Fabrication and characterization of hydroxyapatite reinforced with 20 vol % Ti particles for use as hard tissue replacement.

Hydroxyapatite(HA)-based composite reinforced with 20 vol % titanium (Ti) particles was fabricated by hot pressing based on the studies of the structural stability of HA phase in HA-Ti composite by means of FTIR spectrometry and X-ray diffractometry. The mechanical properties and biological behaviors of the composite were investigated by mechanical and in vivo studies. The existence of Ti metal phase can promote the dehydration and decomposition of HA ceramic phase into the more stable calcium phosphate phases, such as alpha-Ca(3)(PO(4))(2) (alpha-TCP) and Ca(4)O(PO(4))(2) at high temperatures. Comparing with pure HA ceramic manufactured under the same conditions, HA-20 vol % Ti composite with higher fracture toughness (0.987 MPa m(1/2)), bending strength (78.59 MPa), work of fracture (12.8J/m(2)), porosity (9.8%) and lower elastic modulus (75.91 GPa) is more suitable for use as hard tissue replacement. Crack deflection is the chief toughening mechanism in the composite. Histological evaluation by light microscope shows HA-20 vol % Ti composite implant could be partially integrated with newborn bone tissues after 3 weeks and fully osteointegrated at 12 weeks in vivo. The excellent biological properties of HA-20 vol % Ti composite may be contributed to the coexistence of high porosity and the decomposition products of HA phase in the composite.