Pan American Materials Congress: Advanced Biomaterials: Bioinspired, Drug Delivery and Biomimetic Materials
Sponsored by: Third Pan American Materials Congress Organizing Committee
Program Organizers: Carlos Elias, Instituto Militar de Engenharia; Wen Yang, University of California, San Diego

Wednesday 10:10 AM
March 1, 2017
Room: Mission Hills
Location: Marriott Marquis Hotel

Session Chair: Wen Yang, Swiss Federal Institute of Technology in Zurich (ETHZ); Po-Yu Chen, National Tsing Hua University

10:10 AM  Invited
Bioinspired Phase Transforming Cellular Materials: Pablo Zavattieri1; David Restrepo1; Yunlan Zhang1; Nilesh Mankame2; 1Purdue University; 2General Motors Research & Development
    Active materials like shape memory, ferroelectric and magnetostrictive alloys obtain their characteristic properties due to phase transformations. In these materials, phase transformations occur by changing the packing arrangement of the atoms in a process that resembles multistable mechanisms switching between stable configurations. A similar behavior has been observed in folded proteins in which a change in configuration provides the mechanism through which biological materials obtain remarkable properties such as combinations of strength and toughness, superelasticity and shock energy dissipation, among others. We combine concepts learned from biomineralized systems, with auxetic and counter-auxetic mechanisms, to extend the notion of phase transformations to periodic cellular materials by introducing materials whose unit cells have multiple stable configurations. In this work we study 1D and 2D phase transforming cellular materials through numerical/analytical models and experiments to understand the underlying mechanics of the unit cell that allows the material to exhibit phase transformations.

10:40 AM  
An Approach to Study Materials-structure Relationships in Bio-inspired Microstructures: Alejandro Gutierrez1; Lilian Davila1; 1University of California, Merced
    Diatoms, microscopic algae with intricate porous shell morphologies, have been proposed as templates for drug delivery carriers, optical devices and metamaterials design. Several studies have found diatom shells show unique mechanical properties such as high specific strength and resilience. One hypothesis is that these properties stem from the structural arrangement of the material at the nanometer and micrometer scales, challenging the concept of what constitutes a “material” versus a “structure”. We have conducted a systematic simulation-prototyping study on the mechanics of diatom-inspired hierarchical microstructures. The Finite Element Method was used to replicate 3-D diatom shells under compressive forces. The intricate hierarchical structure observed in nature was reproduced in detail. A Coscinodiscus species frustule model was created, and the resulting mechanical response was compared to measurements. Simulation parameters were selected to reproduce nanoindentation experiments. Additionally, select designs were prototyped using Direct Laser Writing to evaluate the feasibility of manufacturing diatom-inspired devices.

11:00 AM  
Heparin-based Self-assemblies for Controllable Drug Delivery Application: Lin Ye1; 1Beijing Institute of Technology
    Heparin was a versatile platform to prepare various self-assemblies for drug delivery applications due to its excellent biocompatibility and abundant modification sites. Three heparin-based carriers were synthesized and investigated herein. Firstly, heparin-polycaprolactone(PCL) conjugate was synthesized and self-assembled into micelle in water. The micelle can loaded paclitaxel(PTX) in the core and doxorubicin(DOX•HCL) in the shell. Secondly, PTX was covalently incorporated into heparin via pH sensitive bond to form prodrug in order to improve drug load content as well as pH-trigger release behavior. Then, cationic folic acid were absorbed into prodrug via static interaction to endow tumor-targeting ability. Finally, a more simple and feasible strategy which just utilized the static interaction between heparin and dodecyl dimethyl benzyl ammonium chloride(DBAB) was used to prepare drug carrier. The carrier's morphology changed from vesicle to micelle with the decreasing of DBAB in feed. All three carriers showed promising potential in chemotheraphy.

11:20 AM  
Synthesis and Characterization of Bioinspired Freeze-Cast Alumina With A Zr-Based Bulk Metallic Glass Matrix: Amy Wat1; Jein Lee2; Bernd Gludovatz3; Eun Soo Park2; Robert Ritchie1; 1University of California, Berkeley; 2Seoul National University; 3Lawrence Berkeley National Laboratory
    Past work has shown that freeze casting is a relatively simple method to create a nacreous material with a polymer matrix. However, computational work (Begley, et al. 2012) suggests that the strength and toughness of such materials can be improved with a metallic mortar if the mortar has a lower strength than the fracture strength of the ceramic bricks. However, capillary forces prevent infiltration of metals into freeze-cast ceramics. Bulk metallic glasses can infiltrate ceramic scaffolds without any added pressure due to reactive wetting, which is a process where the metal reacts with the alumina to create an interfacial layer it readily wets. This study focuses on the effects of ceramic content and infiltration temperatures on the mechanical properties of such materials. The results show that the infiltration temperatures determine the thickness of the intermetallic phase, which in turn affects the mechanical properties of the brick-and-mortar materials.

