Lara Estroff, Cornell University
Seung-Wuk Lee, University of California, Berkeley
Jwa-Min Nam, Seoul National University
Edward Perkins, U. S. Army Corps of Engineers
Symposium Support National Science Foundation
F3: Peptide and Protein Assembly I
Monday PM, December 01, 2014
Sheraton, 2nd Floor, Independence West
2:30 AM - *F3.01
Multi-Stimuli Responsive Polypeptides and Block Copolypeptide Assemblies
Timothy Deming 1 2 Jessica Kramer 2
1UCLA Los Angeles USA2UCLA Los Angeles USAShow Abstract
We have developed synthetic methods that allow incorporation of unprecedented levels of functionality into polypeptide materials. We report on the design and properties of stimuli responsive polypeptide motifs that are able to respond differently to different individual stimuli, such as redox, temperature, or enzymes. These materials allow multimodal switching of polypeptide properties to obtain desirable features, such as coupled responses to multiple external inputs. The reversible, multiresponsive nature of these polypeptides makes them particularly attractive as components in molecular devices or nanoscale assemblies capable of sequential, or triggered, responses to different stimuli, akin to switches capable of performing Boolean-like operations. We will describe how these motifs can be incorporated into self-assembled materials such as vesicles and hydrogels.
3:00 AM - *F3.02
Peptide-Based Hollow Spherical Nanoparticle Superstructures: Syntheses, Structures, and Emergent Properties
Nathaniel Rosi 1
1University of Pittsburgh Pittsburgh USAShow Abstract
Carefully designed peptide conjugate molecules are used to direct the synthesis and assembly of a diverse class of ‘hollow&’ spherical nanoparticle superstructures. In this talk, we describe the design of these structures, with particular emphasis on methods for controlling sphere diameter and composition. In addition, we discuss several unique emergent properties of these materials, ways in which these properties can be tuned, and how these properties enable cargo storage and release applications.
3:30 AM - F3.03
Self-Assembled Suprastructures from Recombinant Oleosin
Daniel A Hammer 1 Kevin B Vargo 1 Gao Chen 1 Ranganath Parthsarathy 1 Eric Wang 2 Paul Heiney 3
1University of Pennsylvania Philadelphia USA2University of Pennsylvania Philadelphia USA3University of Pennsylvania Philadelphia USAShow Abstract
The self-assembly of suprastructures from recombinant amphiphilic proteins would allow precise control over surfactant chemistry and the facile incorporation of biological functionality. We used cryo-TEM to confirm self-assembled structures from recombinantly-produced mutants of the naturally-occurring sunflower protein, oleosin (1). Oleosin is an amphilphilic protein with two hydrophilic blocks separated by an interior hydrophobic block with a proline knot that causes the folding of the protein into the shape of a “U.” We studied the phase behavior of a subset of truncation mutants of the wild-type molecule, as a function of solution ionic strength and protein hydrophilic fraction, observing nanometric fibers, sheets, and vesicles. Vesicle membrane thickness correlated with increasing hydrophilic fraction for a fixed hydrophobic domain length. The existence of a bilayer membrane was corroborated in giant vesicles through the localized encapsulation of hydrophobic Nile red and hydrophilic calcein. Circular dichroism revealed that changes in nanostructure morphology in this family of mutants were unrelated to changes in secondary structure.
We further modified the protein in a variety of ways - removing structure from the internal hydrophobic component and adding less bulky residues to the hydrophobic core. This family of molecules are surfactants that form spherical micelles (as measured by DLS, cryo-TEM and X-ray scattering) and have a low CMC. Using recombinant methods, we have also incorporated bio-functionality into these proteins, including receptor binding peptide and affibodies, protease cleavable domains, biotinylation, and temperature dependent switches. Ultimately, we envision using recombinant techniques to introduce novel functionality into these materials toward numerous biological applications and the construction of responsive, self-assembled soft matter.
K. B. Vargo, R.Parthasarathy and D. A. Hammer. Proceedings of the National Academy of Sciences USA109, 11657-11662 (2012).
3:45 AM - F3.04
Targeting Collagen Strands by Triple Helical Hybridization
Michael Yu 1
1University of Utah Salt Lake City USAShow Abstract
Collagen, the most abundant protein in mammals, plays a crucial role in tissue development and regeneration, and its structural and metabolic abnormalities are associated with debilitating genetic diseases and numerous pathologic conditions. The ability to target collagens in diseased tissue could lead to new diagnostics and therapeutics, as well as applications in regenerative medicine. In this talk, I will present a new collagen targeting strategy that is based on triple helical hybridization between denatured collagen strands (of diseased tissues) and synthetic collagen mimetic peptide (CMP). This hybridization results in robust collagen specific binding in vivo which allows detection of degraded collagens present in normal tissues undergoing fast remodeling (e.g. bones and cartilage) and those in diseased tissues with persistent wound healing activity (e.g. tumor, fibrosis). I will describe various experiments designed to elucidate the mechanism of the hybridization as well as those verifying the CMP&’s collagen binding capacity both in vitro and in vivo. This is an entirely new way to target the microenvironment of malignant tissues and could lead to new opportunity for management of numerous pathologic conditions associated with high collagen degradation and remodeling activity.
F4: Peptide and Protein Assembly II
Monday PM, December 01, 2014
Sheraton, 2nd Floor, Independence West
4:30 AM - *F4.01
Syntax of ldquo;Smartrdquo; Peptide Polymers Governs Their Function
Ashutosh Chilkoti 1
1Duke University Durham USAShow Abstract
“Smart” polymers that respond to stimuli in their aqueous environments with a pronounced physical change are of great utility in biotechnology and medicine. Currently, however, only few peptide polymers show this behavior. Here, we uncover the relationship between the syntax of peptide polymers and their lower critical solution temperature (LCST) transition behavior as well as a class of peptide polymers that show the reverse -upper critical solution temperature (UCST)- behavior. I will show that the syntax of these functional peptide polymers ranges from polymers composed of simple repeats of a few amino acids to those whose syntax resembles the complex non-repetitive syntax of protein domains, and that the concept of syntax can be deployed to re-program bioactive peptides to exhibit dual functions, as seen by their stimulus responsiveness and biological activity. The unique linguistic features exhibited by these peptide polymers suggests that peptide polymers can be best described as linear macromolecules that are composed of amino acid “letters” that are organized as “words”, with higher order organization of one or more words that repeat or recur to create a “phrase” (the macromolecule) and postulate that the syntax -word order- of this class of polymers controls their function. Hence, by analogy to syntax in natural language —defined as the arrangement of words in a phrase that controls its meaning, I will introduce new concept -syntactomers- to describe polymers whose properties are controlled by their organization as a collection of letters into words and the higher order organization of words into functional phrases.
5:00 AM - *F4.02
Predicting Protein Biomaterial Functions from Protein Designs: Interfacing Experimental and Modeling Approaches
David L. Kaplan 1 Joyce Wong 2 Markus Buehler 3
1Tufts University Medford USA2Boston University Boston USA3MIT Cambridge USAShow Abstract
Designing protein-based biomaterials with specific functional properties is desirable for fundamental interest as well as for applied needs such as medical devices, scaffolding in regenerative medicine and drug delivery. To improve predictability of biomaterials function, multiple parameters in protein polymer design need to be considered, including sequence chemistry, molecular weight and domain distribution. Concurrent with the experimental design of such protein polymers, appropriate mathematical models are needed to predict how the engineered polymers will self-organize at different length scales with consideration for structural hierarchy to relate to material functions. The importance of multi-scale bioengineering and the combined use of modeling and experiment in advancing designs of biomaterials will be the focus of the talk. This is an emerging field where modeling can inform polymer design and vice versa. The approaches being pursued in protein-polymer design and bioengineering, polymer processing and modeling/predictions of function will be described as an example on how this iterative approach can be used to broaden predictive structure-function relationships in the field.
5:30 AM - *F4.03
Biotemplating of Bimetallic Nanoparticles Using Self-Assembled Protein Scaffolds and TEThER Peptides
Sarah Heilshorn 1
1Stanford University Stanford USAShow Abstract
The use of biological scaffolds to template inorganic material offers unique strategies to synthesize precise composite nanostructures of different sizes, shapes, and compositions. Proteins are unique biological scaffolds that consist of multiple binding regions, or epitope sites, that site-specifically associate with conserved amino acid sequences within protein binding partners. These binding regions can be exploited as synthesis sites for multiple inorganic species within the same protein scaffold, resulting in bimetallic inorganic nanostructures. We demonstrate this strategy with the scaffold protein clathrin, which self-assembles into spherical cages. Specifically we design tether peptides that noncovalently associate with distinct clathrin epitope sites while initiating simultaneous synthesis of two inorganic species on the assembled clathrin protein cage. We demonstrate the versatility of this unique biotemplating strategy by synthesizing two types of composite structures, silver-gold mixed bimetallic nanoparticles and silver-gold core-shell nanostructures, from a single clathrin template. This noncovalent, Template Engineering Through Epitope Recognition, or TEThER, strategy can be readily applied to any protein assembly with known epitope sites to template a variety of bimetallic structures without the need for chemical or genetic modifications.
F1: DNA Nanostructure and Assembly I
Monday AM, December 01, 2014
Sheraton, 2nd Floor, Independence West
9:00 AM - *F1.01
The Nature of the DNA Bond
Chad A. Mirkin 1
1Northwestern University Evanston USAShow Abstract
For decades the biological roles of nucleic acids as catalytic enzymes, intracellular regulatory molecules, and as the carriers of genetic information have been studied extensively. More recently, the sequence-specific binding properties of DNA that make it so ubiquitous among all living systems have been hijacked to direct the assembly of materials at the nanoscale. In such cases, it has become useful to consider the DNA as an artificial bond that facilitates nearly infinite tailorability in the interactions between nanomaterials via bond (i.e. oligonucleotide) length, strength, orthogonality, and even directionality. Although this powerful concept can be applied in variety of contexts including DNA tiles, origami scaffolds, and supramolecular constructs, here we explore the use of rigid inorganic nanoparticles functionalized with DNA that act to orient oligonucleotides perpendicular to their surfaces to dictate DNA bonding interactions. By elucidating a series of design rules for the nature of these DNA bonds, we show the construction of nanoparticle superlattices with over 20 different crystal symmetries with precise control over particle size and spacing. In some cases, these materials can be prepared so that they form large single crystalline domains with a well-defined crystal habit indicative of the minimum energy Wulff polyhedron of the parent superlattice. Finally, we show opportunities for dynamic and reconfigurable superlattices facilitated by the unique properties of the DNA bond.
F5: Poster Session: Reverse Engineering of Bioinspired Nanomaterials
Monday PM, December 01, 2014
Hynes, Level 1, Hall B
9:00 AM - F5.01
Using Nano-Carbons to Promote Collagen Fibril Alignment
Emily C Green 1 Dilinazi Aishanjiang 1 Yiying Zhang 1 Marilyn L Minus 1
1Northeastern University Boston USAShow Abstract
Due to the rigid-rod characteristics of carbon nanotubes (CNT) they have been shown to aide and induce atomic and nano-scale ordering of polymer materials. In this work, this CNT trait is exploited to understand its potential along with other rigid nano-carbons to promote ordered assembly of biological materials. For the synthetic formation of collagen materials highly aligned collagen fibrils are necessary in order to replicate the native collagen structure in bone, tendon, and ligaments. This study also allows for fundamental understanding regarding collagen self-assembly. The ability to form highly aligned collagen fibrils may also lead to new fiber processing methods to enable in the development of novel applications for collagenous materials. In this work collagen fibers were self-assembled in the presence of both single-wall carbon nanotubes (SWNT) and carbon nano-chips (CNC) using a gel-spinning approach. The morphology and dispersion quality of the nano-carbons was found to play a significant role in the overall collagen fibril alignment. Small-angle X-ray Scattering (SAXS) analysis shows that low concentrations (0.5 wt%) of well-dispersed SWNT promote collagen molecular alignment leading to banding structure similar to native collagen. Fiber morphology was analyzed by both Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Beyond ordering, the nano-carbons used were also able to reinforce the collagen composite fibers. Mechanical property characterization showed a considerable increase in both strength and elastic modulus (100% and 122%, respectively), as compared to control fibers. This work is the first to show direct evidence that nano-carbon fillers may promote collagen molecular and fibril alignment during self-assembly processes.
9:00 AM - F5.02
Cage-Shaped Proteins Assisted Carbon Nanotubes Synthesis for Dye-Sensitized Solar Cells
Ippei Inoue 1 Kenichi Toyoda 2 Yasuaki Ishikawa 2 Hisashi Yasueda 1 Ichiro Yamashita 2 Yukiharu Uraoka 2
1Ajinomoto Co., Inc. Kawasaki Japan2Nara Institute of Science and Technology Ikoma JapanShow Abstract
Carbon-nanotubes (CNTs) are one of the most promising nano-materials and have been applied for various nano-electric devices, such as solar cells, batteries, and sensors, due to their superb physical properties, chemical inertness and excellent electron conductivity. One of the most basic issues in CNTs synthesis is a control of CNTs diameter and quality, since variations of CNTs cause dispersion of device characteristics. To address the issue, there have been many reports on a CNTs synthesis using catalysts of iron nanoparticles which were produced utilizing physicochemical and biological approaches.
