Andreas Lendlein Institute for Polymer Research
Ken Gall Georgia Institute of Technology
Tomiki Ikeda Tokyo Institute of Technology
Prasad Shastri Vanderbilt University
NN1: Shape Memory I
Tuesday PM, April 14, 2009
Room 3018 (Moscone West)
9:30 AM - **NN1.1
Color-Changing Shape Memory Polymers
Jill Kunzelman 1 , Kun Li 2 , Taekwoong Chung 1 2 , Christoph Weder 1 , Patrick Mather 2 3 Show Abstract
1 Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, Ohio, United States, 2 Syracuse Biomaterials Institute, Syracuse University, Syracuse, New York, United States, 3 Biomedical and Chemical Engineering Department, Syracuse University, Syracuse, New York, United States
The field of shape memory polymers (SMPs) has advanced to the point where some researchers are manipulating properties at the molecular level, both architecturally and compositionally, while others are creating composites that bridge SMP phenomena with other complex material behavior. Here, we report on the design, synthesis, processing, and characterization of new SMPs with built-in temperature sensing capabilities. The materials were prepared by incorporating a fluorescent, chromogenic oligo(p-phenylene vinylene) dye into a family of cross-linked poly(cyclooctene-co-cyclooctadiene) P(CO-co-COD) matrices by imbibing from a dye solution. The new SMP copolymers were designed to feature tailored melting temperature and were prepared by ring-opening metathesis polymerization via ruthenium catalysis, followed by thermal crosslinking with dicumyl peroxide. The dye concentration was chosen to allow for self-assembly of the dye upon drying, resulting in the formation of excimers. Heating the phase-separated blends to temperatures above the SMP melting point (Tm) caused dissolution of the dye molecules, and associated change optical absorption and fluorescence color. These changes are quite reversible - aggregate absorption and are restored upon cooling below Tm – and the transition is determined by copolymer composition. Utilization of these phenomena for detailed studies of heterogeneity in SMP crystallization and melting and as sensors will be discussed.
10:00 AM - NN1.2
Effect of Crosslinking on the Shape-memory Behavior of Photopolymerizable (meth)acrylate-based Polymer Networks.
Alicia Ortega 1 , Christopher Yakacki 2 3 , Alan Greenberg 1 , Ken Gall 3 4 Show Abstract
1 Department of Mechanical Engineering, University of Colorado, Boulder, Colorado, United States, 2 Research and Development, MedShape Solutions Inc., Atlanta, Georgia, United States, 3 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 4 Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
The goal of this study is to investigate the fundamental relationship between the extent of crosslinking and shape-memory behavior of amorphous, photopolymerizable, (meth)acrylate-based polymer networks. The polymer networks were produced by copolymerization of tert-butyl acrylate (tBA) and poly(ethylene glycol) dimethacrylates of differing molecular weights (PEGDMA). Polymerization was carried out at room temperature using 2,2-dimethoxy-2-phenylacetophenone as the initiator. Polymer compositions were tailored (weight percent (wt%) and molecular weight of the PEGDMA crosslinking agents) to produce four materials with varying levels of crosslinking (0, 2, 10, and 40 wt% crosslinking agent corresponding to 0, 0.6, 3.2, and 16.6 mole%) and nearly equal glass transition temperatures (Tg). An increase in crosslink density with the increase in weight percent of the PEGDMA crosslinking agent added to the tBA was confirmed via a corresponding decrease in equilibrium swelling ratios and an increase in rubbery modulus values. The development of four network compositions with different degrees of crosslinking and equivalent Tg values enables a direct analysis of the effect of crosslinking density (ranging from uncrosslinked to highly crosslinked) on the shape-memory behavior of these materials without complication from varying Tg values and/or storage temperatures. The effect of crosslinking on three distinct aspects of shape-memory behavior are explored: (1) the deformation limits at which each material demonstrates useful and complete free-strain recovery; (2) constrained-strain stress generation; and (3) the effect of room-temperature storage time on the temporary, stored shape fixity and free-strain shape recovery of the network materials. This study highlights fundamental considerations with respect to the available range of storage and recovery characteristics for amorphous, photpolymerizabe shape-memory polymer networks with various levels of crosslinking. In addition, the results provide important insights regarding the link between polymer structure, deformation limits, optimal strain and stress recovery, and storage capabilities of this class of shape-memory polymers. An improved understanding of these relationships is critical for optimizing system response for a range of applications including those focused on biomedical device design.
10:15 AM - NN1.3
The Role of the Glass Transition on the Deformation and Recovery of Shape-Memory Polymer Networks.
Christopher Yakacki 1 2 , Kathryn Smith 3 , Alicia Ortega 4 , Ken Gall 3 2 Show Abstract
1 Research and Development, MedShape Solutions, Inc., Atlanta, Georgia, United States, 2 School of Materials Science and Engineering, The Georgia Institute of Technology, Atlanta, Georgia, United States, 3 Woodruff School of Mechanical Engineering, The Georgia Institute of Technology, Atlanta, Georgia, United States, 4 Department of Mechanical Engineering, University of Colorado , Boulder, Colorado, United States
Shape-memory polymers (SMPs) are a class of smart and active materials than can be programmed to recover large amounts of strain in response to a stimulus such as heat or light. Typically, shape memory is triggered via heating the polymer to a transition temperature associated with either melting of a soft segment or a glass transition to increase chain mobility and allow for macroscopic motion resulting in shape-memory. This presentation focuses on shape-memory networks and how properties of the glass transition relate to deformation and shape recovery in light of potential biomedical applications. SMP networks were photo-synthesized using mono- and di-functional acrylates such as methyl methacrylate, poly(ethylene glycol) dimethacrylate, 2-hydroxyethyl methacrylate and more. The glass transition temperature (Tg) and the crosslink density of the networks were tailored by controlling the amount and molecular weight of the crosslinking monomer. In deformation experiments, the strain-to-failure of networks with varying crosslink density were investigated as a function of temperature. The maximum strain to failure in the networks occurred at the onset of the glass transition and was not dependent on the amount of crosslinking in the network. This maximum in strain to failure is termed the “deformability peak” and suggests typical deformation protocols of SMPs above the glass transition temperature are not maximizing the strain capabilities of the polymer. Furthermore, the networks show a maximum value of toughness below Tg that similarly correlates to the deformability peak. Networks were also tested in an aqueous environment to examine the affects of monomer chemistry, crosslinking density, and Tg on the change in toughness of the networks to simulate post-implantation water absorption. To examine the role of the glass transition on recovery, MMA-co-PEGDMA networks were synthesized with independently tailored Tg and rubbery modulus values. Free- and fixed-strain recovery tests were performed under transient and isothermal heating conditions to fully characterize shape-memory of the networks. Free-strain recovery was shown to be primarily influenced by Tg and independent of crosslink density. Conversely, stress generation in fixed-strain recovery was a function of the crosslink density. Networks with a higher crosslinking density also initiated stress generation than their low-crosslinking density counterparts with an equal Tg. The results are presented along with several potential biomedical applications of SMP networks.
10:30 AM - NN1.4
A Thermoviscoelastic Model for Amorphous Shape Memory Polymers: Effects of High Temperature Stress Relaxation
Thao Nguyen 1 Show Abstract
1 Mechanical Engineering, The Johns Hopkins University, Baltimore, Maryland, United States
Thermally activated shape memory polymers are an emerging class of active materials that respond to a specific temperature event by generating a shape change . A thermally active SMP device is processed into its permanent shape using conventional techniques for thermoset polymers. The permanent shape is determined by the network of crosslinks, loosely defined here as junctions in the macromolecular network that persist through the temperature and deformation range of operation. The molecular mechanisms controlling the time-dependence of the shape memory response of amorphous SMPs are structural relaxation and stress relaxation. Structural relaxation is the time-dependent process in which the macromolecular structure and mobility evolve to equilibrium in response to a temperature and/or pressure change. Stress relaxation describes the process in which the stress response evolves to equilibrium in response to a change in deformation. To examine the relative importance of the structural and stress relaxation mechanisms, a constitutive model has been developed for the finite-deformation time-dependent behavior of thermally active amorphous SMPs that includes structural relaxation in the glass transition region, viscoelasticity in the rubbery and transition regions, and viscoplasticity in the glassy region . This works represents a new approach to modeling the thermomechanical behavior of amorphous SMPs that is fundamentally different than current phase-transition approaches . The important innovations of the model includes the incorporation of a time-dependent model of the glass transition in a finite-deformation thermoviscoelastic framework for the molecular "switching" mechanism of shape recovery. The model was implemented in a finite element program and applied to simulate the constrained strain and unconstrained stress recovery response. The results showed excellent quantitative agreement with experiments in the low temperature region, confirming the importance of structural relaxation. However, it underestimated the stress relaxation behavior under large strains in the high temperature region. As a result, the model underestimated the unconstrained recovery time. Recent work has been focused on incorporating additional mechanisms for nonlinear strain-dependence of the stress relaxation response at high temperature to improve predictions of the unconstrained recovery response. A.S. Lendlein, S. Kelch, K. Kratz, J. Schulte, Encyclopedia of Materials: Science and Technology, Elsevier, pp. 1–9, 2005.  T. D. Nguyen, H. J. Qi, K. N. Long, Journal of Physics and Mechanics of Solids, 58, pp. 2792-2814, 2008.  H. J. Qi, T. D. Nguyen, F. Castro, C. Yakacki, R. Shandas, Journal of Mechanics and Physics of Solids, 56, pp. 1730-1751, 2008.
10:45 AM - NN1.5
Binary Multiblock Copolymer Blends Having Shape-Memory Capability with Hard and Switching Domains Provided by Different Components
Marc Behl 1 , Ute Ridder 2 , Yakai Feng 3 , Steffen Kelch 4 , Andreas Lendlein 1 Show Abstract
1 Institute of Polymer Research, GKSS Research Centre Geesthacht GmbH, Teltow Germany, 2 , Freudenberg Forschungsdienste KG, Weinheim Germany, 3 Department of Polymer Science and Technology, Tianjin University, Tianjin China, 4 , Sika Technology AG, Zürich Switzerland
The structural concept of shape-memory polymers requires two key components: covalent or physical crosslinks (hard domains) determining the permanent shape and switching domains fixing the temporary shape as well as influencing the switching temperature Tsw
[1, 2]. In conventional thermoplastic SMP hard and switching domains determining segments are combined in one macromolecule, e.g. block copolymers such as polyurethanes [3, 4]. These multiblock copolymers can be designed as polymer systems in which mechanical and thermal properties can be adjusted in a wide range by variation of different molecular parameters, for instance the weight ratio of hard to switching segment. This concept was extended to multifunctional polymer systems that are biodegradable and have a shape-memory capability . However, any new combination of material properties in this system requires synthesis of a new material.Here, we report on binary polymer blends from two different multiblock copolymers, whereby the first one is providing the segments forming hard domains and the second one the segments forming the switching domains . A mediator segment based on poly(alkylene adipate) is incorporated in both multiblock copolymers to promote their miscibility as the hard segment poly(p-dioxanone) and the switching segment poly(ε-caprolactone) are non-miscible. Shape-memory properties of all investigated polymer blends were excellent. The melting point associated to the PCL switching domains Tm,PCL
was almost independent from the weight ratio of the two blend components. The processing of the polymer blends from solution as well as from extrusion allows systematic variation of the mechanical properties. In this way complex synthesis of new materials can be avoided. Its biodegradability, the variability of mechanical properties and a Tsw
around body temperature are making this binary blend system an economically efficient, suitable candidate for diverse biomedical applications.
A. Lendlein, S. Kelch, Angewandte Chemie-International Edition 2002, 41, 2034.M. Behl, A. Lendlein, Soft Matter 2007, 3, 58.A. Alteheld, Y. K. Feng, S. Kelch, A. Lendlein, Angew. Chem., Int. Ed. Engl. 2005, 44, 1188.J. Hu, Shape memory polymers and textiles, Woodhead Publishing Limited, Cambridge; England 2007.A. Lendlein, R. Langer, Science 2002, 296, 1673. M. Behl, U. Ridder, Y. Feng, S. Kelch, A. Lendlein, Soft Matter, 2008, accepted.
11:00 AM - NN1:Shapmem
11:30 AM - **NN1.6
Multiphase Polymer Networks with Shape-Memory.
