Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session R31: Focus Session: Assembly & Function of Biomimetic & Bioinspired Materials II |
Hide Abstracts |
Sponsoring Units: DMP DPOLY DBIO Chair: Mark Stevens, Sandia National Laboratories Room: 339 |
Wednesday, March 20, 2013 2:30PM - 2:42PM |
R31.00001: Self-assembly of elastin-like polypeptides diblocks into micelles of various morphologies Wafa Hassouneh, Ekaterina Zhulina, Michael Rubinstein, Ashutosh Chilkoti Elastin-like polypeptides (ELPs) are a promising class of biopolymers for biomedical applications such as drug delivery. These biopolymers are composed of the pentapeptide repeat VPGXG, where X is any amino acid except proline. ELP diblocks, each block of which contains a different X residue composition, self-assemble into spherical micelles for certain lengths and ratios of hydrophobic and hydrophilic blocks. Our objective is to study morphological transitions, from spherical to cylindrical to lamellar structures, for the ELP diblock system by examining a wider range of diblock ratios and lengths. We employ a model that derives the phase boundaries of spherical-to-cylindrical and cylindrical-to-lamellar by balancing the corona elastic energy, the core elastic energy and the surface tension between the core and corona. Theoretical predictions from the model are compared with experimental results by independently measuring 1) surface tension at the core-corona interface and 2) second virial coefficient of the hydrophilic block monomer-monomer interaction. We report the measurements of these parameters and the initial comparison of experimental and theoretical phase boundaries for the ELP diblock system. [Preview Abstract] |
Wednesday, March 20, 2013 2:42PM - 2:54PM |
R31.00002: Design of biomimetic super-lubricants by hydrogel-biopolymer aggregates Raymond Seekell, Rachel Dever, Yingxi Zhu Inspired by the superb lubricity of natural synovial fluids for moving articular cartilage joints, we investigate a biomimetic artificial lubricant based on a hydrogel-biopolymer mixture with optimized rheological properties at a microscopic level. Specifically, we examine the structure and rheological relationship of stimuli-responsive poly (N-isopropylacrylamide) (PNIPAM) hydrogel added with hyaluronic acid (HA) to simulate the complexes of HA with a globule protein, lubricin, which are credited as the two key lubricious constituents in natural synovial fluids. By combined microscopic structural characterization and rheology measurement, we tune the rheological and frictional behaviors of HA solutions by optimizing the content of added micron-sized PNIPAM hydrogel particles to form stable PNIPAM-HA network. In a recent work on using zwitterionic hydrogel particles instead of negatively charged PNIPAM, comparable structure and rheological properties of hydrogel-HA aggregates are observed, which may give insight to design new biocompatible lubricants and lubricious coatings for medical ramification. [Preview Abstract] |
Wednesday, March 20, 2013 2:54PM - 3:06PM |
R31.00003: Forming Self-rotating Pinwheels from Assemblies of Oscillating Gels Debabrata Deb, Pratyush Dayal, Olga Kuksenok, Anna C. Balazs By using computational modeling, we show that millimeter-sized polymer gels undergoing the self-oscillating Belousov-Zhabotinsky (BZ) reaction not only respond to a chemical signal from the surrounding solution, but also emit this signal and thus, multiple neighboring gel pieces can spontaneously self-aggregate into macroscopic objects. We also show that the gels' coordinated motion can be regulated by light, allowing us to achieve selective self-aggregation and control over the shape of the gel aggregates, as well as reconfiguration of the entire structure. We find that the aggregated gel pieces can rotate as a unit. For example, four millimeter-sized gels can associate into a structure that resembles a pinwheel and then undergo spontaneous, autonomous rotation. With eight gel pieces, the system can form two pinwheels, which communicate and coordinate their motion. Notably, this communication can be controlled with light. In particular, light can be used to translate the pinwheels and to control the relative rotation of two such clusters. These findings reveal a new route for creating dynamically reconfigurable materials using self-oscillating BZ gels where reconfiguration is achieved by using auto-chemotatic behavior of the gels, and also applying external light. [Preview Abstract] |
Wednesday, March 20, 2013 3:06PM - 3:18PM |
R31.00004: Repairable, nanostructured biomimetic hydrogels M. Firestone, S. Brombosz, S. Grubjesic Proteins facilitate many key cellular processes, including signal recognition and energy transduction. The ability to harness this evolutionarily-optimized functionality could lead to the development of protein-based systems useful for advancing alternative energy storage and conversion. The future of protein-based, however, requires the development of materials that will stabilize, order and control the activity of the proteins. Recently we have developed a synthetic approach for the preparation of a durable biomimetic chemical hydrogel that can be reversibly swollen in water. The matrix has proven ideal for the stable encapsulation of both water- and membrane-soluble proteins. The material is composed of an aqueous dispersion of a diacrylate