Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session W11: Assembly and Function of Biomimetic and Bioinspired Materials |
Hide Abstracts |
Sponsoring Units: DMP DBIO Chair: Elaine Zhu, University of Notre Dame Room: 203 |
Thursday, March 6, 2014 2:30PM - 2:42PM |
W11.00001: Impact of Hydrogel Structure and Composition on Autonomic Chemo-Mechanical Behavior Ryan Kramb, Philip Buskohl, Richard Vaia Autonomic materials harvest energy to change size, shape, or color in response to a set of environmental conditions. At the core of this biomimetic behavior is a material that transduces energy between forms (e.g. chemical to mechanical). The most widely studied of these materials are self-oscillating, Ru-containing PNIPAAm hydrogels driven by the Belousov$-$Zhabotinsky (BZ) reaction; and if correctly designed, BZ gels mimic biological process such as a quorum sensing or beating like a heart. However, establishing relationships between chemo-mechanical response and gel characteristics, such as crosslinking density, monomer composition, catalyst content, and gel stiffness, has remained elusive due to the limited material set and challenges in determining the appropriate balance of reaction kinetics and mechanical response necessary to establish self-sustaining oscillations. To address this challenge, we have broadened the suite of available monomers through a modular synthesis of the Ru-containing constituent; and thereby demonstrating facile tuning of the aforementioned characteristics of the BZ gel. From the resulting correlations between gel properties and chemo-mechanical response, we discuss the material design of composite autonomic gels for maximum shape change, directionality of oscillations, and synchronization of oscillations analogous to a natural pacemaker cell cluster. [Preview Abstract] |
Thursday, March 6, 2014 2:42PM - 2:54PM |
W11.00002: Mechanical tuning of elastomers via peptide secondary structure Nandula Wanasekara, J. Casey Johnson, LaShanda T.J. Korley Nature utilizes an array of design tools for engineering materials with multiple functions and tunable mechanical properties. The precise control of hierarchical structure, self-assembly, and secondary structure is essential to achieve the desired properties in bio-inspired materials design. We have developed a series of peptidic-poyurea hybrids to determine the effects of peptide secondary structure and hydrogen bonding arrangement on morphology, thermal and mechanical properties. These materials were fabricated by incorporating peptide segments containing either poly($\beta $-benzyl-\textsc{l}-aspartate) or poly($\varepsilon $-carbobenzyloxy-\textsc{l}-lysine) into non-chain extended polyureas to form either $\beta $-sheets or $\alpha $-helix conformations based on peptide length. Infrared analysis proved the retention of peptide secondary structure when incorporated into peptidic-polyureas. The polymers containing $\beta $-sheet forming peptide blocks exhibited higher modulus and toughness due to intermolecular H-bonding. Additionally, higher peptide weight fractions lead to higher plateau moduli due to a transition of continuous domain morphology from a soft segment continuous to a fibrous and interconnected stiffer peptide domain. All the polymers exhibited microphase separated morphology with nanofibrous or ribbon-like structures. It is observed that fiber aspect ratio and percolation were influenced by the peptide secondary structure and the weight fraction. [Preview Abstract] |
Thursday, March 6, 2014 2:54PM - 3:06PM |
W11.00003: Zwitterionic Hydrogel-Biopolymer Assembly towards Biomimetic Superlubricants Raymond Seekell, Elaine Zhu One superlubricant in nature is the synovial fluid (SF), comprising of a high molecular weight polysaccharide, hyaluronic acid (HA), and a globule protein, lubricin. In this bio-inspired materials research, we have explored hydrogel particles to mimic lubricin as a ``ball-bearing'' and control their interaction with the viscoelastic HA matrix. Biocompatible poly(N-[2-(Methacyloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide) (PMSA) hydrogel particles are synthesized to examine the electrostatic induced assembly of PMSA-HA supramolecular complexes in aqueous solutions. Fluorescence microscopy and rheology experiments have characterized the tunable network structure and viscoelastic properties of PMSA-HA aggregates by HA concentration and ionic conditions in aqueous solution. When being grafted to a solid surface, the PMSA-HA composite thin film exhibits superior low biofouling and friction performance, suggesting great promises as artificial superlubricants. [Preview Abstract] |
Thursday, March 6, 2014 3:06PM - 3:18PM |
W11.00004: Metal-coordination: using more of nature's tricks to assemble new soft materials Niels Holten-Andersen Growing evidence supports a critical role of metal-coordination in soft biological material properties such as self-healing, underwater adhesion and autonomous wound plugging. Using bio-inspired metal-coordinating polymers, initial efforts to mimic these properties have shown promise. In addition, with polymer network mechanics dictated by coordinate crosslink dynamics material properties can be easily tuned from visco-elastic fluids to elastic solids. Given their exploitation in desirable material applications in nature, metal-coordinate crosslinking provides an opportunity to advance synthetic polymer materials design. Early lessons from this pursuit are presented. [Preview Abstract] |
