Polyetheretherketone (PEEK) was reinforced with 0-40 vol% hydroxyapatite (HA) whiskers using a novel powder processing and compression molding technique. A powder mixture was uniaxially pressed into a composite powder compact and compression molded into a flat composite bar using an open-channel die, such that the HA whiskers exhibited a preferred orientation along the length of the bar and tensile specimens. As expected, increased HA whisker reinforcement resulted in increased elastic modulus, but decreased ultimate tensile strength and strain- or work-to-failure. PEEK reinforced with 40 vol% HA whiskers exhibited an elastic modulus of 16-18 GPa. PEEK reinforced with 20 vol% HA whiskers had an ultimate tensile strength of 70-80 MPa. Human cortical bone exhibits an elastic modulus of 17-26 GPa and an ultimate tensile strength of 80-150 MPa in the longitudinal direction (direction of principal stress). Stiffness coefficients measured by ultrasonic wave propagation indicated a level orthotropy also similar to that of human cortical bone tissue.

The Russian “Theory of Inventive Problem Solving” was developed to solve technological problems, but it can equally well be applied to biology and the way organisms have solved similar problems. As such it can also be used to bridge the gap between biology and engineering, and to provide a theoretical basis for Biomimetics.

The shape-memory effect was examined in polymer stents intended for cardiovascular applications. Four polymer networks were synthesized from poly(ethylene glycol) dimethacrylate and tert-butyl acrylate with 10 wt% and 20 wt% crosslinker, and with glass transition temperatures (Tg) of 52°C and 55°C. Solid and 50% porous stents were manufactured and tested for free strain recoverability at temperatures at or just above 37°C. Stents with lower glass transition temperatures and a higher degree of crosslinking recovered faster than their counterparts. Lower deformation (packaging) temperatures and higher recovery temperatures induce more rapid recovery. The presence of geometrical features, such as pores, initiated recovery sooner, but had negligible influence on overall recovery.

White spot lesions are clinically detectable areas of demineralized enamel that often form during orthodontic treatment. Fluoride has been shown to prevent demineralization from occurring. Mechanical properties of white spot lesions are not well characterized. Bovine enamel slabs, with and without fluoride treatment, were placed under demineralization conditions. Through a series of microindentations at incremental loads, mechanical strength was measured using a novel method, SVAE. Specific Volume Absorbing Energy (SVAE) is equal to work energy divided by the indentation volume. The supra-surface area (outmost 5 μm) of enamel slabs with fluoride demonstrated decreased mechanical strength compared to those without fluoride. Fluoride may not impart protection over long periods of demineralization.

Thin films of type 1 collagen fibril networks fabricated on alkanethiol-functionalized surfaces have been previously shown to provide an excellent protein matrix for cultured cells in applications such as drug toxicity studies and studies of cell signaling pathways. Cell phenotypic parameters, including cell morphology and rate of proliferation, can depend on the processing conditions used for fabrication of the protein films. The mechanical characteristics of the collagen fibril network appear to be particularly important, and as such, understanding the mechanical properties of individual fibrils, as well as their interactions with each other and the underlying substrate is critical for assuring a predictable response from cells. In this study, scanning probe microscopy and instrumented indentation are used in conjunction with small force metrology to examine the mechanical properties of these collagen fibrils and fibril networks.

Skeletal fractures represent a significant medical and economic burden for society. It is generally thought that a high incidence of musculoskeletal fatigue loading results in damage accumulation at too high of a rate to be efficiently remodeled, leading to skeletal fracture. The state of damage in bone at a given time is therefore the net result of damage and repair processes, and is dependent upon extrinsic factors such as mechanical history, but also upon intrinsic factors, such as composition of bone mineral and matrix. In this invited paper, we review investigations on the coupling of Raman spectroscopy with mechanical loading of bone, providing insight into mechanisms of ultrastructural deformation in bone at smaller scales than previously understood. We also present new data showing that in-vivo mechanical loading results in increased resistance to fatigue damage, coupled with an increase in phosphate to amide I ratio and decrease in carbonate to phosphate ratio. Taken together, the data demonstrates the ability to modulate the mechanical and chemical properties of bone via exogenous mechanical stimulation.

Compositional and structural variations at various scale levels have been investigated in the shells of the modern brachiopod Megerlia truncata combining transmission electron microscopy (TEM), cathodoluminescence (CL), laser-ablation-inductively-coupled-mass-spectrometric (LA-ICP-MS) and micro-Raman spectroscopical (µRS) analyses. Our results show that these shells can be addressed as hierarchially structured, multi-scaled organic/inorganic fibre composites. A significant chemical as well as a mechanical inhomogeneity is observable within the shells. This occurs on various scale levels ranging from less then one to a few houndred microns. In concert to systematic variations in micro- and nanohardness the µRS and CL analyses reveal a systematic distribution and incorporation of organic material within the shells, which is negligible within the nanocrystalline primary layer but is present in a significant amount in the innermost part of the secondary layer, next to the organic tissue of the animal. Mechanical performance (hardness and fracture toughness) of this biomaterial is mainly determined by textural features, an extreme variation of crystallite size and a purpose oriented interlikage of organic and inorganic components.

Water is a somewhat neglected parameter in the mechanical properties of biological materials. In some instances it takes over a role of actuation, even in dead structures.

Thermal gelation and structure properties of high concentration triblock copolymer poly (ethylene oxide)99-poly(propylene oxide)69-poly(ethylene oxide)99 (Pluronic F127)-clay aqueous solutions were characterized by rheological measurements and scanning electron microscopy (SEM). The sol-gel transition temperature, as well as the viscosity of the F127 solution was found to depend both on the concentration of polymer and clay filler. In all cases, Pluronic F127 gels are pseudoplastic, showing the shear-thinning behavior. Above the gel transition, the viscosity of the solutions increased with increasing the clay concentration. The corresponding macrostructure of the gels was studied by lyophilizing thick samples and scanning them with a scanning electron microscope (SEM). A well-ordered network of porosity was observed as a function of polymer concentration and orientation.