Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session C37: Physics of Bioinspired Materials I |
Hide Abstracts |
Sponsoring Units: GSOFT DBIO DPOLY Chair: Qiming Wang, University of Southern California Room: 340 |
Monday, March 14, 2016 2:30PM - 2:42PM |
C37.00001: Condensation on Slippery Asymmetric Bumps Kyoo-Chul Park, Philseok Kim, Joanna Aizenberg Controlling dropwise condensation by designing surfaces that enable droplets to grow rapidly and be shed as quickly as possible is fundamental to water harvesting systems, thermal power generation, distillation towers, etc. However, cutting-edge approaches based on micro/nanoscale textures suffer from intrinsic trade-offs that make it difficult to optimize both growth and transport at once. Here we present a conceptually different design approach based on principles derived from Namib desert beetles, cacti, and pitcher plants that synergistically couples both aspects of condensation and outperforms other synthetic surfaces. Inspired by an unconventional interpretation of the role of the beetle's bump geometry in promoting condensation, we show how to maximize vapor diffusion flux at the apex of convex millimetric bumps by optimizing curvature and shape. Integrating this apex geometry with a widening slope analogous to cactus spines couples rapid drop growth with fast directional transport, by creating a free energy profile that drives the drop down the slope. This coupling is further enhanced by a slippery, pitcher plant-inspired coating that facilitates feedback between coalescence-driven growth and capillary-driven motion. We further observe an unprecedented six-fold higher exponent in growth rate and much faster shedding time compared to other surfaces. We envision that our fundamental understanding and rational design strategy can be applied to a wide range of phase change applications. [Preview Abstract] |
Monday, March 14, 2016 2:42PM - 2:54PM |
C37.00002: Long-lived Multifunctional Superhydrophobic Heterostructure via Molecular Self-supply Yongfeng Huang, Sheng Meng Superhydrophobic (SHO) surfaces with a large contact angle ($\ge $150°) and low sliding angle (\textless 10°) are highly desirable in both fundamental science and myriad applications. Current approaches to fabricate such surfaces require calcinating at high temperatures, tedious and time-consuming treatments, toxic chemicals, and/or processing with intricate instruments. Long-duration SHO surfaces are even more challenging due to easy contamination by organic pollutants in dry conditions. To overcome these difficulties we design a simple approach via self-supplying of low surface tension chemicals to nanoparticles to fabricate multifunctional SHO heterostructures. Our method features room temperature, rapid processing, with environment-friendly raw materials. With multiple functions such as photocatalysis and transparency SHO surfaces extend their lifetime and enable self-sustaining environment maintenance. [Preview Abstract] |
Monday, March 14, 2016 2:54PM - 3:06PM |
C37.00003: Biphilic Surfaces for Enhanced Water Collection from Humid Air Jason Benkoski, Konstantinos Gerasopoulos, William Luedeman Surface wettability plays an important role in water recovery, distillation, dehumidification, and heat transfer. The efficiency of each process depends on the rate of droplet nucleation, droplet growth, and mass transfer. Unfortunately, hydrophilic surfaces are good at nucleation but poor at shedding. Hydrophobic surfaces are the reverse. Many plants and animals overcome this tradeoff through biphilic surfaces with patterned wettability. For example, the Stenocara beetle uses hydrophilic patches on a superhydrophobic background to collect fog from air. Cribellate spiders similarly collect fog on their webs through periodic spindle-knot structures. In this study, we investigate the effects of wettability patterns on the rate of water collection from humid air. The steady state rate of water collection per unit area is measured as a function of undercooling, angle of inclination, water contact angle, hydrophilic patch size, patch spacing, area fraction, and patch height relative to the hydrophobic background. We then model each pattern by comparing the potential and kinetic energy of a droplet as it rolls downwards at a fixed angle. The results indicate that the design rules for collecting fog differ from those for condensation from humid air. [Preview Abstract] |
Monday, March 14, 2016 3:06PM - 3:18PM |
C37.00004: Transition dynamics from macro- to micro-phase separation in asymmetric lipid bilayers Shunsuke Shimobayashi, Masatoshi Ichikawa, Takashi Taniguchi In general, phase separation in binary liquid mixtures completes by relaxation below the transition temperature. The coarsening dynamics to complete phase separation have been extensively investigated in binary mixture systems. In contrast, the reverse dynamics from macro- to micro-phase separation remains poorly understood because no appropriate experiments and models exist for investigating this phenomenon. In this talk, we present the direct observations of morphological transitions from macro- to micro-phase separation using micrometer-sized asymmetric lipid vesicles exposed to externally added glycolipids (GM1:monosialotetrahexosylganglioside). The transition occurs via stripe morphology as a metastable state. During the transition, monodisperse micro domains emerge through repeated scission events of the stripe domains. Moreover, we numerically confirmed the transitions by the time-dependent Ginzburg-Landau model, which describes phase separation and bending elastic membrane. Numerical results suggest crucial roles of the local spontaneous curvature induced by the local asymmetric lipid composition. [Preview Abstract] |
