Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session J32: Focus Session: Assembly & Function of Biomimetic & Bioinspired Materials I |
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Sponsoring Units: DMP DPOLY DBIO Chair: Jim de Yoreo, Lawrence Berkeley National Laboratory Room: 340 |
Tuesday, March 19, 2013 2:30PM - 3:06PM |
J32.00001: DILLON MEDAL BREAK
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Tuesday, March 19, 2013 3:06PM - 3:18PM |
J32.00002: Designing ``catch and release'' systems by utilizing functionalized oscillating fins Yongting Ma, Amitabh Bhattacharya, Olga Kuksenok, Ximin He, Joanna Aizenberg, Anna C. Balazs Designing a biomimetic ``catch and release'' device for the selective removal of target species from the surrounding solution is critical for developing many useful sensors and sorters. Via computational modeling, we simulate an array of oscillating fins that are localized on the floor of a microchannel and immersed in a two-fluid stream. The fins reach the upper fluid when they are upright and are located entirely within the lower stream when they are tilted. We introduce specific adhesive interactions between the fins and particulates in the solution and determine conditions where the oscillating fins can selectively bind (``catch'') target nanoparticles within the upper fluid stream and then release these particles into the lower stream. Using our hybrid computational approach, which combines the lattice Boltzmann model for binary fluids and a Brownian dynamics model for the nanoparticles, we isolate systems parameters (e.g., frequency and amplitude of fins' oscillations) that lead to the efficient extraction of target species from the upper stream and placement into the lower fluid. Our findings provide fundamental insights into the system's complex dynamics, as well as a unique solution for detection, separation, and purification of multi-component mixtures. [Preview Abstract] |
Tuesday, March 19, 2013 3:18PM - 3:30PM |
J32.00003: The Study of Lipid-Based Nanodis as a Novel Carrier for Hydrophobic Cargo Ying Liu, Mu-Ping Nieh, Hyunsook Jang, Yike Huang, Yong Wang Monodispersed nanodiscs can be self-assembled in an aqueous mixture of 1,2-dipalmitoyl-sn-glycero- 3-phosphocholine (DPPC), 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC) and 1,2-dipalmitoyl-sn-glycero-3-phospho- (1'-rac-glycerol) (sodium salt)(DPPG) and 1,2-distearoyl-sn-glycero- 3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-2000] (ammonium salt) (PEGylated DSPE). The stability of discs and the effect of polyethylene glycol (PEG), including molecular chain length and concentration, on the disc morphology are characterized by dynamic light scattering, negative staining transmission electron microscopy and small angle neutron scattering. Fluorescent Spectroscopy is used to study the loading capacity of a hydrophobic dye, Nile red entrapped in the nanodiscs. The exchanging of Nile red between discs will be correlated with the release of hydrophobic molecule. In-vitro studies indicate that the non-specific binding of these Nile-red loaded nanodiscs to the CCRF-CEM cells is greatly reduced upon the addition of PEGylated DSPE. The system has a potential application of delivering hydrophobic molecules. The incorporation of targeting molecules with the nanodiscs is also investigated. [Preview Abstract] |
Tuesday, March 19, 2013 3:30PM - 3:42PM |
J32.00004: Harnessing Fluid-Driven Vesicles to Pick Up and Drop Off Janus Particles Xin Yong, Isaac Salib, Emily Crabb, Nicholas Moellers, Gerald McFarlin, Olga Kuksenok, Anna Balazs Using dissipative particle dynamics (DPD) simulations, we model the interaction between nanoscopic lipid vesicles and Janus nanoparticles in the presence of an imposed flow. Both the vesicle and Janus nanoparticles are localized on a hydrophilic substrate and immersed in a hydrophilic solution. The fluid-driven vesicle successfully picks up Janus particles on the substrate and transports these particles as cargo along the surface. The vesicle can carry up to four particles as its payload. Hence, the vesicles can acts as nanoscopic ``vacuum cleaners'', collecting nanoscopic debris localized on the floors of the fluidic devices. Importantly, these studies reveal how an imposed flow can facilitate the incorporation of nanoparticles into nanoscale vesicles. With the introduction of a hydrophobic domain on the substrate, the vesicles can also robustly drop off and deposit the particles on the surface. The controlled pickup and delivery of nanoparticles via lipid vesicles can play an important step in the bottom-up assembly of these nanoparticles within small-scale fluidic devices. [Preview Abstract] |
Tuesday, March 19, 2013 3:42PM - 3:54PM |
