuators is vital to the advancement of soft robotics. Here, we propose an investigation at the intersection of 3D printing and electroactive polymers (EAPs) to develop electromechanical actuators for soft robotics and other soft-matter applications. Specifically, we investigate the bending mode of actuation using a dielectric elastomer actuator (DEA) in a unimorph configuration. DEAs are a class of electroactive polymers that are composed of a thin dielectric layer sandwiched between two layers of compliant electrodes, and exhibit mechanical deformation in response to applied electrical stimuli. For this purpose, we used a silicone elastomer as the dielectric layer, mainly due to its fast electromechanical response, low mechanical loss, and availability in a wide range of viscosities, curing rates, and mechanical properties. We also tailored the composition of the silicone elastomer for improved dielectric functionality. In addition, we replaced the common electrode materials used for DEAs with a soft, stretchable, and transparent ionic hydrogel. Previous work has demonstrated that the ionic hydrogel electrodes yield functional DEAs and can sustain high voltages while maintaining mechanical integrity and without limiting the deformation of the dielectric elastomer layer. Indeed, after optimizing the material compositions for performance and printability, and overcoming the material incompatibilities using effective surface engineering strategies, we 3D printed the layered structure of a DEA with unimorph configuration and characterized the device actuation performance in response to large applied electric fields. Longer term, the outcomes of this work can serve as a stepping stone for the freeform fabrication of untethered mechanical devices and soft robots, with implications in artificial life and programmable matter.
10:30 AM - BM05.04.07
A New 3D Printing Strategy by Harnessing Deformation, Instability and Fracture of Viscoelastic Inks
Hyunwoo Yuk 1 , Xuanhe Zhao 1 Show Abstract
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Direct ink writing (DIW) has demonstrated great potential as a versatile method to 3D print multi-material and multi-functional structures for applications in diverse fields including stretchable electronics, organ on a chip, soft robotics, biomedical implants, and smart composites. While the inks for DIW 3D printing span as diverse as conductive pastes, elastomers, and hydrogels; they usually possess common rheological properties such as viscoelasticity, shear thinning, and yield stress flow to aid printing processes. During DIW, pressurized viscoelastic inks are extruded out of the 3D printer’s nozzles in form of printed fibers, which are deposited into patterns based on the prescribed motion of nozzles. In most DIW printing processes, a single set of printing conditions is adopted through trials and errors, and rarely changed during printing. As a result, the resolution of printed fibers is usually limited by the nozzle’s diameter, and the printed pattern is limited by the nozzle’s motion paths. Such limitations have greatly restricted the versatility and applications of existing DIW 3D printing approaches.
Here, we report a new strategy to overcome the limits of DIW 3D printing by harnessing deformation, instability, and fracture of viscoelastic inks. We show that a single nozzle can print fibers with resolution much finer than nozzle diameter by stretching the extruded ink, and print various thickened or curved patterns with straight nozzle motions by accumulating the ink. To rationally select parameters for the new printing strategy, we construct a phase diagram to quantitatively guide deformation, instabilities, and fracture of viscoelastic inks. This new strategy provides a wide new avenue to opportunities beyond the limits of existing DIW 3D printing approaches. We also demonstrate novel applications of the new 3D printing strategy including stretchable structures with tunable stiffening and 3D structures with gradient properties, and programmable swelling properties, all printed with a single nozzle. With this capability beyond the conventional DIW 3D printing approaches, the new 3D printing strategy will be broadly applicable and impactful for diverse fields of science and engineering.
10:45 AM - BM05.04.08
Controllable Dynamic Reconfiguration in Fiber-Decorated Thermo-Responsive Gels
Anna Balazs 1 , Tao Zhang 1 , Victor Yashin 1 Show Abstract
1 , University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Using computational modeling, we simulate gels where elastic fibers are localized on the surface of the polymer network. Our computational approach, the gel lattice spring model (gLSM) is based on a finite element approach and thus, allows us to numerically solve the elastodynamic equations that characterize the behavior of thermo-responsive polymer gels. Via this model, we determine how to arrange the fibers on the outer layer(s) of the gel to achieve new shape changes that could not be achieved with the fibers localized in the bulk of the material. We focus on gels with a lower critical solubility temperature (LCST) and show that the fibers inhibit the swelling of the gel as the temperature is lowered and inhibit the shrinking of the gel as the temperature is increased. This behavior can lead to novel 3D shape changes. In particular, we show that if an arrangement of fibers is placed on the top of an initially planar gel and the same arrangement is placed in an adjacent region at the bottom of the gel, the system can form a corrugated structure when the temperature is decreased. Hence, the material can be dynamically and reversibly switched between a planar and corrugated geometry with variations in temperature. We use the same approach to design gels that encompass both positive and negative curvatures around a saddle point. In this manner, we are attempting to design gels with 3D printed architectures that undergo structural reconfiguration and enable new functionality.
11:00 AM - BM05.04.09
Application of Functional Polymer Inks—Two-Dimensional Crystals Production and Enhancement of Their Polymer Composites Properties
Silvia Gentiluomo 1 2 , Peter Toth 1 , Emanuele Lago 1 2 , Sanjay Thorat 1 , Mirko Prato 1 , Vittorio Pellegrini 1 , Francesco Bonaccorso 1 Show Abstract
1 , Istituto Italiano di Tecnologia, Genova Italy, 2 Dipartimento di Chimica e Chimica Industriale, Università degli Studi di Genova, Genoa Italy
Two-dimensional (2D) crystals-based polymer composites have attracted great attention in the field of materials science during the last decade, enhancing the mechanical, electrical and thermal properties with respect to the pristine polymers . However, in order to develop high-performance 2D-crystals-based composites, it is essential to solve two main issues, the scalability of the 2D crystals production  and their optimal dispersion in the polymer matrix .
Liquid phase exfoliation (LPE), due to its up-scalability, is one of the most used techniques for the 2D crystals production. The most suitable solvents, whose surface tension matches the 2D crystals surface energy to minimize the interfacial tension for LPE of layered materials , mostly possess high boiling point, with the addition of toxicity issues (e.g. N-Methylpyrrolidone ). The use of water with the aid of a surfactant  for the LPE process leads to subsequent issues, such as the surfactants removal.
In this study we propose the use of poly methyl methacrylate (PMMA), as a multifunctional component for the production of 2D crystals flakes in acetone and their acrylonitrile butadiene styrene (ABS) composites. In the LPE process, using different PMMA concentrations, the thinnest flakes (3-4 layers) were produced with 1 w% of PMMA. Indeed, the polymer can act both as a stabilizer, avoiding the flakes restacking due to its steric effect, and as a compatibilizer, enhancing the interaction between the flakes surface and the ABS polymer matrix. The PMMA aided LPE is used to produce few layer graphene (FLG) and molybdenum disulfide (MoS2) flakes. The presence of the polymer improves the LPE process in both cases, for example it increases the FLG concentration and hinders the MoS2 flakes oxidation, with respect to the bare acetone dispersions.
Moreover, the compatibility enhancement of the 2D crystals with ABS, due to the PMMA presence, is shown by the polymer composites properties improvement with respect to the pristine ABS. In fact, we achieved improvements in the mechanical properties with the FLG-based composites (e.g. +20%, and +22% for Young’s modulus, and tensile strength, respectively at 0.001 w% of FLG) and in the thermal properties with the MoS2-based composites (+40°C in the degradation temperature at 0.1 w% of MoS2).
Subsequently, the PMMA is also exploited to boost the impregnation of polyamide 6 (PA6) pellets up to 20 w% of FLG, due to the increased compatibility between the filler and the PA6. Then, the impregnated pellets are extruded to filaments, which are processed by 3D printer to obtain custom-made samples, showing an enhancement in both mechanical and electrical properties, with respect to pristine PA6.
 J. R. Potts, et al., Polymer, 52 (2011) 5
 F. Bonaccorso et al., Adv. Mater., 28 (2016) 6136
 J. N. Coleman et al., Science, 331 (2011) 568
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 M. Lotya et al., JACS,131 (2009) 3611
11:15 AM - BM05.04.10
3D Inkjet Printing Hydrogels—Multi-Material Printability and Feature Resolution
Fei Zheng 1 , Jason Wong 1 2 , Brian Derby 1 Show Abstract
1 , University of Manchester, Manchester United Kingdom, 2 , University Hospitals South Manchester, Manchester United Kingdom
A number of 3D and 4D printing techniques are compatible with hydrogels including extrusion writing (also termed robocasting and fused deposition modelling), stereolithography (both scanning laser and digital light projection), and inkjet printing. All three of these methods have their own particular strengths and weaknesses, however because of the exceptionally low equipment entry cost, extrusion writing has emerged as the most common method in the literature. This presentation will focus on inkjet printing because of its two major advantages over other methods, namely: 1) the potential for high spatial resolution coupled with parallel multinozzle deposition enabling relatively high build rates and 2) parallel or rapid sequential deposition of multiple materials in the same device allowing, heterogeneous, complex, multifunctional components to be printed.
The printability of a given ink is reasonably well predicted by the dimensionless grouping 1 < Z < 10 where Z = (γρd)1/2/η, where γ, ρ and η are the surface tension, density and dynamic viscosity of the ink respectively and d is the printer nozzle diameter. In practice for most aqueous inks, the critical parameter is the viscosity and typically η < 30 mPa.s for a printable ink. This is much more fluid than inks used for extrusion writing and thus the surface profile of a printed drop is controlled by capillarity because the timescale for drop spreading is significantly lower than the drop solidification/gelling/drying kinetics. Thus unlike filament extrusion and stereolithography, where feature resolution is controlled by the nozzle diameter and illuminated spot size respectively, the resolution of an inkjet 3D printed structure depends on solid/liquid interactions either with the original substrate or the previously printed layer.
Here we present a study of the 3D inkjet printing of two hydrogels, Pluronic F127 a well-known thermal reversible gel used as a sacrificial material to allow the printing of hollow structures and modified cross-linkable gelatins such as gelatin methacrylate (GelMA). Hollow channels fabricated using Pluronic F127 and surrounded by cross-linked GelMA show narrower minimum feature widths than those printed on a crosslinked GelMA surface and then surrounded by further GelMA. Simple equilibrium models can be used to design the desired 3D structure and the possibility of controlling the surface energy of modified gelatins and triblock polymers to improve 3D printed feature resolution is explored.
11:30 AM - BM05.04.11
3D Printing of Photocurable Cellulose Nanocrystal PEGDA Hydrogel Nanocomposites
Rigoberto Advincula 1 Show Abstract
1 , Case Western Reserve University, Cleveland, Ohio, United States
The 3D printing of polymers and polymer composites are of high interest especially with respect to additive manufacturing. While the most popular 3D printing materials include commodity polymers such as PLS, ABS, PCL, PC, etc. there is a growing interest on more high-performance polymers including nanocomposites to improve thermo-mechanical properties. There are a number of 3D printing methods that have become popular due to the advent of low-cost 3D printers which are largely based on fused deposition modeling (FDM). Other techniques include selective laser sintering (SLS), and stereolithographic apparatus (SLA). SLA stands out to be the most amenable to monomer and crosslinking chemistry modification due to the use of in-situ photopolymerization to synthesis and fabricate the material. In this talk, we will highlight the use of SLA to fabricate cellulose nanocrystal based polyethylene glycol diacrylate nanocomposites. PEGDA is a well-known hydrogel that has wide used in biomedical devices because of its biocompatibility. By utilizing cellulose nanocrystal (CNC) additives for nanocomposite preparation, improved thermo-mechanical properties were observed including controlled swellability under buffer conditions. Various thermo-mechanical characterization methods were employed to observed structure-composition-property relationships as well as prove its utility in possible prosthesis device applications. Other 3D printed SLA polymers materials and biocompatible polymers will be reported and compared.
11:45 AM - BM05.04.12
Blue-Light Triggered Tough Interpenetrating Polymeric Network (IPN) from One-Pot CuAAC and Methacrylate Reactions
Abhishek Shete 1 , Chris Kloxin 1 2 Show Abstract
1 Materials Science and Engineering, University of Delaware, Newark, Delaware, United States, 2 Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware, United States
Interpenetrating polymeric networks (IPNs) are used in an array of commercial applications ranging from medical dressing to automobile bumpers, but there has been a renaissance of new one-pot synthetic routes to design IPNs using a range of orthogonal chemistries. A radical initiated methacrylate network formed via chain polymerization is well-known to possess heterogeneous network structure and brittle-like mechanical properties, whereas the step-polymerized CuAAC network is homogenous and tough. Our work demonstrates a novel approach to photo-trigger the CuAAC and methacrylate polymerizations independently in one-pot reaction scheme from a single photoinitiating system using blue-light to form a bulk (solvent-free) IPN structure. The photo-IPNs have rapid polymerization rates (>90% conversion within 15 minutes) with a unique polymerization sequence providing an excellent integration of polymer chains. The resultant IPN films are glassy and transparent, and their thermo-mechanical properties are readily tuned by varying the ratio of its two monomer components. Moreover, the presence of triazole rings formed via the CuAAC crosslinking reaction mitigates the brittleness of methacrylate providing an enhanced toughness and high strain tolerance to the IPN material. This photoinitiated approach provides spatio-temporal control over where and when the polymerization occurs, allowing photopatterning of the IPN. We demonstrate a unique shape recovery upon thermal treatment after flexural deformation in these glassy photopolymerized IPNs. These novel approaches for bulk photo-CuAAC polymerizations establish these material as a viable substitute for traditionally employed UV/visible-curable methacrylate- and epoxy-based network materials in many applications, including photolithographic resists, coatings, and self-healing 3D printed networks.
BM05.05: Gels in Biology and Medicine
Tuesday PM, November 28, 2017
Sheraton, 2nd Floor, Back Bay C
1:30 PM - *BM05.05.01
Cartilage Extracellular Matrix (ECM) is a Composite Medium
Peter J. Basser 1 , Ferenc Horkay 1 Show Abstract
1 Section on Quantitative Imaging and Tissue Sciences, NICHD, National Institutes of Health, Bethesda, Maryland, United States
To describe the functional properties of cartilage extracellular matrix (ECM), such as its load bearing and lubricating abilities, requires treating its collagen network and proteoglycan (PG) components as distinct phases, and the hydrated ECM tissue itself as a composite medium. We propose a modeling framework in which the PG hydrogel phase exerts a large swelling pressure, while the collagen network phase acts to restrain it. We compare and contrast this polymer physics-based approach to biomechanical modeling approaches that aggregate the collagen and PG phases into a single homogeneous 'solid-like' elastic tissue matrix phase. We show that this homogenization process fails to embody the action of the opposing stresses generated by the collagen and PG phases, and to incorporate the critical role of tissue hydration on the mechanical properties of the tissue. We also propose the use of the osmotic modulus of the aggregate ECM tissue as a way to characterize its load bearing ability, and show how it can be related to the mechanical moduli of the separate collagen and PG phases. We also demonstrate how these various moduli can be measured in a stress titration experiment.
2:00 PM - *BM05.05.02
Transport and Mechanical Properties of Gel-Like Articular Cartilage
Alan Grodzinsky 1 Show Abstract
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Traumatic joint injury can initiate early cartilage degeneration in the presence of elevated levels of inflammatory cytokines, leading to post-traumatic osteoarthritis (PTOA). The effects of mechanical loading on cartilage degradation and repair associated with joint remobilization in vivo after injury are not well-understood, but very important to clinical rehabilitation. In addition, there are currently no disease modifying drugs for osteoarthritis, and a major challenge is the ability to achieve sustained levels of potential therapeutics inside a target tissue, with no side effects, after intra-articular delivery. We use in vitro organ culture models to study the beneficial effects of dynamic strain and combination therapeutics (e.g., glucocorticoids, growth factors) to inhibit matrix degradation and cell apoptosis in cartilage explants challenged with cytokines and impact injury. Parallel in vitro and animal studies are aimed at approaches to targeted tissue drug delivery. In particular, charge based intra-cartilage delivery of single dose dexamethasone using Avidin nano-carriers suppressed cytokine-induced catabolism long term in a cartilage explant model. In studies of cartilage degradation and repair, it is important to assess the mechanical function of newly synthesized tissue and constituent matrix molecules at the molecular scale. We recently developed an AFM-based wide-bandwidth rheology system to measure the dynamic nanomechanical behavior of normal and degraded cartilage as end-grafted aggrecan brush layers in the frequency range 1Hz to 10 kHz (with high frequencies relevant to impact injury).