end-derivatized PEO-PPO-PEO macromer, a saturated phospholipid and a zwitterionic co-surfactant that self-assembles into a nanostructured physical gel at room temperature as determined by X-ray scattering. The addition of a water soluble PEGDA co-monomer and photoinitator does not alter the self-assembled structure and UV irradiation serves to crosslink the acrylate end groups on the macromer with the PEGDA forming a network within the aqueous domains as determined by FT-IR. More recently we have begun to incorporate reversible crosslinks employing Diels-Alder chemistry, allowing for the extraction and replacement of inactive proteins. The ability to replenish the materials with active, non-denatured forms of protein is an important step in advancing these materials for use in nanostructured devices [Preview Abstract] |
Wednesday, March 20, 2013 3:18PM - 3:30PM |
R31.00005: Morphogenesis in Belousov-Zhabotinsky microdroplets Ning Li, Nathan Tompkins, Camille Girabawe, Irving Epstein, Seth Fraden We present experimental evidence for the six cases Alan Turing predicted using linear stability analysis in his 1952 paper ``The chemical basis of morphogenesis'' in our reaction diffusion system. Our experimental system consists of a microfluidically generated microemulsion consisting of Ru(bipy)3 catalyzed light sensitive BZ aqueous droplets which are diffusively coupled through oil gaps. We observed that some droplets grow and others shrink due to the unequal consumption of chemicals in the droplets which leads to an osmotic pressure change, as Turing predicted in his paper. The initial and boundary conditions of our system were controlled by programmable illumination via the light sensitive catalyst Ru(bipy)3. Simulation and linear stability analysis were performed and compared with the experiments. [Preview Abstract] |
Wednesday, March 20, 2013 3:30PM - 3:42PM |
R31.00006: Dynamic Elasticity Model of Resilin Biopolymers Xiao Hu, Solomon Duki Resilin proteins are `super elastic rubbers' in the flight and jumping systems of most insects, and can extend and retract millions of times. Natural resilin exhibits high resilience (\textgreater\ 95{\%}) under high-frequency conditions, and could be stretched to over 300{\%} of its original length with a low elastic modulus of 0.1-3 MPa. However, insight into the underlying molecular mechanisms responsible for resilin elasticity remains undefined. We report on the dynamic structure transitions and functions of full length resilin from fruit fly (D. melanogaster CG15920) and its different functional domains. A dynamic computational model is proposed to explain the super elasticity and energy conversion mechanisms of resilin, providing important insight into structure-function relationships for resilins, as well as other elastomeric proteins. A strong beta-turn transition was experimentally identified in the full length resilin and its non-elastic domains (Exon III). Changes in periodic long-range order were demonstrated during this transition, induced either by thermal or mechanical inputs, to confirm the universality of proposed mechanism. Further, this model offers new options for designing protein-based biopolymers with tunable material applications. [Preview Abstract] |
Wednesday, March 20, 2013 3:42PM - 3:54PM |
R31.00007: Stretching silk-elastin-like peptide polymers induces nucleation of amyloid nanofibers: Mechanistic study using time-lapse lateral force microscopy Nitinun Varongchayakul, Trina Quabili, Sara Johnson, Joonil Seog We studied the nucleation mechanism of silk-elastin-like peptide (SELP) nanofibers using lateral force microscopy. When a single line was repeatedly scanned on SELP coated mica surface, a sudden height increase was observed, indicating that the nucleus of amyloid fiber was formed during lateral scanning. The detailed analysis of frictional force profiles revealed that increase of frictional force was followed by a nucleus formation. The profile of increased frictional force was well fitted with exponential function, suggesting that AFM tip stretches multiple SELP molecules to the scanning direction. The probability of nucleus formation was highly dependent on the maximum level of increased frictional force, implying that the highly stretched SELPs are more likely to form nucleus for nanofiber growth. [Preview Abstract] |
Wednesday, March 20, 2013 3:54PM - 4:30PM |
R31.00008: Biopolymer networks in cells Invited Speaker: David Weitz This talk will discuss the role of biopolymer networks in cells. We probe their properties through measurements of fluctuating motions of particles within the cell. These motions have many similarities to thermal motion and, in fact, are often misinterpreted in the context of passive microrheology. Here, we demonstrate that the motion is, instead, driven by the presence of molecular motors within the cell, and we show how this motion can be interpreted quantitatively to determine the nature of the fluctuating forces in the cell due to the molecular motors. [Preview Abstract] |
Wednesday, March 20, 2013 4:30PM - 4:42PM |