Steffen Kelch 1 Show Abstract
1 Corporate Research, Sika Technology AG, Zurich Switzerland
Shape-memory polymers are dual shape materials which can fix a temporary shape besides their original shape. In thermally activated shape-memory polymers the shape change is realized by heating the material above the transition temperature. One basic concept in the development of biodegradable polymer systems with shape-memory properties is based on polymer networks containing switching segments from semi-crystalline poly(ε-caprolactone) [1,2] or poly[(ε-caprolactone)-co-glycolide]. AB copolymer networks were prepared by adding n-butyl acrylate as comonomer. At temperatures higher than the melting temperature of the crystalline part of the poly[(ε-caprolactone)-co-glycolide]-phase acting as physical crosslinks the Young’s modulus of the polymer networks is lowered by up to two orders of magnitude. Amorphous polymer networks were developed based on poly[(L-lactide)-ran-glycolide)]-chain segments. This material is transparent and has a shape-memory capability, but its mechanical properties had to be further improved. By incorporation of a second amorphous phase with a low glass transition temperature the elastic properties of poly[(L-lactide)-ran-glycolide]-segment based networks could be enhanced. Formation of an amorphous mixed phase was identified as key to realize increased toughness and elasticity at room temperature. Multi-phase polymer networks were synthesized from amorphous and degradable ABA triblock macrodimethacrylates based on poly[(rac-lactide)-b-poly(propylene oxide)-b-poly(rac-lactide)]. Variation in poly(rac-lactide)-block length was used as molecular parameter to vary switching temperature, elasticity of the materials in the temporary shape, and hydrolytic degradability. An alternative concept for the introduction of a second amorphous phase is using poly[(L-lactide)-ran-glycolide]dimethacrylate as crosslinker for polyacrylates. Amorphous AB copolymer networks could be prepared by polymerizing various acrylates and poly[(L-lactide)-ran-glycolide)]dimethacrylate using UV-light. While the molecular weight of the poly[(L-lactide)-ran-glycolide)]-segments was kept constant, both the type of acrylate comonomer and the copolymer ratio in the synthesis were varied. Enabling higher elasticity, adjustable hydrolytic degradability, and the possibility to tailor the transition temperature of shape-memory to a temperature between room temperature and body temperature are considered to be substantial steps to improve the applicability of these active polymers in medicine. (1)Lendlein, A; Schmidt, A.M; Langer, R. Proc. Natl. Acad. Sci. 2001,18,842. (2)Lendlein, A; Schmidt, A. M; Schroeter, M; Langer, R. J. Polym. Sci., Part A: Polym. Chem. 2005,43,1369. (3)Kelch, S; Steuer, S; Schmidt, AM; Lendlein A; Biomacromolecules 2007,8(3),1018. (4)Choi, N.-Y; Lendlein, A. Soft Mater 2007,3,901. (5)Choi, N.-Y; Kelch, S; Lendlein, A. Adv. Eng. Mater. 2006,8,439. (6)Kelch, S; Choi, N.-Y.; Wang, Z; Lendlein, A. Adv. Eng. Mater. 2008,10,494.
12:00 PM - NN1.7
Characterization of Toughness in Photopolymerizable Acrylate Networks.
Kathryn Smith 1 , Ken Gall 1 Show Abstract
1 Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Polymer networks formed through photopolymerization have emerged as candidate biomaterials for applications where it is advantageous to have in situ formation, quick synthesis rates, and easy processing into diverse geometries. However, these polymer networks lack the “mechanical integrity” or toughness for implementation in areas where a device or scaffold must function under rigorous loading regimes. The purpose of this study is to characterize how the toughness of polymer systems, specifically photopolymerizable acrylate networks, is affected by chemistry, network structure (i.e. crosslinking density), and environmental conditions including temperature and saline solution. Polymer systems consisting of at least one monofunctional acrylate and one difunctional crosslinker were copolymerized under UV light. The monofunctional acrylates chosen were methyl methacrylate (MMA), methacrylate (MA), and 2-hydroxyethyl methacrylate (2HEMA) while the crosslinker was poly(ethylene glycol) dimethacrylate (PEGDMA). Networks were developed with varying ratios of monomer components to create networks with different glass transition temperatures (Tg), crosslinking density, and hydrophilicity. Dynamic mechanical analysis was performed to determine the Tg and storage modulus as a function of temperature. In order to observe the influence of temperature on stress-strain properties, samples were strained to failure under isothermal conditions at temperatures both above and below each network’s Tg. Subsequently, networks were soaked in phosphate buffered saline (PBS) and strained under the same testing conditions in an environmental bath at different temperatures. A maximum in toughness was observed in all polymer networks at a temperature below the glass transition temperature. At “equivalent” test temperatures relative to Tg, networks with different crosslink densities demonstrate varying levels of toughness, with low crosslink density offering better toughness relative to highly crosslinked systems. When immersed in PBS, networks exhibited modulus and toughness values indicative of conditions above their Tg in air with the extent of toughness change related to the amount of water uptake by the network. These results suggest that the underlying mechanisms for toughness are tied to the chemical structure and macromolecular arrangement of polymers, in particularly the chemical components that interact strongly with PBS. From this study, important fundamental relationships between toughness and network structure are established that can be utilized in developing tough photopolymerizable polymer networks.
12:15 PM - NN1.8
Relationship Between Materials Properties and Shape Memory Behavior in Epoxy-Amine Polymers.
Ingrid Rousseau 1 Show Abstract
1 , General Motors, Warren, Michigan, United States
Although epoxy-based polymers remain infrequently used as shape memory polymers (SMP’s), they are a promising base material for highly demanding applications due to their intrinsic physical properties and ease of processing. In a previous study, a series of epoxy SMP’s was synthesized with varying mechanical properties and with glass transition temperatures ranging from 31 to 93 oC, tunable via the variations of the molecular structures (crosslinking density, crosslink functionality, and chain flexibility). In the current study, the influence of chemical structures and physical properties of these epoxy SMP’s on their shape memory (SM) behavior is examined in detail. In addition, the impact of the shape memory cycling conditions on the SM behavior was investigated. Specifically, the deformation load, the recovery heating rate, the number of SM cycles, and the holding time in the deformed or temporary shape were varied. The results showed that lower crosslink densities and/or higher molecular flexibility/mobility leads to a reduction of the SM performance. In addition, at low crosslink density, the effect of molecular flexibility/mobility appears to become the dominant factor influencing the SM behavior.
12:30 PM - NN1.9
Controlling the Switching Temperature of Biodegradable, Amorphous Shape-Memory Poly(ester)urethane Networks by Incorporation of Different Comonomers.
Joerg Zotzmann 1 , Yakai Feng 2 , Armin Alteheld 3 , Steffen Kelch 4 , Marc Behl 1 , Andreas Lendlein 1 Show Abstract
1 Institute of Polymer Research, GKSS Research Center Geesthacht, Teltow Germany, 2 Department of Polymer Science and Technology, Tianjin University, Tianjin China, 3 , BASF AG, Ludwigshafen Germany, 4 , Sika Technology AG, Zürich Switzerland
Degradable polymeric implant materials  such as aliphatic (co)polyesters [2,3] are of high technological importance and are used today in numerous medical applications including surgical devices, and drug release systems. The combination of degradability and shape-memory capability resulted in multifunctional polymers. Their potential as intelligent implant materials for minimally invasive surgery leads to tremendous attention for such polymeric materials.[4,5] Their dual-shape capability enables the implantation of a bulky device in a compressed temporary shape through a small incision. Upon application of heat, and thereby exceeding a certain switching temperature Tsw
the device changes into its original shape. According to various application strategies Tsw
should either be between room - and body temperature for automatically inducing a shape change or slightly above body temperature for on demand activation. Tsw
and the degradation rate of amorphous polymer networks from star-shaped polyester macrotetrols crosslinked with a diisocyanate can be controlled systematically by incorporation of different comonomers into the poly(rac
-lactide) prepolymers. The polymer architecture with star-shaped prepolymers was selected because of the advantageous elastic properties of such networks. Tsw
is influenced by the melting point Tm
or the glass transition temperature Tg
of the switching domain that is varied using diglycolide, ε-caprolactone or p
-dioxanone as comonomers in the prepolymer generating ring-opening polymerization.In cyclic thermomechanical experiments it was shown that Tsw
could be adjusted between 14 and 60 °C by selection of comonomer type and ratio without affecting the advantageous elastic properties of the polymer networks.Finally, the hydrolytic degradation rate could be controlled by the ratio of easily hydrolysable ester bonds and the hydrophilicity of the material.
Langer, R.; Tirrell, D. A. Nature 2004, 428, 487-492.Vert, M. Biomacromolecules 2005, 6, 538-546.Putnam, D. Nat. Mater. 2006, 5, 439-451.Lendlein, A.; Langer, R. Science 2002, 296, 1673-1676.Min, C.; Cui, W.; Bei, J.; Wang, S. Polym. Adv. Technol. 2005, 16, 608-615.Alteheld, A.; Feng, Y.; Kelch, S.; Lendlein, A. Angew. Chem. Int. Ed. 2005, 44, 1188-1192.
12:45 PM - NN1.10
Three-dimensional Finite Deformation Constitutive Model for Shape Memory Polymers and its Applications.
Vikas Srivastava 1 , Shawn Chester 1 , Lallit Anand 1 Show Abstract
1 , M.I.T., Cambridge, Massachusetts, United States
Thermally activated shape memory polymers have the ability to temporarily store large recoverable strain after a pre-deformation following which the original shape can be recovered with thermal actuation. The ability of shape memory polymers to recover to a desired original shape from a pre-deformed temporary shape has found several applications in places such as aviation and biomedical devices. To predict the temperature dependent load-deformation behavior, the expected temporary shape, the residual stresses in the temporary shape, and the thermally actuated large strain recovery behavior, we have developed a thermo-mechanically coupled three-dimensional constitutive model for large deformations of thermally activated shape memory polymers. The temperature and rate dependent large deformation behavior of an amorphous shape memory polymer was experimentally characterized, and the material parameters in the model were calibrated using this experimental data. The constitutive model was then implemented in ABAQUS Standard by writing a user subroutine UMAT. The predictive capability of the constitutive model and its numerical implementation were validated by comparing the experimental and simulation results for a vascular-stent application.
Tuesday PM, April 14, 2009
Room 3018 (Moscone West)
2:30 PM - **NN2.1
Pattern Formation in Reversibly-Actuated Nanostructures.
Joanna Aizenberg 1 , Alexander Sidorenko 2 , Peter Fratzl 3 Show Abstract
1 , Harvard University, Cambridge, Massachusetts, United States, 2 , University of the Sciences, Philadelphia, Pennsylvania, United States, 3 , MPI, Golm Germany
An important feature of biological systems is their response to external stimuli with subsequent changes in properties and function. The ability to ‘‘engineer’’ adaptiveness into next-generation materials is becoming a key requirement and challenge in materials science and engineering. We have developed hybrid architectures in which arrays of high-aspect-ratio silicon nanocolumns, either attached or free-standing, are embedded into a hydrogel film and are actuated into highly controlled, complex microstructures upon contraction and/or swelling of the polymer. The actuation is fast, reversible, reproducible, and robust. We show that these architectures lead to a variety of applications, including actuators, controlled reversible-pattern formation, microfluidics, reversible switching of the wetting behavior, tunable photonic structures, artificial muscles, and release systems.
3:00 PM - NN2.2
Membranes with Responsive Subnanometer Size Selectivity.
Ayse Asatekin 1 , Anne Mayes 2 Show Abstract
1 Department of Chemical Engineering, MIT, Cambridge, Massachusetts, United States, 2 Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
Uncharged nanofiltration (NF) membranes can potentially operate as molecular sieves and perform separations of molecules based on size. Thin film composite (TFC) membranes prepared by coating a porous support with amphiphilic comb copolymers, specifically poly(vinylidene fluoride)-graft-poly(oxyethylene methcarylate) (PVDF-g-POEM) and polyacrylonitrile-graft-poly(ethylene oxide) (PAN-g-PEO), have this capability, as well as exceptional fouling resistance and high pure water permeability. The selectivity and permeability of these membranes arises from the microphase separation of the hydrophobic backbone and polyethylene oxide (PEO) side chains into bicontinuous hydrophobic and hydrophilic phases, the hydrophobic domains providing mechanical integrity, and the PEO domains acting as “nanochannels” whose dimensions control molecular transport through the membrane. The size cut-off of the membrane is determined by the size of these nanochannels and the conformation of PEO chains lining them. Therefore, the selectivity of the membrane can be adjusted by many parameters that affect the conformation of PEO in water, including temperature, pressure, ionic strength, and solvent polarity. Membrane permeability to water and to organic dye molecules of approximately 1 nm diameter is found to increase when the solvent quality of the feed for the PEO chains is reduced by raising the temperature, pressure, or ionic strength, or by the addition of ethanol. This property holds promise for applications in the biochemical, pharmaceutical and food industries for low-cost, high-throughput fractionation of molecules.