3:00 PM - BM05.05.03
Enhanced Biodegradation of Atrazine by Bacteria Encapsulated in Organically Modified Silica Gels
Joey Benson 3 , Jonathan Sakkos 3 , Adi Radian 1 , Lawrence Wackett 2 4 , Alptekin Aksan 3 4 Show Abstract
3 Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota, United States, 1 Department of Environmental, Water and Agricultural Engineering, Israel Institute of Technology, Haifa Israel, 2 Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota, United States, 4 BioTechnology Institute, University of Minnesota, St Paul, Minnesota, United States
Biodegradation by cells encapsulated in silica gel is an economical and environmentally friendly method for the removal of toxic chemicals from the environment. Organically modified silica (ORMOSIL) gels can introduce a wide range of chemical groups into the gel, allowing the chemical and physical properties to be tuned. In this work, ORMOSIL gels containing encapsulated recombinant E. coli expressing atrazine chlorohydrolase (AtzA) were designed and optimized to degrade atrazine. The atrazine dechlorinating enzyme AtzA catalyzes the hydrolysis of atrazine to hydroxyatrazine. The silica gels were composed of tetraethoxysilane (TEOS), silica nanoparticles (SNPs), and either phenyltriethoxysilane (PTES) or methyltriethoxysilane (MTES). SNPs were used in combination with the silicon alkoxides to give greater control over the permeability and structure of the gel, and increase the gel biocompatibility. The atrazine biodegradation rates were greater in ORMOSIL gels than inorganic silica gel, except for PTES gels with a low ratio of SNP : silicon alkoxide. The atrazine biodegradation rates in optimized PTES and MTES gels were 0.041 ± 0.003 and 0.047 ± 0.004 μmol/ml of gel in 20 minutes respectively. These biodegradation rates were 80% and 86% greater than biodegradation rates in inorganic TEOS gel. ORMOSIL gels adsorbed much higher concentrations of atrazine than inorganic TEOS gel, increasing the local concentration within the gel. The highest concentration of atrazine adsorbed by ORMOSIL gels was 48.91×10-3 μmol/ml gel, compared to 8.71×10-3 μmol/ml gel by hydrophilic TEOS gels. A direct correlation between adsorption and biodegradation was observed in all gels except PTES gels with a low SNP: silicon alkoxide ratio. We expect the gel microstructure and atrazine transport across the gel to be critical factors altering the direct correlation between enhanced adsorption and biodegradation rate. Atrazine diffusion was slower in the ORMOSIL gels than the hydrophilic TEOS gels, which was envisioned to decrease the biodegradation rates of the gels. Phase separation of the hydrophobic precursors was also expected to decrease the biodegradation rate by sequestering atrazine into hydrophobic aggregates where it could not be degraded. Phase separation occurred in all ORMOSIL gels, and was visualized by staining the gel with the hydrophobic probe Nile red. Phase separation was much greater in PTES gels than MTES gels, and increased with increasing organic content. Confocal microscopy images showed that cells were in contact with the hydrophobic aggregates, but no cells were observed within any aggregate. Phase separation was therefore expected to decrease biodegradation by concentrating atrazine in regions that contained no cells. ORMOSIL gels without severe phase separation or severely hindered atrazine diffusion had greater biodegradation rates than inorganic TEOS gels, indicating that adsorption had a more significant effect on the biodegradation rate.
3:15 PM - BM05.05.04
Mineral Plastic Hydrogel as Injectable, Reusable and Optically Clear Adhesive Inspired by Anomia Simplex
Ang Li 1 , Shengtong Sun 2 , Yisheng Xu 1 3 , Xuhong Guo 1 3 Show Abstract
1 , East China University of Science and Technology, Shanghai China, 2 , Donghua University, Shanghai China, 3 , Shihezi University, Shihezi China
Marine life forms that have a sedentary life style need reliable strategies to establish underwater adhesion. The mussel (Mytilus Edulis) has been most extensively studied for its underwater adhesion by means of protein-based byssus threads, which are rich in the catecholic amino acid, 3,5-dihydroxyphenylalanine (DOPA). Since DOPA is a versatile naturally oxidizable, pH-sensitive cross-linker, it can convert secreted fluids into tough solids under relevant conditions, which explains why it occurs in biological adhesives. However, mussel-inspired adhesives also suffer from some typical drawbacks; the complex crosslinking chemistry that follows oxidation of DOPA moieties triggered by basic pH or oxidants, as well as complexation with transition metals such as Fe3+, often results in irreversible, dark hydrogels or solids, which largely restricts its wide applications.
In this context we note that, in contrast to the “soft” byssus attachment of mussels, a number of anomiidae molluscs have evolved a different strategy for adhesion. For example, Anomia Simplex, or the common jingle shell, possesses a single byssus that is highly mineralized (over 90% CaCO3 by weight), and by which the animal strongly attaches on stones or shells.
On the other hand, wet bioadhesion was recently approached from a slightly different angle by Leibler et al, who demonstrated that gels, in particular biological tissue, could be glued together by means of inorganic nanoparticles. This highlights the role of physisorption of macromolecular chains on the surface of mineral particles, reminding us that such particles can act as reversible cross-linkers in polymeric systems, thereby converting a common polymer solution into an adhesive.
Following the above aspects, we report in this paper the preparation and characterization of a new type of Anomia-inspired injectable, reusable, and optically clear adhesive based on mineral-loaded polymer hydrogels that show comparable adhesion performance to DOPA-based adhesives, under both dry and wet conditions. And The formed hybrid hydrogel is composed of very small amorphous calcium carbonate (ACC) nanoparticles which physically crosslink the PAA chains via chelation between Ca2+ and COO- to form a visco-elastic material. Furthermore, the adhesion strength can be significantly reinforced by incorporating negatively charged nanoparticles which introduce multiple crosslinks of PAA chains with more loops, tails, and bridging strands. The present mineral-crosslinked hydrogel represents a new type of bio-inspired adhesive material that may find a variety of potential applications, such as tissue repair, adhesive coating, antifouling, biosensors, or surface functionalization of nanomaterials.
3:30 PM - BM05.05.05
Deciphering the Adhesive Properties of Mussel-Inspired Metal-Coordinate Gels
Erica Lai 1 , Bavand Keshavarz 1 , Niels Holten-Andersen 1 Show Abstract
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
In recent years, researchers have incorporated mussel-inspired metal coordination into tough adhesive gels for wet environments that are mechanically responsive to environmental conditions, like pH and choice of metal ion. However, not much is known about how this chemistry produces a quality adhesive material with both bulk cohesive and surface adhesive strength. In this study, both rheological and tack tests were performed on gels of varying specifications. By controlling a gel’s characteristic relaxation time and energy dissipation mechanism, we can influence its adhesive behavior. Understanding how the ligands favor participation in either metal-coordination complexes or surface adhesion under given conditions will help us determine the correlation between linear parameters (i.e. rheological characteristics) and resulting nonlinear behavior (i.e. failure during a tack test). With this understanding, incorporating metal coordination into adhesive materials could provide condition-dependent control of adhesive properties.
3:45 PM - BM05.05.06
Direct Imaging of the Internal Structure of Bottlebrush Homopolymers via Helium Ion Microscopy and Coarse Grain Simulations
Matthew Burch 1 , Dongsook Chang 1 , Jan-Michael Carrillo 1 , Anton Ievlev 1 , Bobby Sumpter 1 , Kunlun Hong 1 , Alex Belianinov 1 , Olga Ovchinnikova 1 Show Abstract
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Bottlebrush polymer thin films have been intensely investigated in the past decade due to their novel size, ordering, and structure, which could lead to their use for a number of applications from photonics to even drug delivery. However, despite their importance, there remain few direct ways to observe the internal structure of these polymers. Due their polymeric nature, diffraction based imaging techniques, such as transmission electron microscopy (TEM), is very difficult without the addition of stains or other contrast inducing mechanisms. Further, the use of scanning electron microscopy (SEM) generally requires the use of a conductive coating when imaging non-conductive samples such as bottlebrush polymers. An alternative imaging technique, helium ion microscopy (HIM), utilizes positive He-beam instead of electrons, which allows for charge compensation with the use of an electron flood gun, therefore, allowing for very detailed surface analysis.
In this work, we utilize HIM to analyze the internal structure of bottlebrush polymers. Through plasma cleaning of the polymer thin films, we have the ability to directly observe the internal structure of the bottlebrush backbones. Through the use of modern image analytics techniques, we have the ability to extract both the bottlebrush length and structure. To understand the structure of the bottlebrush samples, we utilized coarse grain simulations of the polymers and directly compared these simulations. We determined that the distributions of the polymers we observe with our HIM imaging technique closely match the observed simulation distributions. Through these observations we’ve created a technique to directly observe the internal structure of the bottlebrush thin films with HIM and are able to directly compare our results to coarse grain simulations.
Research was supported and conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy.
4:15 PM - BM05.05.08
Transparent Soils for Plant Root Phenotyping
Lin Ma 1 , Yichao Shi 1 , Ludovico Cademartiri 1 Show Abstract
1 , Iowa State University, Ames, Iowa, United States
We will show our work on the development of transparent soils (TSs) for the optical characterization of plant roots in vivo.
Understanding roots, the rhizosphere and their response to their environment will be an essential step in the prediction (e.g., climate change and its consequences), protection (e.g., soil remediation), utilization (e.g., biorenewables), and modification (e.g., GxE interactions and the impact of microbiome on agricultural yields of the biosphere. On the other hand, the root x microbiome x soil x environment ecosystem is so complex that developing a predictive understanding of it can appear overwhelming.
The phenotyping of roots is still technically challenging for the following reasons (Table I): (i) the structure of roots is three-dimensional and usually fractal (i.e., has important features at many length scales), which makes its analysis complex and the data subject to errors (e.g., thresholding, misidentification of soil carbon as root, inability to detect fine roots); (ii) the phenotyping effort focuses on “physiological conditions” that are usually ill defined and incompletely reported, thereby exposing findings to hidden variables (phenotyping in media like gels, while much simpler and highly controlled, is unambiguously not representative of field conditions); (iii) these “physiological conditions” (e.g., soil media) are opaque to most radiation.
The mechanistic understanding and establishment of causality in complex systems (like the root and its microbiome) requires model systems. Solutions are needed for low cost, highly controlled, and highly reproducible phenotyping systems for the root and its microbiome. These systems must produce data that is (i) representative enough to be predictive of field phenotypes, (ii) accurate enough to be used in developing and testing hypotheses, and (iii) affordable enough to be within reach of the average laboratory: the large scale involvement of the science community is essential in tackling such hard problems.
The state of the art on “TSs” uses chemically processed Nafion™ as a growth medium, since it can be transparent in aqueous solutions due to an RI similar to water’s. This technology has severe limitations: (i) high material costs ($0.13/g - wholesale price; a one gallon pot would cost ~$1000), (ii) material must be chemically processed, (iii) shape of the particles is non-homogeneous and the size is only roughly controlled by milling, (iv) particles are hydrophobic and nonporous: the plant must grow in a partially saturated medium as in hydroponic conditions, (v) root can only be imaged in an index matching solutionwith sorbitol concentrations as high as 13%, which can potentially cause significant osmotic stress.
Our solution, by comparison, cost few dollars per liter, allows for imaging in vivo, provides water and nutrients to the plants, allows control over porosity of the system and allows for colorimetric detection of plant exhudates in vivo.
BM05.06: Poster Session II
Wednesday AM, November 29, 2017
Hynes, Level 1, Hall B
8:00 PM - BM05.06.01
Understanding Metal-Coordinating Polymer Bonding Structure with UV-Vis Spectroscopy
Matthew Dodaro 1 , Seth Cazzell 1 , Niels Holten-Andersen 1 Show Abstract
1 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
In this study, we utilize UV-Vis spectroscopy to investigate the relationship between chemical stimuli and bonding behavior of mussel-inspired metal-coordinating polymers to further the understanding of transient network engineering. We measured the absorption of poly(ethylene glycol) end functionalized with nitrocatechol over a range of pH and iron concentrations. We then decomposed the spectra into Gaussian peaks representative of mono, bis, and tris coordination. Insight on how changing the chemical environment can manipulate the bonding structure and by extension the dynamics that dictate the material's mechanical properties will guide how we can control structure to better engineer bio-inspired viscoelastic materials.
8:00 PM - BM05.06.02
Investigation of Coordinate Network Based Films
Rebecca Gallivan 1 2 , Niels Holten-Andersen 2 Show Abstract
1 , California Institute of Technology, Pasadena, California, United States, 2 Material Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Bulk coordinate network hydrogels are known to exhibit self-healing, self-assembling, and stimuli-responsive behaviors. They also change mechanical and optical characteristics as a function of pH and can be formed under standard room and atmospheric conditions. This study investigates the mechanical and optical properties of coordinate network thin films through studying energy dissipation and color change of Fe(III) crosslinked tannic acid and Fe(III) crosslinked 4 arm catechol polyethylene glycol films on alginate hydrogels. These investigations provide evidence for strong mechanical dependence on molecular architecture. They also show pH induced mechanical and optical shifts in the films. Ultimately, these coordinate network thin films display potential for future development as advanced materials for functional applications in aqueous environments.
8:00 PM - BM05.06.03
Control of Degradation of Oxidized Dextran-Based Hydrogel Formed via Michael Addition
Punnida Nonsuwan 1 2 , Suong-Hyu Hyon 3 , Kazuaki Matsumura 1 Show Abstract
1 School of Materials Science, Japan Advanced Institute of Science and Technology, Nomi Japan, 2 Faculty of Science, Chulalongkorn University, Bangkok Thailand, 3 Center for Fiber and Textile Science, Kyoto Institute of Technology, Kyoto Japan
Hydrogels are materials prepared from cross-linked polymers that are able to provide sustained, local delivery of a variety of therapeutic agents that have been developed in biomedical applications including control release for drug delivery system. Use of the biopolymer, dextran, as the material in hydrogels has been highly pursued due to its biocompatibility, low toxicity, and biodegradability. In this work, the degradation of polysaccharide-based hydrogel for control release of drug was accomplished. Glycocidyl methacrylate was introduced into dextran to obtain Dex-GMA and then oxidation by periodate was done to introduce aldehyde groups in Dex-GMA (oxidized-Dex-GMA). Dextran based hydrogel was prepared by cross-linking oxidized-Dex-GMA with dithiothreitol (DTT) in PBS. Two processes to form gel were take place via the reaction of methyl acrylate with DTT and aldehyde part with DTT. The gelation time was controlled by varying the concentration of oxidized Dex-GMA and DTT. In our previous work , we reported the hydrogel forming by the Schiff base formation reaction of aldehyde dextran and amino group which showed self-degradation in main chain scission in oxidized dextran. In such case, degradation cannot be controlled after hydrogel formation. However, the prepared hydrogel forming of oxidized-Dex-GMA without amino group was stable in PBS but could be degraded in glycine solution through Schiff base formation. These finding suggested that we could control the degradation rate of hydrogel by the amino group addition after hydrogel formation.
 W.Chimpibul, T. Nagashima, F. Hayashi, N. Nakajima, S-H. Hyon, K. Matsumura, Dextran Oxidized by a Malaprade Reaction Shows Main Chain Scission through a Maillard Reaction Triggered by Schiff Base Formation between Aldehydes and Amines. J. Polym. Sci., A, 54, 2254-2260, 2016.
8:00 PM - BM05.06.05
Inkjet Printing for Microparticle Fabrication for the Incorporation of Multiple Drugs
Michael Marin 1 3 , Eva Harth 3 Show Abstract
1 Chemical Engineering, Vanderbilt University, Nashville, Tennessee, United States, 3 , University of Houston, Houston, Texas, United States
Conventional microparticle fabrication methods result in particles that are not precise in size yielding unpredictable drug release kinetics and drug distribution within the body. We demonstrate the strength of piezoelectric inkjet printing to prepare precise microparticles for drug delivery applications overcoming the drawbacks of conventional fabrication methods. Additionally, we prepare microparticles that are polymerized post printing via UV or visible light. In general, we will discuss the process engineering and optimization of ink chemistry to yield a method that prepares precise microparticles with tunable drug delivery properties and is easily scalable.