11:40 AM  Cancelled
Analysis of Biomimetic Surgical Clip Using Finite Element Modeling for Geometry Improvement and Biomaterials Selection: Thays Brito1; Bianca dos Santos1; Leonardo Ara˙jo1; Luiz de Almeida1; Marysilvia da Costa1; 1Universidade Federal do Rio de Janeiro
    An absorbable suture clip (MU9002473-7) for surgical applications was developed based on the bite mechanism of ant Atta. As the ant mandible, the clip naturally falls after some time and there is no need to be removed. The clip design consists of a metallic support with a polymeric absorbable end. This study aims to optimize the clip geometry and select the best pair of biomaterials by analyzing his mechanical performance using the finite element method (FEM). Four biomaterials will be used in the simulations - AISI 316L and 420 stainless steel, poly(lactic acid), poly(glycolic acid). FEM analysis will be performed using ABAQUS, after the characterization of the parameters that describes the mechanical behavior of the polymeric materials in the software. The stress and strain distribution of each material and geometry changes will be analyzed. This work will enable the manufacture and application of this less traumatic and self-sufficient clip.

12:00 PM  Invited
Multiscale Bio-inspired Design of Nanocomposites: Horacio Espinosa1; 1Northwestern University
    In contrast to man-made materials, nature produces structures with remarkable mechanical properties. Seashells are compelling examples: while mostly comprised by mineralized materials, they exhibit high levels of strength and toughness. A surprisingly stiff, hard and tough hierarchical microstructure, which contains a small volume fraction of interfacial biopolymers, is responsible for creating composite materials that enable protection from predators. The high strength and toughness of seashells contrasts man-made engineering materials that sacrifice strength to achieve greater toughness. First, I will present hierarchical features and mechanisms observed from in situ microscopy experiments which enable remarkable mechanical properties. This understanding is applied to the computational design of artificial bio-inspired nanocomposites that are strong and tough. Graphene oxide-polymer composites are used to illustrate the validation of models used to design materials of interest to the material community. A strategy combining multiscale experiments and simulations, to select optimal constituents and geometric parameters, will be presented.

12:20 PM  
Pangolin Armor: Overlapping, Structure, and Mechanical Properties of the Keratinous Scales: Wen Yang1; Bin Wang2; Vincent Sherman2; Marc Meyers2; 1Swiss Federal Institute of Technology in Zurich (ETHZ); 2University of California, San Diego
    The pangolin has a flexible dermal armor consisting of overlapping keratinous scales. When predators threaten pangolins, they roll up into a ball exposing hard, sharp-edged scales. These tough yet flexible scales are made of a hard nail-like material. The scales have a cuticle of several layers of loosely attached flattened keratinized cells, while the interior structure exhibits three regions distinguished by the geometry and orientations of the keratinized cells, which form densely packed lamellae; each one corresponds to one layer of cells. A nano-scale suture structure, observed for the first time, outlines cell membranes and leads to an interlocking interface between lamellae, thus enhancing the bonding and shear resistance. Based on the interesting hierarchical structure, the mechanical behavior as well as the toughening mechanisms were investigated.

12:40 PM  
On the Strain Rate Sensitivity of Keratin Hair Fibers: Yang Yu1; Wen Yang1; Marc Meyers1; 1University of California, San Diego
    Keratinous fibrous materials, such as wool and hair, have been observed to exhibit viscoelasticity. Our previous study on human hair shows that the yield stress is dependent on the strain rate. In order to better understand the strain rate sensitivity and the contributing component, both human and horse hair were studied before and after the matrix was disrupted. Human and horse hair were first treated with an established method to disrupt the disulfide bonds within the keratin matrix. Preliminary results show that human hair shows a much decrease in strain rate sensitivity (from 0.11 to 0.05), while horse hair doesn't exhibit much difference due to the treatment. After treatment, both fibers show a similar sensitivity (0.05 and 0.06 for human and horse hair, respectively). Therefore, it is shown that the matrix ratio affects the strain rate sensitivity of the keratin fibers.