3:15 PM - NN2.3
Global Signaling of Localized Impact in Three-Dimensional Chemo-responsive Gels
Anna Balazs 1 , Olga Kuksenok 1 , Victor Yashin 1 Show Abstract
1 , University of Pittsburgh, Pittsburgh, Pennsylvania, United States
A vital function performed by skin is to send a chemical alarm signal throughout the system in response to irritation or damage. Using our recently developed 3D model for chemo-responsive gels, we design a coating that can perform an analogous, biomimetic function. Our system consists of a polymer gel undergoing the Belousov-Zhabotinsky (BZ) reaction. We show that such three-dimensional coatings respond to a spatially localized mechanical force by exhibiting a range of signaling behavior, which depend on the system parameters. For example, an initially stationary gel can emit transient chemical waves in response to a sufficiently weak, localized impact. A stronger localized impact, however, can generate a global signal, which encompasses both chemical waves and surface ripples that propagate across the entire sample. This complex dynamical response of the sample persists even after the force is lifted. Furthermore, the spatial patterns formed by these oscillating gels reveal the location and magnitude of the applied force. Our findings open up the possibility of harnessing BZ gels for a range of applications; for example, in creating sensors that transmit a global signal in response to a local mechanical impact.
3:30 PM - NN2.4
Photo-induced Locomotion of Chemo-responsive Polymer Gels.
Pratyush Dayal 1 , Olga Kuksenok 1 , Anna Balazs 1 Show Abstract
1 Chemical and Petroleum Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Using theory and simulation, we model the dynamic behavior of polymer gels undergoing the photo-sensitive Belousov-Zhabotinsky (BZ) reaction. Driven by the periodic reduction and oxidation of catalysts that are grafted to the polymer chains, the BZ gels exhibit a self-sustained, rhythmic swelling and deswelling. One means of controlling these oscillations is to use light as an external stimulus. To probe the effect of light on the mechanical behavior of the BZ gels, we use our recently developed 3D gel lattice spring model (gLSM), which couples the BZ reaction kinetics to the gel dynamics. Using this approach, we simulated the effect of illuminating the BZ gels with a non-uniform distribution of light intensity. When one end of a rectangular gel sample is exposed to light and the other end is not illuminated, we find that there is a net movement of the gel towards the dark region. In effect, the sample undergoes autonomous motion away from the light. We further find that we can manipulate the direction and the velocity of the gel’s motion by varying the intensity profile of the incident light. This ability to control the movement of the BZ gels can be utilized in a variety of applications, ranging from bio-actuators to controlled drug release systems.
3:45 PM - NN2.5
Effect of Confinement on the Dynamics of Three-Dimensional Chemo-responsive Gels
Olga Kuksenok 1 , Victor Yashin 1 , Anna Balazs 1 Show Abstract
1 Chemical Engineering Department, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Chemo-responsive gels undergoing the Belousov-Zhabotinsky (BZ) reaction can be ideal candidates for creating materials that can perform sustained mechanical work. In particular, due to the periodic oscillations of the BZ reaction, the gels undergo a self-sustained rhythmic expansion and contraction. These periodic volumetric changes could be harnessed to create a range of devices, from micro-pumps to micro-actuators. In these applications, the BZ gels would typically form one component of a larger system and thus, be anchored to a substrate or confined between two surfaces. For this reason, it is important to understand how the physical confinement of the BZ gels affects their dynamics. Here, we use theory and simulation to investigate the behavior of three-dimensional samples of BZ gels that are spatially confined in various geometric arrangements and show that the spatial confinement has a dramatic effect on the dynamics of the sample. We first consider two limiting cases, where a sample is either completely free or attached at all the boundaries to fixed, hard walls, and perform a linear stability analysis on these two scenarios. Through these analyses, we can calculate the critical reaction parameters at which the gels undergo a transition from a stationary steady state to an oscillatory system. We carry out computer simulations of the corresponding cases using our 3D “gel lattice spring model” (gLSM) and show that the simulation results are in excellent agreement with the analytical predictions. We also show that the analysis of the limiting cases allows us to predict the behavior of larger samples that are confined in more complex spatial arrangements, i.e., when only a portion of the sample is attached to a wall. In particular, we show that the changes in confinement can induce transitions between the oscillatory and non-oscillatory states. The results provide guidelines for designing BZ-gel based devices or responsive coatings.
4:00 PM - NN2: Hydrogel
4:45 PM - NN2.7
From Reactive Polymers to Functional Stimuli-Responsive Polymers.
Patrick Theato 1 Show Abstract
1 Institute of Organic Chemistry, University of Mainz, Mainz Germany
In the past, reactive polymers, such as activated ester polymers, have found extensive scientific application as useful synthetic platforms for the preparation of functional polymers. Activated ester polymers based on N-hydroxysuccinimide (NHS) are used mainly in polymer science in the form of NHS-(meth)acrylates. Other activated ester polymers, based on pentafluorophenylacrylate or acetone oxime acrylate, offer various synthetic advantages over the classical poly(NHS acrylates). Besides their superb solubility, the main advantage of these monomers is that they can be polymerized under controlled radical polymerization conditions and thus open a new route to functionalized polymers with a precise architectural control. Functionalization of activated ester polymers is performed by a polymer analogous reaction with aliphatic amines, resulting in the respective functionalized polyacrylamides. Thus, they provide an ideal basis for the preparation of stimuli-responsive polymers. Poly(N-isopropylacrylamide) homopolyners as well as block copolymers are easily be prepared. Additionally, we investigate the synthesis and polymerization behavior of 4-vinylbenzoyl azide and 4-vinylbenzoates. Their polymerization behavior as well as the reaction conditions in polymer analogous reactions using alcohols or aromatic amines will be presented. Further, base labile networks on the basis of actiavted esters will be presented, providing new stimuli-responsive hydrogels.
5:00 PM - NN2.8
Lithographically Fabricated Gels with Motion Driven by Solvent Mixing.
Noy Bassik 1 4 , Beza Abebe 2 , David Gracias 1 3 Show Abstract
1 Dept of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 4 School of Medicine, Johns Hopkins University, Baltimore, Maryland, United States, 2 Dept of Material Science, Johns Hopkins University, Baltimore, Maryland, United States, 3 Dept of Chemistry, Johns Hopkins University, Baltimore, Maryland, United States
We investigated the solvent driven motion of lithographically structured gels. The gel material was poly-N-isopropylacrylamide (PNIPAm) photopatterned from a mixture of high and low molecular weight precursors. The gels were soaked in an organic solvent such as ethanol and then transferred to water, where they moved spontaneously. This movement was driven by the expulsion of the solvent from the gel and subsequent solvent spreading at the air-water interface. Gels were lithographically patterned with features less than 100 microns, and exhibited remarkably high linear and rotational velocities of up to 31 cm/sec and 3529 rpm over time spans of seconds to minutes. We utilized lithographic patterning of the gels at the micron-millimeter length scales to investigate the effect of size, shape and symmetry. By coupling linear to rotational motion around a fixed central pivot the gels rotated in place, permitting high speed imaging and analysis with ditigal photographic hardware. We observed a reciprocal dependence of maximum rotational velocity on linear dimension. The linear velocity for all types of motion, along a line or curve, was analyzed and found to be similar across different shapes and sizes. This linear velocity of motion was in the range of 17-39 cm/sec even though gel sizes and shapes varied across orders of magnitude. We show that this velocity is related to the velocity of spreading of ethanol on water, which peaks at 53 cm/sec close to the source with no ethanol in the bulk. Additionally, we demonstrated that the gels could be further modified using standard microengineering, generating complex materials with the possibility for quiet, clean, solvent powered motion. We demonstrated applications in moving lithographically integrated metallic payloads on top of the gels and utilized the gels to move larger floating objects, without on-board wiring, batteries, or catalysts. The patterning method can be further extended to incorporate smart monomers and active polymers to interface with the environment.Reference:Solvent Driven Motion of Lithographically Fabricated GelsNoy Bassik, Beza T. Abebe, and David H. GraciasLangmuir, 24 (21), 12158–12163, 2008. 10.1021/la801329g
5:15 PM - NN2.9
Photothermal Patterning of Motor Proteins on Switchable Polymer Layers.
Cordula Reuther 1 , Robert Tucker 2 , Leonid Ionov 1 , Stefan Diez 1 Show Abstract
1 , Max Planck Institute of Molecular Cell Biology and Genetics, Dresden Germany, 2 , University of Florida, Gainesville, Florida, United States
Patterning functional proteins on engineered surfaces is of interest for the development of nanotechnology, tissue engineering, biosensors and cell biology. Here, we present a novel patterning technique based on localized light-to-heat conversion combined with a surface-grafted thermoresponsive polymer layer. Specifically, we switched the conformation of poly(N-isopropylacrylamide) (PNIPAM) molecules in aqueous solution between the swollen state at T < 30°C (protein-repelling conformation) and the collapsed state at T > 33°C (protein-binding conformation). Thereby, patterned polymer switching based on localized heating was evoked by the incidence of visible light onto a light-absorbing layer on the substrate. To demonstrate this method we allowed kinesin-1 motor proteins out of solution to bind to the illuminated areas and confirmed the functionality of the patterned proteins by microtubule-based gliding motility assays. We found that the microtubules were transported exclusively in the patterned areas. While the pattern sizes in our experiments were in the range of ten micrometers, we used finite element modeling (implemented in COMSOL) to show that increased optical powers allow to significantly scale down the pattern dimensions. We foresee a great potential of our novel method, because: (i) the produced patterns can be reversibly activated and deactivated at high and low temperature, respectively, (ii) sequential patterning of multiple kinds of proteins on the same surface will be possible without the need for specific linker molecules or elaborate surface preparations, and (iii) visible light without particular constraint on wavelength is used and avoids protein damage as charactistic to many UV-based photopatterning techniques.
NN3: Poster Session: Shape Memory Polymers and Stimuli-sensitive Hydrogels
Tuesday PM, April 14, 2009
Exhibition Hall (Moscone West)
6:00 PM - NN3.1
Tuning the Mechanical Properties of Electron Beam Crosslinked Shape-memory Polymers.
Walter Voit 1 , Taylor Ware 1 , Ken Gall 1 2 Show Abstract
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Shape-memory polymers (SMPs) are active self-adjusting materials in which both shape and stiffness changes can be accurately controlled at very specific, tailored temperatures. SMPs were originally used in shrink wrap tubing applications and have since seen a rise in importance in custom biomedical devices. Thermoplastic SMPs lose their “memory” properties near melt temperatures and do not possess fully recoverable strains, while another class of thermosetting SMPs relies on fully crosslinked networks to overcome these problems. However the use of thermosetting SMPs has been limited in mass-manufacture and commodity markets thus far because traditional plastics processing techniques like injection molding are not possible. In this study of thermosetting SMPs, beyond adjusting the glass transition temperature (Tg) between -20 and 100○C and tuning the recoverable force between .5 and 10 MPa, a novel manufacturing process is described that allows injection molding and traditional plastics processing. The customizable mechanical properties of traditional shape memory polymers are coupled with traditional plastic processing techniques to enable a new generation of mass producible plastic products with thermosetting shape-memory properties: fully recoverable strains, tunable recoverable force and adjustable glass transition temperature. Specifically, this study assess a model poly(methyl acrylate-co-isobornyl acrylate) (MA-co-IBoA) polymer system blended separately with both triallyl isocyanurate (TAIC®) and trimethylolpropane triacrylate (TMPTA) in varying concentrations. These blended systems are subsequently exposed to electron beam (EB) radiation at dosages ranging from 5 to 300 kilograys and mechanically assessed. Gel fraction, Tg, glassy and rubbery moduli, toughness, and stress-strain responses of blended TAIC® and TMPTA into MA-co-IBoA systems are shown as methods to target specific mechanical properties are explained. MA-co-IBoA systems blended with 3wt% TMPTA and exposed to EB radiation display high gel fractions (above 90%) across all dosages above 10 KGy while 3wt% blended TAIC® systems require at least 100 KGy to be only 85% crosslinked. The results of this study are intended to enable future advanced applications where mass manufacturing, the ability to accurately and independently position Tg and the ability to tune recoverable force in shape memory polymers are required.
6:00 PM - NN3.11
Spiral Photonic Actuator.
Jin Kwang-Yong 1 , Jang Ji-Hyun 2 , Jeong Kwang-Un 1 2 3 , Koh Cheong Yang 2 , Graham Matthew 3 , Park Soo-Jin 1 , Nah Changwoon 1 , Lee Myong-Hoon 1 , Cheng Stephen 3 , Thomas Edwin 2 Show Abstract
1 Polymer-Nano Science & Technology, Chonbuk national university, Jeonju, chonbuk, Korea (the Republic of), 2 Institute for Soldier Nanotechnologies and Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 3 Department of Polymer Science, The University of Akron, Akron, Ohio, United States
By combining the multi-faceted environmental responsiveness of polymer hydrogels with dielectrical structures, there has been a significant effort to create spiral sensors by changing either the periodic d-spacing of the structure or the dielectric constants of the materials. Here, we show that reversible spiral switches with dimensional functionalities that respond to environmental chemistry can be constructed. When the spiral switch is swollen in hydrophilic acetic acid, right-handed spiral structures are formed. When the spiral switch is swollen in hydrophobic hexane, left-handed spiral structures are formed. After deswelling, all switches returned back to the planar state. These reversible spiral switches can be useful as mechanical actuators, and electrical devices as well as optical components.
