Showing papers by "Marc A. Meyers published in 2014"

Bioinspired Scaffolds with Varying Pore Architectures and Mechanical Properties

Abstract: Scaffolds with potential biological applications having a variety of microstructural and mechanical properties can be fabricated by freezing colloidal solutions into porous solids. In this work, the structural and mechanical properties of TiO2 freeze cast with different soluble additives, including polyethylene glycol, NaOH or HCl, and isopropanol alcohol, are characterized to determine the effects of slurry viscosity, pH, and alcohol concentration on the freezing process. TiO2 powders mixed with water and these different additives are directionally frozen in a mold, then sublimated and sintered to create the porous scaffolds. The different scaffolds are characterized to compare the compressive strength, modulus, porosity, and pore morphology. For all scaffolds, the overall porosity remains constant (80–85%). By changing the concentration of each additive, the lamellar thickness, pore area, and aspect ratio vary significantly, showing inverse relationships to both the compressive strength and modulus. The strength is predicted from the pore aspect ratio of the scaffolds when subjected to compressive loading with the primary failure mode identified as Euler buckling. TiO2 scaffolds freeze cast with different soluble additives are suitable for biomedical applications, such as bone replacements, requiring high porosity and specific pore morphologies.

Atomistic simulation of tantalum nanoindentation: Effects of indenter diameter, penetration velocity, and interatomic potentials on defect mechanisms and evolution

Abstract: Nanoindentation simulations are a helpful complement to experiments. There is a dearth of nanoindentation simulations for bcc metals, partly due to the lack of computationally efficient and reliable interatomic potentials at large strains. We carry out indentation simulations for bcc tantalum using three different interatomic potentials and present the defect mechanisms responsible for the creation and expansion of the plastic deformation zone: twins are initially formed, giving rise to shear loop expansion and the formation of sequential prismatic loops. The calculated elastic constants as function of pressure as well as stacking fault energy surfaces explain the significant differences found in the defect structures generated for the three potentials investigated in this study. The simulations enable the quantification of total dislocation length and twinning fraction. The indenter velocity is varied and, as expected, the penetration depth for the first pop-in (defect emission) event shows a strain rate sensitivity m in the range of 0.037-0.055. The effect of indenter diameter on the first pop-in is discussed. A new intrinsic length-scale model is presented based on the profile of the residual indentation and geometrically necessary dislocation theory.

Biological Materials Science: Biological Materials, Bioinspired Materials, and Biomaterials

Abstract: 1. Evolution of materials science and engineering: from natural to bioinspired materials Part I. Basic Biology Principles: 2. Self assembly, hierarchy, and evolution 3. Basic building blocks 4. Cells 5. Biomineralization Part II. Biological Materials: 6. Silicate and calcium carbonate-based composites 7. Calcium phosphate-based composites 8. Biological polymers and polymer composites 9. Biological elastomers 10. Biological foams (porous solids) 11. Functional biological materials Part III. Bioinspired Materials and Biomimetics: 12. Bioinspired materials 13. Molecular-based biomimetics.

Reinforcing Structures in Avian Wing Bones

Abstract: Nearly all species of modern birds are capable of flight; therefore mechanical competency of appendages and the rigidity of their skeletal system should be optimized. Birds have developed extremely lightweight skeletal systems that help aid in the generation of lift and thrust forces as well as helping them maintain flight over, in many cases, extended periods of time. The humerus and ulna of different species of birds (flapping, flapping/soaring, flapping/gliding, and non-flying) have been analyzed by optical microscopy and mechanical testing. The reinforcing structures found within bones vary from species to species, depending on how a particular species utilizes its wings. Interestingly, reinforcing ridges and struts have been found within certain sections of the bones of flapping/soaring and flapping/gliding birds (vulture and sea gull), while the bones from the flapping bird (raven) and non-flying bird (domestic duck) did not have supporting structures of any kind. The presence of these reinforcing structures increases the resistance to torsion and flexure with a minimum weight penalty, and is therefore of importance in flapping/gliding birds. Vickers hardness testing was performed on the compact section of the bones of all bird species. The data from the mechanical testing were compared with microstructural observations to determine the relevance behind the reinforcing structures and its mechanical and biological role. Finite element analysis was used to model the mechanical response of vulture ulna in torsion.

A Comparison on the Structural and Mechanical Properties of Untreated and Deproteinized Nacre

Abstract: The contribution of the individual constituents of red abalone (Haliotis rufescens) to the strength of the nacre structure is investigated. Nacre sections were deproteinized to establish the contribution of the organic components. Tensile testing, scratch, and nanoindentation tests are performed on the isolated mineral constituent (deproteinized nacre) and the untreated nacre of red abalone shell. Specimens are characterized by scanning electron and atomic force microscopies to verify the deformation mechanisms. Results obtained from the isolated mineral validate the importance of the organic constituent, as the mechanical properties decline greatly when the organic component is removed. Scratch tests reveal the anisotropy of the material and the effects of the thick layers of protein (mesolayers) on the deformation behavior. This approach confirms the importance of the integrated structure to the overall mechanical behavior of nacre.