Monday, March 14, 2016 3:18PM - 3:30PM |
C37.00005: Bio-inspired design of geometrically interlocked 3D printed joints. S Kumar, Noel Oliva The morphology of the adhesive-adherend interface significantly affects the mechanical behavior of adhesive joints. As seen in some biocomposites like human skull, or the nacre of some bivalve molluscs' shells, a geometrically interlocking architecture of interfaces creates toughening and strengthening mechanisms enhancing the mechanical properties of the joint. In an attempt to characterize this mechanical interlocking mechanism, this study is focused on computational and experimental investigation of a single-lap joint with a very simple geometrically interlocked interface design in which both adherends have a square waveform configuration of the joining surfaces. This square waveform configuration contains a positive and a negative rectangular teeth per cycle in such a way that the joint is symmetric about the mid-bondlength. Both physical tests performed on 3D printed prototypes of joints and computational results indicate that the joints with square waveform design have higher strength and damage tolerance than those of joints with flat interface. In order to identify an optimal design configuration of this interface, a systematic parametric study is conducted by varying the geometric and material properties of the non-flat interface. [Preview Abstract] |
Monday, March 14, 2016 3:30PM - 3:42PM |
C37.00006: Multiobjective topology optimization of trabecular Bone Structure in the spine and the femur: Implications for biomimcry Ahmed Elbanna, Darin Peetz Bone is classically considered to be a self-optimizing structure in accordance with Wolff's law. However, while the structure's ability to adapt to changing stress patterns has been well documented, whether it is fully optimal for compliance is less certain (Sigmund, 2002). Given the complexity of many biological systems, it is expected that this structure serves several purposes. We present a multi-objective topology optimization formulation for trabecular bone in the human body at two locations: the vertebrae and the femur. We account for the effect of different conflicting objectives such as maximization of stiffness, maximization of surface area, and minimization of buckling susceptibility. Our formulation enables us to determine the relative role of each of these objective in optimizing the structure. Moreover, it provides an opportunity to explore what structural features have to evolve to meet a certain objective requirements that may have been absent otherwise. For example, inclusion of stability considerations introduce numerous horizontal and diagonal members in the topology in the case of human vertebrae under vertical loading. However, the stability is found to play a lesser role in the case of the femur bone optimization. Our formulation enables investigation of bone adaptation at different locations of the body as well as under different loading and boundary conditions (e.g. healthy and diseased discs for the case of the spine). We discuss the implications of our findings on developing design rules for bio-inspired and bio-mimetic architectured materials. [Preview Abstract] |
Monday, March 14, 2016 3:42PM - 3:54PM |
C37.00007: Dynamics of spider glue adhesion: effect of surface energy and contact area Gaurav Amarpuri, Yizhou Chen, Todd Blackledge, Ali Dhinojwala Spider glue is a unique biological adhesive which is humidity responsive such that the adhesion continues to increase upto 100\% relative humidity (RH) for some species. This is unlike synthetic adhesives that significantly drop in adhesion with an increase in humidity. However, most of adhesion data reported in literature have used clean hydrophilic glass substrate, unlike the hydrophobic, and charged insect cuticle surface that adheres to spider glue in nature. Previously, we have reported that the spider glue viscosity changes over five orders of magnitude with humidity. Here, we vary the surface energy and surface charge of the substrate to test the change in \textit{Larnioides cornutus} spider glue adhesion with humidity. We find that an increase in both surface energy and surface charge density increases the droplet spreading and there exists an optimum droplet contact area where adhesion is maximized. Moreover, spider glue droplets act as reusable adhesive for low energy hydrophobic surface at the optimum humidity. These results explain why certain prey are caught more efficiently by spiders in their habitat. The mechanism by which spider species tune its glue adhesion for local prey capture can inspire new generation smart adhesives. [Preview Abstract] |
