Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session H16: Physics of Bio-inspired Materials IIFocus
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Sponsoring Units: GSOFT DBIO Chair: Megan Valentine, University of California, Santa Barbara Room: 275 |
Tuesday, March 14, 2017 2:30PM - 2:42PM |
H16.00001: Probing nonlinear optical coefficients of self-assembled peptide nanotubes Soma Khanra, Kartik Ghosh, Fabio F. Ferreira, Wendel A. Alves, Francesco Punzo, Ping Yu, Suchismita Guha Self-assembled L,L-diphenylalanine (FF) peptide micro/nanotubes represent a class of biomimetic materials with a non-centrosymmetric crystal structure and strong piezoelectricity. The peptide nanotubes synthesized by liquid phase method yield tube lengths in the hundreds of micron range, inner diameters in the few hundred nanometer range, and outer diameters in the 5-15 $\mu $m range. Second harmonic generation (SHG) polarimetry from individual self-assembled FF nanotubes is used to obtain the nonlinear (NLO) optical coefficients as a function of the tube diameter and thermal treatment. The ratio of the shear to the longitudinal component (d$_{\mathrm{15}}$/d$_{\mathrm{33}})$ of the NLO coefficient increases with the diameter of the tubes. One of the transverse components of the nonlinear coefficient is found to be negative, and its magnitude with respect to the longitudinal component increases with the tube diameter. Thermal treatment of individual FF tubes has a similar effect as increasing the diameter of the tubes in SHG polarimetry. Concurrent Raman scattering measurements from individual FF tubes show a distinct change in the low frequency \textasciitilde 100 cm$^{\mathrm{-1}}$ region with the diameter of the tubes, reflecting subtle effects of water. [Preview Abstract] |
Tuesday, March 14, 2017 2:42PM - 2:54PM |
H16.00002: Non-equilibrium, motor-driven active DNA hydrogels Byoung-jin Jeon, Deborah Fygenson, Omar Saleh We have explored the molecular motor-driven, non-equilibrium mechanics of an artificial hydrogel system. We have synthesized DNA hydrogels with embedded tracer particles using highly specific, tunable DNA hybridization. The hydrogel's mechanical properties are varied by preparing composite gel systems that contain an appreciable fraction of stiff filaments (DNA origami nanotubes) linked to flexible DNA strands in the gels. We posit that these stiff filaments help the motor-induced strain propagate further. We employ microrheological techniques to probe the temporal and spatial strain fields created by contractile forces driven by the activity of a protein motor, FtsK. We discuss our experimental results on this non-equilibrium network system, seeking to establish fundamental principles of motor-driven active soft matter. [Preview Abstract] |
Tuesday, March 14, 2017 2:54PM - 3:06PM |
H16.00003: Unleashing elastic energy: dynamics of energy release in rubber bands and impulsive biological systems Mark Ilton, Suzanne Cox, Thijs Egelmeers, S. N. Patek, Alfred J. Crosby Impulsive biological systems - which include mantis shrimp, trap-jaw ants, and venus fly traps -- can reach high speeds by using elastic elements to store and rapidly release energy. The material behavior and shape changes critical to achieving rapid energy release in these systems are largely unknown due to limitations of materials testing instruments operating at high speed and large displacement. In this work, we perform fundamental, proof-of-concept measurements on the tensile retraction of elastomers. Using high speed imaging, the kinematics of retraction are measured for elastomers with varying mechanical properties and geometry. Based on the kinematics, the rate of energy dissipation in the material is determined as a function of strain and strain-rate, along with a scaling relation which describes the dependence of maximum velocity on material properties. Understanding this scaling relation along with the material failure limits of the elastomer allows the prediction of material properties required for optimal performance. We demonstrate this concept experimentally by optimizing for maximum velocity in our synthetic model system, and achieve retraction velocities that exceed those in biological impulsive systems. This model system provides a foundation for future work connecting continuum performance to molecular architecture in impulsive systems. [Preview Abstract] |
Tuesday, March 14, 2017 3:06PM - 3:42PM |
H16.00004: Controlling toughness and dynamics of polymer networks via mussel-inspired dynamical bonds Invited Speaker: Emmanouela Filippidi For dry, thermoset, polymer systems increasing the degree of cross-linking increases the elastic modulus. However, it simultaneously compromises the elongation under tension, usually reducing the overall total energy dissipated before fracture (toughness). Dynamic reformable bonds and complex network topologies have been used to circumnavigate this issue with moderate success, mainly in hydrated network systems. Hydration, however, which swells these networks limits how far one could increase the modulus, while their chemistry prevents improvement of the mechanics upon drying. Employing the mussel byssus-inspired strategy of iron-catechol coordination bonds, we have synthesized and studied epoxy networks comprising covalently attached catechol moieties capable of forming additional iron-catechol complex cross-links that still function in dry conditions. In such a fashion, we create