Effect of silver and strontium incorporation route on hydroxyapatite coatings elaborated by rf-SPS

Hydroxyapatite coatings have been currently used on hip prostheses for their ability to promote faster osseointegration and bone growth. Nevertheless, post-operative infections remain a recurring problem. To overcome this issue, doping with antibacterial elements has become a new trend. In this work, hydroxyapatite coatings elaborated by radio-frequency suspension plasma spraying (rf-SPS) were doped with silver and strontium. Several doping strategies were explored thanks to the versatility offered by SPS compared with conventional spraying. First way: calcium phosphate doped powders were synthesized by coprecipitation and then dispersed into water before plasma spraying; second way: undoped powder was dispersed into aqueous medium in which nitrates or nanoparticles of the dopant(s) were respectively dissolved/dispersed. XRD revealed a high level of crystallinity ratio (ISO 13 779) and hydroxyapatite proportion for most of the coatings, with the presence of Ag/Ag2O nanoparticles whatever the doping route. SEM-EDS and STEM have demonstrated a more homogeneous distribution of the strontium within the coating made from the doped powder. Adherence of the coatings was estimated via a 3-point bending test, while bacteriological tests with S. aureus and proliferation of mesenchymal stem cells (hMSC) were performed. The results indicated a preferential incorporation of strontium into the secondary phases, showed efficient bactericidal properties, excellent mechanical properties in comparison with an APS reference coating, and no evidence of cytotoxic effect. This opens the way of a new type of coatings with a finer structure and a higher homogeneity through a better control of physicochemical properties using a suspension as the precursor.