8:00 PM - BM05.06.06
3D Printing of Flexible Two Terminal Electronic Memory Devices
Iulia Salaoru 1 , Salah Maswoud 1 , Shashi Paul 1 , Krishna Manjunatha 1 Show Abstract
1 , De Montfort University, Leicester United Kingdom
Recent strategy in the electronics sector is to ascertain the ways to make cheap, flexible and environmentally friendly electronic devices. The 3D Inkjet printing technology is based on the Additive Manufacturing concept  and it is with no doubt capable of revolutionizing the whole system of manufacturing electronic devices including: material selection; design and fabrication steps and device configuration and architecture. 3D Inkjet printing technology (IJP) is one of the most promising technologies to reduce the harmful radiation/ heat generation and also achieve reduction in manufacturing cost.
Here, we explore the potential of 3D – inkjet printing technology to provide an innovative approach for electronic devices in especially information storage elements by seeking to manufacture and characterize state-of-art fully inkjet printed two terminal electronic memory devices.
In this work, an ink-jettable material was formulated, characterized and printed by a a piezoelectric Epson Sylus P50 Inkjet printing machine on a flexible substrate. The active printed layers were deposited into a functioning simple metal/insulator/metal structure. Firstly, from ink perspective, the main physical properties such as rheological behaviour; surface tension and wettability were investigated. Furthermore, an in-depth electrical characterization of the fabricated memory cells was carried out using HP4140B picoammeter and an HP4192A impedance analyser.
 N.Hopkinson, R.Hague, P.Dickens, Rapid manufacturing; an industrial revolution for the digital age. West Sussex, UK, John Wiley and Sons; 2006
 Iulia Salaoru, Zuoxin Zhou, Peter Morris, Gregory Gibbons, Inkjet printing of polyvinyl alcohol multilayers for addiive manufacturing applications, J.Appl.Polym.Sci., 133(25), 43572 (2016)
 Ruth Cherrington, B.M.Wood, Iulia Salaoru, Vannessa Goodship, Digital printing of titanium dioxide for dye sensitized solar cells, JoVE, e53963, (2016)
 Iulia Salaoru, Zuoxin Zhou, Peter Morris, Gregory J. Gibbons, Inkjet-printed Polyvinyl Alcohol Multilayers, JoVE,123, e55093-e55093, (2017).
8:00 PM - BM05.06.07
Synthesis and Properties of UV-Curable Acryl-Polyurethane for High-Speed Curing
Hyo Jin Jung 1 , Kyung Seok Kang 1 , Chanhyuk Jee 1 , Jihong Bae 1 , PilHo Huh 1 Show Abstract
1 Polymer Science and Engineering, Pusan National University, Busan Korea (the Republic of)
Thermoplastic UV-curable PU was successfully synthesized by the additional reaction of methylene diphenyl diisocyanate (MDI), poly(tetramethylene ether) glycol, and several diacrylate derivatives as a crosslinking point. The crosslinked PU-acrylate elastomers were formed by the short exposure to 300~400μm UV radiation. The structures and properties of the resulting Acryl-PUs were evaluated by Fourier transform infrared spectroscopy (FT-IR), 1H nuclear magnetic resonance (1H NMR), gel permeation chromatography (GPC), and Universal Test Machine (UTM). The flow dependence of photo-curing rate was studied using viscosity tests. The increase of diacrylate concentration in PU-acrylate elastomers led to higher tensile strength and hardness due to the increased crosslinking density and the enhanced interchain hydrogen bonding.
8:00 PM - BM05.06.08
Investigation of 2,2-dimethoxy-2-phenyl-acetophenone Concentration Effects on PEGDA-Based Hydrogels
Ozlem Yasar 1 , Ozgul Yasar-Inceoglu 2 , Hanna Kerolos 1 Show Abstract
1 , City University of New York, Brooklyn, New York, United States, 2 Mechanical Engineering, California State University, Chico, Chico, California, United States
In recent years, Tissue Engineering has been studied to improve or regenerate the damaged tissues. In this promising field, tissues can be regenerated only if the right biomaterials, cell types and scaffolds with the required mechanical properties are used. Currently, synthetic, natural polymers and linear aliphatic polyesters are extensively used to fabricate the scaffolds. In this research, we propose to use poly(ethylene glycol) diacrylate (PEGDA) which is a biocompatible and also biodegradable scaffold fabrication material. Since PEGDA is also a photocurable material, it can be easily fabricated with photolithography. In this technique, 2,2-dimethoxy-2-phenyl-acetophenone (DMPA) was used as a photoinitiator to initiate the polymerization process. In this study, the effects of photoinitiator on compressive mechanical properties of PEGDA based hydrogels were investigated. Firstly, 0.02% (w/v), 0.06% (w/v), and 0.1% (w/v) photoinitiator-solvent mixtures were prepared to alter the DMPA concentration. Then, each batch was mixed with PEGDA and exposed to the UV light for about 3 minutes. As a result of interaction between UV light and PEGDA-photoinitiator mixture, PEGDA got solidified and took the shape of the cylindrical mold that was used to keep the initial liquid form of PEGDA-photoinitiator solution. After that, INSTRON 3369 testing machine was used to do the compression tests. Our experimental results indicated that, as the DMPA concentration was increased, ultimate strength of PEGDA decreased. For the 0.02% (w/v), 0.06% (w/v) and 0.1% (w/v) DMPA-solvent mixture average ultimate strengths were 6.36 MPa, 4.75 MPa and 4.03 MPa, respectively. Therefore, these results showcases, compressive mechanical properties of PEGDA can be controlled by changing the photoinitiator concentration.
8:00 PM - BM05.06.09
Dry and Wet Stiffness Increase and Structure Stabilization of Cellulose Nanofibrils (CNF) Aerogels in Aqueous Environment
Muhammad Hossen 1 , Michael Mason 1 Show Abstract
1 , University of Maine, Orono, Maine, United States
Aerogels composed from porous cellulose nanofibrils (CNF) are capable of absorbing and storing a significant quantity of liquid inside their 3D structure, with total absorption capacity increasingly linearly with porosity. One of the challenges of high porosity CNF aerogels is their propensity to break down rapidly in aqueous environments. Here we describe a method to overcome this deficiency by incorporating methacrylate functionalized carboxymethyl cellulose (MetCMC) into the CNF system followed by UV irradiated cross-linking of the methacrylate groups of MetCMC. The resultant polymer composite matrix successfully maintains a robust 3D structure, without collapsing, when rewetted and stored in aqueous environments. When rewetted and subsequently freeze dried, the CNF-MetCMC composite maintains its size and shape whereas air drying induces significant shrinkage. In contrast, air dried CNF-MetCMC swells when rewetted. Air dried CNF-MetCMC with a greater mass fraction of CNF swells less in an aqueous environment compared to the composite with more MetCMC. This behavior is attributed to increased structural stabilization due to larger relative mass fractions of CNF in the composite while cross-linking between methacrylate groups enhances the dry and wet modulus of CNF-MetCMC aerogels.
8:00 PM - BM05.06.10
Modeling Pattern Formation in Polymer Gels with Temperature–Sensitive Crosslinks
Yao Xiong 1 , Chandan Choudhury 1 , Olga Kuksenok 1 Show Abstract
1 Materials Science and Engineering, Clemson University, Clemson, South Carolina, United States
Polymer gel treatments play an important role in both conventional and emergent enhanced oil recovery (EOR) techniques. One of the challenges during the oil recovery process is preventing the flow of the diverted water back into the so–called thief zones of higher permeability, thereby bypassing oil–containing regions. One example of a recently developed deep reservoir treatments to address this issue consists of dual cross-linked gel particles with both permanent and thermally breakable cross–links1,2. High temperatures deep within the injection walls results in breaking the temperature-sensitive cross–links; the particles then swell and block the rock pores, thus reducing the permeability of the rock in the thief zones. Herein, we develop a model based on the 3D gLSM approach3 that captures the process of blocking a confinement of a given size via swelling caused by breaking the temperature–sensitive cross–links. We characterize dynamics of the pattern formation within these gels and quantify the heterogeneities within the gel particle, such as dynamical changes in number, size, and distribution of clusters with different degrees of swelling. We show that the dynamics of these gels is affected if the gel is placed into the oil–water mixtures; we relate the parameters describing gel–oil interactions using our Dissipative Particle Dynamics (DPD) approach to simulate the systems on the larger scale. We consider gels with the parameters chosen close to that of the experimental system used in the EOR approaches (polyacrylamide gels with thermally sensitive cross–links2); our results show how tailoring the gel properties can potentially optimize blocking of the pore for the enhanced oil recovery.
1. Kelland, M. A. Production chemicals for the oil and gas industry. CRC press, (2014).
2. Chen, Z. et al. Journal of Applied Polymer Science 134.13 (2017).
3. Kuksenok, O. et al Physical Review E 78.4 041406 (2008).
Ferenc Horkay, National Institutes of Health
Jun Fu, Chinese Academy of Sciences
Marc In het Panhuis, University of Wollongong
Jie Zheng, University of Akron
MilliporeSigma (Sigma-Aldrich Materials Science)
Multifunctional Materials | IOP Publishing
BM05.07: Biorelated Polymers and Gels
Peter J. Basser
Wednesday AM, November 29, 2017
Sheraton, 2nd Floor, Back Bay C
8:30 AM - *BM05.07.01
Imaging Tissues, Cells and Nanostructures in 3D Using Focused Electron Probes
Richard Leapman 1 , Maria Aronova 1 Show Abstract
1 NIBIB, National Institutes of Health, Bethesda, Maryland, United States
Scanned electron probes can be used to characterize inorganic, organic and biological structures, as well as the interfaces between them in 3-D at the nanoscale. Here, we illustrate the application of scanning transmission electron microscopy (STEM), electron energy loss spectroscopy (EELS), electron tomography (ET), and serial block face scanning electron microscopy (SBF-SEM) to study tissues, cells, and nanostructures. The use of focused probes offers important advantages for determining 3-D cellular architecture since it is possible to optimize signals generated by the interaction between the incoming electrons and the specimen. Axial bright-field STEM-tomography, and serial block face SEM are proving valuable for quantitative 3-D ultrastructural analysis of cells and tissues. For example, we have applied these approaches quantitatively to study ultrastructural changes that occur in blood platelets when they are activated, the arrangement of organelles in hormone-secreting cells in pancreatic islets of Langerhans, and the interface between osteocytes and mineralized matrix in bone formation. The ability to synthesize multicomponent hybrid nanocarriers with controlled architecture and chemical functionality offers great potential for developing in vivo and ex vivo medical diagnostics and therapeutics. For example, we have used a combination of STEM, EELS and ET to characterize plasmonic gold nanovesicles designed for photothermal therapy, optical nanosensors that detect enzymes expressed by cancer cells, and nanocomplexes taken up by stem cells as magnetic labels for MRI imaging.
9:00 AM - *BM05.07.02
Novel 3D Printing Inks and Magnetically Responsive Gels via Capillary Engineering of Multiphasic Polymer Systems
Orlin Velev 1 , Sangchul Roh 1 Show Abstract
1 , North Carolina State University, Raleigh, North Carolina, United States
The talk will present magnetically responsive and self-repairing gel networks and novel inks for 3D printing that were made by controlling the capillary forces in multiphasic liquid/liquid/solid systems. In the first part of the talk, we will describe three types of Magnetically Responsive Capillary Gels (MRCGs). The first gel system is made of filaments from super-paramagnetic iron oxide nanoparticles inside water-oil systems (Nature Mater. 2015). The nanoparticles are coated by condensed, surface-anchored lipid shells. The field collects the nanoparticles into filaments by magnetophoresis, while their lipid shells form on contact nanocapillary liquid bridges between them. The nanocapillary binding allows for easy particle rolling and sliding, resulting in ultra-high filament flexibility. We used similar principles to prepare two types of MRCGs made of water, polydimethylsiloxane (PDMS) beads, and magnetic nanoparticles. In MRCG Type 1 the nanoparticles were dispersed in the liquid phase. Alternatively, MRCG Type 2 was constituted of magnetically responsive elastomer microspheres with internally embedded Fe2O3 NPs. We characterize MRCG 1 and 2 in terms of yield stress, rheology, magnetic response, and ability to re-assemble on field application, and correlate the data to their structure and response. In the second part of the talk, we will discuss how these principles were applied in the development of new 3D printing inks consisting of water and two silicone-based components: crosslinked PDMS microbeads and liquid non-crosslinked PDMS phase. Owing to the capillary binding of the microbeads, suspensions containing certain fractions of PDMS liquid precursor behave like thixotropic pastes, which are flowable at high shear stress but possess high storage moduli and yield stresses needed for direct ink writing. These PDMS gels can be directly extruded with air pressure and shaped on a 3D printer. The liquid PDMS bridges were thermally crosslinked after printing, resulting in remarkably elastic and flexible structures. Their porosity and mechanical properties, such as tensile modulus, could be controlled by the fraction of liquid precursor in the original multiphasic dispersion. As this ink is made of porous biocompatible silicon and can be 3D printed under water, it may find applications such as direct printing of bio-scaffolds on live tissue. The high softness, elasticity, and resilience of these 3D printed structures open new opportunities in the making of soft stimuli-responsive macrostructures (Adv. Mater. 2017).
10:00 AM - BM05.07.03
Structure-Property Relationship of Photoactivable Polyamidoamine Based Bioadhesives
Ankur Shah 1 , Terry Steele 1 Show Abstract
1 , Nanyang Technological University, Singapore Singapore
Adhesives have raised tremendous interest to either improve or completely replace the current tissue fixation technologies. Over the last two decades, there are many adhesives from fibrin glue to acrylates have been investigated but have had limited success in achieving clinical translation due difficulty in achieving on-demand adhesion in short time, especially in wet environment. The narrow range of mechanical properties that can be achieved also limits its application to specific tissues. To address these two issues, we have developed a solvent free polyamidoamine conjugated diazirine (PD) adhesive using polyethylene glycol (PEG 400) as a liquid plasticizer. The formulation is activated with UV (360nm) light to achieve high degree of adhesion due to formation of carbenes (-CH insertion). When cured, the adhesive has a macroporous architecture due to the concomitant evolution of N2. Addition of PEG 400 (120 mPa.S viscosity) give control over the flow properties as well as fine tuning the deformation profiles of cured adhesives. With increasing the PEG content, the viscosity can be reduced by 3 orders of magnitude allowing it be spray coated or syringed in. With combination of varying PEG content and 365 nm UV doses the effective elastic modulus can be tuned by 1 order of magnitude as confirmed by detailed rheometer analysis. Effect of the formulation on bioadhesion to ex-vivo swine aorta tissues was assessed by the lap shear strength test.
10:15 AM - BM05.07.04
Wear Rates of Polyacrylamide Surfaces under Physiological Pressures
Shabnam Bonyadi 1 , Michael Atten 1 , Jiho Kim 1 , Alison Dunn 1 Show Abstract
1 , University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Hydrogel materials have exponential potential as synthetic or hybrid biointerfaces. The mechanical stresses applied to their surfaces by physiological systems range from negligible, such as the low-Reynolds shear flows of the cardiovascular system, to extreme, such as in the impact loading of articular cartilage up to megapascals. Normal and shear loadings force the surface to respond in lubrication, and eventually degradation and even wear.
Candidate hydrogel materials for load-bearing components have demonstrated biocompatibility in various aspects such as immune system neutrality, low friction, sufficient toughness, active drug delivery responses, and even self-cleaning. Currently, many devices avoid the need to study degradation and wear by limiting their duration of use: catheters, contact lenses, and dermal patches are discarded to limit infection and retain predictable material surfaces. However, the increasing demands on long-term devices in a heavier and younger population require durability investigations. In addition, most total knee and hip replacements require revision due to material degradation and wear. To realistically consider hydrogel materials for orthopedic implant candidates, their wear behavior must be better understood.
This study quantifies the wear volumes and wear rates of polyacrylamide hydrogel surfaces under a range of physiological pressures. We first emulate the ocular system by wearing under 1kPa of applied pressure using both smooth and roughened probes. We also wear at higher pressures approaching the effective elastic modulus of the hydrogel with a smooth and roughened glass probe.
