Nano-mechanical properties of hydroxyapatite coatings with a focus on the single solidified droplet

Hydroxyapatite (HAp) is a common implant material choice for orthopaedic implants and is mostly used as a coating to improve the biocompatibility of implants and stimulate tissue growth. This is a desirable material for implants, but the thermal instability requires strict control of the processing conditions to produce a crystalline coating. A coating with well molten particles has been produced from flattened solidified droplets. This development has allowed further investigation of the coating surface with nanoindentation, profilometry and electron microscopy. Instrumented indentation testing, also known as depth-sensing indentation or nanoindentation, was used to gather information on the hardness and elastic modulus. It was found that the surface topography can lead to elevated values of the hardness and elastic modulus. The micromechanical properties will be higher when conducted on a sloped surface. It is recommended that any micromechanical data from a thermally sprayed coating be accompanied with topographic map of the flattened solidified droplet.