In this presentation, we report a novel method for synthesis of diameter controlled multi-walled CNTs (MWNTs) by utilizing two-kinds of biomineralized iron nanoparticles as catalysts for chemical vapor deposition (CVD). The iron nanoparticles were 7 nm and 4.5 nm in diameter and were produced by utilizing cage-shaped proteins, ferritin and Dps, respectively. The two kinds of protein had silicon-binding peptide aptamers and could carry iron nanoparticles onto a surface of silicon substrate. Diameters of the MWNTs could be controlled in a range of 5-10 nm by the ratio of two kinds of the proteins. Structures of MWNTs were essentially maintained even at 600°C in atmospheric air. A weight loss peak of thermo-gravimetric analysis appeared at 678°C corresponds to a loss of 63 wt% which was attributable to the MWNTs themselves. We applied the thin MWNTs to electrodes of dye-sensitized solar cells (DSSCs). The MWNTs were coated with TiO2 by biomineralizing activity of a genetically modified Dps. The TiO2-coated MWNT improved an electric resistance of a DSSC photoelectrode. As a result, the power conversion efficiency of the DSSC with the protein-templated TiO2-MWNT was enhanced from 5.8% to 6.6%. Moreover, the MWNTs were able to be applied for counter electrodes instead of rare metal Pt. Those results indicated that the thin MWNTs can be used as an excellent material for solar cells.
9:00 AM - F5.03
Fabrication of Discrete Protein Polygons for Multivalent Display of Functional Proteins in Defined Nanostructures
Young Eun Kim 1 Yongwon Jung 1
1Korea Advanced Institute of Science and Technology Daejeon Korea (the Republic of)Show Abstract
Proteins have recently attracted much attention as a building block for supramolecular structures due to their functional diversity as well as biocompatible and biodegradable properties. Several strategies for the construction of protein nanostructures including nanowires, nanotubes and nanorings have been described [1-4]. These approaches were based on the specific molecular recognition such as metal ion-protein, enzyme-inhibitor and protein-protein interaction . Although various sophisticated structures of protein have been developed, the design of protein supramolecular structures is still challenging because of the structural complexity of proteins. Herein, we presented the fabrication of highly discrete protein polygons from cellular self-assembles of green fluorescent protein (GFP). The rationally designed GFP monomer is expressed in cell, and it undergoes the cellular self-assembly into polymeric forms of protein, thereby offering a highly simple and versatile way to prepare protein polymers. Furthermore, these protein polygons could be functionalized through introduction of the desired ligand into either N-terminus or C-terminus of a monomer protein using genetic manipulation. Notably, GFP polygons from dimer to decamer were individually purified, indicating that these GFP polygons can display the exact number of ligands. Finally, we showed that fabrication of discrete GFP polygons depending on the valency of functional proteins.
. R. Matsunaga, S. Yanaka, S. Nagatoishi, K. Tsumoto Nat Commun. 4 (2013)
. TF.Chou, C. So, BR. White, JC. Carlson, M. Sarikaya, CR. Wagner ACS Nano 2, 12 (2008)
. ER. Ballster, AH. Lai, RN. Zuckermann, Y. Cheng, JD. Mougous Proc Natl Acad Sci U S A. 105, 10 (2008)
. K. Oohora, A. Onoda, T. Hayashi Chem Commun., 48 (2012)
9:00 AM - F5.04
Preparation of Structural Colored Colloidal Amorphous Arrays by Layer-by-Layer Deposition
Masanori Iwata 1 Yukikazu Takeoka 1 Takahiro Seki 1 Shinya Yoshioka 2
1Nagoya University Nagoya Japan2Osaka University Suita JapanShow Abstract
Recently, structural colored materials attract many researchers&’ attention as environmentally friendly color materials. Structural color is observed in the materials that have the microstructures comparable to the wavelength of visible light. We can obtain brightly colored materials, without any toxic dyes or pigments, by utilizing structural colored materials. There exist so many informative examples in living things for making artificial structural colored materials. In this paper, we describe the preparation of structural colored materials imitating the bird&’s feather that displays an angle-independent structural color.
Here, we have an interest in a blue bird, Steller&’s jay. This bird&’s feather contains the amorphous structure of air cavities in keratin matrix (spongy layer) above the assembly of melanin granules, and reveals an angle-independent bright blue structural color. However, an amelanotic Steller&’s jay&’s feather having the same type of spongy layer displays a white color due to the lack of melanin granules. This fact indicates that the brightly structural colored materials having amorphous structure require the existence of a black background.
Therefore, for making artificial angle-independent structural colored materials, we prepared the membranous colloidal amorphous arrays of mono-dispersed submicron-sized silica particles (SiO2 thin films) on a black quartz glass substrate by Layer-by-Layer (LbL) deposition technique that enables us to control the film thickness of SiO2 thin films.
For LbL deposition, we employed a cationic polyelectrolyte, poly(diallyldimethylammonium chloride) (PDDA) (MW = 400,000-500,000), and silica particles of 190 nm in diameter of which surface was negatively charged. First, a black quartz glass substrate with negative charges was dipped into PDDA aqueous solution (0.2 wt%) for 10 min, followed by rinsing with water. Then, the substrate was dipped into the silica particles aqueous suspension (10 wt%, containing NaCl 0.02 M) for 10 min, followed by washing. We defined these operations as one cycle and prepared SiO2 thin films by varying the number of repeating times of the cycle.
Symmetrical and circular pattern around origin in two-dimensional fast-Fourier transform power spectrum of the scanning electron microscope (SEM) image on the surface of the resultant SiO2 thin film confirmed that silica particles formed isotropic amorphous array with short-range order. From the results of the SEM observations on the SiO2 thin films with various thicknesses, we found that the thickness was directly proportional to the number of repeating times of the cycle. Additionally, the saturation of the structural color from the SiO2 thin films was decreased when using a clear glass plate as a substrate.
In summary, we succeeded to prepare the structural colored materials imitating the feather of the blue bird by depositing mono-dispersed submicron-sized silica particles with short-range order on a black substrate.
9:00 AM - F5.05
Hydrogels Containing Biomimetic Topographical Features for Small Intestinal Model Systems
Megha Kamath 2 1 Abigail N Koppes 2 Rebecca Carrier 2
1Northeastern University Boston USA2Northeastern University Boston USAShow Abstract
There is an urgent need for improved cultured intestinal models for studying oral drug delivery and intestinal disease, or to serve as a potential treatment for short bowel syndrome (SBS). Common intestinal epithelial culture models are 2-dimensional, which limit the understanding of cell behavior in their natural environment. However, native small intestinal tissue consists of multi-scale structures, such as crypts and villi, as well as extra-cellular matrix (ECM) that play an important role in aiding cellular growth and impacting cellular phenotype. To this end, we have developed a method that allows for the growth of Caco-2 in a monolayer on substrates mimicking the natural topography of the small intestinal tract. Using replica molding of PDMS, we obtained biomimetic collagen-I hydrogel substrates that showed enhanced growth of epithelial cells. This system will contribute to a better understanding of the growth of intestinal cells and eventually to efficient drug delivery in the GI for various disorders.
Porcine small intestinal tissue was washed, fixed, sectioned and placed in 0.1%OsO4 in 0.1M PBS (4 °C, 72 hours) followed by agitation to remove the epithelial cells. Samples were rinsed, dehydrated in ethanol, critically point dried (CPD) and silanized. A thin layer of PDMS (10:1 v:v) was applied on the tissue and baked for 2 hours at 60°C, and separated with via differential swelling in TEA. Positive bovine collagen-I replicas were solution cast on PDMS molds and allowed to gel at 37°C for 2-3 hours. Caco-2 cells were seeded at a density of 76,000 cells/mL and grown for 8 days. Fluorescence microscopy images were taken at day 8 to capture cell behavior on the replica and flat controls. To image the collagen gels, they were fixed, ethanol dehydrated and CPD. The dried gels were sputter coated with platinum and imaged using a Field Emission Scanning Electron Microscope (FE-SEM).
SEM images show that negative PDMS crypt-villi structures exhibit similar size features compared to native intestinal tissue, ranging from millimeter macrofolds to hundreds of micron villus protrusions. The CPD collagen gels have similar micro-scale size features compared to the native intestinal tissue, but there was a loss in height of villus-like structures due to dehydration and heat processing of the hydrogels for SEM. The hydrogels provided environmental and topographical cues, allowing seeded cells to proliferate and mature. Fluorescence microscopy images show that Caco-2 grown on the porous collagen replicas formed monolayers and exhibit a 3.8-fold increase in proliferation compared to flat controls that remained subconfluent after 8 days in culture. Ongoing studies involve characterizing the hydrogel surface topography to understand and quantify Caco-2 and primary intestinal stem cell behavior on these biomimetic materials. This model will serve as stepping-stone to enhance drug delivery as well as play a crucial role in regenerative medicine.
9:00 AM - F5.06
Apoferritin Encapsulated Rare Earth Luminescent Nanoparticles
Hideyuki Yoshimura 1
1Meiji University Kawasaki JapanShow Abstract
Luminescent europium (Eu) and dysprosium (Dy) doped Yttrium-Vanadate (Y-V) nanoparticles (NPs) were synthesized in a cavity of the protein, apoferritin. The use of inorganic nanoparticles (NPs), instead of organic dyes, is becoming popular for molecular labeling because of their strong resistance to photobleaching. Since structure of protein is strictly regulated by DNA, the size of NPs in the protein also becomes homogeneous. Moreover, apoferritin is thermally stable water soluble protein, and thus encapsulated NPs are also stably dispersed in aqueous solution. The sequence of a protein can be modified by protein engineering to enable the protein to bind to a specific molecule, e.g. an aptamer, these NPs are likely to be biocompatible and would have significant potential for biological imaging applications.
Y-V NPs were synthesized by incubating a solution of apoferritin with Y3+ and VO3- ions in the presence of ethylene diamine-N-N'-diacetic acid (EDDA). EDDA plays an important role in preventing Y-vanadate precipitation in bulk solution by chelating the Y3+ ions. Using high resolution electron microscopy, the obtained NPs in the apoferritin cavities were confirmed to be amorphous, and to consist of Y and V. The average size of the obtained NPs was 6.6 ± 0.7 nm.
Eu-doped Y-V (Y-V:Eu) NPs were synthesized by the same procedure as Y-V NPs, except that Eu(NO3)3 was added. Y-V:Eu NPs exhibited a strong absorption peak due to the O-V charge transfer transition and remarkable luminescence at 618 nm due to the 5D0 - 7F2 transition. Luminescence showed maximum intensity at Eu doping ratio of 11.4%. Strong red luminescence was easily observed by eye, even in a brightly lit room.
It is known that O-H vibrations play a dominant role in the non-radiative transition from excited Eu3+ ions and that transition is greatly reduced by substituting hydrogen (H) to deuterium (D). To investigate the non-radiative transition pathway of Y:Eu and Y-V:Eu NPs, the luminescence lifetime of these NPs in water (H2O) and heavy water (D2O) were compared. The lifetime difference in H2O solution and D2O solution is six times larger in Y:Eu than Y-V:Eu NPs at low Eu concentration. This means non-radiative transition due to the O-H vibration is smaller in Y-V:Eu NPs. Accordingly, Y-V NPs showed strong luminescence compared to Y:Eu NPs which we reported previously . Dy-doped Y-V (Y-V:Dy) NPs were also synthesized in apoferritin cavities and showed luminescence peaks at 482 nm and 572 nm, corresponding to 4F9/2 - 6H15/2 and 4F9/2 - 6H13/2 transitions. Luminescence showed maximum intensity at Dy doping ratio of 3.5%. This solution had a yellow color under UV irradiation.
 T. Harada and H. Yoshimura, J. Appl. Phys, 114, 044309 (2013).
9:00 AM - F5.07
A Dip-Stick Colorimetric Sensor Based on Morphological Changes of Plasmonic Nanoparticles
Brian Malile 1
1York University Toronto CanadaShow Abstract
There is a constant need for economical and portable point-of-care biodiagnoistic devices. Numerous colorimetric sensors are based on the aggregation of plasmonic nanoparticles; however, colloidal solutions present limitations on the portability of the sensor. We present a new sensing platform in which the colorimetric signal comes from changes in the morphology of substrate-bound nanoparticles. The sensing platform consists of immobilized gold-coated silver nanoparticles on a glass substrate, on top of which a stimulus-responsive polyelectrolyte-aptamer film is assembled. Binding of the target to the aptamer leads to the swelling of the polyelectrolyte layer as conferred by ellipsometry, and results in an increase in the diffusion rate of etchant molecules. The etchant changes the size and shape of the nanoparticles and therefore the colour or intensity of the film. We achieve a discernible colorimetric difference between the control film and the target bound film, and investigate the concentration dependence and effects of interference species. Characterization techniques such as ellipsometry and cyclic voltammetry will help to advance the understanding of the mechanisms involved. Further development of this platform may provide facile field analysis by using consumer electronics in addition to presenting new opportunities for aptamer-based sensing.