6:00 PM - NN3.12
Synthesis, Characterization and Performance Evaluation of Self-healing Coatings.
Jamil Baghdachi 1 , Heidi Perez 1 Show Abstract
1 Coatings Research Institute, Eastern Michigan University, Ypsilanti, Michigan, United States
In an effort to mimic self-healing functions in living systems, we have the developed polymeric coating systems that are stimuli responsive. The most attractive feature of this system is that the factors that damage the coating the most, such as humidity, exposure to high temperatures etc., are the same factors that initiate self-healing phenomenon. This property is unique since the extent of the healing is proportional to the magnitude of the damage, i.e., release on demand.Surface coatings function to protect or improve the appearance of a substrate or both. No matter how carefully the coatings are designed, manufactured and applied, all will eventually fail through some type of force in excess of the tolerance level of the coating or its ingredients. Failure of a coating system occurs by any number of failure modes and can often be attributed to a number of root causes including coating degradation, mechanical damage, or polymer fatigue upon service and exposure to elements of weather. The concept of self healing materials has drawn significant attention of researchers all over the world. Self-healing and self-repair concept, using both organic and inorganic materials have been applied to composites, plastics, concrete, adhesives, artificial skin, and most recently to functional coatings. The healing of the coating is demonstrated by comparing the stress-strain behaviors of exposed and unexposed samples of the coatings. For this purpose, the free-film samples of controls and self-healing coatings (SH) were stored in controlled environmental conditions of 65-70% relative humidity and 45-50 oC temperature for 24 hours. Characterization by dynamic mechanical analysis showed that the self healing coating had a increase in Young’s modulus as cpmpared to control which should substantial loss. Such behavior may be explained by reduction in free volume, voids and cracks and tighter packing of the already cured and adhered coating due to healing resulting in added crosslinking and repair. Similarly the water permeability of test of self-healing coating much reduced permeability. The lower water vapor permeability of self-healing films presumably indicates lower porosity due to higher extent of cross linking. The unexposed self-healing films also showed less permeability toward water vapor as time proceeded, which may be attributed to reaction of isocyanate with water vapor reducing the porosity of the panel. The results of corrosion testing of the panels coated with control and self-healing polyurethane coatings confirmed the self-repair phenomenon triggered by the conditions of exposure and treatments This trend indicates that the microcapsule release of the healing agent, either during initial heat aging, or upon the mechanical forces of scribe or due to the diffusion of salt water during the exposure period.
6:00 PM - NN3.14
An Infrared Electrochromic Shutter.
Amanda Holt 1 , Justin Wehner 2 , Andreas Hampp 2 , Daniel Morse 1 Show Abstract
1 Institute for Collaborative Biotechnologies, UC Santa Barbara, Santa Barbara, California, United States, 2 , Raytheon Vision Systems, Inc., Goleta, California, United States
Current infrared imaging systems use mechanical shutters for both calibration and imaging purposes. But these systems are bulky, mechanically fragile and power-hungry. We have developed a polymer-based electrochemical shutter to achieve on and off states with 100% and 0% transmission respectively in the mid-infrared region. The shutter is lightweight, inexpensive and reduces the system complexity because typical polymer solution processing techniques allow for device deposition on any part of the infrared detector system - including individual pixels. The device consists of a poly(3-hexyl thiophene) (P3HT) layer and a gel electrolyte layer sandwiched between two infrared-compatible electrodes. We have optimized the polymer and electrolyte thicknesses as well as the electrolyte composition to achieve high optical contrast in the infrared region of interest. We are currently attempting to simplify the structure by blending the electroactive polymer with an ion-conducting polymer to create a single layer solid-state device architecture. This research has significance in infrared imaging and sensing technology, including applications for example in search-and-rescue and fire-fighting operations, aerospace and satellite technology, and diagnostic medical imaging.
6:00 PM - NN3.15
Stimuli-Responsive Cyclodextrin-covered Silica Nano-containers
Hyehyeon Kim 1 , Chiyoung Park 1 , Kyuho Lee 1 , Chulhee Kim 1 Show Abstract
1 Department of Polymer Science and Engineering, Inha University, Incheon Korea (the Republic of)
Stimuli-responsive nanomaterials have attracted muchattention as controlled nanodevices, actuators and biomedical materials due to their ability to change their physical or chemical properties in response to external triggers. In particular, nano-containers with stimuli-responsive function can provide unique benefit for controlled release with precision in specific conditions. However, traditional nanocarriers such as liposomes and polymer micelles have suffered from their instability, whereas mesoporous silica particle (Si-MP) provides a rigid framework with porous reservoir, which can encapsulate large amount of guest molecules. Therefore, the use of Si-MP with a controllable gate function can provide a unique opportunity for biomedical applications. In this study, we described novel approaches to prepare stimuli-responsive Si-MPs, which exhibit controlled release characteristics in response to external triggers such as pH, light, and enzyme. For this purpose, the surface of nano-containers has been tethered with switchable supramolecular functional motifs toward these stimuli, which can open and close the pore on demand. We expect that the Si-MP systems described here can be used as a versatile multifunctional stimuli-responsive nano-container providing a unique opportunity in nanomedicine and materials science.
6:00 PM - NN3.16
Synthesis and Characterization of a Series of Novel Azo-dyes Bearing Two Amino-nitro Substituted Azobenzene Units Linked by Well-defined Oligo(ethylene glycol) Spacers.
Carolina Cano 1 , Ernesto Rivera 1 Show Abstract
1 Instituto de Investigaciones en Materiales, Universidad Nacional Autonama de México, México D. F. Mexico
In this work, we report the synthesis and characterization of a novel series of liquid crystalline azo-dyes bearing two amino-nitro substituted azobenzene units connected via a well-defined oligo(ethylene glycol) spacer (DIRED-PEG-n, where n = 2, 3, 4 and 6). These compounds were fully characterized by FTIR, 1H- and 13C-NMR spectroscopies. Their thermal properties were evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). On the other hand, their optical properties were studied by absorption spectroscopy in the UV-vis region. Finally, the properties of these compounds were compared to those of the precursor RED-PEG-n azo-dyes in order to see the influence of the azobenzene content on them. The general structure of these new azo-dyes is shown in Figure 1:
6:00 PM - NN3.18
In-situ X-ray Scattering Studies to Investigate Triple-shape Capability of Polymer Networks Based on poly(ε-caprolactone) and poly(cyclohexyl methacrylate) Segments.
Wolfgang Wagermaier 1 , Dieter Hofmann 1 , Karl Kratz 1 , Marc Behl 1 , Andreas Lendlein 1 Show Abstract
1 , Institute of Polymer Research, GKSS Research Center, Teltow Germany
The molecular structure and morphology of shape-memory polymers have an evident influence on the shape-memory mechanism. Shape-memory polymers have the ability to memorize a permanent shape which can be recovered from a different temporarily fixed shape upon application of an external stimulus (e.g. temperature) [1, 2]. These active polymers can show either dual- or triple-shape  capability depending on the number of switching domains. It is important for the applicability of the shape-memory-technology to design materials with accurate setting parameters such as switching temperature and recovery stress. The understanding of molecular mechanisms behind the shape memory effect therefore plays a crucial role, but still more detailed information on these structure-function relations during the dynamic process of shape recovery is required. Here we explore whether wide and small angle x-ray scattering (WAXS, SAXS) in combination with in-situ deformation experiments can help to characterize and better understand the respective materials structure (crystallinity, crystallite-sizes, domain-sizes and -arrangements) and its changes upon varying chemical composition, mechanical loads and external stimuli. Polymeric networks based on poly(ε-caprolactone) and poly(cyclohexyl methacrylate), whose molecular structures allow formation of at least two separated domains, were investigated using WAXS and SAXS, i.e. the description of the polymer structure and its change during cyclic thermomechanical tensile tests repeating shape-memory programming and recovery. The creation of the triple-shape capability for this AB polymer network system is performed by a simple one-step process, which is similar to a conventional dual-shape programming process . We could show that in these polymer networks a long period between crystalline domains exists and that as a consequence of programming and resulting elongation the value of this long period changes by some nanometers. From investigating diffraction peaks, detected at different steps during the thermomechanical treatment, it could be shown that crystal sizes in this polymer system remain unaffected of the programming process, while the crystallization of the stretched samples during the cooling process leads to a spatial rearrangement of crystalline domains.  A. Lendlein, S. Kelch, Angew. Chem. Int. Ed., 41, 2034-2057, 2002.  M. Behl, A. Lendlein, Soft Matter, 3, 1, 58-67, 2007. I. Bellin, S. Kelch, R. Langer, A. Lendlein, PNAS, 103, 18043-18047, 2006. M. Behl, I. Bellin, S. Kelch, W. Wagermaier, A. Lendlein, Adv. Funct. Mater., 2008, accepted.
6:00 PM - NN3.2
Functional Fatigue of Shape Memory Polymers.
Christina Schmidt 1 , Klaus Neuking 1 , Gunther Eggeler 1 Show Abstract
1 Institut für Werkstoffe, Ruhr-Universitaet Bochum, Bochum Germany
The present study represents a first step towards an understanding of what we refer to as the functional fatigue behaviour of shape memory polymers. These materials have a processing shape B and a programmed shape A . And when the material is exposed to an appropriate stimulus (in our case: heating above a critical temperature), a one way effect is observed: A → B (one way effect: 1WE). The objectives of the present study were to find out whether and how often programming can be repeated, whether repeated programming affects the 1WE and whether the material accumulates irreversible strain. We study the effect of different stress levels, and consider the effect of temperature and time. We examine the commercial amorphous shape memory polymer Veriflex® and subject it to 45 programming/1-WE cycles. The material is characterized by a transition temperature Ttrans of 70°C. During tensile testing at 21°C (TTtrans) the material can be strained up to 225 % before rupture occurs and stresses only reach values as low as 0.5 MPa. Thermomechanical cycles including programming, cooling, unloading and heating to trigger the 1WE result in an increase of irreversible strain associated with a corresponding decrease of the intensity of the 1WE in the early stages of thermomechanical cycling. M. Behl, A. Lendlein, Shape-memory polymers, materials today, 10 (2007) pp. 20-28
6:00 PM - NN3.20
Rational Design of Nanostructured Hybrid Materials for Photovoltaics.
Seth Darling 1 , Ioan Botiz 1 , Sanja Tepavcevic 2 , Steven Sibener 2 , Tijana Rajh 1 , Nada Dimitrijevic 1 Show Abstract
1 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 2 Department of Chemistry, The University of Chicago, Chicago, Illinois, United States
Efficient conversion of photons to electricity in organic and hybrid materials depends on optimization of factors including light absorption, exciton separation, and charge carrier migration. Bulk heterojunction devices target these processes, but disorder on the nanoscale results in inefficiencies due to exciton recombination and poor mobility. By rationally designing the morphology at appropriate length scales, one can enhance the effectiveness of internal processes and, therefore, the performance of photovoltaic devices . In this work, we have implemented this approach in two hybrid material systems—both of which may provide pathways to low-cost, large-area fabrication. The first involves a rod-coil block copolymer which is used both as an optoelectronically active material and as a structure-directing agent to pattern active material into ordered nanostructures. The second system uses electrochemically prepared titania nanotube arrays in concert with in situ polymerization of electron-donating material. In both cases, the characteristic donor-acceptor length scale is controlled to be comparable to the exciton diffusion length throughout the active layer, and the domains are oriented perpendicular to the incident light direction to encourage efficient charge migration. Use of the Center for Nanoscale Materials was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract #DE-AC02-06CH11357. Parts of this work were also supported by the NSF-MRSEC at the University of Chicago.
6:00 PM - NN3.21
Triple-Shape Capability of Thermo-sensitive Nanocomposites from Multiphase Polymer Networks and Magnetic Nanoparticles.
