Structure, properties, and biomedical performance of osteoconductive bioceramic coatings

The development of bioceramic materials is at the forefront of health-related issues in many countries. Arguably, research into ceramic biomaterials has reached a level of involvement and sophistication comparable only to electronic ceramics. Despite the fact that calcium phosphate-based coatings on hip, knee and dental implants have a long history of clinical success the quest of improving the longevity of implants and to impart them with better physiological properties is high up on the agenda of numerous research groups around the world. Coating the stem of modern cementless endoprostheses with a layer of plasma-sprayed hydroxyapatite improves the ingrowth of bone cells and thus assists in anchoring the implant to the cortical bone matter. However, since the high temperature process of plasma spraying leads to incongruent melting and thus thermal decomposition of the hydroxyapatite, knowledge of the complex transformation sequence is essential to design coatings with optimum stability and hence biological performance. This contribution reviews recent research into the thermal history of thermally sprayed calcium phosphate coatings as well as their in vitro behavior in contact with simulated body fluid.

► Plasma spraying of hydroxyapatite leads to dehydroxylation and decomposition.
► During spraying oxyapatite and amorphous calcium phosphate (ACP) form.
► On contact with SBF ACP transforms to nano- and micro-sized hydroxyapatite.
► The transformation is being analyzed by synchrotron XRD and solid state NMR.