Thursday, March 6, 2014 3:18PM - 3:30PM |
W11.00005: Weak Polyelectrolyte-Clay Assemblies: Physical Mechanisms of Biological Response Svetlana Sukhishvili, Svetlana Pavlukhina, Iryna Zhuk We report on a highly efficient, non-leachable antibacterial coating, consisting of an ultrathin nanocomposite hydrogel capable of hosting, protecting and delivering antibiofilm agents in response to bacterial infection. Constructed using layer-by-layer (LbL) deposition of clay nanoplatelets and a weak polyelectrolyte and loaded with an antimicrobial agent (AmA), the coatings was highly resistant to colonization by \textit{Staphylococcus aureus}. The high antibiofilm activity of the coating results from a combination of highly localized, bacteria-triggered AmA release and hydrogel swelling, as well as retention of AmA by clay nanoplatelets. We discuss the dependence of rheological and swelling properties of weak polyelectrolyte-clay assemblies on film thickness, clay platelet orientation and environmental pH. [Preview Abstract] |
Thursday, March 6, 2014 3:30PM - 3:42PM |
W11.00006: Bacillus spores as building blocks for stimuli-responsive materials and nanogenerators Ozgur Sahin, Xi Chen Materials that mechanically respond to external chemical stimuli have applications in a wide range of fields. Inspired by biological systems, stimuli-responsive materials that can oscillate, transport fluid, mimic homeostasis, and undergo complex changes in shape have been previously demonstrated. However, the effectiveness of synthetic stimuli-responsive materials in generating work is limited when compared to mechanical actuators. During studies of bacterial sporulation, we have found that the mechanical response of Bacillus spores to water gradients exhibits an energy density of more than 10 MJ/m3, which is two orders of magnitude higher than synthetic water-responsive materials. We also identified mutations that can approximately double the energy density of the spores, and found that spores can self-assemble into dense, submicron-thick monolayers on substrates such as silicon microcantilevers and elastomer sheets, creating self-assembled actuators that can remotely generate electrical power from an evaporating body of water. The energy conversion mechanism of Bacillus spores may facilitate synthetic stimuli-responsive materials with significantly higher energy densities. [Preview Abstract] |
Thursday, March 6, 2014 3:42PM - 3:54PM |
W11.00007: Utilizing Chemo-mechanically Functionalized Oscillating Fins to ``Catch and Release'' Nanoparticles in Binary Flow Ya Liu, Olga Kuksenok, Amitabh Bhattacharya, Yongting Ma, Ximin He, Joanna Aizenberg, Anna Balazs In biomimetics, designing an effective ``catch and release'' device for the selective removal of target species from the surrounding solution is critical for developing autonomous sensors and sorters. Using computer simulations, we model an array of oscillating fins that are tethered on the floor of a microchannel and immersed in a mixture of binary fluid stream and binary nanoparticles. During the oscillation, the fins with the specific chemical wetting reach the upper fluid when they are upright and are entirely immersed within the lower stream when they are tilted. We introduce specific interaction between the fins and particulates in the solution and determine conditions where the oscillating fins can selectively ``catch'' target nanoparticles within the upper fluid stream and then release these particles into the lower stream. We isolate the effects of wetting contact angle between fins and fluid and the mode of fins' oscillations that lead to the efficient extraction of target species from the upper stream and their placement into the lower fluid. These studies provide fundamental insights into the system's complex dynamics and mechanism for detection, separation, and purification of multi-component mixtures. [Preview Abstract] |
Thursday, March 6, 2014 3:54PM - 4:06PM |
W11.00008: Driven translocation of Polymer through a nanopore: effect of heterogeneous flexibility Ramesh Adhikari, Aniket Bhattacharya We have studied translocation of a model bead-spring polymer through a nanopore whose building blocks consist of alternate stiff and flexible segments and variable elastic bond potentials. For the case of uniform spring potential translocation of a symmetric periodic stiff-flexible chain of contour length N and segment length $m$ (mod(N,2m)=0), we find that the end-to-end distance and the mean first passage time (MFPT) have weak dependence on the length $m$. The characteristic periodic pattern of the waiting time distribution captures the stiff and flexible segments of the chain with stiff segments taking longer time to translocate. But when we vary both the elastic bond energy, and the bending energy, as well as the length of stiff/flexible segments, we discover novel patterns in the waiting time distribution which brings out structural information of the building blocks of the translocating chain. [Preview Abstract] |
