Biological Materials Science: Synthesis of Bio-inspired Composites
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

Monday 8:30 AM
February 27, 2017
Room: Pacific 15
Location: Marriott Marquis Hotel

Session Chair: Po-Yu Chen, National Tsing Hua University; Steven Naleway, University of Utah

8:30 AM  Invited
3D Printing of Hierarchical Porous Materials: Andre Studart1; Clara Minas1; Davide Carnelli1; Elena Tervoort1; 1ETH Zurich
    Porosity is extensively exploited in natural materials as an effective means to reduce weight, minimize resources or enable the transport and storage of fluids and nutrients. Because porosity inevitably reduces the strength of materials, the incorporation of pores should occur with minimum impact on the mechanical performance of the structure. To this end, porous biological materials like plant leaves, animal skulls and bird beaks often exploit porosity gradients at multiple length scales to generate mechanically efficient structures. In this talk, I will present a new processing route for the 3D printing of foams and emulsions into hierarchical and graded porous structures of high mechanical efficiency. Exploiting this concept in engineering applications should lead to the rational utilization of building resources and the minimization of energy demand for transportation without impairing the mechanical stability of the hierarchical structures.

9:00 AM  
Bio-inspired Flexible Armors with 3D Printed Tailored Architectures: Roberto Martini1; Yanis Balit1; David VanZyl1; Francois Barthelat1; 1McGill University
    Flexible natural armors from fish or alligators have unique and attractive combinations of hardness, flexibility and light weight. In particular, the extreme contrast of stiffness between hard plates and surrounding soft tissues give rise to unusual and attractive mechanisms which now serve as model for the design of bio-inspired armors. Here we examine the unstable tilting of individual scales, a critical failure mode we recently observed on natural and bio-inspired scaled armors and which we captured using contact mechanics. The stability of individual plates is governed by the friction at the surface of the plate, by the size of the plate, by the stiffness of the substrate and by the amount of interactions between neighboring scales. We also used 3D printing to explore how the geometry, overlap and interlocking between neighboring scales can be tuned and optimized to delay unstable tilting of the scales and improve overall performance.

9:20 AM  
Intrinsic and Extrinsic Control of Bioinspired Freeze Casting: Steven Naleway1; Marc Meyers2; Joanna McKittrick2; 1University of Utah; 2University of California, San Diego
    Natural materials are capable of providing impressive structural and mechanical properties given a relatively simple set of natural constituents (biopolymers and biominerals). This is in large part due to their hierarchical structuring at numerous length scales. Taking inspiration from this, we present novel methods for the fabrication of bioinspired materials that mimic this complex and hierarchical structure through use of the freeze casting technique, where a ceramic scaffold is templated by the growth of ice crystals. We propose that this bioinspired technique can be controlled through either intrinsic (those that modify from within by altering the constituents) or extrinsic (those that apply external forces or templates) means. Through these classifications, we present novel examples of both intrinsic and extrinsic freeze cast, bioinspired structures with a focus on providing advanced control of the final material structure and properties. Applications as biomedical implants and structural materials will be discussed.

9:40 AM  
Fabrication and Characterization of Bioinspired Alumina with a 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
    Theoretical studies on bioinspired ceramic materials modelled on nacre (Begley, et al. 2012) have suggested that a metallic “mortar” would lead to higher strength and toughness than a polymer “mortar” if the strength of the mortar is lower than the fracture strength of the ceramic “bricks”. One challenge for producing a ceramic with a metallic matrix is that metals typically do not wet ceramics. To resolve this issue, a freeze-cast alumina scaffold was infiltrated with a Zr-based bulk metallic glass that reacts with the surface of the alumina to create an interfacial layer the metal wets. This study focuses on how the mechanical properties of the materials change due to the infiltration temperature and ceramic content to find the optimal processing conditions that utilizes the brick-and-mortar architecture. The results illustrate a trade-off between the fracture toughness and the flexural strength of the resulting materials.

