Design and characterization of highly porous titanium foams with bioactive surface sintering in air

• The bioactive porous Ti foam is fabricated by single-step sintering in air.
• The Ti foam exhibit the rutile TiO2 on the Ti strut surfaces.
• The total porosity is larger than 79%, and open porosity is larger than 74%.
• The mechanical properties of porous Ti foams are comparable to those of natural bone.

Titanium (Ti) foams are attracting increasing interest in bone tissue engineering. The elastic modulus of Ti and its alloys can be reduced through the introduction of a porous structure, thereby addressing the stress shielding problem. Moreover, a porous structure may also provide new bone tissue ingrowth abilities and vascularization. In the present study, highly porous Ti scaffolds were prepared through a sponge replication method. The results showed that the Ti foam samples sintered in air at 800, 900, or 1000 °C exhibit the presence of rutile TiO2 on the Ti strut surfaces, which could bioactivate Ti foams. The oxide layers formed on the strut surface were relatively smooth and the thickness increased with an increase in sintering temperature. Additionally, the total porosities of the Ti foams sintered at three different sintering temperatures are larger than 79%, and open porosity is larger than 74%. The open porosity ratio is in excess of 0.92, suggesting that most pores are interconnected. Moreover, the strength and modulus of the sintered Ti foams conforms to the basic mechanical property requirement of cancellous bones. In this research, the highly porous Ti foams with a bioactive oxide layer were successfully fabricated by single-step sintering in air instead of a conventional vacuum atmosphere.