Comparison of the mechanical properties between tantalum and nickel–titanium foams implant materials for bone ingrowth applications

Metallic porous materials are designed to allow the ingrowth of living tissue inside the pores and to improve the mechanical anchorage of the implant. In the present work, tantalum and nickel–titanium porous materials have been characterized. The tantalum foams were produced by vapour chemical deposition (CVD/CVI) and the NiTi foams by self-propagating high temperature synthesis (SHS). The former exhibited an open porosity ranging between 65 and 73% and for the latter it ranged between 63 and 68%. The pore sizes were between 370 and 440 μm for tantalum and between 350 and 370 μm for nickel–titanium. The Young's modulus in compression of the foams studied, especially for tantalum, were very similar to those of cancellous bone. This similitude may be relevant in order to minimize the stress shielding effect in the load transfer from the implant to bone. The strength values for NiTi foam are higher than for tantalum, especially of the strain to fracture which is about 23% for NiTi and only 8% for tantalum. The fatigue endurance limit set at 108 cycles is about 7.5 MPa for NiTi and 13.2 MPa for tantalum. The failure mechanisms have been studied by scanning electron microscopy.