After the wear cycles, the depth of wear is quantified by intermittent imaging of the surface using confocal microscopy. The quantity and location of 1-µm fluorescent particles deposited on the worn surface is recorded in 3-D space, and the centroids of the particles are interpreted with histograms of their depth of penetration into the sample.
We find significant increases in surface roughness when worn with a roughened probe under higher pressures, and that the surface height drops about 0.2 micrometers per pass by the probe, measured in 100-cycle increments up to N=400 cycles. In addition, the surface modulus as measured by static indentation maps on the atomic force microscope (AFM) confirms a fringe layer due to wear, and surface weakening. These techniques and results show significant promise for candidate material screening and uncovering fundamental material properties which contribute to the wear behavior of hydrogel surfaces.
10:30 AM - BM05.07.05
Reinforcing Agarose Microbeads with Polyelectrolyte Shells as a Means of Generating Mechanically Tunable Plant Cell Environments
Matthew Grasso 1 , Philip Lintilhac 1 Show Abstract
1 , University of Vermont, Burlington, Vermont, United States
Although the importance of mechanical cues in plant development is appreciated, the field currently lacks tools that allow researchers to influence single cell mechanics in a controlled way. A technology that allowed researchers to isolate mechanical variables during cell growth and differentiation could reveal mechanisms of developmental regulation that were previously inaccessible. Over the past decade considerable advances have been made in engineering hydrogel microcapsules with many applications. However, the technologies developed in these fields have not found significant applications in plant studies. In this study, individual plant protoplasts from a BY-2 tobacco suspension culture were isolated and captured in microbeads of agarose using a microdroplet-chip based system. These cell-containing agarose microbeads were then further reinforced with polyelectrolyte (PE) shells. These PE shells are composed of the anionic poly(sodium 4-styrenesulfonate) and the cationic poly(diallyldimethylammonium chloride). Layering these polyelectrolyte shells on our agarose microbeads allows us to make mechanically tunable cellular microenvironments. The shelled hydrogel microbeads are biocompatible and have the potential to mechanically regulate the growth and development of individual cells. This technology has the potential to facilitate novel studies in plant cell biomechanics by creating a system that allows us to examine the response of individual cells to different mechanical environments
10:45 AM - BM05.07.06
Fabrication of Structured Hydrogel Sheets
Esther Amstad 1 , Huachuan Du 1 Show Abstract
1 , Ecole Polytechnique Federale de Lausanne, Lausanne Switzerland
Natural soft materials, such as the cytoskeleton or the mussel byssus, display excellent mechanical properties, such as a high strength, toughness and sometimes even self-healing properties. These materials are composed of proteins that self-assemble into a well-defined hierarchical structure. They are often mimicked using hydrogels, which are highly hydrated polymer networks. Numerous techniques have been developed that offer close control over the shape, composition, and average crosslink density of these hydrogels. Much less work has been devoted to the development of methods that enable control over the structure and distribution of crosslinks. I will present a new method to produce hydrogel sheets whose structure and surface roughness can be can be closely controlled. In addition, the composition and crosslink density of these hydrogel sheets can be abruptly changed, thereby offering new possibilities to tune the mechanical properties of these hydrogel sheets. These structured hydrogel sheets are significantly stiffer than unstructured counterparts. They have the potential to be useful for example as screening assays or for tissue engineering.
11:00 AM - BM05.07.07
Supramolecular Gels Enables Safe Gastric Retention and Extended Oral Drug Delivery
Shiyi Zhang 1 Show Abstract
1 , Shanghai Jiao Tong University, Shanghai China
Medication adherence refers to how well patients take their medications as prescribed. Poor medication adherence may lead to poor outcomes, higher risk of drug resistance, failure of treatment, and increased medical cost. We envision the long-term gastric retention of a drug-delivery vehicle will enable the oral administration of drugs less frequently, potentially even in a one-time manner, to maximize medication adherence. The biggest challenge for this goal is to the safe and prolonged gastric retention of dosage forms, which had limited success (less than 1 day retention in stomach) due to the short gastrointestinal tract fast transit time.
Devices resident in the stomach have been used for a variety of applications including nutritional modulation for weight loss, ingestible electronics for diagnosis and monitoring, and gastric retentive dosage forms for prolonged drug delivery. Here we discuss the development of a novel supramolecular polymer gel as an enteric elastomer. This polymer gel has the capacity of being stable in the acidic environment of the stomach but can be dissolved in the neutral pH environment of the small and large intestines. In a large animal model, prototype devices with enteric elastomer and polycarprolactone demonstrated safe and prolonged gastric retention. This novel material platform with the capacity of increasing the safety profile of gastric resident devices and/or drug carriers promises a wide range of gastric resident devices.  To improve the performance of the enteric elastomer based gastric retentive system, we introduced a strategy to reinforce the interface between polymers. The newer version was able to deliver small molecule therapies for days to weeks or potentially even longer durations.
11:15 AM - BM05.07.08
Ionotactile Stimulation—Ionic Gels for Haptic Human-Machine Interfaces
Samuel Root 1 , Darren Lipomi 1 , Cody Carpenter 1 , Daniel Rodriquez 1 Show Abstract
1 , University of California, San Diego, La Jolla, California, United States
The skin is equipped with a variety of sensing functionalities that can be leveraged to transmit information. The tactile sense, thus, provides a natural route for augmenting human-machine interactions. Electrotactile stimulation is one way for information to be communicated through the skin—in the form of a locally resolved sensation. Conventional electrotactile devices use electronic conductors to activate subcutaneous mechanoreceptors and manifest the sensation of touch. Here, we report the application of an ionic gel as a soft, conductive interface for electrotactile stimulation as part of what we call an “ionotactile” device. Mechanical, electrical, and psychophysical characterization reveal that a novel glycerol-containing ionic gel exhibits better stability in air, improved adhesion to the skin, and a wider window for comfortable stimulation when compared to a conventional aqueous ionic hydrogel. Spatial resolution of the haptic signal is demonstrated through the fabrication of a pixelated device that is worn on the finger.
11:30 AM - BM05.07.09
Tissue-Mimicking Composite Hydrogels with Self-Organizing Nanofiber Network
Lizhi Xu 1 , Nicholas Kotov 1 Show Abstract
1 , University of Michigan–Ann Arbor, Ann Arbor, Michigan, United States
Load-bearing soft tissues, e.g., cartilage, artery walls, ligaments and other connective tissues, are water-rich yet display high stiffness, strength, fracture toughness and deformability. This unique combination of properties is possible due to a sophisticated self-assembled network of stiff collagen nanofibers and soft biomacromolecules. The re-formable non-covalent interactions between the components allow for re-organization under stress, adapting to body-specific load patterns. Known biomimetic hydrogels with multiple polymer networks, nano-reinforcement, or non-covalent crosslinking are able to replicate some of these structural elements. However, the partial sets of suitable mechanical properties are often acquired at the expense of the water content which is essential for nutrient transport in soft tissues. Here we report water-rich composites constructed from aramid nanofibers (ANFs) interlaced with soft poly(vinyl alcohol) (PVA), which exhibit mechanical properties parallel or superior to those of load-bearing soft tissues, as exemplified by articular cartilage. Hydrogen bonding between the stiff ANF framework and soft PVA chains affords synergistic stiffening and toughening of the nanocomposites. Although their water content is 70%-92%, the composites possess tensile moduli of ~9.1 MPa, ultimate tensile strains of ~325%, and compressive strengths of ~26 MPa. Their fracture toughness can be as high as ~9,200 J/m2, exceeding that of cartilage. Furthermore, the nano-fibrous network self-organizes under stress, adapting itself to allow effective load bearing and viscoelastic energy dissipation. The mechanical behavior, chemical composition and biocompatibility of these biomimetic composites permit their wide utilization as load-bearing biomaterials.
11:45 AM - BM05.07.10
Self-Regulating Metal-Coordinating Hydrogel
Seth Cazzell 1 , Niels Holten-Andersen 1 Show Abstract
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Nature uses metal binding amino acids to engineer both mechanical properties and structural functionality. Some examples of this metal binding behavior can be found in both mussel foot protein and DNA binding protein. The mussel byssal thread contains reversible intermolecular protein-metal bonds, allowing it to withstand harsh intertidal environments. Zinc fingers form intramolecular protein-metal bonds to stabilize the tertiary structure of DNA binding proteins, allowing specific structural functionality. Inspired by both these metal-binding materials, we present mechanical and spectroscopic characterization of a model polymer system, designed to mimic this bonding. Through these studies, we reveal the critical role that hydroxide species play in self regulating the bonding structure and mechanical properties of metal-coordinating hydrogels. These understandings further bio-inspired engineering techniques that are used to design viscoelastic soft materials.
BM05.08: Printing in Biomedical Applications
Wednesday PM, November 29, 2017
Sheraton, 2nd Floor, Back Bay C
1:30 PM - *BM05.08.01
3D Printable Hydrogel-Bioinks for Biofabrication—Rheological Implications, Controlled Network Formation and the Potential of Nanotechnology
Juergen Groll 1 , Thomasz Jüngst 1 , Mika Lindén 2 , Tim Woodfield 3 Show Abstract
1 Chair for Functional Materials in Medicine and Dentistry, University Hospital Würzburg, Würzburg Germany, 2 , Institute of Inorganic Chemistry II, University of Ulm, Ulm Germany, 3 , Christchurch Regenerative Medicine and Tissue Engineering (CReaTE) Group, Department of Orthopaedic Surgery and Musculoskeletal Medicine, University of Otago Christchurch, Christchurch New Zealand
Biofabrication is a young and dynamically evolving field of research. It aims at the automated generation of hierarchical tissue-like structures from cells and materials through Bioprinting or Bioassembly . This approach has the potential to overcome a number of classical challenges in Tissue Engineering relating to organization, personalized shape and mechanical integrity of generated constructs, as well as vascularization and innervation.
Although some remarkable successes have been achieved already, it has become evident that the lack of variety in printable hydrogel systems is one major drawback for the complete field . In order to be suitable for Biofabrication, hydrogels have to comply with a number of prerequisites with regards to rheological behavior and especially stabilization of the printed structure instantly after printing, while at the same time allowing the cells to proliferate.
This lecture will focus on printable hydrogels and introduce a model recently developed in the lab that can be used as pre-evaluation for printability of formulations in dispense plotting. It will then discuss some recent examples of bioink developments in my lab, including a physical hydrogel bioink based on recombinant spider silk proteins in which beta-sheet interactions facilitate good printability and stability of the constructs  as well as bioinks that are stabilized post-processing through thiol-ene chemistry as alternative to free radical polymerization [4,5]. Finally, the lecture will present a recent study on how nanoparticles as potential drug vectors can be embedded in 3D printed hydrogel constructs and how their migration and release behavior can be controlled. This presents one possible strategy to design bioinks to direct and control cell behavior post-printing beyond their mere survival.
 J. Groll, et al: Biofabrication: Reappraising the definition of an evolving field. Biofabrication 2016, 8, 013001.
 T. Jüngst, et al: Strategies and Molecular Design Criteria for 3D Printable Hydrogels. Chemical Reviews, 2016, 116 (3), 1496.
 K. Schacht, et al: Biofabrication of Cell-loaded, 3D Recombinant Spider Silk Constructs. Angewandte Chemie International Edition 2015, 54 (9), 2816.
 S. Stichler, et al: Thiol-ene clickable poly(glycidol) hydrogels for biofabrication. Annals of Biomedical Engineering, 2017, 45(1), 273.
 S. Stichler, et al: Thiol-ene cross linkable hydrogels as bioinks for biofabrication. Macromolecular Symposia 2017, 372(1), 102.
 B. Baumann, et al: Control of nanoparticle release kinetics from 3D printed hydrogel scaffolds. Angewandte Chemie International Edition 2017, 56, 4623.
2:00 PM - *BM05.08.02
Longitudinal Mapping of the Mechanics of Newborn Mouse Joint Cartilage
Emilios Dimitriadis 1 , Edward Mertz 3 , Preethi Chandran 2 , Ferenc Horkay 3 , Peter J. Basser 3 Show Abstract
1 NIBIB, NIH, Bethesda, Maryland, United States, 3 NICHD, NIH, Bethesda, Maryland, United States, 2 Chemical Engineering, Howard University, Washington, District of Columbia, United States
Cartilage matrix is composed of a dense collagen mesh within which the highly charged glycoprotein, aggrecan, is entangled in high concentrations and is responsible for matrix osmotic swelling. The equilibrium between swelling and collagen matrix constraints is what provides cushioning of bones at load bearing joints. The composition of the tissue changes across tissue depth. The relationship between osmotic and mechanical properties and composition is poorly understood. Moreover, in growing cartilage, the relative composition and organization of the various components changes along the bone axis and in the vicinity of chondrocytes, the pericellular matrix (PCM). Axial mapping of the mechanics is further complicated due to the need to physically section the tissue to gain access.
Here we study mouse cartilage. Even though mice are extensively used as model systems for a wide range of pathologies including arthritis, there are limited studies mapping matrix mechanics across different regions. Newborn mouse cartilage adds the complication that the tissue is densely populated with chondrocytes creating a complex 3-D composite that is continuously varying both in space and time. Nanomechanical studies, typically performed by indenting tissue sections, are subject to errors due to matrix collapse, surface roughness and diffusional loss of aggrecan from the section surface. Furthermore, data interpretation often poses its own challenges not least because of the natural inhomogeneity of the tissue.
Here, we performed high-resolution (1um) elasticity mapping of the knee cartilage matrix of newborn mice. The indentations were performed on thin (~12um) cartilage sections that were cut parallel to the bone longitudinal axis and mildly fixed to minimize loss of aggrecan. We chose the diameter of the microspheres used as indentation probes and we applied indentations that were large enough as to minimize the effects of surface roughness and geometric inhomogeneities. To consistently analyze the data, we developed a novel method for obtaining an effective contact point on the tissue surface. Our model fitting protocol ensures that we are probing bulk matrix properties and minimizes the effects of surface damage, tissue inhomogeneity and finite sample thickness. Matrix regions were extracted by correlation with optical images. Our results show interesting variation of properties between different regions and large variations in the vicinity of chondrocytes. The latter presented an additional challenge because the septa between chondrocytes are often very narrow adding to the difficulty of interpretation. Further modeling and analysis points to continuously and strongly varying properties of the PCM. The variability of matrix elasticity across the growing cartilage will be described and possible correlations with composition will be discussed.
3:30 PM - BM05.08.03
The Study of Phorocurable, Biodegradable Polymeric Materials and the Effects of 3D Printing toward the Mechanical Properties
June-Yo Chen 1 , Shin-Tian Chien 1 , Wai-Sam Ao-Ieong 1 , Yih-Lin Cheng 2 , Jane Wang 1 Show Abstract
1 Department of Chemical Engineering, National Tsing Hua University, Hsinchu Taiwan, 2 Department of Mechanical Engineering, National Taiwan Univeristy of Science and Technology, Taipei Taiwan
Additive manufacturing, also commonly known as 3D printing, has become one of the most powerful prototyping methods in the past two decades. However, the use of polymeric materials has been mostly limited to either thermoplastics or photocrosslinkable polymers, both of which are considered brittle and lack elasticity. With the high demand of complicated structures from the biomedical field, many of the existing 3D printable polymers are unideal due to the low biocompatibility, high Young’s Modulus and low elasticity. In this work, the combination between three biodegradable polymers is explored through photocuring: Poly(caprolactone) diacrylate (PCLDA), Poly(ethylene glycol) diacrylate (PEGDA) and Poly(glycerol sebacate) acrylate (PGSA). The various combinations of co-polymer ratio lead to products with Young’s modulus ranging between 0.5-10 MPa, right around the general soft tissue mechanical properties, along with elasticity between 8-170%. Through the analysis of substrate stiffness, UTS, elongation at break and the degradation properties, several combinations are identified as useful materials for heart, lung, liver, kidney, and vasculature regeneration. The mechanical properties are further studied to compare between scaffolds created via UV-crosslinking and 3D printing. Preliminary animal testing also proved that the co-polymers were non-toxic with minimum immunoresponses. Through this study, strong device and scaffold fabrication capabilities of additive manufacturing on polymeric materials are demonstrated.