9:00 AM - F5.08
Engineered Phage Based Matrix Stiffness Modulating Osteogenic Differentiation
Hee-Sook Lee 3 2 Kwang Heo 3 So Young Yoo 1 Seung-Wuk Lee 3
1Pusan National University School of Medicine Yangsan Korea (the Republic of)2Ministry of Food and Drug Safety Busan Korea (the Republic of)3University of California, Berkeley Berkeley USAShow Abstract
Although it is known that specific biochemical cues in tissue extracellular matrices (ECM) play a critical role in regulating cellular growth processes and their fate, the role of physical cues of them such as stiffness in guiding the fate of resident stem cells has not been well studied so far. In this study, we have demonstrated engineered phage mediated matrix controlling stiffness for various applications over conventional tissue engineering materials by exploiting its physical and biological structural features (such as the phage&’s self-assembling, selfreplicating and evolving nature). We modified M13 phages to express biotin-like peptides (HPQ) and/or integrin binding peptides (RGD) on their major and minor coat proteins. The stiffness of matrix was controlled by cross-linking the engineered phage with different concentarions and compositions of streptavidin and polymer mixture. Then, we verified that osteogenic differentiation could be controlled according to the rates of stiffness of the constructed phage matrix. Osteogenic gene expressions through mRNA expression quantification and protein activity assays showed that they were specifically increased when bone stem cells were cultured on the M13 matrix with adequate stiffness. Our phage matrices, which can be easily functionalized with various ligands and growth factors to enhance the stiffness modulation using other chemicals, may be used as a convenient tissue matrice platforms for controlling stem cell expansion and differentiation. [This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (2013R1A1A3008484)]
9:00 AM - F5.09
Bioinspired Templates for Nucleation and Growth of Polydopamine during Melanogenesis
Luke Klosterman 1 Christopher Bettinger 1
1Carnegie Mellon University Pittsburgh USAShow Abstract
Melanins are a class of pigments with unique physicochemical properties including redox activity, hybrid ionic conductivity, and efficient photon-phonon conversion. Natural eumelanins and synthetic analogs, termed “polydopamine”, have garnered interest in applications including clean energy, functional interfaces, and biomedicine. However, the structural distinctions between natural and synthetic melanins remain elusive. Parsing out these structural deviations is essential in advancing the use of these materials. Here we present a study in which bioinspired surface chemistries are modulated to elucidate the adsorption and deposition of polydopamine precursors.
We have investigated the effect of fundamentally simple differences in surface chemistries on the growth of polydopamine films. Silicon dioxide and self-assembled monolayers of amino, aromatic, or aliphatic moietes produce melanin films with comparable thickness (ca. 10nm) and morphology of adherent islands. Electrostatically neutral aromatic and aliphatic surfaces produce smoother polydopamine films (RRMS= 0.3-0.7nm) compared to anionic oxide and cationic amine-terminated surface chemistries (RRMS= 1.1-1.6nm). Additionally, catechol dissociation at higher pH prevents film formation on the oxide and reduces the average roughness of the amine-terminated surface to a value similar to the aromatic and aliphatic (RRMS= 1.2nm at pH 8 vs. 0.5nm at pH 10). This suggests multiple modes of adsorption that provide polydopamine with its versatile coating capability. These findings are supported by quartz crystal microbalance studies.
These findings have also been extended to understand the nucleation and growth of melanins on Pmel17 template proteins on two-dimensional surfaces. Taken together, these data suggest that two-dimensional SAMs monolayers are an accurate model to replicate aspects of natural melanin synthesis. These findings will aid in elucidating the fundamental mechanisms of in vivo melanogenesis
9:00 AM - F5.10
Power Generation and Water Savings Using Water-Responsive Materials
Ahmet-Hamdi Cavusoglu 3 Xi Chen 2 Ozgur Sahin 2 1
1Columbia University New York USA2Columbia University New York USA3Columbia University New York USAShow Abstract
Water-responsive materials swell and shrink in response to changes in relative humidity (RH) and can be potentially used to harvest energy from evaporating water . Here, we investigated the potential of harvesting energy from naturally evaporating water due to typical weather conditions across the United States. We modeled the power output, the effect on evaporation rate, and the intermittency of the power output. We first performed steady state calculations over a range of 218 locations across the United States and determined the average energy flux and net water savings due to a reduction in evaporation rates. We then used a non-steady state mass and energy balance approach on three test locations of South-East NY, Western TX, and South-East CA to determine daily and yearly variations in power output. Our calculations show that this system can deliver power densities surpassing wind power and comparable to current installed solar systems. These results suggest that further research into water-responsive materials and devices can provide major benefits in developing a novel renewable energy platform.
1. X. Chen, L. Mahadevan, A. Driks, and O. Sahin. Bacillus spores as building blocks for stimuli-responsive materials and nanogenerators. Nature Nanotechnology, 2014. 9(2): p. 137-141.
9:00 AM - F5.11
Controlled Synthesis and Therapeutic Applications of Plasmonic Core-Petal Nanostructures
Amit Kumar 1 Jwa-Min Nam 1
1Seoul National University Seoul Korea (the Republic of)Show Abstract
Metal nanostructures with highly branched morphologies are an interesting and useful new class of nanomaterials due to their plasmonically enhanced optical properties, large surface area and potential as catalytic substrates. In particular, surface plasmon-derived photo-induced therapeutic effect and catalysis are highly dependent on their surface nanostructures, but the control of their branching structures is challenging. Here, we introduce a strategy for the controlled synthesis of plasmonic core-petal nanostructures (CPNs) with highly branched morphologies. The fine nanostructural engineering of CPNs was facilitated by oxidative disassembly of organic biopolymer-corona around spherical Au nanoparticles and successive anisotropic growth of Au nanopetals. We show that CPNs can act as multifunctional nanoreactors that induce protrusion-dependent controllable photodynamic and photothermal dual therapeutic effects as well as ROS generation. NIR laser-activated CPNs can be used to induce the effective destruction of cancer cells via the synergistic combination of benign plasmonic hyperthermia (~42 °C) and ROS-mediated oxidative intracellular damage. It was also shown that CPNs exhibit very strong surface-enhanced Raman scattering (SERS) signals, and this allows for post-mortem probing of ROS-mediated oxidative structural modifications of DNA that could be responsible for the apoptotic fate of cancer cells. Here, we have showcased the well-tunable synergistic plasmon-based catalytic and thermoplasmonic properties of NIR active branched nanostructures for organic photosensitizer-free bimodal photodynamic-photothermal therapeutic ablation of cancer cells. Synthesis of such biocompatible, non-invasive and aesthetic but highly effective nanotherapeutic platforms have great potential for future clinical applications.
9:00 AM - F5.12
Core-Satellite Nanostructures as SERS Bioimaging Probes for Oxidative and Nitrosative Stresses in Living Cells
Sumit Kumar 1 Jwa-Min Nam 1
1Seoul National University Seoul Korea (the Republic of)Show Abstract
Understanding the role of endogenous or exogenous reactive oxygen species (ROS) and reactive nitrogen species (RNS) at molecular, cellular, and organismal level in a range of physiological processes as well as in the pathogenesis of many diseases, is an emerging area of research in redox chemical biology. ROS and RNS often exhibit interdependent production and roles in the complex signal transduction and oxidative pathways; and sometimes direct the activation of distinct signaling mechanisms determining cell fate. Simultaneous and distinguishable monitoring of ROS and RNS is crucial to understanding their biochemistry and effects on signal transduction pathways. Surface-enhanced Raman scattering (SERS)-based biosensing probes have advantages such as highly sensitive molecular finger-printing, multiplexing and non-invasiveness for in-vitro and in-vivo applications. Here, we designed a ‘core-satellite&’ plasmonic nano-assembly with a sub-nanometer thick insulating molecular spacer between core and satellites for functionalization of heme protein. Intense SERS signals corresponding to characteristic Raman bands of Fe-porphyrin reporter moieties located in ‘hot-spot&’ junctions could be obtained due to extensive plasmonic coupling among core and satellite AuNPs. Our SERS probe was found to be highly sensitive towards exposure of ROS and RNS as distinct Raman signals were produced in both the cases. Biological experiments revealed facile internalization of core-shell bioprobes in the living cells and excellent biocompatibility. Finally, we were able to quantitatively and distinctly monitor ROS and RNS in normal and cancer cells using our SERS bioprobes. This method enables sophisticated hot plasmonic assemblies to be used for unraveling the etiology and pathophysiology of many diseases involving alterations of oxidative and nitrosative stress, such as cancer, neurological disorders, pancreatic malfunction, and inflammatory diseases.
9:00 AM - F5.13
Characterization of MgO Nanoparticles as Antibacterial Materials for Orthopedic Tissue Engineering
Daniel J. Hickey 1 Thomas J. Webster 1
1Northeastern University Boston USAShow Abstract
Regeneration of complex orthopedic tissues (such as ligaments, bones, and the tendon-to-bone insertion site) is problematic due to a lack of suitable biomaterials with the appropriate chemical and mechanical properties to elicit the formation of tissues with similar structure, organization, and functionality to natural tissues. Additionally, a non-trivial fraction of implanted biomaterials become infected by bacteria, which can lead to implant failure, secondary surgeries, and the spread of infection to other tissues throughout the body. To address these issues, the current study investigated magnesium oxide (MgO) nanoparticles as novel materials to improve orthopedic tissue regeneration and reduce bacterial infection.
Here, MgO nanoparticles and hydroxyapatite (HA) nanoparticles were dispersed within poly (l-lactic acid) (PLLA) composites and then tested for their mechanical properties, surface roughness, antibacterial properties, and their ability to support the adhesion and proliferation of fibroblasts and osteoblasts. Free nanoparticles (MgO and HA) in solution were also exposed to cells and bacteria to characterize the nature of the cellular responses to these materials.
Results showed that MgO nanoparticles in solution enhanced fibroblast and osteoblast proliferation, suggesting that magnesium plays an important role in improving cell functions. When dispersed within PLLA composites, MgO nanoparticles improved osteoblast and fibroblast adhesion and proliferation compared to plain PLLA. Osteoblasts proliferated best on nanocomposites containing both HA and MgO nanoparticles, as MgO nanoparticles were believed to enhance the osteogenic properties of HA nanoparticles. Nanocomposites containing both HA and MgO nanoparticles also exhibited the most suitable mechanical properties for application within cancellous bone. Bacterial experiments with Staphylococcus aureus showed that MgO nanoparticles exhibit powerful bactericidal efficacy, suggesting that MgO nanoparticles should be incorporated into scaffolds for orthopedic tissue engineering to improve cell functions and reduce the risk of bacterial infection.
9:00 AM - F5.14
Preparation of Mussel-Inspired Nano Scale Polymer Particle Platforms for Anchoring Inorganic NPs under High Salt Concentration Conditions
Hiroki Satoh 1 Masaaki Kanahara 1 Yuta Saito 1 Takeshi Higuchi 2 Hiroshi Yabu 2 3
1Graduate School of Engineering Tohoku University Sendai Japan2IMRAM Tohoku University Sendai Japan3JST-PRESTO Sendai JapanShow Abstract
Organic-inorganic composite particles have attracted much interest due to applications in photonics, electronics and biotechnologies. Especially the applications in biotechnologies, such as contrast agents in magnetic resonance imaging (MRI), drug carriers, heat generators for hyperthermia therapy and so on, are considered to be important in recent years. Organic-inorganic composite particles usually have been prepared by attaching inorganic NPs on polymer particles via electrostatic interaction named heterocoagulation. But since the electrostatic interaction is sensitive for environment of dispersion, the inorganic NPs easily detach from polymer particles at in vivo condition. Therefore preparation of polymer particle platforms for anchoring inorganic NPs stably even in vivo conditions is required.
To prepare that kind of polymer platforms, a catechol group is one of the good candidates. The catechol group is found in the adhesive protein of mussels and high adhesive properties of catechol groups onto many kinds of substrates have been reported. We have reported a synthesis of amphiphilic copolymer containing the catechol group and a simple preparation method of polymer particles by evaporating a good solvent from a polymer solution containing a poor solvent(SORP).
In this report, we show preparation of polymer particles containing catechol groups by using SORP. We found that these particles are successfully anchoring inorganic NPs stably under high salt concentration conditions.
The amphiphilic copolymer containing a catechol group was synthesized from dopamine methacrylamide and N-dodecylacrylamide by free radical polymerization(Polymer 1). Polymer 1 and polystyrene(PS) were respectively dissolved in tetrahydrofuran (THF) to prepare 1 g L-1 solution. A solution of Polymer 1 (0.5 mL) and that of PS (0.5 mL) were mixed, and then MilliQ membrane filtered water (1 mL) was added to the mixed solution with stirring. THF was evaporated at 25 °C in a water bath. Polymer particles of hydroxy terminated PS (PSOH) were prepared by the same method. Aqueous dispersion of Au NPs was mixed with aqueous dispersion of polymer particles, and then the mixtures were kept at 25 #8451; in a water bath. An aqueous solution of potassium chloride(2M) was added into the mixtures. The mixtures were dialyzed over night and observed by scanning electron microscopy (SEM).
SEM images showed that the AuNPs were attached homogeneously to the surface of the polymer particles containing catechol groups. On the other hand, the aggregated AuNPs were observed on the surface of the PSOH particles and on the grid. These results indicate that catechol groups were localized at the surface of polymer particles and contributed to immobilization of inorganic NPs. We succeeded in preparing polymer particles comprised of PS and amphiphilic copolymers containing catechol groups, and they succeeded in anchoring inorganic NPs stably under high salt concentration conditions.