Monday, March 14, 2016 3:54PM - 4:06PM |
C37.00008: Understanding Cell Shape Phenotypes Associated with Stem Cell Differentiation Induced by Topographical Cues of Nanofiber Microenvironment. Desu Chen, Sumona Sarkar, Wolfgang Losert It is increasingly important to understand cell responses to bioinspired material structures and topographies designed to guide cell functional alterations. In this study, we investigated association between early stage cell morphological response and osteogenic differentiation of human bone marrow stromal cells (hBMSCs) induced by poly($\varepsilon $-caprolactone) (PCL) nanofiber scaffolds (PCL-NF). Accounting for both multi-parametric complexity and biological heterogeneity, we developed an analysis framework based on support vector machines and a multi-cell level averaging method (supercell) to determine the most pronounced cell shape features describing shape phenotypes of cells in PCL-NF compared to cells on flat PCL films. We found that smaller size and more dendritic shape were the major morphological responses of hBMSCs to PCL-NF on day 1 of cell culture. Further, we investigated the shape phenotypes of hBMSCs in PCL-NF of different fiber densities to monitor the transition between 2-D and 3-D topographies. We tracked the genotypic, phenotypic and morphological responses of hBMSCs to different fiber densities at multiple time points to identify correlations between hBMSCs differentiation and early stage morphology in PCL-NF scaffolds. [Preview Abstract] |
Monday, March 14, 2016 4:06PM - 4:18PM |
C37.00009: Exploring elasticity and energy dissipation in mussel-inspired hydrogel transient networks Scott Grindy, Robert Learsch, Niels Holten-Andersen Dynamic, reversible crosslinks have been shown to specifically control the mechanical properties of a wide variety of mechanically tough and resilient biomaterials. We have shown that reversible histidine-metal ion interactions, known to contribute to the strong mechanical properties and self-healing nature of mussel byssal threads, can be used to control and engineer the temporally-hierarchical mechanical properties of model hydrogels orthogonally from the spatial structure of the material. Here, we explore the scaling relationships in our model networks to further inform our abilities to control the relative elasticity and energy dissipation on hierarchical timescales. Scaling arguments suggest that the elasticity is dominated by long-range entanglements, while the dissipation is controlled by the exchange kinetics of the transient crosslinks. Further, we show that by using UV light, we can further control the viscoelastic properties of our mussel-inspired hydrogels \textit{in situ}. This process opens the door for creating biocompatible hydrogel materials with arbitrary spatial control over their viscoelastic mechanical properties. Overall, we show that by understanding the interplay between bio-inspired dynamic crosslinks and soft matter physics allows us to rationally design high-strength hydrogels for specific states of dynamic loading. [Preview Abstract] |
Monday, March 14, 2016 4:18PM - 4:30PM |
C37.00010: Toughening elastomers using mussel-inspired catechol-metal coordination complexes Emmanouela Filippidi, Thomas Christiani, Megan Valentine, J. Herbert Waite, Jacob Israelachvili, Kollbe Ahn Amorphous, covalently-linked elastomers possess excellent reversible extensibility and high failure strain compared to other materials. However, by nature, the large deformability compromises the Young's modulus and the toughness of the elastomer to low values (< 2MPa) and imparts brittle fracture. We employ the mussel-inspired strategy of iron-catechol coordination bonding creating dynamic, reversible cross-links in addition to permanent chemical cross-links in an elastomer used in ambient, dry conditions. This simple additional energy dissipative mechanism results in increased modulus and toughness without affecting the network extensibility, which is based on the covalent network. Control of the chain relaxation time scales can be further tuned using the dynamic bonds, imparting mechanical rate dependent properties to the bulk material. The quantitative understanding of the time scales associated with the chain motion versus the metal coordination may provide another simple and independent control parameter in elastomeric material design. [Preview Abstract] |
Monday, March 14, 2016 4:30PM - 4:42PM |
C37.00011: Bacterial Flagella as a Model Rigid Rod of Tunable Shape Walter Schwenger, Sevim Yardimci, Thomas Gibaud, Henry Snow, Jeff Urbach, Zvonimir Dogic In this research, we study the physical properties of suspensions of bacterial flagella from \textit{Salmonella typhimurium} prepared in a variety of rigid polymorphic shapes. Flagella act as a rigid colloidal particle that can exhibit non-trivial geometry including helices of varying dimensions, straight rods, or a combination of the two in the same filament. By controlling the conditions in which flagella are prepared, the polymorphic shape assumed by the filament can be controlled. Utilizing different polymorphic shapes, we combine results from optical microscopy observations of single filaments with bulk rheological measurements to help understand the role that constituent colloidal geometry plays in complex bulk behavior. [Preview Abstract] |