J32.00005: Cob-Weaving Spiders Design Attachment Discs Differently for Locomotion and Prey Capture Vasav Sahni, Jared Harris, Todd Blackledge, Ali Dhinojwala Spiders' cobwebs ensnare both walking and flying prey. While the scaffolding silk can entangle flying insects, gumfoot silk threads pull walking prey off the ground and into the web. Therefore, scaffolding silk needs to withstand the impact of the prey, whereas gumfoot silk needs to easily detach from the substrate when contacted by prey. Here, we show that spiders accomplish these divergent demands by creating attachment discs of two distinct architectures using the same pyriform silk. A ``staple-pin'' architecture firmly attaches the scaffolding silk to the substrate and a previously unknown ``dendritic'' architecture weakly attaches the gumfoot silk to the substrate. Gumfoot discs adhere weakly, triggering a spring-loaded trap, while the strong adhesion of scaffolding discs compels the scaffolding threads to break instead of detaching. We describe the differences in adhesion for these two architectures using tape-peeling models and design synthetic attachments that reveal important design principles for controlled adhesion. [Preview Abstract] |
Tuesday, March 19, 2013 3:54PM - 4:06PM |
J32.00006: ABSTRACT WITHDRAWN |
Tuesday, March 19, 2013 4:06PM - 4:18PM |
J32.00007: Self-Tailoring of Amphiphilic Block Copolymer Assemblies by Osmotic Pressure Jinhye Bae, Ryan Hayward Compartmentalization is a crucial architectural principle employed by eukaryotic cells, and correspondingly, pathways to assemble multi-compartmental polymeric assemblies are of considerable research interest. We report a study of the self-generation of water-in-oil-in-water (w/o/w) double emulsions with inner droplet sizes of $\sim$ 2-3 micrometers due to the osmotic pressure provided by salts initially dissolved in the organic phase. We show that this process can explain previously mysterious examples of spontaneous emulsion formation, due to the presence of initiator salt impurities within copolymer samples. Further, we harness it to tailor the structures of multiple emulsions, which upon solvent evaporation can yield multi-vesicular structures or hierarchically structured porous films. Such osmotically-driven polymer assemblies may have potential applications in therapeutic, pharmaceutical, cosmetic, and separation technologies. [Preview Abstract] |
Tuesday, March 19, 2013 4:18PM - 4:30PM |
J32.00008: Effect of Intrinsic Twist on Length of Crystalline and Disordered Regions in Cellulose Microfibrils Abdolmadjid Nili, Oleg Shklyaev, Zhen Zhao, Linghao Zhong, Vincent Crespi Cellulose is the most abundant biological material in the world. It provides mechanical reinforcement for plant cell wall, and could potentially serve as renewable energy source for biofuel. Native cellulose forms a non-centrosymmetric chiral crystal due to lack of roto-inversion symmetry of constituent glucose chains. Chirality of cellulose crystal could result in an overall twist.~Competition between unwinding torsional/extensional and twisting energy terms leads to twist induced frustration along fibril's axis. The accumulated frustration could be the origin of periodic disordered regions observed in cellulose microfibrils. These regions could play significant role in properties of~cellulose bundles and ribbons as well as biological implications on plant cell walls.~ We propose a mechanical model based on Frenkel-Kontorova mechanism to investigate effects of radius dependent twist on crystalline size in cellulose microfibrils. Parameters of the model are adjusted according to all-atom molecular simulations. [Preview Abstract] |
Tuesday, March 19, 2013 4:30PM - 4:42PM |
J32.00009: The Effect of Small Molecule Additives on the Self-Assembly and Functionality of Protein-Polymer Diblock Copolymers Carla Thomas, Liza Xu, Bradley Olsen Self-assembly of globular protein-polymer block copolymers into well-defined nanostructures provides a route towards the manufacture of protein-based materials which maintains protein fold and function. The model material mCherry-b-poly(N-isopropyl acrylamide) forms self-assembled nanostructures from aqueous solutions via solvent evaporation. To improve retention of protein functionality when dehydrated, small molecules such as trehalose and glycerol are added in solution prior to solvent removal. With as little as 10 wt\% additive, improvements in retained functionality of 20-60\% are observed in the solid-state as compared to samples in which no additive is present. Higher additive levels (up to 50\%) continue to show improvement until approximately 100\% of the protein function is retained. These large gains are hypothesized to originate from the ability of the additives to replace hydrogen bonds normally fulfilled by water. The addition of trehalose in the bulk material also improves the thermal stability of the protein by 15-20 $^\circ$C, while glycerol decreases the thermal stability. Materials containing up to 50\% additives remain microphase separated, and, upon incorporation of additives, nanostructure domain spacing tends to increase, accompanied by order-order transitions. [Preview Abstract] |
Tuesday, March 19, 2013 4:42PM - 4:54PM |