Narendra Kumar Uttamchand 1 , Karl Kratz 1 2 , Marc Behl 1 , Andreas Lendlein 1 2 Show Abstract
1 , GKSS Research Center Geesthacht GmbH, Institute of Polymer Research, Kantstr.55, 14513, Teltow Germany, 2 , Berlin-Brandenburg Center of Regenerative Therapies (BCRT), Berlin Germany
Thermo-sensitive multiphase polymer networks with triple-shape capability have been recently introduced as a new class of active polymers that can change on demand from a first shape A to a second shape B and from there to a permanent shape C1,2. Such multiphase polymer networks consist of covalent cross-links that determine shape C and at least two phase segregated domains with distinct thermal transitions (Ttrans,A and Ttrans,B ), that are associated to shape A and B. For creation of triple-shape functionality the application of a two step programming procedure is required.Here a series of nano-composites consisting of silica coated magnetite nano particles incorporated in a multiphase graft-network matrix (CLEG) from crystallisable poly-(ε-caprolactone) diisocyanatoethyl dimethacrylate (PCLIDMA: Mn = 8300 g.mol-1, Tm = 57 °C) acting as covalent cross-linker and poly(ethylene glycol) monomethyl ether monomethacrylate (PEGMA: Mn = 1000 g.mol-1, Tm = 38 °C) introduced as crystallisable side chains are investigated. Form stable composites could be obtained for PCL content between 30-wt% and 70-wt% with particle loading in the range from 2.5-wt% to 10-wt%. Gel content values higher than 93% and the degree of swelling up to 940% were determined. The particle distribution was investigated by means of SEM and STEM and the thermal and mechanical properties as well as the degree of crystallinity (DOC) were explored by means of DSC, DMTA, tensile tests and WAXS. The triple-shape properties were quantified in cyclic thermomechanical experiments, which consist of a two step heating-deformation-cooling programming procedure and a recovery module for restoration of the shapes B and C performed under stress-free conditions.All investigated composites showed a homogenous particle distribution within the different polymer matrices. Thermal properties of the multiphase networks were not affected by incorporation of the nanoparticles, whereas the elongation at break (εB) decreases with increasing particle content while the Young’s modulus is not influenced. For CLEG composites with 30-wt% to 40-wt% PCL content excellent triple-shape properties are obtained showing a well separated two step shape recovery process.References 1. Bellin, I., Kelch, S., Langer, R., and Lendlein, A., Polymeric triple-shape materials, Proceedings of the National Academy of Sciences of the United States of America 103 (48), 18043-18047, 2006.2. Bellin, I., Kelch, S., and Lendlein, A., Dual-shape properties of triple-shape polymer networks with crystallizable network segments and grafted side chains, Journal of Materials Chemistry 17 (28), 2885-2891, 2007.
6:00 PM - NN3.22
Shape-memory Properties of Radio Opaque Micro-composites from an Amorphous Multiblock Copolymer and BaSO4 Particles Designed for Medical Application.
Jing Cui 1 , Karl Kratz 1 2 , Andreas Lendlein 1 2 Show Abstract
1 , Institute of Polymer Research, GKSS Research Center, Teltow Germany, 2 , Berlin-Brandenburg Center of Regenerative Therapies (BCRT), Berlin Germany
Biocompatible shape-memory polymers are of high significance as medical devices and instruments for minimally invasive surgery. Radioopacity of the polymer would enable to follow the device placement by imaging method. Barium sulphate micro-particles were incorporated in an amorphous matrix of multiblock copolymer  prepared from methylene bis(p-cyclohexylisocyanate), poly(tetramethylene glycol) and 1,4-butanediol chain extender by application of co-extrusion technique. The BaSO4 content of the composites varied from 5 wt-% to 40 wt-%, which was confirmed by TGA measurements, while the particle distribution was analysed by performing SEM investigations. The thermal and mechanical properties of the composites were investigated by means of DMTA and tensile tests. While no impact of the particle incorporation was obtained in the DMTA results, a significant decrease in Young’s modulus as well as in elongation at break with increasing amount of BaSO4 was observed.The shape-memory properties were quantified in cyclic thermomechanical experiments, which consist of a heating-deformation-cooling programming procedure and two different recovery modules for restoration of the original shape under stress-free conditions as well as under constant strain conditions.Only the micro-composite with 5 wt-% particle content exhibited good shape-memory properties with apparent shape recovery rate Rrapp ranging from 28% to 44% for applied extensions εm from 100% to 250%, which are comparable to the pure multiblock copolymer. Additionally a potential application as intelligent radiopaque catheter was demonstrated.  Mohr R, Kratz K, Weigel T, Luka-Gabor M, Moneke M, Lendlein A, Initiation of shape-memory effect by inductive heating of magnetic nanoparticles in thermoplastic polymers. Proc. Nat. Acad. Sci. U.S.A., 2006, 103, 3540
6:00 PM - NN3.7
Mechanically Reinforcing Polyacrylate/Polyacrylamide Hydrogels through the Addition of Colloidal Particles.
Bryan Baker 1 , Valeria Milam 1 2 3 Show Abstract
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 Petit Institute for Bioengineering and Bioscience, Georgia Institute of Technology, Atlanta, Georgia, United States
Polyacrylamide is a popular hydrogel material for numerous bio-related applications ranging from electrophoretic separation of biomacromolecules to cellular supports for in vitro studies. A key limitation of polyacrylamide-based hydrogels, however, is their mechanical compliance, especially if compared to the compliance of many mammalian tissues. The current study examines the effects of employing colloidal particles as a reinforcing phase to effectively stiffen polyacrylamide-polyacrylate hydrogels. Polystyrene microspheres with cationic surface groups derived from both long and short polymer chains as well as negatively charged microshperes were added to the negatively-charged hydrogels. Oscillatory rheology shows that at a fixed polymer volume fraction, the presence of the colloidal particles generally resulted in an increase of the shear storage modulus of the hydrogel composite compared to the hydrogel alone. The results of this study indicate that modest changes in mechanical compliance of polyacrylamide-based hydrogels can be achieved through colloid particle additions.
6:00 PM - NN3.9
Phase Behavior and Equilibration Kinetics of poly(N-Isopropylacrylamide-2-Hydroxyethyl Methacrylate).
Christine Leon 1 , Brent Vernon 1 , Francisco Solis 2 Show Abstract
1 the Harrington Department of Bioengineering, Arizona State University, Tempe, Arizona, United States, 2 Integrat Natural Science, Arizona State University West, Phoenix, Arizona, United States
We investigate the phase composition and kinetics of the physically gelling thermo-sensitive Poly(N-isopropylacrylamide-2-hydroxyethyl methacrylate)[Poly(NIPAAm -HEMA)].This material belongs to a class of “smart” polymers, with potential medical applications including injectable controlled drug delivery systems, tissue engineering, and as basis for treatment of endovascular embolizations (1,2). At their Lower Critical Solution Temperature these polymers undergo a transition from liquid to a two phase liquid-gel state. Analysis of the phase behavior of these systems is crucial for their application, and provides a tool for their systematic chemical modification to optimize their properties. The LCST found using Differential Scanning Calorimetry and Cloud Point was 31 C and did not significantly vary with respect to weight percentage, simplifying the phase diagram. At higher temperatures, the polymer solution separates into a polymer-dilute phase, and a gel. These states are characterized by the volume fraction of the two phases. The extreme points of the phase diagram were found from the data of gel fraction versus weight percentage at equilibrium. The volume fraction of the gel was monitored during its approach to equilibrium. We analyzed digital images of the polymer obtained at intervals of 1 minute after the onset of the transition, and at intervals of 1 hour for the later stages of the process. The evolution of the gel fraction is well described by a double exponential decay of the form: φ=a exp(-a1 t) + b exp(-b1 t) + φ∞where φ∞ = 1-a-b is the volume fraction at equilibrium. Fitting the experimental data to this functional form we determined the amplitudes a, b and exponents a1, b1 as a function of weight percentage and temperature. The inverse time scale a1 is associated with the fast initial phase separation, while b1 captures the slower late stages of the equilibration process. The first stage is characterized by the expulsion of the liquid from the gel phase, and is found to be quicker for smaller weight percentages. The second stage is associated with reorganization of the polymers to optimize their gel-forming contacts which are sterically hindered. With increased weight percentage, we observed slower relaxations (smaller b1 exponents) and larger volume reductions (larger b amplitudes). At higher temperatures, both process become faster, and larger values of a1and b1 are observed. The presence of these two equilibration subprocesses has long been known in chemically crosslinked gels (3). Our results show that similar scenarios are also found in thermoreversible gels. References 1. Jeong B, Gutowska A, Trends Biotech, 20(7):305-311(2002). 2. Jeong B, Bae YH, Lee DS, Kim SW, Nature, 388(6645):860-862(1997).3. Suzuki, A, Yoshikawa, S, Bai, G,J. Chem. Phys. 111(1):360-367(1999).
6:00 PM - NN3: posters
NN3.13 Transferred to NN10.2 Show Abstract
Andreas Lendlein Institute for Polymer Research
Ken Gall Georgia Institute of Technology
Tomiki Ikeda Tokyo Institute of Technology
Prasad Shastri Vanderbilt University
NN6: Biomaterial I
Wednesday PM, April 15, 2009
Room 3018 (Moscone West)
2:30 PM - **NN6.1
Design and Realization of Biomedical Devices Based on Shape Memory Polymers.
Duncan Maitland 1 2 , Thomas Wilson 2 , Ward Small 2 Show Abstract
1 Biomedical Engineering Department, Texas A&M University, College Station, Texas, United States, 2 Medical Physics and Biophysics, Lawrence Livermore National Laboratory, Livermore, California, United States
Our experience with shape memory polymers (SMP) began with a project to develop an embolic coil release actuator in 1996. This was the first known SMP device to enter human trials. Recent progress with the SMP devices include multiple device applications (stroke treatments, stents, other interventional devices), functional animal studies, synthesis and characterization of new SMP materials, in vivo and in vitro biocompatibility studies and device-tissue interactions for the laser, resistive, or magnetic-field activated actuators. The talk will highlight engineering lessons learned in working with clinicians, the FDA and commercial partners as well as material-specific challenges for successful adoption of SMP as a medical device material.
3:00 PM - NN6.2
Semi-crystalline Polymer Networks Combining Controlled Drug Release, Biodegradation, and Shape Memory Capability.
Axel Neffe 1 2 , Bui Hanh 1 , Susi Steuer 3 , Christian Wischke 1 2 , Andreas Lendlein 1 2 Show Abstract
1 Centre for Biomaterial Development, GKSS Forschungszentrum Geesthacht, Teltow Germany, 2 , Berlin-Brandenburg Centre for Regenerative Therapies (BCRT), Berlin Germany, 3 , Intervet Innovation GmbH, Schwabenheim Germany
Biodegradable shape-memory polymers have been described as a prominent example for multifunctionality. Biomedical application of these materials includes intelligent surgical sutures. We explored whether controlled drug release can be integrated as an additional function. This would allow combining the shape-memory effect for enabling minimally invasive implantation of bulky devices, biodegradability to avoid a second surgery for implant removal, and controlled drug release for treating infections, reducing inflammatory responses, or, later, supporting regeneration processes. Such a combination of functions is demanded by biomaterial assisted therapies, e.g. for vascular and urinary stents or as scaffold material for tissue engineering applications.For the development of such a system with three independent functionalities and adjustable properties, we selected hydrolytically degradable shape-memory networks (N-CG), which were prepared by UV-curing of Oligo[ε-caprolactone-co-glycolide]-dimethacrylates as precursors (1). The precursors were varied in Mn between 3500 and 13500 g●mol-1, and had a glycolide content of 0-30 mol-%, resulting in a Tm of the networks of 24-52 °C. These networks have covalent netpoints and, in the temporary shape of the material, semi-crystalline switching segments. The latter are determining the switching temperature Tsw which needs to be exceeded to induce the shape change. Incorporated drug molecules are most likely localized in the amorphous domains of the remaining non-crystalline parts of the switching segments. Utilizing crystallizable switching segments, we aimed to reduce the influence of the drug molecules on the thermal and mechanical properties and shape-memory capability.Drugs could be incorporated into the networks by soaking (0.6-0.72 wt.-%) and co-extrusion (0.2-5.7 wt.-%) (2). It is demonstrated that the incorporation of hydrophilic and hydrophobic test drugs do not influence the thermal and mechanical properties and the shape-memory functionality for networks with a Mn of the precursors of ≥ 6900 g●mol-1, a glycolide content of ≤ 14 mol-%, and low drug contents as reached by soaking. Drug incorporation into networks with other compositions and hence lower crystallinity, or high drug contents from at least 5.7 wt.-% result in a decreased Young’s modulus and σmax. A diffusion controlled release was demonstrated which was independent from the biodegradation, and the programming process and shape recovery does not change the drug release kinetic. The networks with sufficient crystallinity have also the desired Tsw close to body temperature. Furthermore, a demonstration object for a potential ureter stent has been developed.1: S. Kelch, S. Steuer, A.M. Schmidt, A. Lendlein. Biomacromolecules 2007, 8, 1018-1027.2. A.T. Neffe, B.D. Hanh, S. Steuer, A. Lendlein, Adv. Mat. submitted.