9:00 AM - F5.15
One-Step Conjugation of Recombinant Proteins to Semiconductor Nanocrystals for Scalable Assembly of Functional Devices
Zhengtao Deng 1 Timothy K. Lu 1
1Massachusetts Institute of Technology Cambridge USAShow Abstract
Colloidal semiconductor nanocrystals, such as quantum dots (QDs), have fascinating physical properties of relevance to biology include high fluorescence quantum yield, narrow and symmetric photoluminescence spectra, broad absorption profiles, remarkable chemical, photonic, and colloidal stability, large effective Stokes shift, and high multiphoton excitation cross sections. The successful conjugation of quantum dots with biological molecules, such as proteins and DNA, is a critical step for their utility as fluorescent bio-probes, engineered biosensors, photodynamic therapy agents or sensitizers, and bio-inspired functional materials for light harvesting. Over the past 15 years, there have been continuous efforts to develop new QD-protein conjugation methods. Among them, carbodiimide crosslinker chemistry, such as 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) /N-Hydroxysuccinimide (NHS), is often used to attach QDs with proteins, typically by amide bond formation between terminal carboxyls on the QD ligands and ubiquitous amines on proteins. However, the presence of the same ubiquitous target groups on target proteins means that this approach can often result in uncontrolled heterogeneous orientation and valence on the QD and undesirable cross-linking. Furthermore, QD conjugates formed with this chemistry require multi-step synthesis and purification, which results in low conjugation efficiency, reduced fluorescence quantum yield, and less colloidal stability. Herein, we developed a new strategy to achieve robust QD-protein conjugates with a single-step synthesis in a short time. Our strategy takes advantage of a two-cysteine/six-HisTag linkage, that are genetically encoded with the SpyCatcher protein expressed by Escherichia coli, and could be directly attached to the QD shell surface during the core/shell QD synthesis in aqueous solution. This synthetic route results in robust core/shell QD-protein conjugates that are highly stable, highly fluorescent, and versatile for a wide range of semiconductor materials with various sizes, compositions and morphologies. We further demonstrated the organization of micron-scale one-dimensional QD chain structures and related heterosystems by specific SpyCatcher-SpyTag chemistry, which is high yield, highly specific and compatible with diverse pH, temperature, and buffer in vitro and in vivo environments. Since the reactive units are conveniently introduced by genetic engineering in either prokaryotic or eukaryotic expression systems, we recognized that the SpyTag-SpyCatcher chemistry is an excellent platform for QD-proteins conjugates with tunable fluorescence properties, and could be used an ideal platform for bacterial cell directed self-assembly of functional devices in large-area. While the present work applies to QD-SpyCatcher, we expect the general applicability of our approach to other materials and recombinant proteins for scalable assembly of multiplexed functional devices.
9:00 AM - F5.16
De-Coupling Structure from Function: Controlling Hierarchal Polymer Dynamics with Bio-Inspired Metal-Coordination
Scott C. Grindy 1 Rob Learsch 1 Devin G. Barrett 2 Jing Cheng 2 Phillip B. Messersmith 2 Niels Holten-Andersen 1
1Massachusetts Institute of Technology Cambridge USA2Northwestern University Evanston USAShow Abstract
Metal-coordinate bonds inspired by the tough, ductile mussel fiber have recently been demonstrated to act as the reversible crosslinks in self-adhesive polymer hydrogels. The exchange kinetics of these crosslinks can be tuned across several orders of magnitude simply by using different transition metals as the crosslink center. Thus, with the exact same polymer, we are able to engineer materials with vastly different viscoelastic relaxation times.
We show that the individual relaxation times are modular - we can insert and remove viscoelastic relaxation modes by simply changing the relative concentrations of different transition metals in our gels. Traditionally, the polymer architecture and viscoelastic properties are interdependent, but the modularity of metal-coordination complexes allows us to effectively de-couple the polymer structure from the mechanical behavior of the system, as we can modulate the mechanical properties orthogonally from the polymer backbone. Using bio-inspired metal-coordinate complexes in this manner will allow the creation of model viscoelastic systems to explore fundamental questions in soft materials design, such as how incorporating well-controlled reversible interactions into covalent gel networks can be used to control stiffness, toughness, and ductility in hydrogel systems.
9:00 AM - F5.17
Slippery Metallic Surfaces
Alexander B. Tesler 2 1 Philsyok Kim 1 Joanna Aizenberg 2 1 3
1Harvard University Cambridge USA2Harvard University Cambridge USA3Harvard University Cambridge USAShow Abstract
A simple, nontoxic and inexpensive method to prepare mechanically robust surfaces that repels a variety of liquids and solids has immediate relevance in many industrial applications. Unwanted interactions between liquids and surfaces are currently a limiting factor nearly everywhere liquids are handled or encountered. Most state-of-the-art liquid repellent surfaces are modeled after lotus leaves, which are known to exhibit superhydrophobicity and self-cleaning. Despite over a decade of research, these surfaces are still plagued with problems that restrict their practical applications.
Recently, the slippery liquid-infused porous surfaces (SLIPS) technology was introduced by our group. SLIPS technology is inspired by the Nepenthes pitcher plant and provides unique capabilities that are unmatched by any other liquid-repellent surface technologies. SLIPS surfaces function under high pressure conditions, instantly self-heal imperfections, provide optical transparency, repel ice nucleation, and are ultra-repellent to pure and complex fluids such as blood, crude oil, and brine. They also repel solids such as ice and wax. These properties allow the slippery surfaces to be used in a wide variety of applications and environments. Moreover, the slippery surfaces can be constructed from a broad range of simple, inexpensive materials without the need for specialized fabrication facilities.
Here we used a stainless steel, which is widely used in biomedical, household and industrial equipment, surgical instruments, kitchen appliances, transport and architecture, as a substrate. We use an inexpensive and environmentally friendly electrodeposition process to form a thin layer of nanostructured tungsten bronze. Such films are mechanically robust and can be functionalized to increase its hydrophobicity, ideal for integration with SLIPS technology. Moreover, electrochemical deposition provides various control parameters for optimization of the film morphology. We will present that slippery stainless steel surfaces can be optimized to repel simple and complex fluids, reduces ice formation, accelerates frost removal and prevent adhesion of biofilms.
9:00 AM - F5.18
Experimental Design Based Analysis of Novel Poly(L-Lactic Acid) Based Nanocomposites: Relationship between Design Parameters and Compressive Properties
Samin Eftekhari 1 Ihab El Sawi 2 Ginette Turcotte 1 Habiba Bougherara 2
1Ryerson University Toronto Canada2Ryerson University Toronto CanadaShow Abstract
Biopolymer based nanocomposites are great of interest for use as bone scaffolds due to their biocompatibility and adjustable mechanical and biodegradation properties. Mechanical properties of human bone vary tremendously according to location and function (i.e., load or non-load bearing). Therefore, a scaffold's mechanical properties should be tailored to match the demands of the defect site, and to decrease or avoid complications such as stress-shielding. Scaffold properties can be tailored to the particular mechanical and physiologic demands of the host tissue by effectively controlling weight fraction, ratio of the constituents, and morphology.
Current research is focused on investigation of the effects of content parameters of recently developed nanocomposites on mechanical behavior of them were investigated by using factorial design methodology. The poly(L-lactic acid)/microcrystalline cellulose/hydroxyapatite nanoparticles nanocomposites were fabricated using sublimation of polymer solvent and leaching out the porogen out of nanocomposite structure followed by characterization using scanning electron microscopy (SEM), universal compression testing machine. Statistical analysis evaluated the effects of three independent variables on final properties of the nanocomposite. Increasing the concentration of PLLA affected mechanical properties including compressive yield and Young&’s modulus positively. Besides, the higher ratio of MCC/HA ratio (0-4) led to enhancement of compressive yield from 0.32 to 0.87 MPa and Young's modulus from 16.11 to 28.55 MPa. Furthermore, the effect of concentration of PLLA on final compressive properties has been evaluated. Based on optimization with factorial design methodology, by varying the comcentration of PLLA from 10% to 20 %, compressive yield improved from 0.87 to 1.36 MPA, and Young's modulus from 28.55 to 44.64 MPa. The same investigation has been conducted for nanocomposites with the presence of porogen. The comparissive study of nanocomposites with porogen and without porogen revealed that incorporation of porogen during the fabrication of the nanocomposite resulted lower compressive yield in compare with the ones with no porogen. However, SEM images showed that the pore shapes uniformity and interconnectivity were improved. The mechanisms involved for the failour during the compression test also have been discussed.
9:00 AM - F5.19
Self-Assembly of Catalytic Peptides to Mimic Enzymes
Yuka Kanetsuki 1 Yoshiaki Maeda 1 Nadeem Javid 2 Krystyna Duncan 2 Yasuhiro Ikezoe 1 Rein V Ulijn 2 3 Hiroshi Matsui 1
1City University of New York, Hunter College New York USA2University of Strathclyde Glasgow United Kingdom3City University of New York New York USAShow Abstract
Natural enzymes have been evolved as impressive catalysts for taking a long time. Although they have effective functions in many chemical reactions, it is difficult for researchers to optimize the functions and improve the yield of products because of the complexity and lack of fully understanding of the catalytic mechanism. In our study, to discover efficient peptide biocatalysts and evolve the catalytic functions, (i) we constructed a novel screening methodology that enables the selection of catalytic peptides from sequence libraries based on the phage display technique and (ii) we fused hydrophobic tail of amyloid β mimicking peptide (ABP)1) at the C-terminus of catalytic peptide which can provide hydrophobic part as well as self-assembling property to accumulate catalytic center. This approach using libraries of M13 phage viruses consists of 109 different phages, each displaying five copies of peptide sequence at the tip. The peptide catalysts in chemical reaction were selected via supramolecular gelation2) of targeted products on phage viruses for the mass-separated panning process. In this methodology, when a phage library is exposed to precursors in aqueous solution, the product is gelated by the activity of catalytic peptide on phages. Based on catalytic gelation combined with phage display we selected several catalytic peptides which can catalyze to bond between two molecules by amide condensation.
To confirm the generated compound by amide condensation occurred in selected peptide display region of phages, transmission electron microscopy (TEM) was carried out. The TEM images showed that the hydrogel was observed in reaction sample including selected catalytic peptide, while no such hydrogel was observed in control sample which is absence of the peptide. We also confirmed the product in the reaction sample by HPLC. In the sequences of the selected peptides, we found some of peptides contain nucleophilic amino acids and also the most common catalytic triads (histidine, serine and aspartic acid or glutamic acid). They might have not only amide condensation activity but also amide hydrolase activity because these catalytic triads are found in a range of amidases. Natural enzymes have hydrophobic pocket to capture substrates in order to enhance catalytic selectivity and activity. By addition of ABP to catalytic peptide, the catalytic activity was increased rather than without ABP peptide. The result showed that the assembly of catalytic peptides is important for evolution of catalytic function.
The discovery of these peptides for mimicking protease has significantly impact because the peptide consisting of the only 12 amino acids is useful and can be designed easier for synthesis of chemical compound such as drug molecules.
1) M. J. Krysmann, V. Castelletto, I. W. Hamley, Soft Matter, (2007), 3, 1401-1406.
2) R. J. Williams, A. M. Smith, R. Collins, N. Hodson, A.K. Das, R. V. Ulijn, Nat Nanotechnol., (2009), 4, 19-24.
9:00 AM - F5.20
Artificially Engineered Protein Hydrogels that Mimic Selective Gating by the Nuclear Pore Complex
Minkyu Kim 1 Wesley G. Chen 2 Matthew J. Glassman 1 Jeon Woong Kang 3 Katharina Ribbeck 2 Bradley D. Olsen 1
1Massachusetts Institute of Technology Cambridge USA2Massachusetts Institute of Technology Cambridge USA3Massachusetts Institute of Technology Cambridge USAShow Abstract
A polypeptide-based hydrogel fills the nuclear pore channels embedded in the nuclear membrane of a eukaryotic cell and acts as a selective gate allowing passage of less than 0.1% of all proteins in the cell while translocating over 1,000 molecules per second. The gel-forming proteins are nucleoporins, containing “FG” repeat sequences which are known to associate with one another to construct physical gels and give rise to the hydrogel&’s selective filtering property. This biologically specific selectivity of nucleoporin hydrogels, which is unprecedented in synthetic polymer gels, makes them scientifically interesting materials with a potential for broad impacts on separation technologies. However, major obstacles in utilizing nucleoporin hydrogels for advanced technology include low biosynthetic yield of the natural protein; long gel processing time, delaying immediate use; and incomplete knowledge of sequence-structure property-function relationships of the nucleoporin hydrogel due to the complexity of natural protein sequences, hindering creating tunable selective filters.
Herein, we report for the first time artificially engineered protein hydrogels that mimic the selective permeability of nucleoporin hydrogels, are produced in high yields, and possess reduced gelation times. Analysis of a well-investigated nucleoporin, Nsp1, yielded a pair of consensus sequences for a 19 amino acid nucleoporin repeat which is repeated 16 times in the native protein with extremely high consensus at each position except one. This fundamental repeat unit was cloned into an artificial protein polymer by ligating 16 such units in a row to produce a nucleoporin-like protein (NLP). To facilitate hydrogel formation, NLP sequences were flanked with coiled-coil domains as endblocks of NLPs, creating three dimensional polymer networks.
Simplified NLP sequences allowed investigation of the sequence-structure property-function relationships of nucleoporin hydrogels. Using a combination of techniques including the hydrogel inversion test, selective transport assay, shear rheology, and Raman spectroscopy, we found that only recombinant NLPs with coiled-coil endblocks constructed hydrogels with different levels of selective permeability. A pair of NLPs with a single amino acid replacement within the repeat unit presented significantly different amounts of cargo transportation into the hydrogels and hydrogel relaxation times, suggesting that physicochemical properties of NLP sequences are correlated with the selective permeability and mechanical properties of the hydrogels. Moreover, our findings revealed that not only “FG” sequences but also other sequences of natural nucleoporins would be important for gel structure and the selective filtering function. Tunable mechanical properties and selective permeability of nucleoporin-mimicking hydrogels with high yields can potentially advance the technology in drug delivery, food toxicology, and defense applications.
