Biological Materials Science: Structural Biological Materials I
Sponsored by: TMS Functional Materials Division, TMS Structural Materials Division, TMS: Biomaterials Committee
Program Organizers: Po-Yu Chen, National Tsing Hua University; Francois Barthelat, McGill University; Michael Porter, Clemson University; Steven Naleway, University of Utah

Tuesday 2:00 PM
February 28, 2017
Room: Pacific 15
Location: Marriott Marquis Hotel

Session Chair: Steven Naleway, University of Utah; Dwayne Arola, University of Washington

2:00 PM  Invited
Biological Materials Science: Challenges and Opportunities: Marc Meyers1; 1UCSD
    Biological materials science is a new and vibrant field of materials science and engineering. We present the unique and defining characteristics of biological materials through the Arzt heptahedron. The plethora of different structures and mechanical properties is systematized through a new paradigm: eight structural design elements, which are motifs appearing on different species and scales, and which enable analytical treatment and lead to enhanced understanding. We apply this knowledge to feathers and explain their complex structures. Research sponsored through AFOSR MURI.

2:30 PM  
Biological and Bio-inspired Flexible Armor Based on Chiton’s Girdle Scales: Ling Li1; Matthew Connors2; Ahmed Hosny1; Douglass Earnisse3; Mason Dean4; James Weaver1; Christine Ortiz2; 1Harvard University; 2Massachusetts Institute of Technology; 3California State University; 4Max Planck Institute of Colloids and Interfaces
    In this work, we study the ultrastructural, geometrical, and mechanical designs for the flexible biological armor based on the dorsal girdle scales from a group of mollusks called chitons. This composite armor system consists of three main components: aragonite-based scales on top, a soft tissue in the middle, and an assembly of mineralized microrods covering the bottom. By using synchrotron X-ray micro-computed tomography, we quantified the 3D geometries of scales from multiple species (families Chitonidae and Ischnochitonidae). We then demonstrate a biologically inspired flexible protective material system based on a full 3D parametric model of the scales. We explore the trade-off between mechanical protection and flexibility through direct mechanical testing of 3D-printed prototypes derived from the parametric model. Our results show that the scale curvatures result in interlocking of scales when a critical bending curvature is achieved, leading to a dramatic increase in bending stiffness after the initial low-stiffness regime.

2:50 PM  
On the Stress Relaxation and Tear Resistance of Skin: Wen Yang1; Andrei Pissarenko2; Vincent Sherman2; Eric Schaible3; Katherine Brown4; William Proud5; Alun Wiliams4; Robert Ritchie3; Marc Meyers2; 1Swiss Federal Institute of Technology in Zurich (ETHZ); 2University of California, San Diego; 3Lawrence Berkeley National Laboratory; 4University of Cambridge; 5Imperial College London
    Skin is the organ protecting human from environment. After interacting with the external force, young adult's skin can easily take the repeated small load without a vital damage. Tear resistance is of importance in the various functions of skin, especially protection from predatorial attack. Here, we mechanistically quantify the stress relaxation and the extreme tear resistance of skin and identify the underlying structural features, which lead to its sophisticated recovery and failure mechanisms. We explain how the skin recovers at the small load and why it is virtually impossible to propagate a tear in skin. We express the deformation in terms of four mechanisms of collagen fibril activity in skin under tensile loading that virtually eliminate the possibility of tearing in pre-notched samples: fibril straightening, fibril reorientation towards the tensile direction, elastic stretching and interfibrillar sliding, all of which contribute to the redistribution of the stresses at the notch tip.

3:10 PM  
On the Impact Resistance of Horn and Hoof in Different Loading Orientations: Wei Huang1; Alireza Zaheri2; Horacio Espinosa2; David Restrepo3; Pablo Zavattieri3; Joanna McKittrick1; 1University of California, San Diego; 2Northwestern University; 3Purdue University
    Bighorn sheep (Ovis canadensis) rams hurl themselves at each other at speeds of ~ 9 m/s (20 mph) to fight for dominance and mating rights. This necessitates that impact resistance is a predominate feature of their horns. Hooves from African zebra (Equus burchelli) support large dynamic, compressive impact loads during a relatively long cyclic period. Remarkable convergence of both structures and materials found in horns and hooves are observed. Optical and scanning electron microscope images show similar tubular structures in both horns and hooves, while the porosity is around 7% and 3.5%, respectively. Quasi-static compression and dynamic Hopkinson bar experiments in three orthogonal directions (longitudinal, radial and transverse) indicate the radial directions are the most energy absorption especially in a higher strain rate, while the highest stiffness comes from the longitudinal direction. This work is supported by a Multi-University Research Initiative through the Air Force Office of Scientific Research (AFOSR-FA9550-15-1-0009).