a high modulus, high elongation, high toughness material. The iron-catechol coordination bonds play multiple roles that enhance the mechanical performance of the system: at low strain and fast strain rates, they act like permanent cross-links with bonding strength similar to covalent bonds, but start disassociating at high elongation. They are also reformable, enabling material self-healing in a matter of minutes in the absence of load. Finally, the dissociative crosslink cleavage alters the local chain topology, creating length scales that unfold upon elongation. The elegance of this system lies on its general versatility. Both the polymer and metal ion can be used as control parameters to study the interplay of covalent and dynamical bonds as well as explore the limits of the design of elastomers with enhanced toughness. [Preview Abstract] |
Tuesday, March 14, 2017 3:42PM - 3:54PM |
H16.00005: Organic-inorganic Interface in Nacre: Learning Lessons from Nature Nima Rahbar, Sina Askarinejad Problem-solving strategies of naturally growing composites such as nacre give us a fantastic vision to design and fabricate tough, stiff while strong composites. To provide the outstanding mechanical functions, nature has evolved complex and effective functionally graded interfaces. Particularly in nacre, organic-inorganic interface in which the proteins behave stiffer and stronger in proximity of calcium carbonate minerals provide an impressive role in structural integrity and mechanical deformation of the natural composite. The well-known shear-lag theory was employed on a simplified two-dimensional unit-cell of the multilayered composite considering the interface properties. The closed-form solutions for the displacements in the elastic components as a function of constituent properties can be used to calculate the effective mechanical properties of composite such as elastic modulus, strength and work-to-failure. The results solve the important mysteries about nacre and emphasize on the role of organic-inorganic interface properties and mineral bridges. Our results show that the properties of proteins in proximity of mineral bridges are also significant. More studies need to be performed on the strategies to enhance the interface properties in manmade composites. [Preview Abstract] |
Tuesday, March 14, 2017 3:54PM - 4:06PM |
H16.00006: Mechanical nonlinearity in the soft layers of Nacre Yuko AOYANAGI, Ko Okumura A number of biocomposites have remarkable hierarchical structures and extraordinary toughness and as such nacre is the most studied biomaterials. Such tough biomaterials always combine soft and hard ingredients and the mechanical responses of the soft elements are quite often nonlinear, while such nonlinearities may originate from some mechanical advantages. In nacre hard sheets are glued by thin soft sheets on submicron scale to form a layered structure. Recently, detailed nonlinear mechanical behaviors of the soft element of nacre have been revealed experimentally. A simple linear model of nacre both in analytical and numerical studies already showed reduction of the stress concentration by existence of soft layers. In this study, in order to explore the importance of the nonlinearity in the soft layers of nacre, we consider a simple nonlinear layered model of nacre. By taking into account the nonlinearity in simulation and scaling models of nacre, we showed that the nonlinearity is essential to reduce stress concentration around crack tips and thus to enhance the strength. Surprisingly, we found that the nonlinearity is optimized both for the strength with avoiding difficulties of the biofabrication of highly nonlinear materials. [Preview Abstract] |
Tuesday, March 14, 2017 4:06PM - 4:18PM |
H16.00007: Resilience Despite Damage: Structure and Mechanics of Multicycle Loading in the Mussel Plaque Menaka Wilhelm, Emmanouela Filippidi, J. Herbert Waite, Megan Valentine The proteinaceous byssal plaque-thread structures created by marine mussels exhibit extraordinary load-bearing capability. Knoweldge of nanoscopic protein interactions that support interfacial adhesion in the plaque has improved in recent years, but supramolecular mechanisms of energy dissipation that confer toughness are less understood. We have used multicycle loading in the plaque-thread structure, complemented with scanning electron microscopy of strained plaques, to probe force response and strain-induced structural changes. We find that multicycle loading decreases small-strain stiffness, but does not compromise the critical strength or maximum extension, as compared to plaques that are monotonically loaded to failure. The strain-dependent plastic damage does not appear to be reversible or repairable on hours-long timescales, but this work suggests that a redundancy of load-bearing mechanisms contributes to plaque toughness in repeated loadings. Improved understanding of energy dissipation on lengthscales ranging from microns to millimeters provides new insight into the mussel system, and offers potential strategies for the design of soft, tough and resilient synthetic structures. [Preview Abstract] |
Tuesday, March 14, 2017 4:18PM - 4:30PM |
H16.00008: Abstract Withdrawn
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Tuesday, March 14, 2017 4:30PM - 4:42PM |