3:45 PM - BM05.08.04
Stereolithography of Silicone for Patient-Specific Devices for the Left Atrial Appendage
Sanlin Robinson 1 , Cameron Aubin 1 , Thomas Wallin 1 , Robert Shepherd 1 Show Abstract
1 , Cornell University, Ithaca, New York, United States
More than 90% of thromboembolisms in patients with atrial fibrillation (AF) are thought to originate in the left atrial appendage (LAA). The LAA is pocket of tissue that protrudes from the left atrium, blood can become trapped in this hooked structure and clot. These clots can embolize from the LAA into the atrium and then flow to other regions of the body, such as the brain where they could cause ischemic stroke to occur. Occlusion of the LAA offers an alternative to oral-anticoagulants, which are strongly influenced by diet, drugs, and insufficient monitoring. Current occluders are composed of nitinol mesh and fabricated in standard circular architectures with a limited number of sizes. The nitinol mesh can cause perforation of the paper-thin walls of the LAA tissue, and the circular geometry often results in residual blood flow into the LAA. It is possible that the high variability in size and morphology of the LAA is linked to this incomplete LAA closure. Therefore, using stereolithography, we have designed and fabricated a patient-specific, soft device that occludes the LAA by completely conforming to its anatomy.
We obtained cardiac computed tomography (CT) images of a variety of morphologies of human LAAs. Through methods of CT segmentation and computer aided design (CAD) we produced a 3D rendering of the blood volume within the LAA. We used this 3D structure as a design template to make the patient-specific, hollow devices. We added a valve to the design to enable transcatheter delivery, and safe filling of these occluders during deployment. We used a high-resolution stereolithographic printer (Ember, Autodesk) with a custom silicone resin previously developed in our lab to print these hollow designs with integrated valves. Since these are blood contacting devices, we coated them in a commercially available polycarbonate urethane known to be thromboresistant. We characterized the wall thickness variation, surface coating, burst pressures, and biocompatibility of these devices. Additionally, we demonstrate the efficacy of this patient-specific, soft device using in vitro flow loops.
4:00 PM - BM05.08.05
Ferromagnetic 4D Printing of Programmable Soft Active Matter
Yoonho Kim 1 2 5 , Hyunwoo Yuk 1 5 , Ruike Zhao 1 5 , Shawn Chester 3 , Xuanhe Zhao 1 4 5 Show Abstract
1 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 5 Soft Active Materials Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 , Department of Mechanical and Industrial Engineering, New Jersey Institute of Technology, Newark, New Jersey, United States, 4 Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Soft active materials capable of transforming into programmed shapes in an untethered, controllable manner can bring promising applications in diverse fields such as drug delivery, tissue engineering, and minimally invasive surgery. Several types of shape-programmable soft matter have been proposed but often limited to simple geometries, while lacking sufficient responsiveness, limiting their functionalities in such potentially useful areas.
We introduce a method of ferromagnetic 4D printing to realize highly responsive and fully programmable active materials that can transform from a printed shape into a prescribed three-dimensional structure in the presence of external magnetic field. Our approach is based on printing an uncured elastomeric material containing ferromagnetic microparticles using direct ink writing. The particles dispersed in the elastomer matrix are magnetized to possess magnetic dipoles and act as small permanent magnets. Applying external magnetic field around the dispensing nozzle while printing, we make those particles aligned along the printing direction upon deposition, which gives rise to overall magnetic polarity in a printed filament towards external field.
This method allows us to design ferromagnetic domains in a printed three-dimensional structure, which, after curing, exhibits dynamic response of fast transforming into a programmed shape under the applied magnetic field and reverting to its original shape upon the removal of external field. Programming of such magnetically active soft materials is guided by finite element simulation, which enables us to design complex structures with multiple modes of programmed actuation. Furthermore, our fabrication technique based on direct ink writing provides a high degree of design flexibility, unlike many of other shape-programmable materials which have failed to achieve complex shapes due to their limited fabrication methods.
Combined with the design flexibility of our fabrication method, the fast and dynamic response of 3D-printed magnetically active soft materials is expected to provide a wide range of potential applications, especially in biomedical fields such as drug delivery and tissue engineering, where untethered actuation of such programmable active materials can be useful as multifunctional devices. To open this new avenue, we present a set of demonstrations from simple 1D to complex 3D structures that exemplify the concept and potential applications of the proposed method of ferromagnetic 4D printing.
4:30 PM - BM05.08.07
Development of a Flexible MIP-Based Biosensor Platform for the Thermal Detection of Neurotransmitters
Marloes Peeters 1 , Kai Betlem 1 , Bart van Grinsven 2 , Thomas Cleij 2 , Craig Banks 1 Show Abstract
1 , Manchester Metropolitan University, Manchester United Kingdom, 2 Chemistry, Maastricht University, Maastricht Netherlands
Molecularly Imprinted Polymers (MIPs) are synthetic antibody mimics; similar to antibodies, they have high affinity for a chosen template molecule but their advantages include low-cost, superior chemical and thermal stability, and straightforward production process. In this contribution, we will focus on Molecularly Imprinted Polymers (MIPs) that are synthesized for drug compounds such as antidepressants (Prozac). These polymers gels are mixed with screen-printed ink to produce mass-producible bulk modified MIP Screen-Printed Electrode (MIP-SPEs). We will explore different SPE supporting surfaces, including polyester, tracing paper and household-printing paper1.The performance of these MIP-SPEs is studied with two (patented) thermal techniques, including the Heat-Transfer Method (HTM) and Thermal Wave Transport Analysis (TWTA). Advantages of this thermal techniques include that it is label-free, low-cost and data processing is straightforward. The sensors are mounted into a flowcell (volume 110 μL) that is coupled to a thermal device with an in-house design. This gives advantages. The thermal response through the MIP-SPEs is determined by measuring the temperature gradient between the sensor surface and liquid. Changes at the solid-liquid interface, by binding of the target molecule, is reflected into the temperature at the liquid and calculated as the corresponding thermal resistance. Thereby, it is possible to detect drug compounds at the low nanomolar range, which is well within the psychologically relevant range and this makes is a very powerful analytical tool for drug screening.
Sensors mixed with polymer gels and printed onto household-printing paper were considered the most promising as they had the highest recognition capabilities for these drug compounds and possess advantageous material properties, including sustainability and flexibility of the material. TWTA, a thermal method that was first introduced in 2016, was proven to be a promising alternative compared to HTM as it had a shorter measurement time (2 min) and significantly higher signal to noise ratio. In recent work, the technique has been further exploited to determine the presence of pathogenic bacteria2, growth of microorganisms and evaluation of enzyme catalysis. With thermal methods, it is possible to develop a portable sensor platform that is capable of low-cost and straightforward detection of biomolecules on-site. A sensor platform has been designed that is flexible and therefore holds great potential for the use in biomedical devices and complex sensor architectures.
 S. Casadio, J.W. Lowdon, K. Betlem, J.T. Ueta, C.W. Foster, T.J. Cleij, B. van Grinsven, O.B. Sutcliffe, C.E. Banks, M. Peeters, Chem. Eng. J. 2017, 315, 459-468.
 E. SteenRedeker, K. Eersels, O. Akkermans, J. Royakkers, S. Dyson, K. Nurekeyeva, B. Ferrando, P. Cornelis, M. Peeters, P. Wagner, H. Dilien, B. van Grinsven, T.J. Cleij, accepted in ACS Inf. Dis. DOI: 10.1021/acsinfecdis.7b00037
4:45 PM - BM05.08.08
Direct-Writing of Polysaccaride and Protein-Based Tubular Soft Materials and Assemblies
Wuyang Gao 1 , Nima Vaezzadeh 1 , Axel Guenther 1 Show Abstract
1 , University of Toronto, Toronto, Ontario, Canada
Tubular structures are abundant in tissues and characterized by a wide range of luminal diameters, wall thicknesses, and compositions. In spite of their importance, our ability to rapidly define tubular structures with different shapes and morphologies from a variety of different biopolymers and gelation mechanisms remains limited. Here, we direct-write soft tubular structures using a microfabricated printhead. A biopolymer solution and two flow confining solutions are supplied to different printhead layers where they are co-axially organized. Gelation of the biopolymer is initiated at the interfaces with the confining solutions and progresses while passing through a cylindrical confinement until a biopolymeric tubular structure with tunable dimensions and composition emerges. We prepare tubular structures in different polysaccharide- and protein-based biomaterials at gelation times of up to 200s. Morphologies include homogeneous tubes with smooth and buckled walls as well as Janus, stripe patterned and multilayered tubes. Importantly, we prepare collagen tubes in a template-free manner with inner diameters and wall thicknesses that favorably agree with predictions from an analytical model. Direct writing of a collagen tubes creates perfusible constructs. We expect the demonstrated approach to be readily compatible with extrusion-based bioprinters and enable bioprinting of tubular tissues, bio-hybrid systems and soft robotic elements.
BM05.09: Poster Session III
Thursday AM, November 30, 2017
Hynes, Level 1, Hall B
8:00 PM - BM05.09.01
Structure Property Relationships in Nanocomposite Hydrogels
Ha Dang 1 , Jianyuan Zhang 1 , Robert Macfarlane 1 Show Abstract
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Hydrogels are an important class of soft materials consisting of a crosslinked network of water-soluble polymer chains that have significant promise for applications in drug delivery and tissue engineering. Their utility in these fields is derived from their tunable Young’s moduli, high degree of porosity, and potential for self-recovery from mechanical or chemical damage. These properties can be further improved by synthesizing composite hydrogels consisting of both flexible polymers and rigid inorganic particles that act as crosslinking points for the polymer chains. However, systematic studies that correlate the structure of the inorganic particles (e.g. size, shape, concentration, and surface coating) to the physical properties of the gel (e.g. young’s modulus, porosity, toughness) remain underdeveloped. In other words, while it is known that inorganic materials can augment a gel’s properties, it is not always readily obvious which particular particle composition should be used to target a predetermined physical characteristic of the desired gel. This project focuses on controlling nanoscale variables such as polymer composition, polymer conformation, particle size, and particle weight percentages to tune hydrogels’ mechanical properties and then uses that knowledge to design a hydrogel network with desirable mechanical response. We employ coulombic interactions between oppositely charged ABA triblock copolymers as a driving force for gelation, and incorporate hard materials, i.e. charged silica nanoparticles, to modify the crosslinked network within the gels. Rheology assays such as frequency sweeps and step strain relaxation curves are used to study the composite hydrogels’ elasticity, recovery behavior, and mechanical strength. Colorimetric dyes are also used to measure the hydrogels’ porosity via their release rates of these networks. Together, these studies provide a fundamental understanding of the correlation between nanoscopic structure within a gel and the physical properties of the resulting material, enabling for better design of gels for future applications in biological and biomedical applications.
8:00 PM - BM05.09.02
Fast-Reacting Biosensors Based on Smart Hydrogels with Low Space Requirements
Christopher Reiche 1 , Julia Koerner 1 , Hsuan-Yu Leu 1 , Jules Magda 1 , Florian Solzbacher 1 Show Abstract
1 , University of Utah, Salt Lake City, Utah, United States
Smart hydrogels are hydrophilic polymer materials that are tailored to express a binding affinity for various analytes, e.g. glucose, pH or protein biomarkers. The binding of the specific analyte induces a volume-phase transition resulting in a swelling or shrinking of the hydrogel. Typically, hydrogels are highly biocompatible and are therefore an excellent candidate for the development of health-related sensors targeting biomarkers.
The challenge for such an application lies in the sensitive, reliable and robust detection of the hydrogel’s volume change. Furthermore, in order to create implantable devices or integrate the sensors in existing equipment both the hydrogel and the transducer need to be sufficiently compact. Previous detection methods include sensing of the swelling pressure of hydrogel by using piezo resistive pressure sensors or the deformation of cantilever beams. The latter, while highly sensitive, requires large laser-based detection setups and is therefore often unsuited for the applications mentioned above. Pressure sensors can be miniaturized but due to their rather low sensitivity larger amounts of hydrogels need to be incorporated.
A critical parameter for a biosensor, however, is its reaction time. With respect to hydrogels, the speed of the volume change is diffusion limited and therefore, depending on the size of the hydrogel it can take minutes up to hours until a detectable volume change of the gel occurs.
We have developed a novel transduction mechanism reminiscent of the cantilever methods in which a very thin layer of hydrogel creates a fast response when the analyte solution gets into contact with the hydrogel’s surface. We employ a very thin double layer polyimide with embedded meandering metal leads. The hydrogel is attached to one side of the polyimide by using an adhesion promoting process. When the hydrogel is exposed to the analyte, its surface responds quickly and bends the thin polyimide, thereby altering the electric properties of the meander structure. This can be detected as an amplitude and phase change of the measured sensor output voltage at high frequencies (above 10 MHz). Based on the very low profile of the polyimide – hydrogel layer structure, this novel sensing method is ideal for applications with strong spatial restrictions and for example allows the incorporation in a medical catheter to detect analytes in the bloodstream. Since the sensing relies on the initial surface response of the hydrogel instead of the slow diffusion based reaction, sensor response times could be significantly decreased to a few minutes or even less.
We present first proof-of-principle experiments that indicate a great potential of this bending- based transduction approach and discuss simulations and further optimization of the meander structure.
Florian Solzbacher declares financial interest in Blackrock Microsystems LLC and Sentiomed Inc.
8:00 PM - BM05.09.03
Development of Brain Phantom for Evaluation of Transcranial Magnetic Stimulation
Hamzah Magsood 1 , Ahmed El-Gendy 1 , Kshitij Jha 2 , Ravi Hadimani 1 , Mesfin Tsige 2 Show Abstract
1 , Virginia Commonwealth University, VA, Virginia, United States, 2 , University of Akron, Akron, Ohio, United States
Transcranial Magnetic Stimulation (TMS) is a non-invasive technique used for treatment and diagnosis of many neurological conditions–. However, the experimental measurements of induced electric fields in the brain tissues is not well reported due to non-availability of anatomically realistic head/brain phantoms. We have developed a 3-D anatomically realistic brain phantom using MRI images, segmentation of tissues, 3-D printing technique and by preparation of polymer that mimics the electrical conductivity and mechanical stiffness of different regions of the brain. The phantom will be used for the purpose of evaluation of the neuromodulation such as transcranial magnetic stimulation (TMS) and transcranial Direct Current Stimulation (tDCS). It enables the professional in the field of the brain modulation and treatment to test and perform actual brain stimulations on the phantom that are accurate and match the clinical setting of the of TMS and tDCS treatment. There are currently no brain phantoms that can experimentally verify TMS and tDCS parameters. To produce the phantom for the work at hand, we 3-D printed shells for each tissue layer of the brain. Brain tissues are divided mainly into cerebrospinal fluid (CSF), white matter (WM), grey matter (GM), ventricles, and cerebellum. These layers are made into shells and after 3D printing them, they are filled with a conductive material (silicon with graphite, multi walled carbon nanotubes (MWCNT) and silver nanoparticles) that is capable of mimicking the electrical conductive properties of different brain tissues. The electrical conductivity of different brain tissue that we are matching in this phantom is as follows, ventricles & CSF=1.77 Sm-1, GM=0.23 Sm-1, WM=0.24 Sm-1, and cerebellum=0.65 Sm-1. A rational design of polymers with varied loading of fillers, based on functional performance and processability, is planned to advance the state of the art in the field
 M. Kobayashi and A. Pascual-Leone, “Transcranial magnetic stimulation in neurology,” Lancet, vol. 2, no. 3, pp. 145–156, 2003.
 S. H. Lisanby, B. Luber, T. Perera, and H. a. Sackeim, “Transcranial magnetic stimulation: applications in basic neuroscience and neuropsychopharmacology.,” Int. J. Neuropsychopharmacol., vol. 3, no. 3, pp. 259–273, 2000.
 E. M. Wassermann and S. H. Lisanby, “Therapeutic application of repetitive transcranial magnetic stimulation: a review,” Clin. Neurophysiol., vol. 112, pp. 1367–1377, 2001.
