Nanostructured Hydroxyapatite Coatings for Orthopaedic Implants: Synthesis, Characterisation, and Biocompatibility Testing Using Nigerian Derived Calcium Sources

Hydroxyapatite (HA) coatings on orthopaedic implants enhance osseointegration by mimicking the mineral phase of natural bone. However, dependence on imported precursor materials limits local production capacity in Nigeria. This study investigates the synthesis, physicochemical characterisation, and in vitro and in vivo biocompatibility of nanostructured HA coatings derived from locally sourced Nigerian calcium carbonates including eggshell, snail shell, and limestone from Benue and Enugu States. Synthesis will employ a wet chemical precipitation method followed by sintering, with phase purity characterised by X-ray diffraction, Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Coating deposition on medical-grade titanium substrates will be achieved using electrophoretic deposition. Mechanical adhesion, porosity, and in vitro dissolution will be assessed. Biocompatibility will be evaluated using cell viability assays with human osteosarcoma (MG-63) cell lines, and in vivo osseointegration assessed in a rat femoral implant model at eight weeks using histomorphometry and biomechanical pull-out testing. The study hypothesises that Nigerian-derived HA coatings achieve equivalent crystallinity, stoichiometry, and in vivo osseointegration performance to commercially imported coatings. This research constitutes an original contribution to Nigerian biomaterials science, establishing a framework for local implant coating manufacturing that could substantially reduce the cost of orthopaedic implants across the country. Keywords: hydroxyapatite, orthopaedic implants, nanostructured coatings, biomaterials, osseointegration.