H16.00009: Infrared and Raman Study of the Recluse Spider Silk S. L. Wang, Qijue Wang, Zhen Xing, H. C. Schniepp, M. M. Qazilbash Spider silk exhibits remarkable mechanical properties, such as high tensile strength and toughness. We want to gain insight into the composition and structure of spider silk to discover the origin of these properties. We are especially interested in the organization of the crystalline beta sheets that are expected to contribute to the high strength of the silk from the recluse spider, \textit{Loxosceles laeta}. The recluse spider produces a silk that has a unique geometry amongst arachnids. We measure the silk's optical properties, particularly the infrared-active and Raman-active vibrations. Broadband infrared transmission spectra were collected in the spectral range between 600 cm$^{\mathrm{-1}}$ and 4000 cm$^{\mathrm{-1}}$, with light polarized parallel and perpendicular to the long axis of the silk. Raman micro-spectroscopy was performed in the spectral range 500 cm$^{\mathrm{-1}}$ and 4000 cm$^{\mathrm{-1\thinspace }}$with a 514 nm laser. The infrared and Raman vibrational modes are fit with Lorentzian and pseudo-Voigt functions. The vibrational modes are assigned to specific structures and electronic bonds in the silk. [Preview Abstract] |
Tuesday, March 14, 2017 4:42PM - 4:54PM |
H16.00010: Stress in the Mikado Model Mathijs Vermeulen, Anwesha Bose, Cornelis Storm, Wouter G. Ellenbroek The Mikado model is an often employed method to generate computer model architectures for fibrous networks. While it was originally devised for semiflexible polymers, it is regularly studied in the flexible limit (zero bending stiffness). In this limit, the Mikado method gives a floppy network in which every node has 4 or fewer springs connecting it to the rest of the network. While this guarantees that these networks should have many floppy modes, this in itself does not guarantee anything about their mechanics, as there could additionally be states of self-stress that would have a significant effect on the mechanical properties. In this talk, we first show that periodic Mikado networks, upon creation, do not have any states of self-stress (so that counting degrees of freedom following Maxwell’s simple argument gives the correct answer). However, the swelling (or shearing) of these networks gives rise to special geometric features in the network that can induce the states of self-stress. [Preview Abstract] |
Tuesday, March 14, 2017 4:54PM - 5:06PM |
H16.00011: Designing active microcapsules to capture nanoparticles dispersed in fluid Alexander Alexeev, Svetoslav Nikolov, Alberto Fernandez-Nieves Tactfully utilizing the large volume change associated with the volume-phase transition of hydrogels enables design on new microscopic system and devices with biomimetic functions. We use mesoscale computational modeling to design an active microcapsule capable of selectively capturing nanoparticles which are dispersed throughout the solvent. The microcapsule is comprised of a rigid spherical shell with six perforated holes and a stimuli-sensitive gel, which is placed inside the spherical shell. Upon application of an external stimulus the gel swells, expanding through the perforated holes in the shell and making contact with the nearby solvent and nanoparticle mixture. When the external stimulus is removed the gel collapses and returns into the microcapsule interior, bringing in nanoparticles, from the outside, in the process. Functionalizing the microcapsule with a polymer brush prevents nanoparticles from randomly diffusing into the microcapsule which gives us the ability to precisely control the nanoparticle concentration within the microcapsule interior. [Preview Abstract] |
Tuesday, March 14, 2017 5:06PM - 5:18PM |
H16.00012: Ni-DNA-based nanowires and nanodevices Chia-Ching Chang, Chiun-Jye Yuan, Wen-Bin Jian, Yu-Chang Chen, Massimiliano Di Ventra DNA is a highly versatile biopolymer that has been a recent focus in the field of nanomachines and nanoelectronics. DNA exhibits high stability, adjustable conductance, self-organizing capability, programmability and vast information storage. It is an ideal material in the applications of nanodevices, nanoelectronics, and molecular computing. Low conductance of native DNA renders applications difficult. However, doping with nickel ions tunes the DNA into a conducting polymer. Further studies showed that nickel ions containing DNA (Ni-DNA) nanowires exhibit characteristics of memristor and memcapacitor making them a potential mass information storage system. In summary, Ni-DNA has promising applications in a variety of fields, including nanoelectronics, biosensors and memcomputing. [Preview Abstract] |
Tuesday, March 14, 2017 5:18PM - 5:30PM |
H16.00013: Engineering hydrogel viscoelastic mechanics with bio-inspired supramolecular metal-coordinate dynamics. Niels Holten-Andersen Growing evidence supports a critical role of metal-coordinate transient crosslinking in soft biological complex material properties. Given their exploitation in desirable material applications in nature, bio-inspired metal-coordinate transient crosslinking provides unique possibilities to further our understanding of how to engineer synthetic polymer materials with advanced properties. Using simple bio-inspired metal-binding polymers, new fundamental insights on how hydrogel mechanics can be strongly coupled to supramolecular crosslink dynamics are emerging. Early lessons from such studies of metal-coordinate supramolecular chemo-mechanical couplings will be presented. [Preview Abstract] |
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