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Abstract

Sintering in air and hot isostatic pressing are production methods regarded as being capable of producing fibre-reinforced hydroxyapatite ceramics for biomedical applications. These composites may have the advantage of improved mechanical properties and be suitable for applications in areas where there are significant levels of load on the material. The use of pure hydroxyapatite is restricted to those free of dynamical load. Obtaining improved mechanical strength is a question of the bond between the matrix phase and the fibre-reinforcement phase. However, a chemical bond between both phases, indicated by large diffusion zones, might lead to the dehydration of the hydroxyapatite leading to undesired tricalcium phosphate in the matrix resulting in a weakening of the mechanical and biological stability of the composites. Composites with three fibre types, alumina, 316L-stainless steel and titanium were prepared and sintered in air or hot isostatically pressed. A reaction zone was noted around the titanium and stainless steel fibres, but not around the alumina fibres. The reaction zone was larger for stainless steel than titanium. Hot isostatic pressing also reduced the reaction zone markedly compared to sintering in air.

Short Fiber Reinforced Hydroxyapatite‐based Bioceramics

“…Firstly, there is insufficient optimization of the fiber-matrix interface. [12,13] Secondly, there can be defects within the ceramic matrix, like cracks or porosity. [2,14,15] Diffusion between fibers and hydroxyapatite was evaluated by Knepper et al [12] Elements from the hydroxyapatite matrix (calcium, phosphorous) appear to diffuse into metallic short fibers, like stainless steel and titanium fibers.…”

“…[22] Impurities decrease the temperature at which the decomposition begins and the addition of reinforcements acts in the same way. [12,23,24] Possible reasons for this are the change of the dehydroxylation behaviour and a change of the Ca:P-ratio due to different diffusion of calcium and phosphorous into the reinforcement or chemical reactions.…”

“…[31] As stated before, diffusion of calcium and phosphorous can occur into the reinforcing components. [12] Due to this diffusion, the Ca:P-ratio can be changed. Subsequently, the formation of calcium phosphates with Ca:P-ratios, which differ from the stoichiometry of calcium hydroxyapatite, is promoted.…”

“…Hot pressing or hot isostatic pressing retard the decomposition. [11,12,34] In this way, a dense and fine-grained ceramic matrix of pure hydroxyapatite and a tailored fiber-matrix interface are achievable.…”

Reinforcing of a Calcium Phosphate Cement with Hydroxyapatite Crystals of Various Morphologies

“…There are two types of reinforcement phases: bioinert and bioactive. In the case of a bioinert approach, examples include the reinforcement of hydroxyapatite (HA, Ca 10 (PO 4 ) 6 (OH) 2 ) ceramics by adding various biocompatible fibers, such as polymers , , C , SiC , ZrO 2 , or Al 2 O 3 to improve their mechanical properties. Ordinarily, the bioactivity and bioresorbability of such composites is reduced, as the bioinert fillers do not interact with the host tissue.…”