9:00 AM - F5.21
Inhibition of Gram-Positive and Gram-Negative Bacteria Growth on Selenium Nanoparticle Coated Paper Towels
Qi Wang 1 Thomas Webster 2
1Northeastern University Boston USA2Northeastern University Boston USAShow Abstract
Wide spread bacteria contamination has been found on various paper products, such as paper towels hanging in sink splash zones or those used to clean surfaces, filter papers used in water and air purifying systems, and wrapping used in the food industry, which may lead to the potential spread of bacteria and consequent health concerns. Due to the porous structure of fibers in all paper products, such materials are prone to bacteria growth and, thus, are sources for continual contamination. Besides, this porous structure provides an environment that favors the attachment of bacteria and makes it more difficult to kill bacteria once forming a biofilm. One of the most promising approaches towards preventing infections is coating paper products with antimicrobial materials. Therefore, in this study, selenium nanoparticles were coated on normal paper towel surfaces through a quick precipitation method, introducing antibacterial properties to the paper towels. Their effectiveness at preventing biofilm formation was tested in bacterial assays involving Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Staphylococcus epidermidis. The results showed that there were significant and continuous bacteria inhibition with about a 90% reduction from 24 to 72 hours for gram-positive bacteria including S. aureus and S. epidermidis. The selenium coated paper towels also showed significant inhibition of gram-negative bacteria like P. aeruginosa and E. coli growth at about 57% and 84%, respectively, after 72 hours of treatment. Therefore, this study suggested that coating paper products with selenium nanoparticles may be an effective way to decrease various gram-positive and gram-negative bacteria growth on paper products, which might be used for potentially important applications for antimicrobial purposes in the food packaging industry and in clinical environments.
9:00 AM - F5.22
Dopa-Incorporated Recombinant Mussel Bioadhesives with Highly Enhanced Adhesion and Water-Resistance
Byeongseon Yang 1 Dooyup Jung 1 Niraikulam Ayyadurai 5 Hyungdon Yun 3 Yoo Seong Choi 4 Qingye Lu 2 Hongbo Zeng 2 Byeong Hee Hwang 1 Hyung Joon Cha 1
1Pohang University of Science and Technology Pohang Korea (the Republic of)2University of Alberta Edmonton Canada3Konkuk University Seoul Korea (the Republic of)4Chungnam National University Daejeon Korea (the Republic of)5Yeungnam University Gyeongsan Korea (the Republic of)Show Abstract
3,4-Dihydroxyphenylalanine (Dopa), which is a hydroxylated form of the tyrosine residue, has been suggested to be a key factor for rapid and strong underwater adhesion through its mediation of various interactions, such as bidentate hydrogen bonding, complexes with metals and metal oxides, the cation-pi interaction, and oxidative cross-linking, because it is oxidised to Dopa-quinone. Mussel adhesive proteins (MAPs) are one of examples where Dopa chemistry is the core of their underwater adhesion with extremely high Dopa contents of ~10-25 mol%. The biosynthesis of recombinant MAPs in an Escherichia coli system was a good approach to overcome the availability limitation that results from the extremely low yield of natural extraction of MAPs from mussel feet and to apply MAPs as an universal underwater bioadhesive. However, Dopa incorporation always follows as the biggest problem because lack of Dopa in recombinant MAPs critically limited the underwater adhesion. To transform tyrosine residues into Dopa molecules, an in vitro mushroom tyrosinase treatment has commonly been conducted. However, this process exhibits a low (<~15%) modification yield. Here, we explore the in vivo residue-specific incorporation of Dopa into recombinant MAPs. Because Dopa molecules can be misaminoacylated to tRNATyr by endogenous tyrosyl-tRNA synthetase, the quantitative replacement of tyrosine residues by Dopa was achieved with a yield of over ~90 % via an in vivo residue-specific incorporation strategy, to create, for the first time, engineered mussel adhesive proteins (MAPs) in E. coli with a very high Dopa content close to that of natural MAPs. Using several analyses, we confirmed that Dopa-incorporated engineered recombinant MAPs exhibited the superior surface adhesion and water-resistance abilities by assistance of Dopa-mediated interactions including oxidative Dopa cross-linking. In addition, their underwater adhesive properties were comparable to those of natural MAPs. Our results show their great potential as bioglues for use in practical underwater applications.
9:00 AM - F5.23
Sea Anemone Minicollagen: Molecular Structure, Properties, and Nature-Mimicking Recombinant Production
Dooyup Jung 1 Yun Jung Yang 1 Jeong Hyun Seo 2 Yoo Seong Choi 3 Byeong Hee Hwang 1 Hyung Joon Cha 1
1Pohang University of Science and Technology Pohang Korea (the Republic of)2Yeungnam University Gyeongsan Korea (the Republic of)3Chungnam National University Daejeon Korea (the Republic of)Show Abstract
Aquatic species in the Phylum Cnidaria, including sea anemone and jellyfish, have special cell organelle called nematocyst. When stimulated, with waving motion of tentacles, coiled tubular structure in charged nematocyst is instantaneously stretches out to capture prey or keep the organism itself from predators. The driving force of this ultra-speedy discharge is high osmotic pressure maintained in charged nematocyst. Therefore, the capsule wall of nematocyst should be tough enough to withstand this internal pressure. Previous researches have shown that minicollagen is a main component of capsule wall, so it can be thought as critical structural material to meet mechanical requirement. However, almost every research treating minicollagen and its experimental analysis has used Hydra as a source organism. In the present work, estuarine sea anemone Nematostella vectensis was chosen as a novel target organism for minicollagen research. Structural analysis found disulfide crosslinking and triple helix formation among minicollagens, which are regarded as main reason of superior mechanical toughness. Measuring mechanical properties of nematocyst capsule wall were also tried to know how exactly strong the wall is. Forming a part applying this nature-inspired structure and power in engineering, recombinant production of sea anemone minicollagen in Escherichia coli expression system was successfully endeavored. Genetically redesigned E. coli for disulfide bond formation and in vivo incorporation of 4-hydroxyproline was used to mimic natural structure of minicollagen. These approaches cannot only help researchers to acquire homogenous minicollagen for basic analysis, but also suggest its possibility as a plentiful biomaterial in engineering.
9:00 AM - F5.24
Photo-Crosslinked Silk-Like Protein Derived from Sea Anemone for Hydrogel-Based Scaffold Fabrication
Yun Jung Yang 1 Yoo Seong Choi 2 Dooyup Jung 1 Hyung Joon Cha 1
1POSTECH Pohang Korea (the Republic of)2Chungnam National University Daejeon Korea (the Republic of)Show Abstract
Gel-based scaffolds have been utilized as space filling agents, delivery vehicles, and three dimensional structures. However, their weak strength and stiffness (elastic modulus) were considered as limitations to endure physiological stimulus. Here, we exploited recombinant silk-like protein (aneroin), originally derived from sea anemone&’s tentacle, as tough gel material. Aneroin consists of decamer repeats and has similar secondary structure of an elastic silk from spider (flagelliform silk). Photo-initiated crosslinking was tried for hydrogel formation. Additionally, disulfide crosslink was also carried out to enhance mechanical property of gel. We found that elastic modulus of aneroin was three times higher than skeletal muscle, and its strength was two-fold stronger than cardiac muscle. In addition to mechanical properties, photo-crosslinked aneroin showed high transmittance in visible light. Thus, durable and transparent aneroin hydrogel would be expanded its applications to biomolecular carrier as well as structural support.
9:00 AM - F5.25
Virus-Based Piezoelectric Energy Generation
Seung-Wuk Lee 1 2 Kwang Heo 1 2
1University of California, Berkeley Berkeley USA2Lawrence Berkeley National Laboratory Berkeley USAShow Abstract
Piezoelectric materials can convert mechanical energy into electrical energy, and piezoelectric devices made of various inorganic materials and organic polymers have been demonstrated. However, synthesizing such materials often requires toxic materials, harsh conditions and/or complex procedures. Recently, it was shown that hierarchically organized natural materials, such as bones, collagen fibrils and peptide nanotubes, can display piezoelectric properties. In my presentation, I will show our innovative approach to produce virus-based piezoelectric energy generation. Recently, we establish that the piezoelectric and liquid crystalline properties of M13 bacteriophage (phage) can be used to generate electrical energy. Using piezoresponse force microscopy, we characterize the structure-dependent piezoelectric properties of phage at the molecular level. We then show that self-assembled thin films of phage can exhibit piezoelectric strengths of up to 7.8 pm/V. We also demonstrate that it is possible to modulate the dipole strength of phage, and hence tune their piezoelectric response by genetically engineering the phage&’s major coat proteins. Finally, we develop a phage-based piezoelectric generator that produces up to 6 nA of current and 400 mV of potential, and use it to operate a liquid crystal display. Because biotechnology techniques enable large-scale production of genetically modified phages, phage-based piezoelectric materials potentially offer a simple and environment-friendly approach to piezoelectricity generation.
9:00 AM - F5.26
Proangiogenic Multi-Domain Peptide Hydrogels
Vivek Ashok Kumar 1 Nichole L Taylor 1 Abhishek Jalan 1 Benjamin K Wang 1 Siyu Shi 1 Jeffrey D Hartgerink 1
1Rice University Houston USAShow Abstract
Multidomain peptides (MDP) self-assemble into extracellular matrix mimetic nanofibrous hydrogels. These short chain biocompatible matrices, exhibit shear thinning and rapid recovery, allowing for syringe aspiration and directed in situ delivery. Tailoring of terminal residues allows for fined tuned control of molecular, cellular and tissue responses. In this study, we show the development of a hybrid MDP capable of stimulating robust angiogenic responses. A short chain (15 amino acid) peptide sequenced from VEGF 165 was conjugated to a 16 amino acid MDP. Mechanical and ultrastructural characterization showed presence of nanofibrous structure, shear thinning and recovery. Biological function was demonstrated by upregulation of VEGFR1, VEGFR2 and NP-1 activation. Cytocompatibility with HUVEC and hMSCs showed similar cell adhesion, proliferation and scratch wound healing to positive controls. Gross morphology of subcutaneous implants of injectable hydrogels showed large vessels in and around implants, without the development of hemangiomas or leaky vasculature. Histomorphometric analysis showed rapid cellular infiltration as early as 3 days, rapid development of stable blood vessels as early as 7 days suggesting formation of mature blood vessels. These vessels subsequently resorb by 3 weeks. Materials developed in this study may allow for rapid angiogenesis, increased ischemic tissue perfusion, and augmented tissue regeneration.
9:00 AM - F5.27
Advanced Simulations of Peptide-Surface Interactions at the Aqueous Titania Interface
Anas M. Sultan 1 Louise B. Wright 2 Zak E. Hughes 1 Jesus P. Palafox-Hernandez 1 Tiffany R. Walsh 1
1Deakin University Geelong Australia2University of Warwick Coventry United KingdomShow Abstract
Despite the widespread utilization of bio-titania interfaces,1 such as in biomedical implants, drug delivery, biosensors and photovoltaics, biomolecular recognition and interactions at these interfaces remain far from being understood. Predicting and controlling bio-interfacial properties is extremely challenging without a molecular-level comprehension of how biomolecules interact with material surfaces and the factors that influence these interactions. Molecular simulation, using efficient conformational sampling of peptide adsorption to material surfaces is one way of elucidating these mechanisms. Employing advanced sampling techniques is therefore crucial to the understanding, advancement, and optimization of interfacial properties. We utilize cutting-edge techniques such as Replica Exchange with Solute Tempering (REST)2 and Metadynamics3 to study, at the negatively-charged aqueous rutile TiO2 (110) surface, the adsorption of a number of amino acids and titania-binding peptides and calculate their binding free energies.
This is performed by studying analogues of six amino acids (Ala, Arg, Asp, Lys, Phe, and Ser) and two experimentally-identified titania-binding peptides, namely Ti1 (QPYLFATDSLIK) and Ti2 (GHTHYHAVRTQT).4 Our results revealed a stronger affinity between charged amino acids and the titania surface compared to uncharged amino acids. In addition, peptides Ti1 and Ti2 were found to have a similar free energy of adsorption but different binding mechanisms. While Ti2 revealed an enthalpic binding, Ti1 showed an entropically-driven binding mechanism.5 The contribution of each residue to binding to the titania surface was evaluated in both peptides. Moreover, the effect of using Ca2+ counterions, in contrast to Na+, on the adsorption of both peptides at aqueous titania was studied. Finally, the impact of His protonation state on the adsorption of Ti2 was evaluated. Our results provide valuable insights into the complex interplay between peptide sequence, structure, and binding at the aqueous TiO2 interface.
1 Carravetta V and Monti S. Peptide-TiO2 surface interaction in solution by ab initio and molecular dynamics simulations. J. Phys. Chem. C (2006) 110, 6160-6169.
2 Terakawa T, Kameda T and Takada S. On easy implementation of a variant of the replica exchange with solute tempering in GROMACS. J. Comput. Chem. (2010) 32, 1228-1234.
3 Laio A and Parrinello M. Escaping free-energy minima. Proc. Natl. Acad. Sci. U.S.A. (2002) 99, 12562-12566.
4 Puddu V, Slocik JM, Naik RR and Perry C. Titania binding peptides as templates in the biomimetic synthesis of stable titania nanosols: Insight into the role of buffers in peptide-mediated mineralization. Langmuir (2013) 29, 9464-9472.
5 Tang Z, Palafox-Hernandez JP, Law WC, Hughes ZE, Swihart MT, Prasad PN and Walsh TR. Biomolecular recognition principles for bionanocombinatorics: An integrated approach to elucidate enthalpic and entropic factors. ACS Nano (2013) 7, 9632-9646.
