Combination of hydroxyapatite islets with Ti3P surface layer produced on titanium alloy for bone implants

This study is concerned with the properties and bioactivity and biocompatibility of hydroxyapatite islets deposited on a new composite layer Ti3P+Ti2Ni type produced by a duplex method on Ti6Al4V titanium alloy. The microstructure and chemical composition of a produced surface layers and hydroxyapatite coating were investigated using scanning electron microscope equipped with EDS. Their bioactivity were examined in simulated body fluid and analyzed with XPS. Dissolution of hydroxyapatite was tested in culture medium during 12 days of incubation. Biocompatibility was investigated in osteoblast Saos2 line culture in contact with the tested material. Cell proliferation and activity were determined by the MTT test and measurement of alkaline phosphatase activity, respectively. Cell distribution was analyzed under a confocal microscope. The produced surface layers have a diffusion character with fine-grained structure and about 4 microm thick external zone of Ti3P. The experiments revealed higher bioactivity and biocompatibility of the Ti3P in comparison with reference titanium alloy. Hydroxyapatite islets were 0.8 mm in diameter and about 300 nm thick. They partially dissolved during the experiment what lead to formation on Ti3P between hydroxyapatite islets a precipitate containing Ca and P. Biocompatibility analyzed under confocal microscope in range of cell adhesion with osteoblast cells of Saos2 line revealed initial the highest osteoblast adhesion on Ti3P between hydroxyapatite islets and increasing on hydroxyapatite during following days. Cell were characterized by high proliferation and ALP activity. Therefore, the high bioactivity and biocompatibility of Ti3P and profitable hydroxyapatite properties make this composite layer promising for increasing implant fixation in vivo.