Biomimetic bone-like composites fabricated through an automated alternate soaking process.

Hydroxyapatite-gelatin composites have been proposed as suitable scaffolds for bone and dentin tissue regeneration. There is considerable interest in producing these scaffolds using biomimetic methods due to their low energy costs and potential to create composites similar to the tissues they are intended to replace. Here an existing process used to coat a surface with hydroxyapatite under near physiological conditions, the alternate soaking process, is modified and automated using an inexpensive "off the shelf" robotics kit. The process is initially used to precipitate calcium phosphate coatings. Then, in contrast to previous utilizations of the alternate soaking process, gelatin was added directly to the solutions in order to co-precipitate hydroxyapatite-gelatin composites. Samples were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and nanoindentation. Calcium phosphate coatings formed by the alternate soaking process exhibited different calcium to phosphate ratios, with correspondingly distinct structural morphologies. The coatings demonstrated an interconnected structure with measurable mechanical properties, even though they were 95% porous. In contrast, hydroxyapatite-gelatin composite coatings over 2mm thick could be formed with little visible porosity. The hydroxyapatite-gelatin composites demonstrate a composition and mechanical properties similar to those of cortical bone.

Wet-spinning of amyloid protein nanofibers into multifunctional high-performance biofibers.

Amyloid nanofibers derived from hen egg white lysozyme were processed into macroscopic fibers in a wet-spinning process based on interfacial polyion complexation using a polyanionic polysaccharide as cross-linker. As a result of their amyloid nanostructure, the hierarchically self-assembled protein fibers have a stiffness of up to 14 GPa and a tensile strength of up to 326 MPa. Fine-tuning of the polyelectrolytic interactions via pH allows to trigger the release of small molecules, as demonstrated with riboflavin-5'-phophate. The amyloid fibrils, highly oriented within the gellan gum matrix, were mineralized with calcium phosphate, mimicking the fibrolamellar structure of bone. The formed mineral crystals are highly oriented along the nanofibers, thus resulting in a 9-fold increase in fiber stiffness.

The fracture energy of metal fibre reinforced ceramic composites (MFCs)

A model is presented for prediction of the fracture energy of ceramic-matrix composites containing dispersed metallic fibres. It is assumed that the work of fracture comes entirely from pull-out and/or plastic deformation of fibres bridging the crack plane. Comparisons are presented between these predictions and experimental measurements made on a commercially-available composite material of this type, containing stainless steel (304) fibres in a matrix predominantly comprising alumina and alumino-silicate phases. Good agreement is observed, and it's noted that there is scope for the fracture energy levels to be high (~20kJm-2). Higher toughness levels are both predicted and observed for coarser fibres, up to a practical limit for the fibre diameter of the order of 0.5mm. Other deductions are also made concerning strategies for optimisation of the toughness of this type of material. © 2010 Elsevier Ltd.

Damage development in an armor ceramic under quasi-static indentation

The objective of the present study is to assess the capabilities of a recently developed mechanism-based model for inelastic deformation and damage in structural ceramics. In addition to conventional lattice plasticity, the model accounts for microcrack growth and coalescence as well as granular flow following comminution. The assessment is made through a coupled experimental/computational study of the indentation response of a commercial armor ceramic. The experiments include examinations of subsurface damage zones along with measurements of residual surface profiles and residual near-surface stresses. Extensive finite element computations are conducted in parallel. Comparisons between experiment and simulation indicate that the most discriminating metric in the assessment is the spatial extent of subsurface damage following indentation. Residual stresses provide additional validation. In contrast, surface profiles of indents are dictated largely by lattice plasticity and thus provide minimal additional insight into the inelastic deformation resulting from microcracking or granular flow. A satisfactory level of correlation is obtained using property values that are either measured directly or estimated from physically based arguments, without undue reliance on adjustable (nonphysical) parameters. © 2011 The American Ceramic Society.