9:00 AM - F5.28
Computational Modeling of Bacteriophage Self-Assembly during Formation of Hierarchical Structures
Edward Perkins 1 Olexandr Isayev 2 Chris Warner 1 Wayne Hodo 1 David McInnis 1 Laura Walizer 1 Aimee Poda 1 Michael Cuddy 1 Seung-Wuk Lee 3 4
1Army Corps of Engineering Vicksburg USA2University of North Carolina at Chapel Hill Chapel Hill USA3University of California, Berkeley Berkeley USA4Lawrence Berkeley National Lab Berkeley USAShow Abstract
Designing new materials with well-defined structures and desired functions is a challenge in materials science, especially with nanomaterials. Nature, however, solves design of these materials through a self-assembling hierarchically-ordered process. We have investigated how the high- aspect ratio and unique surface chemistry of mutant M13 bacteriophage can give rise to increasingly complex, hierarchically ordered, bundled phage structures with a wide range of material applications. A molecular dynamic simulation of the 3-D structure of an subsection (~80 nm) of wild type (WT) and mutant phage particles were developed based on WT phage crystal structure and ab initio calculations. Simulations of phage particles were then used to examine repulsive and attractive forces of particles in solution. Examination of contact interactions between WT phage indicated an optimal interaction with phage in head to tail orientations. A mutant phage (4E) with a higher negative surface charge than WT also preferentially ordered head to tail in solution. However, a mutant phage (CLP8) with a net positive surface charge had minimal repulsion in a 90-degree orientation. Larger scale interactions were simulated using Discrete Element Modeling where full length, 800 nm, phage were interacted together under different conditions. Understanding the self-assembly process through molecular dynamic simulations and decomposition of fundamental forces driving inter- and intrastrand interactions has provided a qualitative assessment of mechanisms that lead to hierarchical phage bundle structures. We anticipate using this system to further investigate development of hierarchical structures not only from biological molecules but also from synthetic materials.
9:00 AM - F5.29
Developing Bio-Mediated Assembly Strategies for Next-Generation Metamaterials: Structure and Dynamics of Materials-Adsorbed Peptide-Based Switchable Linkers
Kurt Laurence Murray Drew 1 J. P. Palafox-Hernandez 1 Tiffany R. Walsh 1
1Deakin University Geelong AustraliaShow Abstract
An area of growing interest is the development of noble-metal metamaterials because of their unique properties[1,2]. Development of versatile generation strategies for production of these metamaterials remains challenging; these materials comprise assemblies of nanoparticles of different compositions, arranged in 3-D arrays; fine control over the interparticle spacings in these arrays is essential. It is also highly desirable that these arrays can be dynamically reconfigured. As the first steps towards realizing these goals, we investigate Au- and Ag-binding peptide sequences conjugated with light-switchable azobenzene moieites, for the purpose of designing stimuli-responsive biomolecule linkers that can ultimately facilitate assembly of different types of nanoparticles into 3D arrays. Here, we use advanced sampling molecular dynamics simulations to investigate the molecular conformations and materials-binding properties of these molecules. These peptide sequences have a light sensitive thiol-maleimide azobenzene thiol-maleimide (MAM) unit conjugated onto either the N- or the C-terminus of the peptide. We have also carried out well-tempered meta-dynamics simulations to estimate the free energy of binding, of the MAM unit alone, at the Au and Ag aqueous interfaces. Our results indicate that the MAM unit binds more strongly at Au compared with Ag, with the trans conformation of the MAM binding more strongly than the cis for both metals. Our simulations of the N- and C-conjugated peptides reveal that the presence of the MAM unit can significantly affect the adsorbed structures and conformational dynamics of the surface adsorbed peptide. Our findings provide guidance in the design and development of a stimuli-responsive biomolecule linker for nanoparticle assembly purposes.
 P.-Y. Chen, J. Soric and A. Alu, Adv. Mater., 2012, 24, OP281-304.
 K. L. Young, M. B. Ross, M. G. Blaber, M. Rycenga, M. R. Jones, C. Zhang, A. J. Senesi, B. Lee, G. C. Schatz and C. A. Mirkin, Adv. Mater., 2014, 26, 653-9.
 T. Terakawa, T. Kameda and S. Takada, J. Comput. Chem., 2011, 32, 1228-34.
 A. Barducci, G. Bussi and M. Parrinello, Phys. Rev. Lett., 2008, 100, 020603.
 K. L. M. Drew, Z. Tang, J. P. Palafox-Hernandez, Y. Li, M. T. Swihart, C. -K. Lim, P. N. Prasad, M. R. Knecht and T. R. Walsh, in preparation.
9:00 AM - F5.30
Bioinspired Superhydrophobic and Underwater Superoleophobic Surfaces for Oil/Water Separation
Maryna Kavalenka 1 Michael Roehrig 1 Andreas Hopf 1 Stefanie Frenzen 1 Marc Schneider 1 Matthias Worgull 1 Hendrik Hoelscher 1
1Karlsruhe Institute of Technology Eggenstein-Leopoldshafen GermanyShow Abstract
Developing effective and environmentally friendly oil/water separation methods for cleaning oil spills is a worldwide challenge. One approach to this problem involves designing novel materials with special wetting behavior, inspired by superhydrophobic surfaces of plants and insects, and underwater superoleophobic surfaces of fish scales. Materials with superhydrophobic/superoleophilic surfaces are used to absorb or filtrate oil from oil/water mixtures, while superhydrophilic/underwater superoleophobic materials selectively remove water. We fabricated such materials by structuring conventional and wood-based polymers using a highly scalable low-cost hot pulling technique, in which softened polymers are locally elongated during demolding from heated sandblasted or microstructured plates. The resulting surfaces are covered with dense high aspect ratio nano- and microhairs, and are superhydrophobic and superoleophilic. The as-prepared surfaces absorb crude oil out of the water and separate oil/water mixtures. Moreover, the surface properties of the as-prepared materials can be changed to hydrophilic and underwater superoleophobic by a short argon plasma treatment cycle, making the nano- and microhaired surfaces capable of both ”oil-removing” and ”water-removing” oil/water separation methods. Additionally, by combining hot pulling technique with shape-memory polymers processing the hierarchical special wetting surfaces with increased fluid absorption are created.
9:00 AM - F5.31
Self-Organized Peptides on 2-Dimensional Nanomaterials
Yuhei Hayamizu 1 2 Christopher R So 2 Sefa Dag 2 Tamon R Page 2 David Starkebaum 2 Mehmet Sarikaya 2
1Tokyo Institute of Technology Meguro Japan2University of Washington Seattle USAShow Abstract
Establishing controlled structures of biological molecules on nanomaterials with controllable interfaces is the first step in the development of novel bionanodevices. Single-layer graphene, MoS2, and other 2-dimensional (2D) nanomaterials are ideal to form such bio/nano systems due to their atomically flat surfaces and unique electronic and optical properties. We have recently selected graphite binding short peptides using combinatorial mutagenesis which also bind to graphene and other single layer 2D nanomaterials. In particular, the selected peptide (GrBP5 with a sequence IMVTESSDYSSY) not only binds to graphene, but also undergoes self-organization to form ordered biomolecular nanostructures on the surface of graphene. Molecular interactions of the peptides with graphene involve binding, surface diffusion and intermolecular interactions followed by self-assembly. Each of these interactions can be controlled by point mutation of the amino acid domains along the sequence of the peptide which incorporates anchoring (underlined), neck and tail domains. Using atomic force microscopy, we demonstrate that engineered dodecapeptides form monolayer-thick ordered architectures on atomically flat surfaces of graphite commensurate with the underlying honeycomb lattice. Furthermore, via the mutation of the anchoring domain, the designed mutant peptides can also be made to bind to BN, and 2D transition metal chalcogenides, such as MoS2 and WSe2. Among the nanostructures form on the surface, for example, peptide nanowires have uniform dimensions, typically ~1-nm thick, ~12-nm wide, and micro-meters in length. These results indicate the strong structural correlation between self-organized peptide nanostructures and 2D nanomaterials. The coherent peptide conformation in nanowire structures potentially provides new opportunities to study fundamental interactions at the bio/nano interface towards developing novel bionanodevices. Research was co-sponsored by NSF-MRSEC program via DMR#0520567 at UW and JST-PRESTO program in Japan.
9:00 AM - F5.32
Assembly of Calcium Phosphate Structures Using Responsive Particles
Gil Costa Machado 1 Esther Garcia-Tunon 1 Salvador Eslava 1 Peter Tympel 1 Eduardo Saiz 1
1Imperial College London London United KingdomShow Abstract
Calcium phosphate ceramics are considered very promising materials for the repair and regeneration of bone defects. Two of the most commonly investigated are Hydroxyapatite (HA) and β-Tricalcium Phosphate (β -TCP), which can be used together to form Biphasic Calcium Phosphates (BCP), combining the properties of both materials. The performance of calcium phosphate materials depends on their composition and structure at multiple length scales from macro to nano levels. However, it has been very difficult to develop effective manufacturing technologies that enable a fine control of architecture and surface topography in practical calcium phosphate ceramics.
This work describes a novel manufacturing process to fabricate calcium phosphate structures and surfaces with complex architectures based on the design of responsive particles (Angewandte Chemie International Edition 52(30): 7805-7808). The method uses a pH-responsive branched copolymer surfactant (BCS) to functionalize surfaces in situ and to create responsive particles that can self-disperse or assemble between themselves or with soft templates (i.e. in emulsified suspensions) under the action of an external trigger (pH). The system enables a careful control of the viscoelastic properties of the ceramic slurry, and may be integrated in additive manufacturing technologies to obtain materials with complex shapes and tailored microstrucures at different length scales. The structures can mimic to some extent the hierarchical architecture of natural materials such as trabecular bone opening new paths for the optimization of their mechanical and biological performance.
As an example we will show how responsive emulsions can be used to fabricate strong materials with porosities ranging between 50 to 80 vol%, pore size between 3 to 50 mu;m and a range of interconnectivities, surface topographies and structural gradients. The rheological response of the emulsions can be controlled to build materials with complex shapes by coagulation casting, tape casting or three-dimensional printing.
9:00 AM - F5.33
Interaction of Biomimetic Lubricin with Fibronectin Surfaces: Adsorption, Normal Forces and Lubrication
Roberto C Andresen Eguiluz 1 Mingchee Tan 2 Cory Nathan Brown 1 Noah Junil Pacifici 1 Lawrence J. Bonassar 2 David A. Putnam 2 Delphine Gourdon 1 2
1Cornell University Ithaca USA2Cornell University Ithaca USAShow Abstract
Robust synthetic biolubricants have been searched for the coating of implants and the treatment of diseases, such as osteoarthritis, without real success. A mucin known as lubricin, found in the synovial fluid, is believed to be the glycoprotein responsible for the low friction and wear protection of cartilage. However, lubricin cannot yet be obtained recombinantly and is very expensive to extract, hence a suitable lubricin-mimetic molecule is still to be discovered. In this study, we combined Atomic Force Microscopy (AFM) and Surface Forces Apparatus (SFA) spectroscopy to characterize surface coverage as well as normal and friction forces of a lubricin-mimetic pAA-PEG copolymer (pAA-62kDa, PEG-2kDa) interacting with fibronectin (FN), a protein of the extracellular matrix found in the superficial zone of cartilage.
The pAA-PEG polymer coverage, distribution, and roughness were quantified by AFM for three different polymer concentrations, 0.3mg/ml, 1mg/ml, and 3mg/ml. In parallel, both the normal and the lateral (friction) forces of pAA-PEG were recorded using the SFA, in presence and absence of FN. Our AFM data indicated that the pAA-PEG polymer (i) had an average contour length and a diameter of 72nm and 10nm, respectively, and (ii) could self-associate to form a highly interconnected network onto surfaces, at all three concentrations. Our SFA data showed that the pAA-PEG polymer was only weakly adsorbed onto (negatively charged) bare mica surfaces but became firmly attached when FN was added as a polymer linker. FN also appeared to act as an efficient protector against mica surface damage when shear was applied. All our friction data exhibited (i) low friction coefficients (mu; asymp; 0.25) up to applied pressures of circa 3MPa and (ii) Amonton&’s like behavior, although poor wear protection was observed in the absence of FN. Friction coefficients also showed a weak shear velocity dependency. Together, AFM and SFA have allowed us for molecular and microscopic characterization of the pAA-PEG helping us gaining insight into both the lubrication mechanisms and the interactions of the biomimetic polymer with tissue (FN). Collectively, these results indicate that our proposed lubricin-mimetic lubricant might be a promising cheap alternative to lubricin, as it improves lubrication and protects shearing surfaces against wear, in presence of the extracellular matrix proteins present in cartilage.
