Mechanical and biological properties of hydroxyapatite reinforced with 40 vol.% titanium particles for use as hard tissue replacement

Hydroxyapatite (HA)-based composite reinforced with 40 vol.% Ti particles was fabricated by the optimal technical condition of hot pressing technique. The mechanical and biological properties of the composite were studied by mechanical and in vivo methods. The experimental results show that HA and Ti phases are the predominant phases of the composite with partially decomposition of HA phase into α-Ca ₃(PO ₄) ₂ and Ca ₄O(PO ₄) ₂. Comparing with HA20 vol.% Ti composite manufactured under the same conditions, HA-40 vol.% Ti composite with similar elastic modulus (79.3 GPa) and Vicker's hardness (2.94 GPa) has a higher bending strength (92.1 MPa). Moreover, fracture toughness of HA40 vol.% Ti composite with crack bridging as the chief toughening mechanisms can reach 2.692 MPa m ^-1, which can meet the basic toughness demand of the replaced hard tissues for heavy load-bearing applications. Work of fracture of HA-40 vol.% Ti composite is 91.2 J m ², which is 22.9 times that of pure HA ceramic and even 2.4 times that of Al ₂O ₃ bioceramic. The results of in vivo studies show HA-40 vol.% Ti composite has excellent biocompatibility and could integrate with bone. In the early stage after the implantation of the samples, the osteointegration ability of the composite is better than that of pure titanium.