8:00 PM - BM05.09.04
Design and Function of Multi-Stimuli Responsive Hydrogels Based on Silk-Elastin-Like Proteins
Wenwen Huang 1 , Anna Tarakanova 2 , Markus Buehler 2 , David Kaplan 1 Show Abstract
1 , Tufts University, Medford, Massachusetts, United States, 2 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Harnessing proteins to generate stimuli-responsive biomaterials based on protein folding-unfolding offers tremendous opportunities for biomedical applications, ranging from healthcare to bio-nanodevices. Here we report a generic approach for the design of stimuli-responsive, fully degradable, and biocompatible protein hydrogels based on silk-elastin-like proteins (SELPs). The hydrogel fabrication process included a facile approach to obtain functional elastomeric dynamic protein hydrogels via an all aqueous, enzymatic crosslinking method. Select SELP hydrogels exhibited a range of dynamic physical properties including large responsive swelling ratios as well as significant reversible changes in mechanical properties, optical transparency, and micromorphology upon exposure to designed target stimuli, dependent on the silk-to-elastin ratio or the guest amino acid residue designed in the elastin domain. Further, physical modification of the silk domains via β-sheet formation provided a secondary control point to fine-tune mechanical stiffness to match ECMs while preserving stimuli-responsive features. Overall, this work systematically studies the sequence-structure-process-property relationships for producing dynamic biomaterials. These results will be useful to guide future library designs with specific targeted properties, leading to new opportunities in biomimetics, biomaterials, and tissue engineering.
This work was supported by NIH (U01 EB014976), the Tissue Engineering Resource Center (NIH P41 EB002520) and the Air Force Office of Scientific Research.
8:00 PM - BM05.09.05
Macromolecule Entrapment and Reconfiguration in Ultrasoft Zirconium Metallogel Nanocomposites
Amir Sheikhi 1 2 3 , Theo van de Ven 1 2 3 Show Abstract
1 Chemistry, McGill University, Montreal, Quebec, Canada, 2 Pulp and Paper Research Centre, McGill University, Montreal, Quebec, Canada, 3 Quebec Centre for Advanced Materials, McGill University, Montreal, Quebec, Canada
Trapping nano-sized drugs in ultrasoft, shear-thinning hydrogels with micron-sized pores is of particular interest, yet a persistent challenge in nanomedicine due to the lack of hydrodynamic confinement. Engineering molecular interactions between a macromolecule and a supramolecular gel may address this shortcoming, providing a key route to develop advanced drug carriers without compromising matrix elasticity. Here, we show that ultrasoft zirconium-based metallogels are able to trap and reconfigure model nanodrugs (e.g., dextran) through complexation and hydrogen bonding. The diffusion coefficient of dextran molecules (Mw ~ 10-2000 kDa, a ~ 2-20 nm) in zirconium carbonate (ZC) metallogels (G’ < 30 Pa), measured by pulsed field gradient nuclear magnetic resonance (PFGNMR) revealed, for the first time, the co-existence of hindered and enhanced collective diffusion regimes. Inspired by this, A brick-and-mortar-like ultrasoft nanocomposite metallogel is formed by crosslinking cellulose nanocrystals (CNC) with ammonium zirconium carbonate (AZC) to trap and reconfigure dextran. The bricks (CNC) reinforce the metallogel, compete with dextran in reacting with AZC, and decouple long-time dextran dynamics from network formation, while the mortar (AZC) imparts bimodality to the dextran diffusion.
8:00 PM - BM05.09.08
Self-Healing Hybrid Colloidal Gels Based on 2D Nanomaterials and Soft Nanoparticles
Brian Schwartz 1 , Nader Taheri Qazvini 1 , Matthew Tirrell 1 2 , Juan de Pablo 1 2 Show Abstract
1 Institute for Molecular Engineering, University of Chicago, Chicago, Illinois, United States, 2 , Argonne National Laboratory, Lemont, Illinois, United States
Exciting evidence suggests that two-dimensional (2D) materials hold great potential for developing new functional materials in nanomedicine. Despite this, the interactions of these materials with soft polymeric nanoparticles and their bottom-up assembly into mechanically robust materials remains essentially unexplored. Here we show that three-dimensional (3D) macroscopic assembly of 2D silicate nanosheets (Laponite) and gelatin nanoparticles, via pH-induced electrostatic interactions, can result in a highly elastic colloidal gel. The negatively-charged Laponite nanosheets and the positively-charged gelatin nanoparticles aggregate and assemble to form gels. The detailed structural characterization of the material are provided by X-ray scattering and electron microscopy imaging. Depending on the composition and pH, the rheological properties of the colloidal gels can be tuned from a viscoelastic liquid to an injectable gelatinous structure. The colloidal soft solids reveal that via these electrostatic interactions, there is the novel ability for noticeable shear-induced failure, but the elastic properties allow for immediate recovery upon release of shear strain. The tunability of these rheological properties, demonstrated by our hybrid gel, shows promising applications in 3D bioprinting of complex constructs for regenerative medicine and tissue engineering.
8:00 PM - BM05.09.09
Three-Dimensional Chemical Patterning of Micromaterials for Encoded Functionality
Ceren Yasa 1 2 , Hakan Ceylan 1 2 , Metin Sitti 1 Show Abstract
1 , Max Planck Institute for Intelligent Systems, Stuttgart Germany, 2 , Max Planck Eth Center for Learning Systems, Stuttgart Germany
Miniaturization of functional (soft) materials down to the scale of few micrometers promise unique applications in various fields, including biomedicine (e.g., active targeted drug delivery materials and devices), bioengineering (e.g., programmable tissue constructs), active matter (e.g., self-propelled microswimmers), and robotics (e.g., soft robots, mobile microrobots). Eventually, a functional device at an average size of a single cell with well-designed on-board sensing, actuation and self-powering capabilities might provide an unprecedented direct access to deep and complex body sites, such as brain, spinal cord, and eye, for minimally invasive future clinical operations, such surgery or therapeutic cargo delivery. Still far-fetched to realize this goal, though, a growing attention has been given towards this direction with the prospect of transforming many aspects of healthcare and bioengineering in the future.
Here, we present a platform based on two-photon crosslinking chemistry for micromanufacturing light-sensitive materials with programmable functionality. Addressing the large gap between intricate 3D CAD designs and corresponding physical realizations as sophisticated functional micromaterials has been long sought yet unattainable goal thus far. To realize this, we combine structural complexity provided by two-photon microprinting with spatiotemporally controlled chemical patterning and demonstrate a bullet-shape catalytic microswimmer with well-controlled compartmentalization. Since the motion at this small size scale suffers greatly from the viscous drag, an optimal 3D microswimmer body design is an important direction to gain maximum propulsion efficiency. Such untethered active materials could be particularly attractive for microrobotics and medical cargo carrier applications. Novel 3D microswimmer and microactuator designs could drastically increase in number and variety based on the conceptual strategy described herein. This method can generally be applied to any optically clear, light-sensitive material, paving the way to engineering a new generation of geometrically and chemically programmable, functionally active and passive micromaterials that can accomplish previously unconceivable active tasks.
8:00 PM - BM05.09.10
Inkjet Printable and Re-Writeable Full Structural Color
Han Sol Kang 1 , Yujeong Lee 1 , Ihn Hwang 1 , Kang Lib Kim 1 , Sunghwan Cho 1 , Cheolmin Park 1 Show Abstract
1 , Yonsei University, Seoul Korea (the Republic of)
Photonic crystals(PCs) based on the periodic construction of two different structural motives have been of great interest due to their unique structural colors(SC) in visible range. Structural colors are arising from reflection of light corresponding to their forbidden photonic band gaps. Materials engineering by controlling various parameters including dielectric constants, dimensions and shapes of structural elements of a PC allows for facile tuning of SC, making PCs potentially suitable for low-power reflective mode displays, e-books and sensors. In particular, block copolymers (BCPs) which are able to spontaneously develop periodically ordered phase-segregated microstructures upon film formation offer an extremely convenient and cost-effective route for fabricating SCs.
Furthermore, the microstructure as well as dielectric constant of a BCP PC are readily altered upon various external forces and environmental conditions such as electric, magnetic, thermal, solvating and mechanical stimuli, and the resulting stimuli-sensitive change in SC makes the BCP PC potentially useful for a variety of emerging sensors. A rewriteable full color SC display with fast writing speed and high resolution still remains a challenge. Here, we present a full color rewritable and printable BCP SC board. Localized addressing a reversible external stimulus to write and erase the SC in a BCP-based PC using an inkjet printer enables low cost rewriteable displays. Our method is based on position and concentration controlled ink-jet printing of a cross-linking agent, ammonium persulfate (APS) on a self-assembled poly(styrene-block-quaternized 2vinyl pyridine) (PS-b-QP2VP) copolymer SC film with alternating in-plane lamellae of the two blocks. The degree of cross-linking of QP2VP domains with APS is controlled with the concentration of APS droplets, successfully giving rise to R (low cross-linking), G (medium cross-linking) and B (high cross-linking) BCP SC upon selective swelling process of QP2VP domains with ethanol. Printing APS on a BCP SC film with a modified commercial office ink-jet machine, followed by ethanol swelling, allows us to develop a variety of full colored SC information including characters, symbols and images which is very equivalent to that obtained with commercial inkjet inks in resolution. Moreover, the written information is readily erased by the treatment of an un-crosslinking agent, hydrogen bromide (HBr). The reversible crosslinking and un-crosslinking with APS and HBr, respectively enables us to develop a chemically rewritable BCP SC board.
Ferenc Horkay, National Institutes of Health
Jun Fu, Chinese Academy of Sciences
Marc In het Panhuis, University of Wollongong
Jie Zheng, University of Akron
MilliporeSigma (Sigma-Aldrich Materials Science)
Multifunctional Materials | IOP Publishing
BM05.10: Networks and Structure Formation
Thursday AM, November 30, 2017
Sheraton, 2nd Floor, Back Bay C
8:30 AM - *BM05.10.01
Injectable Polymeric Cryogels for Breast Cancer Immunotherapy
Sidi Bencherif 1 2 3 , Dobrin Draganov 4 , Weiwei Li 2 , Ting-Yu Shih 2 , Catia Verbeke 2 , Glenn Dranoff 4 5 , David Mooney 2 Show Abstract
1 Department of Chemical Engineering, Northeastern University, Boston, Massachusetts, United States, 2 Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 3 UTC CNRS UMR 7338, Biomechanics and Bioengineering (BMBI), University of Technology of Compiègne, Sorbonne University, Compiègne France, 4 Department of Medical Oncology and Cancer Vaccine Center, Dana-Farber Cancer Institute and Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts, United States, 5 Institutes for BioMedical Research, Novartis, Cambridge, Massachusetts, United States
Cancer immunotherapy is rapidly emerging as a self-standing therapeutic domain in oncology, set to revolutionize the treatment of cancer. Cancer vaccines with defined antigens are now commonly used. However, using whole tumor cells, as tumor-associated immunogens, is a more promising and versatile approach that could lead to personalized vaccines. Currently, whole cell tumor vaccination is carried out as simple cell infusions that lead to large-scale cell death, little control over cell fate and immunomodulation, and a typically poor clinical outcome. To address these limitations of whole cell tumor vaccination, a minimally invasive polymeric cryogel-based vaccination system was engineered to localize transplanted tumor cells while mimicking key aspects of bacterial infection and directly controlling immune-cell trafficking and activation in the body. This approach provides a sustained release of GM-CSF to recruit host dendritic cells (DCs) to the porous material, and subsequently presents cancer antigens and TLR9 ligand CpG oligonucleotides to activate the resident DCs. Subcutaneous injection of the cryogel vaccines against mammary cancer in mice evoke protective immunity and elicit durable, tumor-specific immunity with minimal extracorporeal manipulation. The cryogel-based vaccination system represents a promising tool for the development of novel active immunotherapeutic approaches to cancer.
Acknowledgement: This work was financially supported by the National Institutes of Health (Grant No. 5R01DE019917-03) and Northeastern University (Tier 1 Provost Grant).
9:00 AM - *BM05.10.02
Surface Properties of Oligosaccharide Coatings and Effect on Polyelectrolyte Dynamics
Saswati Basu 1 , Hashanthi Perera 1 , Jyothirmai Simhadhri 1 , Preethi Chandran 1 Show Abstract
1 Department of Chemical Engineering, Howard University, Washington, District of Columbia, United States
The presentation will explore how surface properties of oligosaccharides can impact the assembly and self-healing of 3D printed hydrogels. The surfaces of tissue components, e.g. the collagen filaments, proteoglycan ground substance, and cells, are typically coated with oligosaccharides. We present the surface interactions attributable to different categories of oligosaccharides: charged vs. uncharged, those exhibiting strong periodic hydrogen bonding vs. those that do not. Uncharged oligosaccharides that strongly engage in hydrogen bonding structure the water network around them and resist the approach of opposing surfaces several nanometers away. The length of the structured water layer increases with the velocity of the approaching body, until the layer exhibits a brittle fracture-like break down. Charged oligosaccharides do not exhibit such water-structuring. However certain charged and uncharged oligosaccharides exhibit strong adhesion that is specific for self. Not all oligosaccharides exhibit self-specific adhesion, implying that there a biological design imperative to the choice of oligosaccharide coating in cells and tissues. We also present a experimental and computational case-study of how the oligosaccharide properties can alter the dynamics of a polyelectrolyte. The surface properties of oligosaccharides are an additional tool in the biomolecular toolbox for designing and optimizing the 3D printing of scaffolds.
10:00 AM - BM05.10.03
The Preparation and Properties of Konjac Glucomannan-Based Double Network Hydrogel
Yunlan Su 1 , Zhiyong Li 2 , Dujin Wang 1 Show Abstract
1 , Institute of Chemistry, Chinese Academy of Sciences, Beijing China, 2 , Institute of Chemistry, Chinese Academy of Sciences, Beijing China
Hydrogels, which are water-swollen polymer networks, are considered as innovative biomedical materials, due to their unique properties such as biocompatibility, responsiveness to various kinds of stimuli, ultralow surface friction and environmental friendliness. However, most of the natural and synthetic hydrogels exhibit a low mechanical strength, which severely restricts their biomedical applications. Hence, many efforts have been focused on improving the mechanical strength of hydrogels to develop a tough hydrogel for use as a scaffold material in tissue engineering. As a representative of tough hydrogels, the double-network (DN) hydrogel is characterized by a special network structure consisting of two types of polymer components with opposite physical characteristics: the minor component is a highly cross-linked rigid skeleton serving as a sacrificial bond, and the major component comprises a sparsely cross-linked ductile substance acting as a hidden length to sustain stress by large extension afterwards. In this study, we present a simple method to synthesize a tough neutral-polymer-based DN hydrogel without any complicated molecular stent, in which neutral polysaccharide konjac glucomannan (KGM) is introduced as the first network, and neutral polyacrylamide (PAAm) is applied as the second network by polymerization. The PVA–KGM hydrogel composite was first developed by a cycle freezing and thawing (CFT) method in the presence of an alkaline substance. Compared to the pure KGM hydrogel, the PVA–KGM hydrogels have a higher compressive strength and initial elastic modulus, indicating that the existence of PVA is helpful to improve the mechanical properties of the PVA–KGM hydrogel. And the improvement in the mechanical properties of the PVA–KGM hydrogels suggests the formation of more intermolecular interactions with the addition of PVA proved by FT-IR results.
The compressive properties of the PVA–KGM/PAAm DN hydrogels have also been investigated quantitatively. The DN hydrogel shows an extraordinarily high compressive strength of 30 MPa, which is more than 93 times higher than that of the PVA–KGM hydrogel (0.32 MPa), and almost 38 times that of the PAAm hydrogel (0.79 MPa). Similarly, the effect of CFT times on the mechanical properties of PVA–KGM/PAAm DN hydrogels was also investigated. The σc increases significantly with increasing the number of FT cycles, i.e. from 30 MPa at 1 FT cycle to 65 MPa at 4 FT cycles. Hence, this tough hydrogel has potential capability to be used as cartilage (exhibiting a compressive fracture stress of 36 MPa) and bone tissue engineering scaffolds.
