Microplasma spraying of hydroxyapatite coatings on additive manufacturing titanium implants with trabecular structures

This paper presents new results of microplasma spraying (MPS) of laboratory-synthesized hydroxyapatite (HA) powder coatings onto trabecular substrates obtained by selective laser melting (SLM) of a certified titanium medical alloy powder. The aim of the study was to establish the possibility of combining the technologies of MPS and additive manufacturing (AM) for the possible production of custom-designed implants with increased surface biocompatibility, as well as to establish the MPS parameters that ensure chemical purity of the HA coating and satisfactory adhesion of the coatings to the substrate. The structural-phase compositions of the initial HA powder and the plasma-sprayed HA coating were studied by X-ray diffraction analysis and transmission electron microscopy, and the adhesion strength of the coating was tested according to the F1147 standard of the American Society for Testing and Materials (ASTM). The main results of the study are the following: the application of the MPS technology for HA coating with an average thickness of 150±50 μm on trabecular substrates obtained by the SLM method has been shown. The parameters of MPS of HA coatings onto titanium implants with a trabecular surface have been established. It is also proved that using the appropriate MPS parameters, it is possible to obtain a HA coating with a 95% level of HA phases, 93% level of crystallinity, and the adhesion strength to the trabecular substrate of 24.7±5.7 MPa, which complies with the requirements of the international medical standard (International Organization for Standardization [ISO] 13779-2:2018). These results are of significance for a wide range of researchers developing plasma spray technologies for the manufacture of biocompatible coatings.