R31.00009: Mechanisms and Dynamics of Collagen Assembly Jinhui Tao, Raymond Friddle, Debin Wang, Jim De Yoreo Collagen is the major structural protein of bone, dentine and it template the nucleation of biomineral phases. Both collagen conformation and architecture on substrate are critical for its function. We studied the mechanism of collagen I assembly on mica by in-situ AFM. At acidic condition, assembled architecture evolved from random fibers to co-aligned fibers and finally to bundles as the K$^{+}$ concentration increased from 100 to 300mM. XPS and NEXAFS showed the concentration of K$^{+}$ within the collagen layer increased and the intensity of absorption peak due to $\pi ^{\ast }$(C$=$O) resonance decreased with higher K$^{+\, }$concentration. The magnitude of collagen-mica (C-M) and collagen-collagen (C-C) interactions were measured by dynamic force spectroscopy. The free energy $\Delta $G$_{b}$ for C-M and C-C at 200mM K$^{+\, }$were 13.7kT and 1.4kT, while $\Delta $G$_{b}$ at 300mM K$^{+}$ were 5.7kT and 12.3kT, respectively. The switch from co-aligned fibers to 3D bundles is driven by the reversal in the magnitude of C-C and C-M interactions. Our results indicate K$^{+}$ complex with C$=$O of collagen and its effect on the strength of collagen-collagen bridging is the likely source of architecture control. [Preview Abstract] |
Wednesday, March 20, 2013 4:42PM - 4:54PM |
R31.00010: Atomistic modeling of bio-based polymeric fibers In-Chul Yeh, B. Christopher Rinderspacher, Jan W. Andzelm, LaShonda T. Cureton, John La Scala We performed molecular dynamics simulations on the amorphous phase of two bio-based polymers, poly (butylene furanamide) and poly (hexamethylene furanamide). Simulations of corresponding petroleum-based polymers, nylon 4, 6 and nylon 6, 6, were also performed. Glass transition temperatures estimated from a series of simulations were in good agreement with experimental measurements. Stress-strain relationships under uniaxial deformation were also analyzed. Bio-based polymers show higher glass transition temperatures and comparable yield points despite having overall weaker hydrogen bonds compared with their counterparts nylons. This result suggests that the furan ring plays an important role in the thermodynamic and mechanical properties of bio-based polymers. [Preview Abstract] |
Wednesday, March 20, 2013 4:54PM - 5:06PM |
R31.00011: Structural Properties of Silk Electro-Gels A.P. Tabatabai, J.S. Urbach, D.L. Blair, D.L. Kaplan The interest in \textit{Bombyx Mori} silk emerges from its biocompatibility and its structural superiority to synthetic polymers. Our particular interest lies in understanding the capabilities of silk electro-gels because of their reversibility and tunable adhesion. We create an electro-gel by applying a DC electric potential across a reconstituted silk fibroin solution derived directly from \textit{Bombyx Mori} cocoons. This process leads to the intermolecular self-assembly of fibroin proteins into a weak gel. In this talk we will present our results on the effects of applied shear on electro-gels. We quantify the structural properties while dynamically imaging shear induced fiber formation; known as fibrillogenesis. It is observed that the mechanical properties and microstructure of these materials are highly dependent on shear history. We will also discuss the role of surface modification, through micro-patterning, on the observed gel structure. Our results provide an understanding of both the viscoelastiticity and microstucture of reconstituted silks that are being utilized as tissue scaffolds. [Preview Abstract] |
Wednesday, March 20, 2013 5:06PM - 5:18PM |
R31.00012: Neural Stimulation via Fractal Electrodes Rick Montgomery, William Watterson, Ian Pilgrim, Kurtis Fairley, Darren Johnson, Heiner Linke, Richard Taylor A host of physical phenomena exhibit fractal geometry and benefit from its enhanced properties, which can include large surface area-to-volume ratios and high network connectivity. These properties are exploited in a fractal electrode designed for neural stimulation and recording. Presented are electric field studies of a fractal electrode with an emphasis on applications in retinal implants. [Preview Abstract] |
Wednesday, March 20, 2013 5:18PM - 5:30PM |
R31.00013: DFT-based prediction of geometric and thermodynamic parameters in the ATP to ADP hydrolysis reaction Mark C. Palenik, Jorge H. Rodriguez Studying covalent (chemical) and noncovalent (physical) mechanisms as well as key structural variations associated with ATP $\rightarrow$ ADP hydrolysis is of interest for understanding a multitude of biophysical and biochemical cellular processes. We have studied geometric variations of the ATP and ADP molecules during their hydrolysis reaction using density functional theory (DFT) with an implicit solvation model. We have computed the change in free energy, $\Delta$G, associated with the hydrolysis reaction and established relationships between key geometric parameters and thermodynamic properties. Our computed values for $\Delta$G were found in good agreement with available experimental data for two different sets of geometric conformations. A link is suggested between these values for $\Delta$G and changes in geometry of the ADP molecule. Of methodological and computational interest, we also determined that, while the conductor-like solvation model in the framework of the polarizable continuum model (C-PCM) was capable of producing biochemically meaningful geometries for ATP and ADP, it also displayed a strong preference for binding between the $H^+$ and $PO_4^{2-}$ ions formed during hydrolysis. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700