3:15 PM - NN6.3
Engineering Adaptive Protein Scaffolds for Tissue Regeneration.
Karin Straley 1 , Sarah Heilshorn 2 Show Abstract
1 Chemical Engineering, Stanford University, Stanford, California, United States, 2 Materials Science and Engineering, Stanford University, Stanford, California, United States
A key attribute missing from many current biomaterials is the ability to independently tune multiple biomaterial properties without simultaneously affecting other material parameters. Because cells are well known to respond to changes in the initial elastic modulus, degradation rate, and cell adhesivity of a biomaterial, it is critical to develop synthetic design strategies that allow decoupled tailoring of each individual parameter in order to systematically optimize cell-scaffold interactions. We present the development of a biomimetic scaffold composed of chemically crosslinked, elastin-like proteins designed to support neural regeneration through a combination of cell adhesion and cell-induced degradation and remodeling. The design of these engineered proteins includes cell adhesion sequences to enable neuronal attachment as well as sequences sensitive to cleavage by urokinase plasminogen activator (uPA), a protease locally secreted from the tips of growing neurites, to enable highly localized and tunable degradation properties. These engineered proteins are produced using recombinant techniques and chemically crosslinked into highly swollen hydrogels with controllable mechanical properties. Through a modest 3% change in the chemical identity of three otherwise identical engineered proteins, we can modify the uPA substrate specificity resulting in tunable changes in protease degradation half-life over two orders of magnitude. Under high concentrations of constant uPA exposure, the designed scaffolds exhibit systematic variation of scaffold lifetime, from being fully degraded within a single day to showing no noticeable degradation within a full week. In vitro studies using the model PC-12 neuronal-like cell line show that the crosslinked proteins support tunable cell adhesion and neuronal differentiation. Increasing the density of RGD peptides present in the protein substrates is directly correlated with increased cell adhesion and more extensive neurite outgrowth. These engineered proteins offer the ability to independently tailor the mechanics, degradation properties, and cell adhesivity of scaffolds for the study of central nervous system regeneration.
3:30 PM - NN6.4
Tunable Redox-responsive Hybrid Nanogated Ensembles.
Rui Liu 1 , Xiang Zhao 1 , Tao Wu 1 , Pingyun Feng 1 Show Abstract
1 Chemistry, University of California, Riverside, Riverside, California, United States
The demand for better treatment of illness has led to ever-increasing efforts in the development of efficient drug delivery system that can transport drug molecules to the targeted site and release the loading in a controlled manner. The emerging nanostructured materials exhibit great potential for applications in controlled drug delivery systems. Among them, ordered mesoporous silica(OMS) are regarded as one of the ideal drug carriers because of their stable structures, large surface areas, tunable pore sizes and pore volumes, well-defined surface properties, and biocompatibility. The great diversity in surface functionalization offers mesoporous silica a unique advantage in site-specific delivery and stimuli-responsive release. Different nanomaterials based on functionalized OMS have been achieved that are responsive to different stimuli, such as pH, temperature, redox, light, and enzyme. By combining organic polymeric materials with inorganic nanostructured porous materials, we have developed a new controlled drug delivery system using mesoporous materials as reservoir and functional polymeric organic materials as valves to perform the controlled responsive functionalities. The system consists of poly(N-acryloxysuccinimide) grafted mesoporous silica (denoted as PNAS-MS), in which the polymers are attached at the pore entrance of MCM-41 particles. The polymeric layer can be cross-linked by the addition of disulfide linker and thus works as gatekeeper to control molecule release from mesoporous silica. The presence of disulfide reducing agent can effectively open the polymeric network and release the loading in a tunable manner. The system reported here is promising for biosensor and in-vivo site-specific drug delivery. This approach could also provide a general route to graft other functional polymers onto the surface of silica particles for various applications.
3:45 PM - NN6.5
Assessment of Accumulation of Degradation Products and of Angiogenesis around AB polymer Networks based on Oligo(ε-caprolactone) Segments Subcutaneously Implanted in Pharyngeal and Dorsal Regions of the Rat Neck.
Bernhard Hiebl 1 2 , Rosemarie Fuhrmann 3 , Friedrich Jung 1 2 , Andreas Lendlein 1 2 , Steffen Kelch 1 , Ralf Peter Franke 1 2 3 Show Abstract
1 Biocompatibility, GKSS Center for Biomaterial Development, Berlin, Berlin, Germany, 2 , Berlin-Brandenburg Center for Regenerative Therapies, Berlin, Berlin, Germany, 3 Centralinstitute for Biomedical Technology, University of Ulm, Ulm Germany
A missing implant integration or even implant loosening in the course of wear particle accumulation was described as “particle disease”  and created concerns on theintroduction of degradable polymers in medical therapies. The formation of blood vessels around and in implants could be the decisive step not only for tissue nutrition but also for the import of cells capable to handle the degradation products and help to maintain tissue homoeostasis and for the removal of degradation products. A new biodegradable ABpolymer network based on oligo(ε-caprolactone) dimethacrylate as a cross linker and nbutylacrylate as a comonomer  was shown to be biocompatible in vitro  and in vivo .The degradation properties of this polymer are fully adjustable to the physiological and anatomical conditions in vivo by the number, distribution and accessibility of hydrolysable ester bonds . We wanted to test in an animal model (rat) the hypothesis of an interrelationbetween the accumulation of particles and the number of capillaries in tissues under consideration. An incision of 1.5 cm was made dorsomedially between the scapulae andventromedially of the larynx and ethylene oxide-sterilised disk shaped copolymer samples (Ø 12mm) were implanted subcutaneously in 12 rats (group A). 12 animals were sham operated (group B). At days 7, 14, 21 and 35 three rats of each group were sacrificed and the pH was measured integrally in the connective tissues adjacent to the copolymer. Implants and adherent tissues were then retrieved and processed for immunhistologal evaluation. There were obvious differences in the amounts of degradation products found in the throat and neck regions. There was also a negative correlation in the numbers of accumulated particle wear debris and the numbers of vessels in the corresponding tissues. Further influences have probably to be regarded, namely the motility of the peri-implant tissue. The motility in the pharyngeal region was probably higher than in the dorsal interscapular region and so was probably the micromotion between implants and surrounding tissues. This may contribute to the higher numbers of accumulated particle wear debris in the pharyngeal region. The simultaneous assessment of the numbers and density of perfused blood vessels and of micro particulate scaffold degradation products could allow a critical estimation of the influence of implant material degradation on implant performance and on maintenance andreformation of tissues in different parts of an organism. H Willert et al. Chir. Orthop. 1972, 58:229 – 246 A Lendlein et al. Proc Natl Acad Sci USA 2001, 98: 842-7 D Rickert et al. Eur Arch Otorhinolaryngol 2006, 263: 215-22 D Rickert et al. Clin Hemorheol Microcirc 2003, 28: 175-181 S Kelch et al. Biomacromolecules 2007, 8(3): 1018-27The authors are grateful to German Federal Ministry of Education and Research for financialsupport under BioFuture Award No. 0311867.
4:00 PM - NN6:Biomat1
4:30 PM - **NN6.6
Infinite Coordination Polymer Nano- and Micro-Particles.
Chad Mirkin 1 , You-Moon Jeon 1 , Jungseok Heo 1 , Alexander Spokoyny 1 Show Abstract
1 Chemistry, Northwestern University, Evanston, Illinois, United States
Our group recently introduced the concept of infinite coordination polymer (ICP) particles (nano- and micro-), which are assembled via organometallic ligands and transition metal ions. Like metal-organic frameworks (MOFs), these structures are assembled via coordination chemistry principles. However, the resulting materials can be either crystalline or amorphous, and both amorphous and crystalline ICPs can be prepared from the same precursor mixtures by judicious choice of an appropriate solvent system. Thus ICP particles are attractive for many applications due to their high degree of tailorability. This flexibility is provided by a metal ion, which controls the coordination geometry and a ligand that dictates the stability, porosity, as well as the chemical functionality of the resulting ICP system. For example, we have shown that one type of ICP particle can be readily converted into three other classes of particles through metal ion exchange without significantly changing the morphology. At the same time, we have also demonstrated the solvent-induced reversible morphological transformation of an amorphous spherical system into crystalline rods. Similarly, an unusual solvent-induced reversible transformation between a triangular macrocycle and a helical coordination polymer was observed. Most recently, we have studied the gas sorption properties of these and related systems. These studies revealed permanent microporous properties of salen, Tröger-base and carborane based coordination polymer systems. Spherical salen and Tröger-base particle structures exhibit isosteric heats of absorption of approximately 8 kJ/mole, indicating strong physisorption of H2 to the internal pores of the particles. At the same time they exhibit no significant N2 uptake. A recent study comparing bulk MOFs and ICP particles derived from carborane-based precursors, showed how subtle changes in conditions can lead to materials with dramatically different morphologies which significantly influence their gas uptake and selectivity properties. In this presentation, the synthesis, characterization, and mechanistic aspects of ICP particle formation, as well as their potential use in gas storage and separation technologies will be discussed.
5:00 PM - NN6.7
Polyelectrolyte Microcapsules as Biological Force Sensors.
Vamsi Kodali 1 2 , James Larsen 1 2 , Stephan Schmidt 3 , Andreas Fery 3 , Jennifer Curtis 1 2 Show Abstract
1 School of Physics , Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Petit Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 Lehrstuhl für Physikalische Chemie II, Universität Bayreuth, Bayreuth Germany
Polyelectrolyte capsules fabricated using a layer-by-layer (LbL) technique have recently been introduced as new microscopic vehicles that have high potential the biomedical field. In this study we show for the first time that polyelectrolyte capsules can also be used as force sensors to quantitatively characterize the mechanical processes that drive phagocytosis. Understanding the receptor kinetics that trigger phagocytosis and the tightly controlled mechanics that drive this extremely expedient event are difficult to measure using traditional methods. Here we present a new method of measuring phagocytotic kinetics and mechanics which uses deformable, mechanically calibrated polyelectrolyte microcapsules. IgG biofunctionalized 4.5 micron diameter hollow capsules are introduced to and then readily ingested by macrophages. Forces exerted by the cell during uptake are then measured by visualization of the capsule’s deformation throughout uptake. We have established the lower limit of phagocytotic forces by identifying capsules, which can be designed to have a specific strength, that collapse during phagocytosis. We have found that capsules which buckle at 130-150nN, as calibrated by AFM measurements, deform and then buckle during phagocytosis. Using this method, we can monitor subtle changes in the capsule shape throughout the event, including the classic squeezing deformations that arise from a contractile actin belt that travels up and around the particle as it is consumed. This method can be extended to unravel the roles of the diverse molecular species involved in phagocytosis including several different myosin motors, actin binding proteins and other signaling molecules. Using drugs or other molecular biology techniques to interfere with certain molecules, the resultant change in the deformation sequence sheds light on the suppressed molecule’s role. In our first series of experiments, PI3-Kinase inhibitor LY294002 has been applied to the macrophages. These preliminary experiments have shown that microcapsules that typically collapse now become extremely deformed but no longer collapse. Polyelectrolyte capsules are shown to not only be used for understanding phagocytosis mechanics but also as a novel sensor for force measurements.
5:15 PM - NN6.8
Effect of Crosslinker Molecular Weight and Chemistry on the Thermo-mechanical and Degradation Properties of Poly(β-amino ester)s.
David Safranski 1 , Victor Uriarte 2 , Martha Lesniewski 1 , Ken Gall 3 Show Abstract
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Department of Mechanical Engineering, Florida International University, Miami, Florida, United States, 3 Woodruff School of Mechanical Engineering and School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Poly(β-amino ester)s are an alternative to common biodegradable polymers, and some of their initial uses have been nonviral transfection vectors and tissue scaffolds. The purpose of this study was to understand how the concentration, molecular weight and the chemistry of the diacrylate influences the thermo-mechanical and degradation properties of poly(β-amino ester)s. Macromers with acrylate endgroups were formed by step-growth polymerization of a primary amine, 3-methoxypropyl amine, with a diacrylate, selected from five varying molecular weights of poly (ethylene glycol) diacrylate (PEGDA) or three varying molecular weights of diol diacrylate (DDA). The macromer chemistry was verified by 1H NMR, and subsequent UV free-radical polymerization was employed to created crosslinked networks. Swelling profiles were used to provide a relative measurement of the hydrophilicity of these materials. PEGDA crosslinkers have shown a higher degree of swelling when compared to the DDA crosslinkers, and the increased water uptake decreases PEGDA degradation time to one day or less. The glass transition temperature and rubbery modulus were evaluated by dynamic mechanical analysis, and the glass transition temperatures ranged from -30°C to -45°C and the rubbery modulus varied from 0.14 MPa to 6.7 MPa. The glass transition temperature decreased as the molecular weight of the crosslinker used to form the macromer increased. The rubbery modulus increases as the diacrylate concentration increases, because the macromer molecular weight decreases as the diacrylate concentration increases. The relationship between crosslinker molecular weight and rubbery modulus was not obvious, thus further characterization by several methods was necessary. ATR-FTIR was used to measure the relative concentration of carbon-carbon double bonds, which are necessary for free-radical polymerization. The ratio of acrylate to carbonyl peak areas, 812 cm-1 and 1730 cm-1 respectively, showed the expected increase in concentration as the rubbery modulus increased. The sol fraction from swelling experiments was highest, 46%, in the networks with the lowest rubbery modulus, further supporting the ATR-FTIR results. In order to fully understand the macromer structure before free-radical network formation, the viscosity, macromer molecular weight, and relative double bond concentration were measured as a function of time during the step-growth polymerization. The characterization as a function of time was able to determine the influence of diacrylate molecular weight on reactivity and extent of reaction, which control the macromer molecular weight and rubbery modulus.