Monday, March 14, 2016 4:42PM - 4:54PM |
C37.00012: Bio-Inspired Micromechanical Directional Acoustic Sensor William Swan, Fabio Alves, Gamani Karunasiri Conventional directional sound sensors employ an array of spatially separated microphones and the direction is determined using arrival times and amplitudes. In nature, insects such as the Ormia ochracea fly can determine the direction of sound using a hearing organ much smaller than the wavelength of sound it detects. The fly's eardrums are mechanically coupled, only separated by about 1 mm, and have remarkable directional sensitivity. A micromechanical sensor based on the fly's hearing system was designed and fabricated on a silicon on insulator (SOI) substrate using MEMS technology. The sensor consists of two 1 mm$^{\mathrm{2}}$ wings connected using a bridge and to the substrate using two torsional legs. The dimensions of the sensor and material stiffness determine the frequency response of the sensor. The vibration of the wings in response to incident sound at the bending resonance was measured using a laser vibrometer and found to be about 1 $\mu $m/Pa. The electronic response of the sensor to sound was measured using integrated comb finger capacitors and found to be about 25 V/Pa. The fabricated sensors showed good directional sensitivity. In this talk, the design, fabrication and characteristics of the directional sound sensor will be described. [Preview Abstract] |
Monday, March 14, 2016 4:54PM - 5:06PM |
C37.00013: Design of Catch-and-release System by Utilizing Thermo-responsive Gel-Hairpin Composites. Ya Liu, Olga Kuksenok, Ximin He, Anna Balazs Inspired by properties of aptamers that can bind (unbind) to target proteins in their specific hairpin (chain) conformation dependent on external temperature, we use computational modeling to design an effective catch-and-release device by attaching an array of thermo-responsive hairpins to the lower critical solution temperature (LCST) thermo-responsive gels. With an increase in temperature, the polymer network swells and the hairpins can catch the target naroparticles in the upper mixture fluid. As the temperature decreases, the polymer network collapses and the hairpins unfold to a chain conformation, releasing the arrested particles into the lower fluid for collection. We pinpoint the optimal values for obtaining the robust structural changes of the hairpins and explore the effects of the shear flow on the catch-and-release process. Our approach can be utilized for the detection, separation, and sorting of the components within the multi-component mixtures. [Preview Abstract] |
Monday, March 14, 2016 5:06PM - 5:18PM |
C37.00014: TUNABLE ALLOSTERIC BEHAVIOR IN RANDOM SPRING NETWORKS Jason W. Rocks, Nidhi Pashine, Irmgard Bischofberger, Carl P. Goodrich, Sidney R. Nagel, Andrea J. Liu Many proteins and other macromolecules exhibit allosteric behavior in which the binding of a ligand to one site affects the activity at a second distant site. Inspired by this biological process, we present an algorithm to tune disordered spring networks to exhibit allostery-like behavior. When the positions of a pair of nodes at one site in a network are perturbed, we can precisely tune the response of nodes located at another distant site in the system by removing only a small fraction of the bonds. This algorithm can be used to create a wide variety of different response types: response nodes can be located far away from each other, a large number of response sites can be simultaneously controlled, and even multiple independent responses can be tuned into the system. In addition, this algorithm can be generalized to account for bond bending, geometric nonlinearities and nonlinear bond potentials. However, even linear calculations match surprisingly well with macroscopic experimental realizations made by laser cutting or 3D printing. [Preview Abstract] |
Monday, March 14, 2016 5:18PM - 5:30PM |
C37.00015: Mechanisms of branching reactions in melanin formation -- Ab initio quantum engineering approach -- Ryo Kishida, Susan Me\"nez Aspera, Hideaki Kasai Melanin, a pigment found in animals, consists of two types of oligomeric unit: eumelanin and pheomelanin. The color of the skin, the hair, and the eyes is controlled by the ratio of eumelanin/pheomelanin production. Especially, dopachrome and dopaquinone are the precursor molecules of melanin which directly affect the composition of melanin through their branching reactions. Dopachrome is converted into two possible monomers of eumelanin. Dopaquinone can undergo both eumelanin and pheomelanin synthesis. To understand the mechanisms and controlling factors that govern the conversions, reactions of the two molecules are investigated using density functional theory-based first-principles calculations. Our results deepen mechanistic understanding of the reactions and open possibilities to design properties and functions of melanin. In this talk, we will discuss about the competitions of the branching reactions. [Preview Abstract] |
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