10:15 AM - BM05.10.04
Ideal Reversible Polymer Gels—Theory and Experiments
German Parada 1 , Xuanhe Zhao 1 Show Abstract
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Model polymer networks are powerful experimental tools to carry out fundamental polymer physics and mechanics studies. Most of these networks, however, are restricted to containing non-reversible covalent bonds. Here, we introduce the concept of ideal reversible polymer networks, analogs to ideal covalent polymer networks, but exhibiting viscoelastic behaviors due to the presence of reversible junctions. We present a theoretical framework to describe their mechanical response and then validate this framework using a model PEG-based hydrogel. The ideal reversible polymer networks are shown to behave as a single Maxwell element (spring and dashpot in series), with the plateau modulus and relaxation times controlled by the reversible bond dynamics and experimental parameters (temperature, polymer concentration). We use this theory to predict experimental trends and to propose how to independently control the plateau modulus and relaxation time of the networks. Also, the theory allows to measure kinetic parameters of the reversible bond from macroscopic mechanical measurements. To validate the proposed theory and strategies, we synthesize and characterize (by small-amplitude oscillatory rheology) a hydrogel composed of end-functionalized 4-arm PEG polymers. All the experiments conducted (varying pH, temperature, polymer concentration and PEG molecular weight) are adequately described by the theoretical framework developed, illustrating the strength and applicability of such theory to describe reversibly-crosslinked networks and predict their properties, a significant step to achieve rational viscoelastic material design.
10:30 AM - BM05.10.05
Rupture of Polymers by Chain Scission
Yunwei Mao 1 , Brandon Talamini 1 , Lallit Anand 1 Show Abstract
1 , MIT, Cambridge, Massachusetts, United States
One of the distinguishing features of elastomeric materials, which consist of a network of flexible polymeric chains, is that the deformation response is dominated by changes in entropy. Accordingly, most classical theories of rubber-like elasticity consider only the entropy and neglect any changes in internal energy. On the other hand, the fracture of strongly cross-linked elastomers is essentially energy dominated, as argued in the well-known Lake-Thomas model for the toughness of elastomers. However, a single model unifying these two phenomena is still lacking. We provide a rational yet simple model for deformation and fracture of cross-linked polymers, based on two ingredients: (i) a non-Gaussian statistical mechanics model of polymer chains that accounts for the increase in energy due to the deformation of molecular bonds; (ii) a chain scission criterion based on the bond deformation energy attaining a critical value. Using this model, we can estimate the rupture stretch of elastomeric materials from fundamental quantities describing the polymer network. We use this model to relate the flaw sensitivity of elastomers to an intrinsic material length scale.
10:45 AM - BM05.10.06
Preparation of PNiPAM Based Hydrogels and Microgels with Functional Crosslinking Points and Variable Degree of Heterogeneity
Apostolos Karanastasis 1 , Bradley Frieberg 2 , Edwin Chan 2 , Chaitanya Ullal 1 Show Abstract
1 Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Poly(N-isopropylacrylamide) (pNiPAm) hydrogels and microgels (gels & μgels) have been the object of numerous studies related to both their structural characteristics as well as their multifaceted chemical functionalization strategies. Still, to the best of our knowledge, the implementation of functional crosslinkers (FCs) in the preparative schemes of PNiPAm gels & μgels remains relatively unexplored. In this contribution we report on the synthesis of a novel hydrophilic methacrylamide FC monomer which was successfully utilized for the preparation of PNiPAm gels & μgels with variable degrees of spatial heterogeneity. The focal point of this study was the quantification of structural perturbations induced by the introduction of the FC in comparison with reference systems formed by the copolymerization of the commonly used crosslinker methylene-bis-acrylamide (BIS). To this end, two distinct cases were examined: (i) systems formed with 99.8% BIS and 0.2% FC conjugated with the model cationic dye rhodamine (FC@Rh) and (ii) systems with pristine FC content. Structural and morphological insight of gel materials was provided by means of turbidimetry, laser confocal scanning microscopy and small angle neutron scattering (SANS) whereas μgels were studied with dynamic light scattering (DLS) and SANS in variable temperature regimes. Our results suggest that the 99.8%BIS/0.2%FC@Rh system can serve as a prospective platform for the study of spatial heterogeneities in soft materials with super resolution microscopy techniques.
11:00 AM - BM05.10.07
Characterizing Supramolecular Crosslink Dynamics via Stress-Relaxation Mechanics—New Insights on How to Control Transient Structural Hierarchy in Polymer Gels
Niels Holten-Andersen 1 Show Abstract
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Efforts to engineer polymer gel mechanics is increasingly coupled to the design of transient crosslink dynamics. Herein, we seek to gain a deeper understanding of how polymer gel mechanical properties can be controlled over multiple hierarchical time-scales via design of supra-molecular metal-coordinate crosslink structure on multiple length-scales. By analyzing the stress relaxation of transient polymer networks assembled via single metal ion-coordination complexes, multi-metal ion-coordination cages or metal nanoparticle-coordination junctions, we explore the correlation between the structural hierarchy of the supra-molecular crosslink designs and the resulting distributions of stress relaxation modes. We confirm that the average timescale of network relaxation in the three model systems is dependent on the number f of stress bearing chains per supra-molecular crosslink structure whereas the distribution of timescales appears to depend on the variation in f. These findings offer deeper insights on how to characterize supramolecular structural dynamics via stress relaxation mechanics and could help improve our understanding of and control over molecular hierarchy in polymer gel materials design.
11:15 AM - BM05.10.08
Controlling Dynamic Mechanics of Self-Healing Hydrogel by Crosslink Engineering
Qiaochu Li 1 , Brian Chapman 2 , Bavand Keshavarz 1 , Sumeet Mishra 2 , Pangkuan Chen 1 , Joseph Tracy 2 , Niels Holten-Andersen 1 Show Abstract
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States
The macroscopic healing rate and efficiency in self-repairing hydrogel materials are largely determined by the dissociation dynamics of their polymer network, which is hardly achieved in a controllable manner. Inspired by mussel’s adhesion chemistry, we developed a novel approach to assemble inorganic nanoparticles and catechol-decorated PEG polymer into a hydrogel network. When utilized as reversible polymer-particle crosslinks, catechol-metal coordination bonds yield a unique gel network with dynamic mechanics controlled directly by interfacial crosslink structure. Taking advantage of this structure-property relationship at polymer-particle interfaces, we designed a hierarchically structured hybrid gel with two distinct relaxation timescales. By tuning the relative contribution of the two relaxation modes, we can finely control the gel’s dynamic mechanical behavior in a broad range, from a viscoelastic fluid to a stiff solid. Self-healing kinetics can also be easily tuned by the ratio of different crosslinking structures. With this strategy, we successfully achieved rapid self-healing behavior in a solid stiff hydrogel.
11:30 AM - BM05.10.09
Scaling Toughness with Macro-Scale Double Network Composites
Daniel King 1 2 , Riku Takahashi 3 , Tsuyoshi Okumura 3 , Yiwan Huang 1 , Tao Lin Sun 1 2 , Takayuki Kurokawa 1 2 , Jian Ping Gong 1 2 Show Abstract
1 Faculty of Advanced Life Science, Hokkaido University, Sapporo Japan, 2 Global Station for Soft Matter Research, Hokkaido University, Sapporo Japan, 3 Graduate School of Life Science, Hokkaido University, Sapporo Japan
Load-bearing biological materials such as ligaments and tendons possess unique mechanical properties including high stiffness, flexibility, and shock absorption, all while containing water. These materials are difficult to replicate synthetically. Traditionally, water containing materials are exceptionally brittle, in contrast to these natural materials. The development of Double Network (DN) hydrogels significantly expanded the applicability of hydrogels, by introducing the first method to create gels with highly enhanced toughness. Through combining two interpenetrating networks, where the first network is extended, stiff, and brittle, and the second network is compliant and ductile, a synergistic increase in performance is achieved, representing a new materials system: water containing materials with extremely high toughness and stiffness. However, structurally, ligaments vary from this architecture. They contain a structure based around a core of stiff, hierarchical collagen fibers, which have a modulus over 1 GPa. This allows a material primarily consisting of a soft and wet extracellular matrix to withstand large loads without fracture. Learning from the fracture process of DN gels and studying the design of natural materials, here we present macro-scale "Double Network" composites, consisting of hard/soft combinations of a rigid frame and soft elastomer or gel matrix. Fracture of the rigid frame dissipates energy, while the soft matrix deforms and maintains mechanical integrity. By tuning the geometry of the frame, the mechanical response can be precisely controlled, including the fracture force, fracture strain, and fracture energy. This process opens up the possibility to create structural composite materials with mechanical properties that greatly outperform their neat components.
BM05.11: Functional Polymer Gels
Marc In het Panhuis
Thursday PM, November 30, 2017
Sheraton, 2nd Floor, Back Bay C
1:30 PM - *BM05.11.01
Polyelectrolyte Hydrogel Particles Used as Internal Curing Agents in High-Performance Concrete
Kendra Erk 1 , Matthew Krafcik 1 Show Abstract
1 School of Materials Engineering, Purdue University, West Lafayette, Indiana, United States
Polymer hydrogels have many industrial uses, from injectable drug-delivery and self-healing materials to the superabsorbent particles used in baby diapers and as soil additives. This presentation will describe the design and use of superabsorbent polymer hydrogel particles as internal curing agents in high-performance concrete. When incorporated into concrete mixtures, the swollen hydrogel particles release their stored water to fuel the curing reaction, resulting in reduced mixture shrinkage and cracking and thus increasing the concrete’s overall durability and service life. However, the hydrogel’s swelling performance and mechanical properties are strongly sensitive to multivalent cations that are naturally present in the mixture (including Ca2+ and Al3+). By synthesizing model poly(acrylic acid-acrylamide)-based hydrogel particles with different chemical compositions and exposing the particles to controlled ionic solutions, we discovered that the presence of multivalent cations decreased the swelling capacity and altered the swelling kinetics to the point where some hydrogel compositions displayed fast deswelling behavior and the formation of a mechanically stiff outer shell. Interestingly, when incorporated into mortar mixtures, the hydrogel particles which displayed rapid water release due to these ionic interactions were found to be the most effective at reducing the overall shrinkage. And while practitioners commonly assume that hydrogel internal curing agents are chemically inert within concrete mixtures, our more recent results have shown that instead, the presence of hydrogel particles of certain compositions appears to encourage the formation of specific inorganic phases within the concrete’s microstructure, including calcium hydroxide. Ongoing work is now focused on optimizing the chemistry of the polymer hydrogels in order to tune and control the microstructure of the concrete, with the ultimate goal of designing new concrete mixtures with increased performance and durability.
2:00 PM - BM05.11.02
Rough Adhesive Hydrogels (RAd Gels) for Underwater Adhesion
Laura Bradley 1 , Nathan Bade 1 , Lisa Mariani 1 , Kevin Turner 1 , Kathleen Stebe 1 , Daeyeon Lee 1 Show Abstract
1 , University of Pennsylvania, Philadelphia, Pennsylvania, United States
Underwater adhesion of soft materials such as hydrogels to various surfaces is important in a wide range of biomedical and environmental applications. Without using specific chemical functionality, however, it is challenging to achieve strong underwater adhesion due to the high volume fraction of water and chemically inert nature of hydrogels. In this work, we present rough adhesive hydrogels (RAd gels) that have strong underwater adhesion to surfaces with water receding contact angle greater than 50°, such as metal and various polymers. RAd gels made of a crosslinked network of poly(2-hydroxyethyl methacrylate)-co-poly(ethylene glycol) diacrylate are synthesized via radical polymerization in an enclosed chamber with air gap above the precursor solution. We identify two critical features that induce underwater adhesion. Surface roughness, known to suppress adhesion between two surfaces in air, is shown to be beneficial for underwater adhesion by facilitating drainage of the lubricating water film between the RAd gel and the surface. We believe a combination of phase separation and Bénard-Marangoni convection leads to the development of surface roughness on the top (vapor) side of RAd gels. The composition of the hydrogel also plays an important role by inducing a large contact area between the gel and the surface via deformation, and hydrophobic interactions with the surface. We also demonstrate the synthesis of double-sided RAd gels by imparting roughness to both sides and show that fibroblasts are able to adhere to and spread on the surface and stay viable, suggesting that these RAd gels are indeed biocompatible.
2:15 PM - BM05.11.03
Microgels for Drug Delivery—Loading and Release in Liquid Flows and Micro-Drops
Per Hansson 1 Show Abstract
1 , Uppsala University, Uppsala Sweden
Polyelectrolyte microgels are hydrogels used as drug carriers for protein-, peptide- and amphiphilic drugs. In liver cancer therapy, drug loaded microgels with diameters of order 100 µm are deposited in the blood vessels at the site of the tumor where they cause embolization following the swelling of the networks during drug release. This increases the efficiency of the therapy by reducing the flow of nutrients to the tumor and decreases side effects by limiting systemic spreading of the toxic drug. The swelling response and release kinetics depend on the strength of interaction between the network and the drug. For amphiphilic drugs it is expected to depend strongly on their self-assembling properties and distribution inside the microgels [1, 2]. We will show how detailed information about the mechanisms of drug loading and release can be obtained from a combination of microscopy studies of single microgels in liquid flows and in microscopic drops , structural information from SAXS, and theoretical modeling [1-8]. The methods will be illustrated by examples from systematic studies of combinations of anionic microgel networks (including polyacrylate, hyaluronate, poly(styrenesulfonate), and commercial DCBead) and a number of different cationic amphiphilic drugs, regular surfactants, and proteins. We will also present evidence of electrostatically driven spontaneous core-shell segregation of protein-rich and surfactant-rich phases in single microgels, interesting for encapsulation of protein drugs.
1. E. Ahnfelt, E. Sjögren, P. Hansson and H. Lennernäs, J. Pharm. Sci., 2016, 105, 3387.
2. J. Gernandt and P. Hansson, J. Chem. Phys., 2016, 144, 064902.
3. C. Jidheden and P. Hansson, J. Phys. Chem. B, 2016, 120, 10030
4. J. Gernandt, G. Frenning, W. Richtering, P. Hansson, Soft Matter, 2011, 7, 10327
5. P. Hansson, R. Månsson, H. Bysell, M. Malmsten, J. Phys. Chem. B 2012, 116, 10964
6. J. Gernandt, P. Hansson, Soft Matter, 2012, 8, 10905
7. J. Gernandt, P. Hansson, J. Phys. Chem. B, 2015, 119, 1717
8. M. Andersson, P. Hansson, J. Phys. Chem. B 2017, DOI: 10.1021/acs.jpcb.7b02215
3:00 PM - BM05.11.04
Conducting PEDOT:Polysaccharide Scaffolds for Tissue Engineering
Isabel Del Agua Lopez 1 2 , Magali Ferro 2 , Charalampos Pitsalidis 2 , Ana Sanchez Sanchez 1 , George Malliaras 2 , David Mecerreyes 1 Show Abstract
1 , University of the Basque Country, San Sebastian Spain, 2 , Ecole de Mines de Saint Etienne, Gardanne France
Highly porous scaffolds have been synthetized by the freeze-drying method for cell culture and sensing. These scaffolds combine the properties of a conducting polymer, poly(3,4-dioxythiophene) (PEDOT), and the good mechanical and biocompatibity properties provided by a biopolymer, a polysaccharide. The key difference of these scaffolds among other available PEDOT scaffolds is the synthetic strategy followed. This strategy consisted of three steps: a first step when an aqueous blend of PEDOT:Polyssacharide is formed by an oxidative polymerization of EDOT in the presence of polysaccharides as stabilizers. A second step, when a novel crosslinker was added to the aqueos dispersion, and a third freeze-drying step. The crosslinker used to impart stability to the porous structure in culture media is divinyl sulfone (DVS). A low-temperature crosslinker which does not reduce the conductivity of PEDOT. The polymerization of EDOT in the presence of polysaccharides provides intimate contact among the polymers. A key advantage of these systems. This innovative method to develop scaffolds overcomes the drawbacks of lack of homogeneity and lack of stability that arise when PEDOT, already in its polymeric form, is blended with polyssacharides. These innovative scaffolds successfully support 3D cell cultures of MDCK II, observing good cell attachment with very high degree of pore coverage. The porosity of the scaffolds can be tuned by the freeze-drying conditions and the solids content of the initial PEDOT:polyssacharide dispersion. Moreover, the properties of the scaffolds in order to host and monitor cells can be tuned by the polyssacharide used: xanthan gum, guar gum, and collagen, among others. Mechanical and electrical properties have been assessed by mechanical testing and impedance spectroscopy, respectively. All in all, we have developed an original synthetic route for porous scaffolds that can be employed for tissue engineering.
