Fabrication of a biodegradable and cytocompatible magnesium/nanohydroxyapatite/fluorapatite composite by upward friction stir processing for biomedical applications.

Biodegradable magnesium (Mg)-based metal matrix composites are promising candidates for orthopaedic applications since magnesium is an abundant mineral in the human body. To improve the bioactivity and cytocompatibility of these Mg composites, hydroxyapatite nanoparticles (HAP) and fluorapatite (FA) microparticles synthesised by a citrate-derived hydrothermal method were introduced into a Mg matrix. These innovative Mg/HAP/FA composites were produced by multi-pass upward friction stir processing (UFSP). Microstructural observation and Micro-CT reconstruction of the composite revealed that HAP and FA particles are well dispersed in the Mg matrix and the magnesium grain size was significantly reduced after the UFSP process. The in vitro bioactivity behaviour of UFSP processed Mg/HAP/FA composites was investigated in simulated body fluid. The results revealed the formation of a fluoride-rich apatite layer on the composites, which was attributed to the release of fluoride ions from the composite and their precipitation in a different configuration. Moreover, cytocompatibility results revealed that the presence of FA particles, together with HAP nanoparticles, were able to favour osteoblasts-biomaterial interaction.