Biomedical titanium alloys with Young's moduli close to that of cortical bone.

Mitsuo Niinomi,Huihong Liu,Masaki Nakai,Hua Li,Yi Liu

doi:10.1093/rb/rbw016

Abstract

Biomedical titanium alloys with Young’s moduli close to that of cortical bone, i.e., low Young’s modulus titanium alloys, are receiving extensive attentions because of their potential in preventing stress shielding, which usually leads to bone resorption and poor bone remodeling, when implants made of their alloys are used. They are generally β-type titanium alloys composed of non-toxic and allergy-free elements such as Ti–29Nb–13Ta–4.6Zr referred to as TNTZ, which is highly expected to be used as a biomaterial for implants replacing failed hard tissue. Furthermore, to satisfy the demands from both patients and surgeons, i.e., a low Young’s modulus of the whole implant and a high Young’s modulus of the deformed part of implant, titanium alloys with changeable Young’s modulus, which are also β-type titanium alloys, for instance Ti–12Cr, have been developed. In this review article, by focusing on TNTZ and Ti–12Cr, the biological and mechanical properties of the titanium alloys with low Young’s modulus and changeable Young’s modulus are described. In addition, the titanium alloys with shape memory and superelastic properties were briefly addressed. Surface modifications for tailoring the biological and anti-wear/corrosion performances of the alloys have also been briefly introduced.

Highlights

With the rapid increase in the elderly population, disturbance of motility, which is one of the three main diseases: alongside cancer, circulatory diseases, is increasing among aged persons
Ti–12Cr has the highest cell density, which is considerably higher than that of SUS 316 L and Ti64 ELI, and similar to that of TNTZ. These findings indicate that Cr in Ti–12Cr can increase the tendency of Ti to passivate [46]
Low Young’s modulus titanium alloys composed of non-toxic and allergy-free elements are highly expected to be used in practical applications for load bearing-implants such as stems of artificial hip joints, bone plates, spinal fixation devices, artificial dental roots, etc., because they are effective in preventing stress shielding, which leads to bone resorption and poor bone remodeling

Summary

Introduction

With the rapid increase in the elderly population, disturbance of motility, which is one of the three main diseases: alongside cancer, circulatory diseases (cardiovascular diseases), is increasing among aged persons. The addition of a small amount of ceramic particles such as TiB2 or Y2O3 into the matrix is expected to improve the fatigue strength of b-type titanium alloys, while maintaining a low Young’s modulus This was confirmed by severe CR of TNTZ containing TiB2 or Y2O3 [40, 41], where Y or B contents are 0.1 and 0.2 mass% for B, or 0.05 and 0.1 mass% for Y, respectively, showing an improved fatigue strength of 550–600 MPa or 500–550 MPa, while their Young’s moduli are 60 MPa. The fatigue strength of TNTZ can be enhanced by solid solution strengthening by O solute [42]. In the application of titanium alloys with changeable Young’s modulus for the rods of spinal fixation devices, their fatigue strength is highly important factors. The development of novel titanium alloys, brings new challenges and chances for the existing surface modification techniques

Summary

Findings

49. ASTM F1717-15