Porous titanium with porosity gradients for biomedical applications

Highly porous titanium and titanium alloys with an open cell structure are promising implant materials due to their low elastic modulus, excellent bioactivity, biocompatibility and the ability for bone regeneration. However, the mechanical strength of the porous titanium decreases dramatically with increasing porosity, which is a prerequisite for the ingrowth of new bone tissues and vascularization. In the present study, porous titanium with porosity gradients, i.e. solid core with highly porous outer shell was successfully fabricated using a powder metallurgy approach. Satisfactory mechanical properties derived from the solid core and osseointegration capacity derived from the outer shell can be achieved simultaneously through the design of the porosity gradients of the porous titanium. The outer shell of porous titanium exhibited a porous architecture very close to that of natural bone, i.e. a porosity of 70% and pore size distribution in the range of 200 - 500 mu m. The peak stress and the elastic modulus of the porous titanium with a porosity gradient (an overall porosity 63%) under compression were approximately 152 MPa and 4 CPa, respectively. These properties are very close to those of natural bone. For comparison, porous titanium with a uniform porosity of 63% was also prepared and characterised in the present study. The peak stress and the elastic modulus were 109 MPa and 4 GPa, respectively. The topography of the porous titanium affected the mechanical properties significantly.