Thursday, March 6, 2014 4:06PM - 4:18PM |
W11.00009: The role of polyelectrolytes in the stabilization of calcium phosphate nanoparticles for the production of biomimetic materials Daniel Krogstad, Dongbo Wang, Sheng Lin-Gibson The exceptional mechanical properties of bone are a result of the hierarchical assembly of hydroxyapatite and the bone matrix, which is primarily composed of collagen. However, it has been shown that without highly acidic, non-collagenous proteins (NCP), which comprise only a few percent of the total organic material, collagen cannot be mineralized correctly. Although the exact roles of these NCP are unknown, it is believed that they are responsible for the stabilization and transportation of the apatite precursor, amorphous calcium phosphate (ACP). In this work, polyaspartic acid was used as a synthetic analog for NCP and the structure and kinetics of calcium phosphate nanoparticle formation were determined at various concentrations using cryo-TEM and scattering. From this investigation, it was determined that the size and stability of the ACP nanoparticles could be directly controlled by the relative ion and polymer concentrations. Interestingly, at high polymer concentrations, the particles remained suspended in solution even after they transformed from ACP to apatite indicating that the polymers have a strong ability to prevent particle aggregation. Through these results, control over the particle size and stability has been increased which will help in the design and development of biomimetic materials. [Preview Abstract] |
Thursday, March 6, 2014 4:18PM - 4:30PM |
W11.00010: Lipid tail protrusions initiate spontaneous insertion of charged, amphiphilic nanoparticles into lipid bilayers Reid Van Lehn, Maria Ricci, Randy Carney, Kislon Voitchovsky, Francesco Stellacci, Alfredo Alexander-Katz Vesicle fusion is a primary mechanism used to mediate the uptake and trafficking of materials both into and between cells. The pathway of vesicle fusion involves the formation of a lipid stalk in which the hydrophobic core regions of two closely associated bilayers merge. The transition state for stalk formation requires the transient protrusion of hydrophobic lipid tails into solvent; favorable contact between these hydrophobic tails then drives stalk creation. In this work, we use unbiased atomistic molecular dynamics simulations to show that lipid tail protrusions can also induce the insertion of charged, amphiphilic nanoparticles (NPs) into lipid bilayers. As in the case of vesicle fusion, the rate-limiting step for NP-bilayer fusion is the stochastic protrusion of aliphatic lipid tails into solvent and into contact with hydrophobic material in the amphiphilic NP monolayer. We confirm our predictions with experiments on supported lipid bilayers. The strong agreement between simulation and experiments indicates that the pre-stalk transition associated with vesicle fusion may be a general mechanism for the insertion of amphiphilic nano-objects that could be prominent in biological systems given the widespread use of NPs in applications ranging from drug delivery to biosensing. [Preview Abstract] |
Thursday, March 6, 2014 4:30PM - 4:42PM |
W11.00011: Hierarchical assembly of peptoid nanosheets catalyzed by an air-water interface Thomas Haxton, Babak Sanii, Gloria Olivier, Ranjan Mannige, Caroline Proulx, Andrew Cho, Ronald Zuckermann, Stephen Whitelam Peptoids are synthetic analogs of peptides created by moving sidechains from the alpha carbon to the nitrogen. Removing backbone hydrogen bonding and chirality allows for assembly of planar structures driven by sidechain interactions. For instance, when exposed to and subsequently compressed at an air-water interface, amphiphilic peptoids adsorb into monolayers, reversibly compress, and finally collapse into free-floating bilayer nanosheets. We use X-ray spectroscopy, coarse-grained modeling, and analytic theory to investigate the mechanisms for structure formation and catalytic activity at the air-water interface. We find that affinity for the air-water interface and neighboring polymers lowers the free energy barrier for nanosheet formation, creates substantial in-plane order in the monolayer phase, and open voids amenable to further adsorption. The resulting monolayer exhibits residue-scale in-plane order conserved and augmented by inter-leaf order during collapse into bilayers. [Preview Abstract] |
Thursday, March 6, 2014 4:42PM - 4:54PM |