3:15 PM - BM05.11.05
Ultrasonic Biosensors Using Smart Hydrogels
Navid Farhoudi 1 , Christopher Reiche 1 , Hsuan-Yu Leu 1 , Jules Magda 1 , Florian Solzbacher 1 Show Abstract
1 , University of Utah, Salt Lake City, Utah, United States
Smart hydrogels are a three-dimensional hydrophilic network of polymers that experience a change in their volume and mechanical properties in response to the presence of specific analytes. Advantages like biocompatibility and the possibility to tailor their response to different stimuli has made them a frequently used material for applications like drug delivery, sensing, actuation and implants. Smart hydrogel sensors can respond to a variety of stimuli such as temperature, pH, gas, and chemical/biological entities. There are also different schemes for readout such as optical, magnetic, capacitive, and piezoelectric. In optical readout scheme, the expansion of an optical grating made from hydrogel in response to the stimuli alternates the periodicity of the grating and, consequently, changes the optical spectrum response of the structure. In magnetic, capacitive, and piezoelectric readout techniques, the hydrogel’s volume change is translated to the deformation of a membrane or cantilever which in turn could be sensed by piezoresistor, capacitor, or inductor.
Here we report on our research to develop a rapid low-cost smart hydrogel biosensor exploiting ultrasonic readout techniques. Ultrasound imaging techniques are widely used because they offer an inexpensive and portable way of in-vivo imaging with minimal side effects on living tissues. Our sensor’s operation principle is based on a periodic pattern of smart hydrogel mechanical resonators that change their frequency response as they experience a change in stimuli concentration resulting in swelling or shrinking of the gel.
The frequency response of a mechanical resonator depends on its geometry and mechanical properties, so the changes in these properties in response to the desired stimuli shifts the resonance frequency peaks. Ultrasound equipment could be used to detect the frequency shift and subsequently deduce the stimuli concentration. We used FEM simulations to model these resonator structures, in order to gain a better understanding and optimize them. A fully three-dimensional simulation shows that a periodic pattern of hydrogel, experiencing expansion, undergoes an easy to measure shift of the resonance peaks towards lower frequencies.
Our sensor inherits its biocompatibility from smart hydrogels. Also since the periodic structure does not need any wiring, these sensors are capable of long-term in-vivo operation. Furthermore, the sensors are very cost effective as they utilize a simple molding technique and are therefore compatible with batch fabrication. Additionally, due to the small size of the features in our periodic structure, an improvement in response time compared to the state of the art smart hydrogel sensors is expected. Therefore, our smart hydrogel ultrasonic sensors show a great potential for implantable real-time monitoring of analytes.
Florian Solzbacher declares financial interest in Blackrock Microsystems LLC and Sentiomed Inc.
3:30 PM - BM05.11.06
Tri-Crosslinking of Alginate-Based Supramolecular Hydrogel for Stem Cell Delivery and Orthopaedic Tissue
Jennifer Etter 1 , Rachael Oldinski 1 2 3 , Canaan McKenzie 1 Show Abstract
1 Mechanical Engineering, The University of Vermont, Burlington, Vermont, United States, 2 Electrical and Biomedical Engineering, The University of Vermont, Burlington, Vermont, United States, 3 Orthopaedics and Rehabilitation, The University of Vermont Larner College of Medicine, Burlington, Vermont, United States
It is well known that articular cartilage, due to many factors including being avascular, will not spontaneously heal or repair any damage.  Articular damage can be caused by an injury or disease, and if not properly treated the damage can lead to serious health problems such as osteoarthritis. If osteoarthritis drastically impairs the joint, major surgery, such as a total knee replacement, may be required. Injectable hydrogels with shear-shinning properties have emerged as promising biomaterials due to their excellent permeability and biocompatibility, and are advantageous for minimally-invasive surgical procedures, providing a convenient and effective approach to administer a wide variety of bioactive agents, including viable cells. Current injectable hydrogels, limited to single polymer networks, utilize a single input/stimulus for crosslinking, require external input for hydrogel or porosity generation, may require long re-assembly times or utilize potentially toxic ultraviolet radiation, and do not mimic the mechanical properties of surrounding tissue. To address these limitations, herein describes the development of a tri-stimuli-responsive smart injectable alginate hydrogel, based on: 1) Supramolecular complex formation between β-cyclodextrin (β-CD) conjugated alginate, and the poly(propylene glycol) (PPG) component of tri-block Pluronic® copolymers (F-108 and F-127), 2) visible light crosslinking of methacrylated alginate repeat units, and 3) ionic crosslinking via exposure to calcium chloride.   The physical and mechanical properties of the hydrogels were reliant on crosslink density and network structure, which were varied through chemical modification, polymer concentration, and Pluronic® material selection. Human mesenchymal stem cells were suspended in modified-alginate solutions, blended with Pluronic® copolymers, and ejected through 18-G needles into multi-well plates forming three-dimensional (3D) hydrogels. Cells were encapsulated throughout the hydrogel, and remained viable for greater than 36 hours. The mechanical properties of the tri-crosslinked, viscoelastic hydrogels were tuned as high as 33 kPa at body temperature. The stimuli-responsive alginate hydrogels hold great potential to improve MSC therapy efficacy, and ultimately control, and optimize, osteochondral tissue regeneration.
 C. Merceron et al., Biomed Mater Eng 20, (2010).
 T. Miao, S. L. Fenn, Biomacromolecules 16, (2015).
 S. L. Fenn, J Biomed Mater Res B Appl Biomater, (2015).
3:45 PM - BM05.11.07
Poloxamers Gels Degradation Kinetics under Flow
Clement Marmorat 1 , Gleb Vasilyev 2 , Arkadi Arinstein 2 , Ishi Talmon 2 , Eyal Zussman 2 , Miriam Rafailovich 1 Show Abstract
1 , Stony Brook University, Stony Brook, New York, United States, 2 , Technion–Israel Institute of Technology, Haifa Israel
Poloxamers hydrogels consist of a micellar network composed of amphiphilic block copolymers. Their unique structure has been proven efficient at encapsulating drugs and provide a controlled release in vivo1. Even though Poloxamers can be cross-linked to generate a stronger network, the physical cubic structure present naturally above a critical temperature and concentration provide a great non cell adhesive and ductile substrate. The kinetics of degradation of these gels in physiological conditions remain unclear and need to be assessed for a better use of these materials in post surgical topical applications to prevent scar tissue formation occurring after lumbar laminectomy procedures. This study focuses on the observation, modeling and properties of Poloxamers gels and their potential application during surgical procedures. Rheology as well as differential scanning calorimetry data showed the colligative nature of the phase transition between micelles in a liquid solution to micelles cubic crystals gels. Elastic moduli of the gels were recorded during cooling and heating cycles at a temperature interval of 5°C - 50°C. Elastic moduli plateaus were observed at 103 and 2x104 Pa indicative of the critical micellization temperature (CMT) and critical gel temperature (CGT) respectively. Cryo-TEM imaging was performed which allowed visualization of the micelles structural arrangement. Models were developed to better describe the network structure and properties relationship of these materials. The effect of poloxamers concentration and molecular entanglement characteristics of the resulting micelles was shown to have a critical impact on the stability of these gels under flow conditions. Finally, a series of flow tests were performed to better understand the degradation kinetics of the gels under different flow conditions. A critical flow rate was recorded, at which the gels are stable due to the inability of their chains to disentangle and swell upon contact with water. These results confirm the usability of poloxamers hydrogels during surgical procedures to avoid scar tissue formation and prevent post operative pain after laminectomies
This work was supported by the NSF, Inspire #1344267.
 Encapsulation of Hydrophobic Drugs in Pluronic F127 Micelles: Effects of Drug Hydrophobicity, Solution Temperature, and pH, Rajib Basak and Ranjini Bandyopadhya, Langmuir 2013 29 (13), 4350-4356, DOI: 10.1021/la304836e
4:00 PM - BM05.11.08
Molecular Control over Gel Polymerization Using Colloidal Nanocrystals—A Journey over Six Decades of Viscoelasticity
Amir Sheikhi 1 2 3 , Han Yang 1 2 3 , Pierre Carreau 4 , Theo van de Ven 1 2 3 Show Abstract
1 Chemistry, McGill University, Montreal, Quebec, Canada, 2 Pulp and Paper Research Centre, McGill University, Montreal, Quebec, Canada, 3 Centre for Self-Assembled Chemical Structures, McGill University, Montreal, Quebec, Canada, 4 , Research Centre for High Performance Polymer and Composite Systems (CREPEC), Chemical Engineering Department, École Polytechnique de Montréal, Montréal, Quebec, Canada
Gaining control over molecular interactions in dynamic, network-forming systems, such as crosslinking hydrogels, polymerizing macromolecules, and assembling supramolecules, without chemical modification of the structural units remains an unmet challenge in a variety of applications, such as bioprinting and scaffold engineering. Hinging on the principles of colloidal interactions, we have been able to finely control the behavior of activated, ready-to-react monomers in non-inert colloidal dispersions. As a model system, a collection of nanocellulose dispersions with strong or weak colloidal forces were synthesized to bind to reactive zirconium carbonate (ZC) monomers undergoing crosslinking. This nano-toolbox includes engineered nanocelluloses with various surface functionalities, steric and electrosteric moieties, and aspect ratios, all of which bind well to ZC. Despite kinetically favorable ZC-ZC polymerization, ZC-conjugated nanocelluloses with a strong colloidal repulsion inhibit the polymerization reaction. Importantly, a decrease in the colloidal repulsive forces by cleaving the steric or electrosteric moieties or through salt-induced charge screening results in systematic increase in the polymerization efficiency. Furthermore, by taking advantage of hydrogen bonding, the viscoelastic moduli are increased up to 4000% at only 0.5 wt % nanoparticles. Colloid-assisted regulation of macromolecules introduces a promising platform for molecular engineering of nanocomposites, opening new horizons for logically-tuned soft materials.
4:15 PM - BM05.11.09
Effect of Glycerol on the Mechanical and Temperature-Sensing Properties of Pectin-Based Films
Vincenzo Costanza 1 , Luca Bonanomi 2 1 , Chiara Daraio 1 Show Abstract
1 , California Institute of Technology, Pasadena, California, United States, 2 Mechanical and Process Engineering, ETH Zürich, Zürich Switzerland
Temperature sensitive thin films have the potential to improve the architectures of electronic skins (e-skins), providing temperature feedback to robots and high-tech prostheses. We recently demonstrated that pectin-based films are two orders of magnitude more responsive than previously reported state-of-the-art temperature-sensing layers. However, the extremely poor mechanical properties of pectin films clog their end-use applications as e-skins, in which the device’s components are subjected to repeated bending and mechanical stresses. Here we show how the addition of glycerol as plasticizer in the fabrication of pectin-based films improves their mechanical properties. We report how this enhancement of the mechanical performance is however accompanied by a decrease of the temperature response. Through thermogravimetric analysis we show that this drop in responsivity can be associated with water retention due to the plasticizer. The link between water content and temperature response demonstrates that a dehydrated state is crucial to record the incredibly high temperature responsivity. Combining electrical and thermal characterization with tensile testing, we estimate the optimal concentration of glycerol to effectively improve the mechanical properties, without compromising the temperature response of the pectin films.
4:30 PM - BM05.11.10
Hydrogel Surface Modification with Highly Stretchable Conductive Single-Walled Carbon Nanotube Films
Evgenia Gilshteyn 1 , Shaoting Lin 2 , Xuanhe Zhao 2 3 , Albert Nasibulin 1 4 Show Abstract
1 , Skolkovo Institute of Science and Technology, Moscow Russian Federation, 2 Department of Mechanical Engineering, Massachusetts Institute of Technology, Boston, Massachusetts, United States, 3 Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Boston, Massachusetts, United States, 4 Department of Applied Physics, Aalto University School of Science, Espoo Finland
Soft materials including elastomers and hydrogels have enabled diverse modern technologies including tissue engineering, drug delivery, biomedical devices, microfluidics, optics, stretchable and bio-integrated electronics, and soft robotics. The applicability of hydrogels across a range of applications mentioned above is driving researchers to develop networks encompassing new tailored properties such as thermal, optical and electrical conductivities. Electrically conductive hydrogels (ECHs) are attracting much interest in the field of biomaterial science due to their unique properties, combining a hydrated 3D structure while imparting electronic functionality. However, exciting approaches to fabrication of ECHs, such as electropolymerization and chemical polymerization, are quite complicated and time consuming. Here we report on novel simple technique of hydrogel surface modification with conductive carbon nanotube films in order to utilize high water content with good electroactive properties.
CNTs are a unique family of materials exhibiting diverse useful chemical and physical properties. The CNTs and especially SWCNTs were found to have exceptional mechanical, thermal and electronic properties, which are strongly determined by their chiralities. SWCNTs are the strongest known material with exceptionally high Young’s modulus of elasticity and tensile strength. The electrical properties of SWCNT films can exhibit excellent characteristics compared to the traditional conductive coatings due to a combination of high elastic moduli and outstanding electrical properties. The SWCNT films used in this study were obtained by aerosol synthesis and can be easily deposited from filter onto practically any substrate and in this case, such preparation method is very simple and can be done in a second time scale.
While hydrogels with extraordinary mechanical properties, or so called tough hydrogels, have been recently developed, it has been challenging to use tough hydrogels in stretchable electronics and devices capable of novel functions. Here we design robust, stretchable, conductive and biocompatible hydrogel/SWCNT structures for applications in the emerging field of soft materials, electronics, and devices. Tough hydrogel matrices that contain significant amounts of water (e.g., 70–95 wt %), which have been used in this study, modified by SWCNTs demonstrate excellent optical properties (up to 80% of transmittance depending on the SWCNT films thickness), mechanical and electrical properties (long-term behavior to stretching/releasing up to 1000 cycles with small degradation in resistance). The resultant SWCNT/hydrogel-based material is mechanically robust, highly stretchable, biocompatible, and capable of multiple novel functions.
This work was supported by Skoltech NGP Program (Skoltech-MIT joint project).
4:45 PM - BM05.11.11
Precision Placement of Neural Progenitor Cells in 3D Bio-Printed Scaffolds for Repair of Spinal Cord Injury
Daeha Joung 1 , Vincent Truong 2 3 , Patrick Walsh 2 3 , David Yang 1 , Joseph Monat 1 , Shuangzhuang Guo 1 , Sung Hyun Park 1 , Fanben Meng 1 , Elizabeth Smith 1 , James Dutton 2 4 , Ann Parr 2 3 , Michael McAlpine 1 Show Abstract
1 Department of Mechanical Engineering, University of Minnesota, Minneapolis, Minnesota, United States, 2 Stem Cell Institute, University of Minnesota, Minneapolis, Minnesota, United States, 3 Department of Neurosurgery, University of Minnesota, Minneapolis, Minnesota, United States, 4 Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, Minnesota, United States
Although human spinal cord injury (SCI) currently has no effective treatment, new technologies combining neural stem/progenitor cells and bio-compatible scaffolds provide an opportunity to test new therapeutic options. Attempts have shown significant advances in the integration of tissue-engineered conduits to bridge nervous system defects by including cell transplants, physical guides, and biological cues. However, it has been a significant challenge to manufacture patient-specific constructs with clinically relevant size, shape, and structural integrity which also contain cells positioned correctly within the desired architecture. To overcome these difficulties, we have developed a novel and versatile three-dimensional (3D) printing technology to fabricate patient-specific scaffolds where cells and biomolecules are embedded in precise positions at specific concentrations within the designed matrix during assembly. The 3D heterogeneous bio-structure is made of bio-compatible hydrogels for both scaffolds and cell-suspension, allowing construct design to provide enhanced mimicry of the tissue-like structure. This approach has shown that 3D bio-printed human spinal neuronal progenitor cells can differentiate and propagate axons in a designed scaffold with ~100 µm sized channels. Such an ability to direct the migration and growth of transplanted neuronal cells will be beneficial in rebuilding axon connections across the damaged area. This paradigm-shifting technology will be harnessed in developing a new therapy that can lead to new clinical treatments to restore function after a spinal cord injury.