Recent Progress in Mechanically Biocompatible Titanium-Based Materials

Recent Progress in Mechanically Biocompatible Titanium-Based Materials

Masaaki Nakai (Institute for Materials Research, Tohoku University, Japan) and Mitsuo Niinomi (Institute for Materials Research, Tohoku University, Japan)
DOI: 10.4018/978-1-4666-2196-1.ch022
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Abstract

Mechanical and biological biocompatibility is important consideration for materials that are used as metallic implants. During the past two decades, many ß-type titanium alloys composed of non-toxic and hypoallergenic elements with low Young’s moduli have been developed worldwide. Recently, the development of new titanium-based materials to improve the mechanical and biological biocompatibility of metallic implants has progressed under advanced concepts. This chapter focuses on the improvement of mechanical biocompatibility, and recent research topics on such material developments are reviewed.
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Further Reducing Young’S Modulus

As mentioned above, a low Young’s modulus equal to that of bone is desired for metallic implants. Among titanium alloys, β-type titanium alloys tend to exhibit lower Young’s moduli than α- or (α + β)-type titanium alloys (Niinomi, 1998). Therefore, extensive efforts have been made to develop β-type titanium alloys with a Young’s modulus close to that of bone. Over the past two decades, controlling β-phase stability via optimization of the chemical composition of the alloys has enabled a reduction of the Young’s modulus to approximately 40–60 GPa in some β-type Ti-Nb based titanium alloys (Ahmed, Long, Silvestri, Ruiz, & Rack, 1996; Hao, Li, Sun, & Yang, 2006; Kuroda, Niinomi, Morinaga, Kato, & Yashiro, 1998; Matsumoto, Watanabe, & Hanada, 2005; Saito et al., 2003. The advantage of a low Young’s modulus for suppressing the stress shielding effect has been demonstrated in animal experiments (Sumitomo et al., 2008). However, even using β-type Ti-Nb-based titanium alloys with a low Young’s modulus, the stress shielding effect could not be completely eliminated. Therefore, a further reduction in the Young’s modulus is desired for metals that are to be used in metallic implants. To accomplish this reduction, the following two methods have been investigated: (1) controlling the crystal orientation using single crystals and (2) controlling porosity using porous materials.

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