9:00 AM - F5.34
Synthetic Glycoclusters with Tunable Lectin Binding Properties Based on Supramolecular Glycopeptide Assemblies
Antonietta Restuccia 2 Ye Tian 1 Joel Collier 1 Gregory Hudalla 2
1University of Chicago Gainesville USA2University of Florida Gainesville USAShow Abstract
Lectin recognition by cell surface glycans influences various cellular behaviors, such as adhesion, migration, proliferation, differentiation, and apoptosis, and therapeutics that can modulate these interactions are receiving increased attention. Lectin binding specificity at the cell surface is governed by the action of glycosyltransferases that alter glycan composition, as well as local glycan density, with high-density glycans providing a “glyco-cluster effect” that stabilizes relatively weak monovalent interactions. We proposed that supramolecular assembly of glycopeptides would provide synthetic analogs of natural glycoclusters with tunable lectin binding properties, namely specificity and affinity. In particular, mixing different ratios of glycosylated and non-glycosylated β-sheet fibrillizing peptides in the pre-assembled state can provide nanofibers with tunable glycan density, whereas glycosyltransferases can be used to modify nanofibrillar glycan composition post-assembly. To test this hypothesis, we created a variant of a β-sheet fibrillizing peptide, QQKFQFQFEQQ (Q11), terminated with a monosaccharide, n-acetylgl
9:00 AM - F5.35
Water-Responsive Hybrid Spore/Plastic Materials for Giant Stroke Actuation and Energy Conversion from Evaporation
Xi Chen 2 Ahmet-Hamdi Cavusoglu 3 Davis M Goodnight 2 Zhenghan Gao 4 Adam Driks 1 Ozgur Sahin 2 4
1Loyola University Medical Center Maywood USA2Columbia University New York USA3Columbia University New York USA4Columbia University New York USAShow Abstract
Water-responsive materials can swell and shrink in response to changes in relative humidity (RH). Bacillus spores are an example of a water responsive material that has demonstrated large energy density, high reversibility, and fast response speed to variations in relative humidity . Spores can self-assemble into a dense monolayer structure on various substrates, and therefore have the potential to serve as building blocks for stimuli-responsive hybrid materials in actuators and energy harvesting devices. Here, we demonstrate that a hybrid material built with spores and plastics can be used for giant stroke actuation and energy conversion from evaporation. We assemble Bacillus spores on thin polyimide strips with specific geometric patterns. When the RH level changes, the spores curve the polyimide substrate into an approximately sinusoidal shape which results in a large linear motion at both ends of the strip. These hybrid materials experimentally show an actuation strain exceeding 200% and fast response speed to the changes in RH (~ 1 sec). The actuation can be scaled up by packaging these spore/plastic hybrid biomaterials in parallel. By using these packaged hybrid materials and combining them with valves controlling the passage of moisture, we built an oscillator that can harvest the evaporation energy when we place it directly above the surface of water. When liquid water is evaporating into the dry air, the oscillator continually shrinks and expands until the water dries out. The mechanical oscillation can drive a generator to produce electricity continuously when water is present. Our results suggest that these hybrid biomaterials are excellent stimuli-responsive materials for high efficiency actuators and energy harvesting devices.
1. Xi Chen, L Mahadevan, Adam Driks and Ozgur Sahin, Bacillus spores as building blocks for stimuli-responsive materials and nanogenerators, Nature Nanotechnology9, 137-141 (2014).
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Molecular Self-Assembly of Engineered Dodecapeptides on Graphite in Buffer and Varying pH
Tamon Page 1 2 David Starkebaum 1 Jordan Holmes 1 Yuhei Hayamizu 2 1 Mehmet Sarikaya 1
1University of Washington Mercer Island USA2Tokyo Institute of Technology Ookayama JapanShow Abstract
The formation of complex biological materials with intricate structures is a source of inspiration for biomimetic approaches in solving a wide variety of technological problems in various fields of study. The modular nature of recently developed solid-binding peptides provides a simplified but versatile platform to study the fundamentals of biomolecular self-assembly. Here, we study the surface behavior of peptides, including binding, diffusion and assembly, using combinatorially selected graphite binding dodecapeptides on an atomically flat surface of graphite under a variety of solution conditions to establish the parameters of self-assembly. In particular, the assembly characteristics of the peptides were investigated with respect to ionic strength and pH of the incubating aqueous solution during the deposition process. The assembled nanostructures, ordered or random (amorphous), were found to be sensitive to both salt concentration and solution pH in the case of the negatively charged variants of the peptide, but was unaffected in case of the net neutral mutant. From these results, we conclude that the effect of both ionic strength and pH on the ordered self-assembly of peptides is predominantly due to the modulation of interpeptide Coulombic interactions. While the effect of ionic strength originates from the electrostatic shielding of interpeptide Coulombic interactions, the pH affects the peptide protonation state, greatly increasing the interpeptide Coulombic repulsion and affecting order versus disorder of the peptides that are bound to the graphite surface. Implications of these results in practical applications will be discussed. Research was co-sponsored by NSF-MRSEC program via DMR#0520567 at UW and JST-PRESTO program in Japan.
9:00 AM - F5.37
Simple Fabrication of Biomimetic Bubble Repellent Surfaces in Tubes by Self-Organization
Jun Kamei 1 Yuta Saito 1 Hiroshi Yabu 2
1Tohoku University Sendai Japan2IMRAM Sendai JapanShow Abstract
In spaceships and space stations, bubble generation in the tubes of heat exchangers and pumps is a critical problem. Under microgravity, low buoyancy causes a permanent adhesion of such bubbles on the inner surfaces of tubes, causing pressure losses, erosion of the surface and drop in the heat transfer efficiency. It has been reported that fish scales exhibit a high repellency toward hydrophobic oil droplets and air bubbles underwater, due to its hydrophilic nature and microstructured surface. We previously reported on the fabrication of self-organized honeycomb patterned porous film (HC) using the breath figure technique, which consist of casting a hydrophobic polymer solution containing an amphiphilic polymer under humid conditions. The condensed dew drops on the surface self-organize in a highly ordered hexagonal array and work as a template for the HC structure. Pincushion-like structures (PC) can also be obtained by peeling the top layer of the HC film. In this research, we report on the fabrication of hydrophilic microstructured surfaces with high bubble repellency on the inner surfaces of tubes by the breath figure technique. A HC film with pore diameter of 7-8 mu;m was obtained by casting a chloroform solution of polystyrene (PS) and amphiphilic copolymer on a glass substrate under high humidity. By peeling the top layer of the HC film, a PC film was also obtained. After UV-ozone treatment to make the films hydrophilic, the bubble repellency of the films was measured underwater by placing a bubble of 3mu;L. The contact angles in the case of HC (148.8°) and PC (165.3°) were higher than that of the flat film (128.0°), suggesting that the bubbles on HC and PC are in contact with a composite surface of water and hydrophilized PS. To calculate the contact angle phi; on a composite surface, we employed the Cassie-Baxter equation cosphi; = fPS costheta;PS + (1-fPS) costheta;water (eq1), where fPS is the fraction of PS at the interface, theta;PS the contact angle of air bubble on a flat PS surface, theta;water the contact angle of air bubble on a layer of water. The calculated values from eq1 matched the measured contact angles, which increased with the decrease of PS fraction in the composite surface. In addition, the sliding angle of the bubble was the lowest for PC film (3.5 °) compared to HC (21. 8°) and flat film (39.1°), suggesting the high bubble repellency of PC structures. To fabricate such surface in a tube, a glass tube with 0.7 mm in diameter was dipped in the polymer solution and humid air was blown inside the tube. As a result, HC structures with pore size of 1-2 mu;m in diameter were observed. Then, the top layer of the HC film was removed by ultrasonic treatment of the tube in water, resulting in PC structures. We showed the fabrication of high bubble repellent surface on the inner surface of the tubes by the breath figure method.
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Chemical Actuation of Cross-Linked Materials Made from the Nereis Virens Jaw Protein, Nvjp-1
Patrick B. Dennis 1 Matthew B. Dickerson 1 Benjamin Floyd 1 Joseph M. Slocik 1 Rajesh R. Naik 1
1Wright Patterson Air Force Base Wright-Patterson AFB USAShow Abstract
Invertebrates have diverse mechanisms for the sclerotization of body structures. For example, the marine polychaete, Nereis virens, has mechanically robust mandibles composed of Nvjp-1, a histidine-rich protein that is involved in the hardening of the mandible after zinc binding. We have developed methods for the expression, purification and manipulation of Nvjp-1 which has enabled the fabrication of fibers and films. Like the worm jaw, these materials have demonstrated an increase in mechanical strength as a result of zinc binding. Unexpectedly, incubation of Nvjp-1 hydrogels with metal salts results in a ~90% reduction in size. Alternatively, exposure of Nvjp-1 hydrogels to low or high pH conditions results in swelling to ~2.5 times the initial cast size. Here, we present structural analysis of the Nvjp-1 materials after contraction in the presence of a variety of transition metal salts. Additionally, changes in structure are probed after swelling under both high and low pH conditions. We have also created a number of Nvjp-1 truncation mutants with the aim of identifying a minimal region responsible for the actuation properties observed with salt and pH changes. These results will be important in the creation of scalable, synthetic biomimetic materials that have tunable properties directed at the spatial and temporal induction of hydrogel actuation and material hardening.
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Electrospinning Silk with Selenium Nanoparticles for Antibacterial Skin Applications
Stanley Chung 2 Batur Ercan 2 Phong Tran 1 Thomas Webster 2
1University of Melbourne Parkville Australia2Northeastern University Boston USAShow Abstract
Healthy skin with robust skin regeneration provides the most effective defense against environmental infectants. Silk has been studied for skin regeneration and has been widely used as an additive for cosmetics. Silk improves collagen synthesis, re-epithelialization, wound healing, atopic dermatitis alleviation, and scar reduction. However, purified silk promotes microbial growth. Here, we propose for the first time, an electrospun silk scaffold doped with selenium nanoparticles to address this issue. Electrospun silk scaffolds have smaller interstices and higher surface areas, allowing for efficient nutrient transfer to skin. In addition, selenium nanoparticles have been shown to have excellent antibacterial properties. By incorporating selenium nanoparticles into silk, we expect to retain silk&’s beneficial skin healing properties while improving its antibacterial ability.
Materials and Methods
Silk was extracted from Bombyx mori by Rockwood&’s protocol1 while selenium nanoparticles were synthesized by Tran&’s protocol2 . Extracted silk was dissolved in formic acid at 8-14%, w/v, and spun at a flow rate of 2-3 mL/hr, distance to a collector at 10cm, and at a voltage of 20kV. Staphylococcus aureus (ATCC -10832D-5) was cultured on the substrates with 0, 7.8, 15.5, and 31 mu;g/mL selenium nanoparticles in 0.3% tryptic soy broth (Sigma-Aldrich). After 3-5 hours after inoculation, the plates were read at 562 nm to determine cell density. All experiments were conducted in triplicate and repeated at least three times. The electrospun scaffold was characterized by SEM and goniometry to determine the physical composition of the scaffolds ± selenium nanoparticles. Selenium nanoparticles were characterized by DLS to determine particle size and dispersity.
Results and Discussion
Electrospun scaffolds possessed fiber diameters of 200-300 nm and pore sizes of ~5µm. Surface contact angles were 500, showing a hydrophilic surface. DLS showed that the selenium nanoparticles were monodisperse, with hydrodynamic diameters around 100 nm. Results of this study showed that S. aureus growth was inhibited in the presence of selenium nanoparticles as early as 3 hours, and bacterial viability at 3 hours decreased from 90% in the control group to 60% in the treated groups. In the presence of selenium, the bacteria showed negligible growth while the control demonstrated continued proliferation.
Selenium nanoparticles are effective in decreasing S. aureus growth at even low time periods. Electrospun silk generates fiber diameter ~200 nm and micron sized pore sizes, ideal for cellular adhesion.
The authors thank William Fowle, Scott McNamara, and the Northeastern University Department of Chemical Engineering for facilities and funding.
References: 1). Rockwood DN, et al. Nat. Protocols. 2011; 6(10): 1612-1631. 2) Tran PA et al. I J Nanomed. 2011; 6: 1553-1558.
9:00 AM - F5.40
Seamless Interfaces for Building High Performance Textiles and Wound Dressing
Andrew Keith Capulli 2 1 Taler Brazell 3 Riley Ping Medvigy 3 Virginia Phillips 3 Holly Golecki 2 1 Michael Phillips 3 Kevin Kit Parker 2 1
1Wyss Institute for Biologically Inspired Engineering Cambridge USA2Disease Biophysics Group Cambridge USA3United States Military Academy, West Point Highlands USAShow Abstract
With small diameters and pore sizes, a large surface area to volume ratio, and tunable properties, nanofibers are an ideal scaffold material for tissue engineering and textile manufacturing. When spun from different polymers, nanofibers can exhibit a range of elasticities and scaffold mechanics necessary to mimic the mechanical properties of the skin. Using a perforated reservoir that uses centrifugal forces to extrude fibers, automated Rotary Jet Spinning (aRJS) has been demonstrated as a rapid and efficient method to produce nanofibers of varying mechanical strength with controlled fiber deposition. Currently, stiff bandages and clothing manufacturing lack a biomimetic range of motion. Although sewing different materials together has been utilized to mimic skin biomechanics in clothing, the seams in multi-material clothing are restrictive and likely points of failure. There is a need for a seamless multi-material solution that can more accurately recapitulate the dynamic properties of the skin. We hypothesize aRJS can be used to create a multi-material sleeve that enables and enhances a full range of motion for the end user in wound dressings and high performance applications. To test this hypothesis, we performed a biomechanical analysis of arm movement to motivate the design of our zoned scaffold. During flexural movement, we show that sections of the human arm experience heterogeneous extension and compression from the forearm to the shoulder. Based on these results, we zoned a soft polyurethane and stiff nylon onto a single cylindrical mandrel to create a seamless textile and tested its mechanical properties biaxially. Using 3D printing technology, we manufactured a scaled model of a human arm mandrel to test our ability to zone different materials at specific sections on the arm. Our results show that aRJS spun seamless materials have integrity at their interface as the structure remained intact when strained along the stitch-free material interface. aRJS can be used to create a multi-material, seamless sleeve to allow for therapeutic compression on the forearm and full range of motion at the elbow and upper arm. Without the need of additional sewing or stitching, zoning materials in this method provides a path to increasing the efficiency of textile manufacturing.