W11.00012: Ion Transport Characteristics of Individual Single-walled Carbon Nanotubes Mimic Those of Biological Ion Channels Hasti Amiri, Kenneth Shepard, Colin Nuckolls Transmembrane ionic channels play a crucial role in vital cellular activities by regulating the transport of ions and fluid across the cell membrane. Their structural complexity and flexibility as well as their many unique operational features, however, make their investigation extremely difficult. The simple, atomically smooth and well-defined structure of carbon nanotubes (CNTs) provides an excellent template for studying molecular transport at nanoscale. Additionally, CNTs have been suggested as analogues to biological pores since they share several common features such as nanometer size diameter, hydrophobic core and ultrafast water flow. Functionalizing the nanotube entrance can also mimic the selectivity filter of ion channels. In this work, we experimentally study ionic transport through individual single-walled CNTs connecting two fluid reservoirs as a function of pore properties and electrolyte type and concentration. We provide strong evidence that the electrostatic potentials arising from the ionized carboxyl groups at the pore entrance significantly influence the ion permeation in a manner consistent with a simple electrostatic mechanism. Lastly, the similarities of ionic transport mechanisms between individual single-walled CNTs and protein ion channels are discussed. [Preview Abstract] |
Thursday, March 6, 2014 4:54PM - 5:06PM |
W11.00013: Diffusion and Controlled Localized Drug Release from an Injectable Solid Self-Assembling Peptide Hydrogel Jessie E.P. Sun, Brandon Stewart, Sigrid Langhans, Joel P. Stewart, Darrin J. Pochan We use an injectable solid peptide hydrogel (first assembled into a solid hydrogel, can shear-thin flow and immediately reheal on cessation of shear) as a drug delivery vehicle for sustained and active drug release. The triggered intramolecular peptide folding into a beta-hairpin leads to intermolecular assmebly of the peptides into the entangled and branched nanofibrillar hydrogel network responsible for its advantageous rheological properties. The hydrogel is used to encapsulate a highly effective chemotherapeutic, vincristine, with hydrophobic behavior. We show that we are able to constantly maintain drug release in low but still potent concentrations after the shear-thinning injection process. Similarly, the mechanical and morphoogical properties of the gels remains identical after injection. Characterization of the hydrogel construct is through tritiated vincristine release, TEM, confocal microscopy, and in vitro methods. [Preview Abstract] |
Thursday, March 6, 2014 5:06PM - 5:18PM |
W11.00014: Soft hydrogel materials from elastomeric gluten-mimetic proteins Mehran Bagheri, Shane Scott, Fan Wan, Scott Dick, James Harden Elastomeric proteins are ubiquitous in both animal and plant tissues, where they are responsible for the elastic response and mechanical resilience of tissues. In addition to fundamental interest in the molecular origins of their elastic behaviour, this class of proteins has great potential for use in biomaterial applications. The structural and elastomeric properties of these proteins are thought to be controlled by a subtle balance between hydrophobic interactions and entropic effects, and in many cases their characteristic properties can be recapitulated by multi-block protein polymers formed from repeats of short, characteristic polypeptide motifs. We have developed biomimetic multi-block protein polymers based on variants of several elastomeric gluten consensus sequences. These proteins include constituents designed to maximize their solubility in aqueous solution and minimize the formation of extended secondary structure. Thus, they are examples of elastic intrinsically disordered proteins. In addition, the proteins have distributed tyrosine residues which allow for inter-molecular crosslinking to form hydrogel networks. In this talk, we present experimental and simulation studies of the molecular and materials properties of these proteins and their assemblies. [Preview Abstract] |
Thursday, March 6, 2014 5:18PM - 5:30PM |
W11.00015: Controlled-surface-wettability-based fabrication of hydrogel substrates with matrix tethering density variations Md. Mahmudur Rahman, Donghee Lee, Divya Bhagirath, Xiangshan Zhao, Vimla Band, Sangjin Ryu It is widely accepted that cells behave differently responding to the stiffness of extracellular matrix (ECM). Such observations were made by culturing cells on hydrogel substrates of tunable stiffness. However, it was recently proposed that cells actually sense how strongly they are tethered to ECM, not the local stiffness of ECM. To investigate the hypothesis, we develop constant-stiffness hydrogel substrates with varying matrix tethering density (the number of anchoring sites between the gel and the ECM protein molecules). We fabricate polyacrylamide gel of static stiffness and conjugate ECM proteins to the gel using a cross-linker. When treating the gel with the cross-linker, we control positioning of cross-linker solutions with different concentrations using superhydrophobic barriers on glass, functionalize the gel by pressing it to the aligned cross-linker solutions, and conjugate an ECM protein of constant concentration to the gel. We expect that the gel will be functionalized to different degrees depending on the concentration distribution of the cross-linker and thus the gel will have variations of matrix tethering density even with constant ECM protein concentration. [Preview Abstract] |
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