5:30 PM - NN6.9
Artificial Cornea, Material Design and in vivo Testing.
Laura Hartmann 1 , Stayce Beck 2 , Luo Luo Zheng 2 , Philip Huie 3 , Jennifer Cochran 2 , Christopher Ta 3 , Curtis Frank 1 Show Abstract
1 Chemical Engineering, Stanford University, Stanford, California, United States, 2 Bioengineering, Stanford University, Stanford, California, United States, 3 School of Medicine, Stanford University, Stanford, California, United States
Worldwide more than 10 million people suffer from blindness due to corneal diseases. However, only 100,000 corneal transplants are performed globally, due to lack of corneal donors and the risk of allograft rejection. In order to overcome the imbalance chemists, chemical engineers, biological engineers and ophthalmologists joined in an interdisciplinary project to build an artificial cornea based on a novel hydrogel material.Besides the need for a novel corneal transplant, the approach to turn a conventional material such as a hydrogel into an implant overtaking all natural properties and functions, still remains one of the major challenges in material sciences. Therefore we are also interested in the fundamental understanding of interactions between the implant and the organism, here focusing on the eye in particular.Our approach is based on a hydrogel material consisting of two interpenetrating polymer networks (IPNs) made from poly(ethylene glycol) (PEG) and poly(acrylic acid) (PAA), both materials approved for their biocompatibility. The surgically integrated implants must be designed to match the natural cornea’s properties, both optically and biologically. In order to embed the implant into the living tissue, the outermost cell layer of the cornea, the epithelium, must adhere to the implant and grow so as to fully cover the surface within a week after surgery. Therefore we developed a chemical protocol allowing for the covalent linkage of several layers of protein onto the hydrogel surface without changing its overall properties. Different extracellular matrix proteins such as collagen, fibronectin and laminin were examined for their ability to promote epithelial cell growth. We could show that a combination of collagen and fibronectin at a distinct surface concentration lead to optimized growth of epithelial cells. An important aspect often not addressed using hydrogel materials for biomedical applications is the long term stability under in vivo conditions. While the material for an implant has to stay stable over years, for other applications such as drug delivery a faster degradation is desirable. Nevertheless in both cases it is important to follow the processing of the material in the biological system and to correlate short as well as long term biological responses to the material properties. In our study, a first generation implant caused problems during the in vivo testing in rabbits’ eyes such as inflammation and turbidity of the implant starting about 3 weeks after surgery. Analysis of the regained implant as well as histology results showed a partial degradation of the material and thus led to the development of a long term stable, second generation implant now showing very promising results. With our redesigned material the animal models’ eyes are completely healed after 5 days, staying healthy and clear to date, i.e. for several months after surgery.
5:45 PM - NN6.10
Externally Tunable, Biocompatible, Multifunctional Nano-Reservoirs as Cell Function Modulators.
Santaneel Ghosh 1 , Tong Cai 2 , Somesree GhoshMitra 3 , Zhibing Hu 2 , DiAnna Hynds 3 , Nathaniel Mills 3 Show Abstract
1 Physics and Engineering Physics, Southeast Missouri State University, Cape Girardeau, Missouri, United States, 2 Physics, University of North Texas, Denton, Texas, United States, 3 Molecular Biology, Texas Woman's University, Denton, Texas, United States
Recent advances in the synthesis of structured and intelligent materials and engineering at micron or nano-scale limits, makes it possible to design multifunctional material systems, capable of performing delivery, detection and precise control simultaneously. In the newly emerging field of magnetically tunable therapeutic applications, many groups have investigated the use of various organic coatings as a means of optimizing the delivery or imaging capability based on fast-responsive magnetic nanospheres; however, no study has been performed to assess the modulation of intracellular system performance by the encapsulated nanomagnets in an oscillating magnetic field exposure that actuates the swelling/shrinkage behavior plus regulates the temperature simultaneously to alter the cellular functions. By optimizing the design constraints for a biocompatible, multifunctional system, low toxicity nanospheres can be designed having the potential of heat shock protein related cell function alterations in combination with drug delivery and detection. The present work highlights on a novel, oscillating field actuated, thermo-reversible, polyethylene glycol biopolymer based nanosphere uptake, intracellular temperature regulation by oscillating field induced relaxation losses and subsequent cellular function alteration on cell line PC12, derived from rat Pheochromocytoma. Embryologically derived from neural crest cells, PC12 cells retain the property to become a proliferating nerve cell in response to neurotrophins as well as maintaining its neuroroendocrine functions unaltered to release catecholamines. Thus, PC12 cell line represents the quantifiable model system to test the viability and capacity to extend neurites in response to Nerve Growth Factor (NGF) exposure in the presence of encapsulated magnetic nanospheres. Since the nano-scale system is synthesized from non-toxic, FDA approved materials, this novel approach might lead to an effective, magnetically modulated multifunctional system for therapeutic applications. Cellular internalization of nanospheres on incubation time, sphere concentrations, sphere size and LCST dependence have been investigated to determine the effectiveness as an intravascular delivery system in terms of uptake and biocompatibility. In order to precisely estimate the amounts of intracellular uptakes against the above mentioned variables, SQUID magnetometry have been performed on different cell lysates. Unaffected neurite growth at considerably higher concentration (upto 12mM) combined with nano-scale intracellular temperature regulation is achieved without compromising the thermo-reversibility, i.e. the drug loading capacity of the system. This neurite growth pattern at higher level of nanosphere internalization is especially promising for further studies with effect on primary neurons in terms of axon regeneration which is a challenging aspect of treatment for several neurodegenerative disorders.
Andreas Lendlein Institute for Polymer Research
Ken Gall Georgia Institute of Technology
Tomiki Ikeda Tokyo Institute of Technology
Prasad Shastri Vanderbilt University
NN9: Shape Changing II
Thursday PM, April 16, 2009
Room 3018 (Moscone West)
2:30 PM - **NN9.1
Application of Shape Memory Polymers as Space Deployables and Novel Actuators.
Steven Arzberger 1 Show Abstract
1 , Composite Technology Development, Inc. (CTD), Lafayette, Colorado, United States
The ability of shape memory polymers (SMPs) to change their shape in response to an external stimulus, along with passive damping, dynamic modulus, and functionality serve as an enabling technology for a range of advanced aerospace and commercial concepts. For example, continuous fiber reinforced SMP composites formed in a carpenter tape-like configuration can be employed to deploy payloads more simply and cheaply than current mechanized systems, and with smaller stowed volume. Recent space flight successes have validated this technology and stimulated larger scale product development. This presentation will detail the development and application of this technology as space deployables and novel actuators, and discuss the next generation of significant opportunities.
3:00 PM - NN9.2
Photodriven Oscillations of Azobenzene Liquid Crystal Polymer Network Cantilevers
Timothy White 1 2 , Svetlana Serak 3 , Uladzimir Hrozhyk 3 , Nelson Tabiryan 3 , Hilmar Koerner 1 4 , Richard Vaia 1 , Timothy Bunning 1 Show Abstract
1 Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright Patterson AFB, Ohio, United States, 2 , General Dynamics IT, Dayton, Ohio, United States, 3 , BEAM Engineering for Advanced Measurements, Winter Park, Florida, United States, 4 , UTC Inc., Dayton, Ohio, United States
We report on the photodriven, fast (30 Hz), and large amplitude (>170°) oscillation of polymer cantilevers consisting of a monodomain azobenzene-containing LCN (azo-LCN). The frequency of the photodriven oscillation is similar to a hummingbird wingbeat, which can range from 20-80 Hz. The oscillation of the azo-LCN cantilever can be turned on and off by switching the polarization direction of the driving laser beam, and the behavior shows little fatigue over 250,000 cycles. The impact of cantilever thickness, laser intensity, and laser wavelength will be discussed.
3:15 PM - NN9.3
Reversible Dynamic Shear Modulus Switching in Photoresponsive Liquid Crystalline Polymers.
Eric Verploegen 3 , Johannes Soulages 4 , Mariel Kozberg 1 , Tejia Zhang 2 , Gareth McKinley 4 , Paula Hammond 1 Show Abstract
3 Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 4 Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 1 Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
The synthesis of a side-chain liquid crystalline polymer with azo containing liquid crystalline (LC) moieties is described. The system developed displays reversible switching of both the morphology and the mechanical properties upon exposure to UV light. UV stimulation induces a trans to cis isomerization in the LC moieties, which will relax to the equilibrium trans conformation upon removal of the UV light. We use in-situ small angle X-ray scattering experiments to characterize the disruption of the smectic LC mesophase due to the photoisomerization of the LC moieties. The viscoelastic properties of the LCP are dependent upon the morphology of the system; when the azo moieties are in the equilibrium trans conformation, the smectic LC mesophase provides inter-chain interactions that reinforce the LCP, leading to the higher storage and loss moduli. Upon exposure to UV irradiation a trans to cis isomerization is induced, resulting in a disruption of the smectic LC mesophase and a subsequent decrease in the storage and loss moduli. In both the linear viscoelastic regime (strain amplitude of 2%) and in the nonlinear viscoelastic regime (strain amplitude of 100%), we have shown that UV irradiation can be used to reversibly alter the storage (G’) and loss (G”) moduli over several cycles.
3:30 PM - NN9.4
The Photo-Mechanical Effect in Azo Polymers: From Reflectometry to Robotics.
Christopher Barrett 1 Show Abstract
1 Chemistry, McGill University, Montreal, Quebec, Canada
Polymers containing Azobenzene have received much interest as photo-reversible materials for a variety of optical and photonic applications. Most recently however, Azo Polymers have also been shown to respond physically and mechanically to light, to act as all-optical patterning materials, and photo-mechanical devices. In particular, a photo-induced pressure in soft amorphous thin films of azo polymers can lead to the facile inscription of efficient surface relief gratings (SRGs) upon irradiation with an interference pattern. Irradiation with CW light is also shown to lead to a reversible photo-expansion of these films, of up to a few %, allowing the materials to function as photo-mechanical switches or light-actuators. New azo polymers to optimize this effect with be presented, and some simple macroscopic devices will be demonstrated that take mechanical advantage of this effect for larger scale motion driven by light, such as bending, rolling, and 'walking'. The mechanism for this effect will be discussed from studies using ellipsometry, surface plasmon resonance spectroscopy, and neutron reflectometry.
3:45 PM - NN9.5
Giant Dry Out-of-plane Actuation of PEDOT:PSS Thin Films.
Dimitri Charrier 1 , Martijn Kemerink 1 , Rene Janssen 1 Show Abstract
1 Applied Physics Department, Eindhoven University of Technology, Eindhoven Netherlands
Because of their principle, most of organic actuators operate in ionic solution  which limits their range of applicability. Here, we demonstrate giant (up to 840%) out-of-plane actuation at first cycle of thin films of the oxidatively doped conjugated polymer blend poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) covering gold interdigitated fingers.To figure out the underlying mechanism, we simultaneously performed transport measurements and optical and atomic force microscopy on spin cast PEDOT:PSS films of different thickness and composition. Additionally, Scanning Kelvin Probe and Tunneling Microscopy respectively gave information on the potential distribution while actuating and on the changed morphology in the channel after actuation.For a 21 nm thick PEDOT:PSS film, the AFM versus time measurements showed that the anode was actuated at an average speed of 0.5 nm/s while a 4 V bias was applied. Saturation was reached at 226 nm after 380 s and remained stable on 0 V bias. More experiments showed that the actuation reaction was no longer reversible once both saturation and color change on the anode were observed. The reversible reaction is explained by a net proton transport from anode to cathode and by adsorption of atmospheric water on the anode due to osmosis. For similar ambient conditions, the maximum attainable actuation on the anode was virtually independent of device geometry and film thickness. The independence of the saturated actuation height is explained by the presence of mobile ions which screen the applied potential in areas more then several nm away from the electrodes, confining the involved reactions to a thin layer near the electrodes. This is confirmed with scanning Kelvin probe microscopy on films of different thicknesses.Hence, the ambient actuation is a two-step process, where during the first, reversible step, proton transport to the cathode takes place. During the second step the ionic screening accompanied with an irreversible reaction on the anode stops the actuation.Reference(1) E. Smela, N. Gadegaard Adv. Mater. 1999, 11, 953-957.