9:00 AM - F5.42
Multifunctional Superamphiphobic TiO2 Nanostructure Surfaces with Facile Wettability and Adhesion Engineering
Jianying Huang 1 Yuekun Lai 1
1National Engineering Laboratory of Modern Silk Suzhou ChinaShow Abstract
Compared with conventional top-down photo-cleavage method, we described a facile bottom-up ink-combination method to in-situ and rapidly achieve water wettability and adhesion transition with a great contrast on the superamphiphobic TiO2 nanostructured film. Moreover, such combination method are suitable for various kinds of superamphiphobic substrate. Oil-based ink covering or removing changes not only the topographical morphology but also surface chemical composition, and these resultant topographical morphology and composition engineering realize the site-selectively switchable wettability varying from superamphiphobicity to amphiphilicity, and water adhesion between sliding superamphiphobicity and sticky superamphiphobicity in micro-scale. Additionally, positive and negative micro-pattern can be achieved by taking advantage of the inherent photocatalytic property of TiO2 with the assistance of an anti-UV light ink mask. Finally, the potential applications of the site-selectively sticky superamphiphobic surface were demonstrated. In a proof-of-concept study, the microdroplets manipulation (storage, mixing, and transportation), specific gas sensing, wettability template for positive and negative ZnO patterning, and site-selective cell immobilization have been demonstrated. This study will give an important input to the field of advanced function materials surface with special wettability.
9:00 AM - F5.43
Light-Controlled Motile TiO2-Based Micromotors by Bubble Propulsion
Fangzhi Mou 1 Yan Li 1 Chuanrui Chen 1 Huiru Ma 2 Jianguo Guan 1
1Wuhan University of Technology Wuhan China2Wuhan University of technology Wuhan ChinaShow Abstract
Micro-/nanomotors have fascinating capabilities to pick up, transport, and release various micro/nanocargoes because of their autonomous motion behaviors in liquid media, and can be used to perform complex tasks, including drug delivery, protein and cell separation, microsurgeries and environmental remediation, etc.. However, these tasks are difficult at microscale because it is still a great challenge to develop the high-speed micromotors with reversible and wirelessly tunable motion behaviors. In this work, other than the low-speed light-driven micromotors by diffusiophoresis, we have demonstrated the first example of the high-speed light-controlled micromotors by bubble propulsion, that is, the amorphous TiO2/Au (Am-TiO2/Au) Janus micromotors propelled by O2 bubble thrust generated from the photocatalytic decomposition of H2O2 by TiO2 under UV irradiation. The power conversion of the micromotor experiences a process from UV light power, to chemical power and finally to mechanical power. The quantum efficiency of O2 bubble evolution from photocatalytic decomposition of H2O2 reaches 33%, and the power conversion efficiency reaches 3.2×10-9, which make the micromotor generate a strong bubble thrust that propels itself forward with the maximum speed of 135 mu;m s-1. The light-controlled TiO2-based micromotors developed in this work may have promising applications in protein and cell separation, drug delivery, and water remediation etc..
9:00 AM - F5.44
SAXS Study of Pegylated Peptide Vesicles for Drug Delivery
Hojun Kim 1 Ziyuan Song 1 Cecilia Leal 1 2 Jianjun Cheng 1 2 3
1University of Illinois at Urbana-Champaign Urbana USA2Materials Research Laboratory Urbana USA3Beckman Institute for Advanced Science and Technology Urbana USAShow Abstract
Peptide vesicles are a new class of biocompatible vectors that display conformation-specific self-assembly. Vesicles composed of helix peptides have drawn attention of the drug delivery community lately because they offer high membrane stability due to helix bundling as well as conformation triggered disassembly.
We synthesized poly(ethylene glycol)-block-poly(γ-(4,5-dimethoxy-2-nitrobenzyl)-L-glutamate) (PEG-b-PDMNBLG), a short lipid-mimic amphiphilic diblock rod-coil copolymer containing an hydrophobic, α-helical and photo-responsive polypeptide segment. The peptides self-assemble into quasi-spherical vesicular aggregates of ca 400nm in diameter, which is a suitable dimension for drug delivery applications. We unexpectedly observed by Cryo-EM that the vesicles have a dense membrane of roughly 40nm thicknesses. In order to get the structural details of these membranes we employed both Wide-Ange and Small-Angle X-ray Scattering (WAXS/SAXS) on concentrated solutions of peptide vesicles.
In this presentation we will reveal our WAXS/SAXS studies of peptide vesicle membranes. The systems displayed a few Bragg reflections that are consistent with the presence of a layered membrane structure with nematic ordering composed of four monomers as building blocks. In order to fully understand the driving force of this multilamellar membrane structure, we prepared three helices attached to PEG of different lengths. When short PEG molecules were used, multilayer membrane structures were formed with PEG buried between polypeptide layers, while the nematic alignment of helices was observed in the lateral direction. Longer PEG copolymers form membranes analogous to those typically obtained in lipid bilayers. In addition to the length of the PEG, the length of helix domain also plays a key role in the overall vesicle shape. It is found that there is an optimum length and ratio of each domain to achieve spherical aggregates. From these observations it is believed that short hydrophilic domains combined with an appropriate length of rigid hydrophobic parts are the key for the stabilization of multilamellar spherical peptide vesicles.
9:00 AM - F5.45
Cyanogenic Coating Inspired by the Bitter Almond to Protect Wheat Seeds during Storage as an Alternative to Pesticides
Jonas Halter 1 Weida David Chen 1 Philipp Stoessel 1 Carlos Mora 1 Fabian Koehler 1 Robert Niklaus Grass 1 Wendelin Jan Stark 1
1ETH Zurich Zurich SwitzerlandShow Abstract
Nature provides us with numerous defense concepts in order not to be eaten. In plants, secondary metabolites often act as toxins.1 For example, over 3000 species of higher plants use cyanogenesis. They are able to release HCN (hydrogen cyanide) from a cyanogenic precursor.2 When the plant tissue is crushed, the cyanogenic glycosides are exposed to enzymes, which results in HCN-formation.3 HCN itself is known for its toxicity and ability to protect the plant from herbivores.
~600 million tons of wheat are harvested per year. This makes it one of the world&’s predominant crops.4 Pest infestation of cereal grains, such as wheat, still constitutes a worldwide issue, especially in developing countries.
In this work, a nature-inspired protection concept was developed.5 Seeds unable of cyanogenesis are intended to get more resistant against herbivore attack by a compartment strategy. Grains were coated with materials that allow HCN-production. These multi-layered seeds were prepared by dip coating and presented the following layers: (1) mandelonitrile lyase, (2) PLA (polylactic acid), (3) mandelonitrile in PLA, (4) pure PLA. As a proof of concept the obtained seeds were brought to germination within 4 days in a closed container. HCN was detected in concentrations (1.1 mmol kg-1) known to have an effect on herbivores.5, 6
1. Ibanez, S.; Gallet, C.; Despres, L., Plant insecticidal toxins in ecological networks. Toxins 2012, 4, 228-243.
2. Poulton, J. E., Cyanogenesis in plants. Plant Physiology 1990, 94, 401-405.
3. Conn, E. E., Cyanogenic glycosides. Academic Press, Inc.: 1981; p 479-500.
4. Ekboir, J., CIMMYT 2000-2001 world wheat overview and outlook: developing no-till packages for small-scale farmers. 2002.
5. Halter, J. G.; Chen, W. D.; Hild, N.; Mora, C. A.; Stoessel, P. R.; Koehler, F. M.; Grass, R. N.; Stark, W. J., Induced cyanogenesis from hydroxynitrile lyase and mandelonitrile on wheat with polylactic acid multilayer-coating produces self-defending seeds. J. Mat. Chem. A 2014, 2, 853-858.
6. Patton, C. A.; Ranney, T. G.; Burton, J. D.; Walgenbach, J. F., Natural pest resistance of Prunus taxa to feeding by adult Japanese beetles: Role of endogenous allelochemicals in host plant resistance. Journal of the American Society for Horticultural Science 1997, 122, 668-672.
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Bio-Inspired Robust, Transparent and Self-Cleaning Ormosil Coatings
Urandelger Tuvshindorj 1 2 Adem Yildirim 1 2 Fahri Emre Ozturk 1 2 Mehmet Bayindir 1 2 3
1UNAM-National Nanotechnology Research Center, Bilkent University Ankara Turkey2Institute of Materials Science and Nanotechnology, Bilkent University Ankara Turkey3Department of Physics, Bilkent University Ankara TurkeyShow Abstract
Wetting behavior of biological surfaces such as the leaves of lotus, wings of morpho butterfly or legs of water strider insects have inspired the design of artificial water repellent surfaces. Over the past decade, we have witnessed many impressive reports demonstrating design and fabrication of superhydrophobic surfaces and explaining the mechanisms behind the non-wetting behavior (i. e. Cassie state of wetting) of such surfaces. Nevertheless, our understanding about the stability of Cassie state of wetting in superhydrophobic surfaces against external stimuli (e. g. pressure, droplet impact and droplet evaporation) is still quite limited. In fact, currently available self-cleaning surfaces generally fail in preserving the stability of non-wetting properties (i. e. transition to sticky Wenzel state) over time, especially in outdoor applications, in contrast with successful examples in natural surfaces. Therefore, improving the stability of Cassie state of wetting in self-cleaning coatings is a prerequisite for utilizing self-cleaning surfaces in real life applications. In addition, many applications of water repellent surfaces require optical transparency, such as self cleaning windows and solar cells in terms of appearance and device performance.
Here we report a facile large area sol-gel method to obtain bioinspired micro/nano structured transparent coatings with enhanced stability against external pressure. Three different organically modified silica (ormosil) coatings; i) nano-porous hydrophobic coating , ii) micro-porous superhydrophobic coating, and iii) double layer superhydrophobic coating with nano-porous bottom and micro-porous top layers were prepared on glass surfaces. We investigated stability of the Cassie state in coatings with droplet compression and evaporation experiments, where external pressures as high as a few thousands of Pa is generated at the interface. The resistance of the micro/nano-porous surface against Wenzel transition during the experiments was higher than of lotus leaves.
The outcomes of this study may provide researchers an adequate ground for designing robust superhydrophobic coatings for outdoor and underwater applications where surfaces are exposed to high external pressures.
9:00 AM - F5.47
A Biomimetic Approach to Neuroregeneration
Fioleda Prifti 1 Ulrike G.K. Wegst 1
1Dartmouth College Hanover USAShow Abstract
Injuries to the nervous system often result in permanent disabilities including sensory deficit, loss of motor function, and development of debilitating neuropathies. Each year, there are approximately 1 million new cases of traumatic peripheral nerve injuries (PNI) and 12,000 new cases of spinal cord injuries (SCI) in the United States alone. Current treatment options for PNIs yield sub-optimal functional recovery, with only 50% of patients recovering useful function, due to design limitations of clinically available nerve conduits. Scaffolds manufactured by freeze casting exhibit a biomimetic structure which overcomes the physical limits of nerve conduits by providing a natural bridge for nerve regeneration. In this contribution we show how structural, mechanical and chemical cues can be custom-designed to produce freeze-cast scaffolds with aligned porosity and reproducible topographies. This biocompatible manufacturing process can be used to incorporate key structural and bioactive components to bridge the gap in nerve repair.#8203;
9:00 AM - F5.48
Investigation of Delamination Resistant Bio-Laminates Using Finite Element Based Modeling Methods
M.D. Nelms 1 W.D. Hodo 2 A.M. Rajendran 1
1University of Mississippi Oxford USA2ERDC Vicksburg USAShow Abstract
During the last few decades, research on biological materials such as abalone shell, fish armor, turtle shell, and human bone revealed that those biological systems possess a carefully arranged multilayered structure whereby each layer comprises unique subscale structures to achieve properties of high strength, high ductility, and light weight, which are far superior to any man-made materials and systems. In this research finite element modeling was used to investigate the delamination resistance for the bio-laminate structures. The Atractosteus spatulas (Alligator gar) was used as the model structure.
The Alligator gar possess a flexible dermal armor consisting of overlapping ganoid scales. Each scale is a bilayer hydroxyapatite and collagen-based bio-laminate and is thought to be used for protection against its predators. The exoskeleton fish scale is comprised of a stiff outer ganoine layer, a characteristic “sawtooth” pattern at the interface and a compliant bone inner layer with all materials exhibiting a decreasing elastic modulus, yield strength and density through the thickness. Experimental testing on ganoid scales display properties such as damage mitigation, tortuous crack path propagation, and energy dissipation that are unique to biological dermal armor. The main objective of this investigation is to quantify the effects of the material grading as a function of depth as well as the influence of the geometrically anisotropic interface between the ganoine and bone layers on the elastic properties. The fish scale interface was modeled using the finite element method. Preliminary results were based on an idealized elastic-perfectly plastic mathematical model. The mathematical model was used to infer the effects of the nonlinear material response in terms of in terms of energy dissipation and stress redistribution at the ganoine-bone interface. The results indicate that at the ganoine-bone interfaces stress is reduced and energy is dissipated across the saw tooth junction points.
Keywords: Biological Materials, Delamination Resistance, Alligator gar, Energy Dissipation
9:00 AM - F5.49
The Gating Mechanism of Mechanosensitive Channels in Droplet Interface Bilayers
Joseph Najem 1 Eric Christopher Freeman 1 Sergei Sukharev 3 Donald Joseph Leo 2
1Virginia Tech Blacksburg USA2University of Georgia Athens USA3University of Maryland College Park USAShow Abstract
Biomolecular unit cells may be described as cell-inspired building blocks, whose repetition forms the basis of a novel biomolecular material system. The unit cell considered herein consists of a lipid bilayer interface formed at the contact of two aqueous droplets encased in lipid monolayers in an oil reservoir -- a technique known as the Droplet I