J32.00010: Material Structure of a Graded Refractive Index Lens in Decapod Squid Jing Cai, Paul Heiney, Alison Sweeney Underwater vision with a camera-type eye that is simultaneously acute and sensitive requires a spherical lens with a graded distribution of refractive index. Squids have this type of lens, and our previous work has shown that its optical properties are likely achieved with radially variable densities of a single protein with multiple isoforms. Here we measure the spatial organization of this novel protein material in concentric layers of the lens and use these data to suggest possible mechanisms of self-assembly of the proteins into a graded refractive index structure. First, we performed small angle x-ray scattering (SAXS) to study how the protein is spatially organized. Then, molecular dynamic simulation allowed us to correlate structure to the possible dynamics of the system in different regions of the lens. The combination of simulation and SAXS data in this system revealed the likely protein-protein interactions, resulting material structure and its relationship to the observed and variable optical properties of this graded index system. We believe insights into the material properties of the squid lens system will inform the invention of self-assembling graded index devices. [Preview Abstract] |
Tuesday, March 19, 2013 4:54PM - 5:06PM |
J32.00011: Phase Transitions in Concentrated Solution Self-Assembly of Globular Protein-Polymer Block Copolymers Christopher Lam, Bradley Olsen The self-assembly of globular protein-polymer bioconjugate block copolymers to form biofunctional nanostructures presents potentially complex behavior due to the tertiary structures and specific interactions of protein blocks. To understand the thermodynamics of these systems, the phase behavior of the model globular protein-polymer block copolymer mCherry-$b$-PNIPAM (mChP) is investigated in concentrated aqueous solution as a function of both concentration and temperature. At low concentrations, mChP forms a homogeneous disordered phase at low temperature and macrophase separates into an ordered conjugate-rich phase and a solvent-rich phase at temperatures above the PNIPAM thermoresponsive transition temperature. mChP solutions undergo a lyotropic, low-temperature ODT and both lyotropic and thermotropic OOTs at high concentration. Similar to coil-coil block copolymers, both coil fraction and solvent selectivity have large effects on the morphologies formed---disordered micelles, hexagonally packed cylinders, lamellae, and perforated lamellae. The order-disorder transition concentration (ODTC) of mChP is minimized for symmetric conjugates, suggesting that repulsive solvent-mediated protein-polymer interactions provide a driving force for self-assembly. [Preview Abstract] |
Tuesday, March 19, 2013 5:06PM - 5:18PM |
J32.00012: Interfacial curvature effects in the self-assembly and responsiveness in polypeptide-based triblock copolymers Daniel Savin, Jacob Ray, Ashley Johnson, Jack Ly, Charles Easterling The self-assembly of amphiphilic block copolymers is dictated primarily by the balance between the hydrophobic core volume and the hydrophilic corona.~ In these studies, ABA and BAB triblock copolymers containing poly(lysine) (PK) and poly(propylene oxide) were synthesized and their solution properties studied using dynamic light scattering, circular dichroism spectroscopy and transmission electron microscopy.~ This talk will present some recent studies in solution morphology transitions that occur in these materials as a result of the helix-coil transition and associated charge-charge interactions. The solution properties and responsiveness of these novel materials will be discussed in terms of their ability to encapsulate and deliver cancer therapeutics. [Preview Abstract] |
Tuesday, March 19, 2013 5:18PM - 5:30PM |
J32.00013: Amphiphilic Spider Silk-Like Block Copolymers with Tunable Physical Properties and Morphology for Biomedical Applications Wenwen Huang, Sreevidhya Krishnaji, David Kaplan, Peggy Cebe Silk-based materials are important candidates for biomedical applications because of their excellent biocompatibility and biodegradability. To generate silk amphiphilic biopolymers with potential use in guided tissue repair and drug delivery, a novel family of spider silk-like block copolymers was synthesized by recombinant DNA technology. Block copolymer thermal properties, structural conformations, protein-water interactions, and self-assembly morphologies were studied with respect to well controlled protein amino acid sequences. A theoretical model was used to predict the heat capacity of the protein and protein-water complex. Using thermal analysis, two glass transitions were observed: Tg1 is related to conformational changes caused by bound water removal, while Tg2 ($>$Tg1) is the glass transition of dry protein. Real-time infrared spectroscopy and X-ray diffraction confirmed that different secondary structural changes occur during the two Tg relaxations. Using scanning electron microscopy, fibrillar networks and hollow vesicles are observed, depending on protein block copolymer sequence. This study provides a deeper understanding of the relationship between protein physical properties and amino acid sequence, with implications for design of other protein-based materials. [Preview Abstract] |
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