3:30 PM Break

3:40 PM  Keynote
Bio-inspired Design of Hierarchical Materials: Horacio Espinosa1; 1Northwestern University
    In contrast to man-made materials, nature assembles materials with remarkable mechanical properties. Exoskeletons are compelling examples: despite being comprised by mineralized materials, they exhibit high levels of strength and toughness. Stiff, hard and tough hierarchical microstructures, which contain a small volume fraction of interfacial biopolymers, are responsible for creating multifunctional composite materials that protect animals. The high strength and toughness of exoskeletons contrasts man-made engineering materials that typically sacrifice strength to achieve greater toughness. First, I will present biologically occurring hierarchical features and mechanisms observed from in situ microscopy experiments which endow remarkable mechanical properties. The acquired understanding is applied towards the design of artificial bio-inspired nanocomposites that are strong and tough. Graphene oxide-polymer nanocomposites illustrate the validation of models used to design materials of interest to multiple communities. A strategy combining multiscale experiments and simulations, to select optimal constituents and geometric parameters, will be presented.

4:20 PM  
Nacre’s Strategy to Enhance Its Mechanical and Fracture Properties: Sina Askarinejad1; Nima Rahbar1; 1Worcester Polytechnic Institute
    Enhanced mechanical and fracture properties of biological composites encourage researchers to focus on the problem-solving strategies of these naturally growing materials. Bone and nacre are prime examples of natural composites with high strength, stiffness and toughness. In addition to nano-scale features, 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 minerals provide an impressive role in structural integrity and mechanical deformation of the natural composite. However, further research on the toughening mechanisms and the role of the interface properties is essential. In this study, a micromechanical analysis of the mechanical response of these composites is presented considering interface properties. The well-known shear-lag theory was employed on a simplified two-dimensional unit-cell of the multilayered composite. The results solve the important mysteries about nacre and emphasize on the role of organic-inorganic interface properties.

4:40 PM  
The Hierarchical Structure of Atractosteus Spatula (Alligator Gar Fish) Boney Scales: XRM and Finite Element Modeling Characterization of Structural Porosity: Kenneth Livi1; Matt Nelms2; Alyssa Browning3; Wayne Hodo4; A.M. Rajendran2; 1Johns Hopkins University; 2University of Mississippi; 3Carl Zeiss X-ray Microscopy, Inc.; 4US Army ERDC-GSL
    The hierarchical structure for the alligator gar’s boney fish scales was investigated using X-ray Microscopy (XRM) (ZEISS Xradia 520 Versa) and Finite Element Modeling (FEM). The scales were comprised of three layers (from top to bottom): hard enamel ganoine, transition zone bone (TZB), and bone. The layers contained differing amounts of bio-modified hydroxyapatite mineral platelets and collagen fiber bundles. Each layer had distinct elemental compositional values for Ca/P, Na, and Mg. The XRM was used to map the porosity characteristics down to the 1 Ám scale. Seven classes of pores have been identified: 1) central channels spanning the entire scale, 2) tubules branching horizontally from channels, 3) vertical bone tubules, 4) vertical ganoine tubules, 5) horizontal TZB boundary tubules, 6) unconnected pores, 7) sub-micron porosity from TEM. Using a micromechanical approach with FEM, the effects of porosity distribution, shape and size were investigated on the mechanical response of the scale.

5:00 PM  
Structure and Mechanical Behavior of Coelacanth Scales: Haocheng Quan1; Wen Yang2; Robert Ritchie3; Marc Meyers1; 1UCSD; 2ETH-Zurich; 3 Lawrence Berkeley National Laboratory
    The “living fossil”, Coelacanth, has lived on earth for more than 300 million years and its morphology rarely changed from its original characteristics. The whole fish body is armored by very rough scales and they are overlapped by each other, which effectively protect the fish from the predator’s attack. The scales have a mineralized outer layer and collagenous laminated inner layer. Morphology characterizations manifest that the arrangement of collagen fibers in the inner layer forms a “double-twisted” Bouligand-like structure and the inter bundle collagen fibrils go through almost whole thickness of scale. Mechanical tests indicate the high mechanical performance of the scale and the in situásynchrotron small-angle X-ray scattering test reveals the toughening mechanisms including collagen fibril sliding, stretching, fiber reorientation and delamination.

5:20 PM  
The First Barrier to Penetration of Fish Scales: Structure and Properties of the Limiting Layer: Sandra Murcia1; Melicent Stossel1; Rishi Pahuja1; Timothy Linley2; Alex Ossa3; Junlan Wang1; Dwayne Arola1; 1University of Washington; 2Pacific Northwest National Laboratory; 3Universidad EAFIT
    Fish scales serve as a flexible natural armor. While most attention has been focused on the composite structure of the elasmodine, limited work has addressed the highly mineralized external coating regarded as the Limiting Layer (LL). The LL serves as the first barrier to penetration and resistance to puncture. In this investigation the structure, composition and mechanical behavior of the LL are evaluated for scales of the Arapaima gigas, the tarpon (Megalops atlanticus) and the carp (Cyprinus carpio). Properties of the LL were compared between fish and with respect to anatomical position. Results show that there are significant differences in the LL thickness of scales, both between the three fish and spatially, which suggests site-specific functional development. There are also differences in the chemical composition and distribution in hardness. Lastly, the surface topography of the LL for the three fish is unique and appears to be important to locomotion.