10:00 AM Break

10:20 AM  Keynote
Bioinspired Structural Materials - “Nacre-Like” Compliant-Phase Ceramics: Where Are We Now?: Robert Ritchie1; Antoni Tomsia2; 1Lawrence Berkeley National Laboratory/University of California, Berkeley; 2Lawrence Berkeley National Laboratory
    It is decade since freeze-casting was first used to develop bioinspired structural ceramics with “nacre-like” brick-and-mortar structures. These materials can exhibit unique combinations of strength and toughness: their strength from the ceramic “bricks” and ductility/toughness from limited inter-brick displacements within the thin compliant “mortar”. Early developments showed great promise with “nacre-like” alumina ceramics containing PMMA displaying record toughnesses above 30 MPam. Although a few notable successes have occurred since, progress has been slow, primarily because of difficulties in processing high volume-fraction porous ceramics with a fully infiltrated compliant-phase. Theoretical modeling suggests that even better strength and toughness can be realized with metallic mortars, but this further compromises processing as metals invariably do not wet ceramics. Here we assess the development of compliant-phase ceramics, and discuss alternative processing techniques, such as reactive wetting, coextrusion and spark-plasma sintering, which are more adaptable to making high volume-fraction, brick-and-mortar, ceramics with a metallic compliant-phase.

11:00 AM  
Porcupine Fish Inspired Radial and Concentric Freeze: Frances Su1; Joyce Mok1; Joanna McKittrick1; 1University of California, San Diego
    Porcupine fish dermal spines must be rigid and tough enough to prevent predators from breaking the spines and ingesting the fish. The spines are composed of radially aligned mineralized collagen sheets embedded in a protein matrix. Radial alignment increases material strength when loaded in the direction of alignment. The spines also have a concentric structure that is similar to tree trunk growth rings. This structure likely helps with crack deflection for impact resistance. For this project, bioinspired ceramic scaffolds with both concentric and radial patterns were synthesized and infiltrated with epoxy to mimic the structure of the porcupine fish spine. Compressive strength and elastic modulus of the scaffold were compared with those of unidirectional freeze casted scaffolds and scaffolds with radial alignment. This work is supported by funding provided by the Multi-University Research Initiative through the Air Force Office of Scientific Research (AFOSR-FA9550-15-1-0009) and the National Science Foundation (DMR-1507978).

11:20 AM  
Fabrication, Characterization and Modeling of Freeze-casted Ceramic Platelet Composites: Majid Minary1; 1University of Texas at Dallas
    In this presentation, we will discuss fabrication, and characterization of platelet ceramic composite fabricated using freeze casting process. Single crystal sapphire platelets with an aspect ratio of ~ 13 were aligned using freeze casting and subsequent freeze drying. The green body ceramic was sintered and subsequently infiltrated with various functional polymers. We discuss effect of annealing the infiltrated polymer and surface functionalization on the mechanical properties of the fabricated composite. The fabricated composite was characterized using uniaxial compression and three point bending tests. In addition, we conducted in situ SEM experiments to observe the deformation mechanism in the specimens. A computational model was developed including the ceramic, polymer and their interface to explain the observed experimental results. The fabricated composite shows promising strength, and toughness and may find applications for lightweight, high performance materials.

11:40 AM  
Synergistic Porous Structures from Magnetic Freeze Casting with Surface Magnetized Alumina Particles and Platelets: Michael Frank1; Sze Hei Siu1; Steven Naleway1; Chin-Hung Liu1; Keyur Karandikar1; Olivia Graeve1; Joanna McKittrick1; 1UC San Diego
    Magnetic freeze casting utilizes the freezing of water, a low magnetic field and surface magnetized materials to make multi-axis strengthened porous scaffolds. A greater magnetic moment was measured for magnetized alumina platelets compared with particles, which indicated that platelets are more likely to align along the magnetic field axis before particles during magnetic freeze casting. Porous scaffolds made of either magnetized particles or platelets produced enhanced stiffness along the magnetic field axis at 75 mT for both conditions. Particles and platelets combined at varying ratios produced porous scaffolds with synergistic structural features at 75 mT. Magnetic freeze casting with magnetized alumina particles and platelets provides interesting avenues for generating complex porous structures without altering additional slurry variables such as freezing agents, additives, etc. This work is supported by a Multi-University Research Initiative through the Air Force Office of Scientific Research (AFOSR-FA9550-15-1-0009) and by a National Science Foundation, Biomaterials Grant 1507978.