4:00 PM - NN9:Shapchan2
Thursday PM, April 16, 2009
Room 3018 (Moscone West)
4:30 PM - **NN10.1
Exploiting Enzymes in Responsive Materials and Nanofabrication.
Rein Ulijn 1 Show Abstract
1 Pure & Applied Chemistry, University of Strathclyde, Glasgow, Scotland, United Kingdom
Most responsive materials rely on stimuli that are non-selective and non-confined such as changes in solvent polarity, ionic strength, temperature, pH or concentration of inorganic/organic molecules. By contrast, in biological systems, many examples exist of nanostructures that are selective and locally triggered under overall constant conditions by spatially confined molecular mechanisms involving enzymes. This talk will summarise our recent results aimed at mimicking these approaches of superior control, and applying them in the design and fabrication of man made molecular materials. First, we will discuss our work on enzyme assisted self-assembly. This approach exploits the use of fully reversible enzyme catalysed reactions to drive molecular self-assembly of peptide nanostructures. We demonstrate that this system uniquely combines three features: (i) self-correction: fully reversible SA under thermodynamic control, (ii) component-selection: the ability to amplify the most stable molecular SA structures in dynamic combinatorial libraries, (iii) spatiotemporal confinement of nucleation and structure growth. The second part of the talk will focus on design, characterisation and application of hydrogel particles with enzyme-responsiveness built-in. These particles change properties (swelling/collapse) when exposed to a (disease specific) target enzyme. We will discuss the design rules of the peptide based actuators that control the responsiveness of these materials. Specifically, we will report on enzyme-responsive hydrogel particles for the controlled release of proteins whereby the peptide actuators are designed to match the specificity of the target enzyme, while also matching the charge properties of the to-be released protein payload, thereby uniquely allowing for tuneable release profiles. Applications of the above systems in biomedicine and nanotechnology will also be discussed.
5:00 PM - NN10.2
Reactive Polymer Coatings: Innovative Design of Functional Surfaces.
Daniel Kessler 1 2 , Patrick Theato 1 Show Abstract
1 Institute of Organic Chemistry, University of Mainz, Mainz Germany, 2 , Max Planck Institute for Polymer Research, Mainz Germany
The modification or functionalization of solid surfaces has gained considerable interest recently because of its importance in various applications. Various coating materials have been developed to permanently alter the wettability of surfaces1-3 or even to switch interfacial properties reversibly using different stimuli. Especially in the development of miniaturized biodevices, the design of the (bio)chemical nature of the interfacial layer at the surface defines the bio-recognition ability and sensitivity of such devices.4 Considerable effort has been made recently to create generally applicable protocols for substrate-independent (active) polymer coatings, offering interesting possibilities for further molecular tailoring via simple wet chemical derivatization reactions.5Poly(methylsilsesquioxane) (PMMSQ)-based hybrid materials are promising candidates to create adherent surface coatings.6,7 By grafting pentafluorophenyl acrylate (PFPA) from PMSSQ, active hybrid polymers can be obtained.8 Via spin- or dip-coating onto various surfaces active surface coatings can be prepared. The pentafluorophenyl esters, present at the surface, allow a specific surface functionalization via conversion with amines in a simple dipping process.To demonstrate the multi-purpose functionalization potential, different functional surfaces were prepared.The wetting behavior of the surface can be permanently adjusted over a wide range by conversion with different amines, e.g. glycin for hydrophilic surfaces or perfluorinated aliphatic amines for hydrophobic surfaces.Coatings featuring a reversibly switchable wetting behavior can be obtained by conversion with functional amines developing a temperature- or light-responsive behavior.Beside tailor-made wettability the biochemical nature of the coating can also be adjusted precisely. Surface derivatization with amino-biotin or nitrilotriacetic acid results in templates for controlled protein assembly.Further the controlled covalent deposition of nanoparticles on top of the coating can be realized by dipping active polymer coatings in suspensions of amino-functionalized SiO2 particles as one example.PMSSQ-PFPA hybrid polymers create stable active surface coatings independent from the underlying substrate and offer the chance to address almost any desired surface function.References G. M. Whitesides, P. E. Laibinis, Langmuir 1990, 6, 87.P. E. Laibinis, C. D. Bain, R. G. Nuzzo, G. M. Whitesides, J. Phys. Chem. 1995, 99,7663.M. K. Chaudhury, G. M. Whitesides, Science 1992, 256, 1539.C. L. Feng, Z. Zhang, R. Förch, W. Knoll, G. J. Vansco, H. Schönherr, Biomacromolecules 2005, 6, 3243.J. Lahann, I. S. Choi, J. Lee, K. F. Jensen, R. Langer, Angew. Chem. Int. Ed. 2001, 40, 3166.D. Kessler, C. Teutsch, P. Theato, Macromol. Chem. Phys. 2008, 209, 1437.D. Kessler, P. Theato, Macromolecules 2008, 41, 5237.D. Kessler, N. Metz, P. Theato, Macromol. Symp. 2007, 254, 34.
5:15 PM - NN10.3
Multifunctional and Bioactive Nanostructured Conducting Polymer Actuators for on Demand, Precisely, and Targeted Delivery of Drugs and Proteins
Mohammad Reza Abidian 1 , David Martin 1 2 3 , Daryl Kipke 1 Show Abstract
1 Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, United States, 2 Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States, 3 Macromolecular Science and Engineering, University of Michigan, Ann Arbor, Michigan, United States
Cortical prosthetics facilitate the recording and stimulation of the cerebral cortex using microelectrodes. In neural prosthetic devices, the recording and stimulating signals must be transduced at the neural interface from the ionically-conductive neural tissue to the electronically-conductive electrode. Current neural electrodes, such as microwires and more advanced microfabricated electrode arrays, suffer from high initial impedances and low capacity of charge transfer because of their small feature geometry. Furthermore, cellular reactive responses increase the electrode–tissue impedance due to insertion trauma and chronic foreign body reactions induced by tethering, micromotion, and device biocompatibility. Conducting polymers such as poly(3,4- ethylenedioxythiophene) (PEDOT) are both electronically and ionically-conductive. They can expand and contract using electrical stimulation and they are biocompatible with living tissue. They have also been suggested as good candidate materials to bridge the hard-soft and electron-ion interface for neural interfaces. Here, we report multifunctional and bioactive conducting polymer nanotube coatings that improve neuronal recordings and release drugs and proteins precisely on demand.We have developed a new approach for preparing drug-loaded conducting polymer nanotubes (CPNTs) on the surface of neural electrodes. The fabrication process includes the electrospinning of biodegradable polymer poly(lactide-co-glycolide) with a neurotrophin incorporated inside, followed by electrochemical deposition of PEDOT. The wall thickness of the resulting PEDOT nanotubes varied from 50-100 nm, and the CPNTs diameter ranged from 100-600 nm. The in-vitro impedance spectroscopy and cyclic voltammetry of electrode sites revealed that the impedance significantly decreased about 2 orders of magnitude and the charge transfer capacity significantly increased about 3 orders of magnitude. By using electrical stimulation, as low as 0.5 V, we could precisely and locally release nerve growth factor (NGF) at desired points in time. After electrical excitation of the site, we observed a significant increase in the amount of NGF released presumably either through the ends of CPNTs or though openings on the surface of nanotubes. The CPTNs-modified microelectrodes were implanted in cerebral cortex of rats and their performance was monitored by impedance spectroscopy, signal amplitude, and noise level over periods of at least 7 weeks. The CPNT sites were found to outperform control sites with respect to signal-to-noise ratio and number of viable unit potentials. We demonstrate that electrodes modified with PEDOT nanotubes registered quality unit activity on 35% more sites then controls.
5:30 PM - NN10.4
Parylene Bilayer Encapsulated Drug-Nanodiamond Complexes as Chemotherapeutic Microfilm Devices.
Robert Lam 1 , Mark Chen 1 , Erik Pierstorff 1 , Houjin Huang 1 , Eiji Osawa 2 , Dean Ho 1 3 Show Abstract
1 Biomedical Engineering and Mechanical Engineering, Northwestern University, Evanston, Illinois, United States, 2 , NanoCarbon Research Institute, Nagano Japan, 3 Robert H. Lurie Comprehensive Cancer Center, Northwestern University, Chicago, Illinois, United States
Nanodiamonds (NDs) possess several characteristics that contribute to their medically-relevant applications in therapeutic delivery. For example, they are platform materials that can be interfaced with nearly any type of therapeutic. Furthermore, they can be batch synthesized, purified, and functionalized, making them highly scalable for broad impact towards the treatment of a multitude of physiological disorders. In this study, ND particles of 2-8nm diameters were bound with the chemotherapeutic doxorubicin hydrochloride (DOX) and embedded between parylene C polymer layers deposited via a scalable chemical vapor deposition (CVD) process, effectively creating a microfilm device. The microfilm architecture consisted of DOX-ND conjugates sandwiched between a thick hermitic base layer of parylene, and a thin semi-porous layer of parylene. Parylene has previously been extensively used as a coating in FDA-approved devices. We utilized parylene as the base material in a stand alone device. Because of the high surface area to volume ratio of the embedded NDs and the facile tailoring of microfilm thicknesses via CVD, small footprint devices could be fabricated towards minimally invasive therapy. The film architecture was characterized via epi-fluorescence microscopy and atomic force microscopy (AFM). AFM and epi-fluorescent images confirmed the dense coverage of DOX-ND conjugates and overlying grainy texture of the porous parylene C layer. The sequestration abilities of the ND surface combined with the thin layer of parylene resulted in a device platform capable of translationally relevant modulation of drug release. Specifically, we have conferred the ability to release drug continuously in a constant manner for a minimum of one month with significant drug in reserve. Characterization of release was achieved via UV-Vis drug elution assays. Microfilms were immersed in pure water at physiological conditions (37°C and 5% CO2) and the eluate was analyzed every 24 hours. Assays attested to the long-term drug release abilities of the non-conformal parylene layer as well as the slow-release and sequestration abilities of the NDs. The retained biological activity of released drug was also analyzed via DNA fragmentation assays. Results additionally alluded to the slow-release abilities of the microfilm as well as the apoptotic efficacy of DOX released from the deposited NDs. With the parylene backbone, these microfilms resemble plastic wrap, with flexibility and versatility in shapes/dimensions towards multifunctional localized therapy. Additionally, NDs can entrap and release several relevant agents. The combination of these components allow for a customizable platform towards a wide range of therapeutic treatments. Continued studies are examining the application of these microfilms towards adjuvant cancer therapy and combinatorial/sequential drug studies.
5:45 PM - NN10.5
Enzyme-Responsible Single Protein Encapsulated Nanogels for Intracellular Delivery.
Zhen Gu 1 2 , Ming Yan 1 , Juanjuan Du 1 , Yunfeng Lu 1 , Tatiana Segura 1 , Yi Tang 1 Show Abstract
1 Department of Chemical and Biomolecular Engineering, University of California at Los Angeles, Los Angeles, California, United States, 2 Department of Mechanical and Aerospace Engineering, University of California at Los Angeles, Los Angeles, California, United States
Intracellular delivery of exogenous proteins holds great promise in biological and medical applications. However, no general method has been developed to date. Here we report a novel intracellular protein delivery system based on enzymatically degradable nanocapsules. Single protein encapsulated nanogels were prepared by first modifying the protein surface with vinyl groups, followed by polymerization using enzymatically cleavable peptide cross-linkers. The peptide sequences can be varied and can be designed to be degraded by different proteases, including matrix metalloproteinases which are overexpressed in various human cancer cell lines. Characterization of the nanogels by dynamic light scattering (DLS), transmission electron microscopy (TEM), and atomic force microscopy (AFM) confirmed that each nanogel contained an individual protein molecule. Benefited from the small size (~15 nm) and positively charged polymeric shell, proteins enclosed in the nanogels were efficiently delivered into HeLa cells. More importantly, the enzymatic activities of delivered proteins were retained after internalization into cells. The incorporation of nuclear localization signals (NLS) to the surface of the nanogels allowed facile protein delivery into the nucleus, which can be also triggered by the protease activity. The ease of preparation, high cell penetration capability, long-term stability, low toxicity and protease-modulated specific degradability render this new protein delivery strategy as versatile candidates for therapeutic agents, vaccines transport or cellular imaging.