Fabrication of open-pored titanium foam for biomedical implants

Open-pored metal foams have been partly used for orthopedic or dental applications because of their good bone ingrowth behavior and low elastic modulus. In this paper, we report a method that can produce open-pored Ti foams using a technique that combines the powder injection molding process and feedstocks containing expandable polystyrene beads as a space holder. The expandable beads in the feedstocks undergo swelling during the foaming process, which causes the spaces occupied by the expandable beads to directly contact each other and become interconnected. This behavior results in the formation of open-pored Ti foams with high porosity (equivalently, low Young's modulus) and large faces (greater than 140 μm). Compared to metallic foams prepared by conventional methods, Ti foams produced in this study have significantly larger face sizes (140-170 μm) and lower Young's modulus (∼17 GPa). These characteristics of the developed foam materials can promote fast bone growth into open-pored porous structures and permit improved fixture installation stability. This paper discusses the mechanism for the formation of the openpored porous structure, and analyzes the effect of various processing conditions on the face size, porosity and Young's modulus of Ti foams.