Newly developed Ti–Nb–Zr–Ta–Si–Fe biomedical beta titanium alloys with increased strength and enhanced biocompatibility

Abstract

Beta titanium alloys are promising materials for load-bearing orthopaedic implants due to their excellent corrosion resistance and biocompatibility, low elastic modulus and moderate strength. Metastable beta-Ti alloys can be hardened via precipitation of the alpha phase; however, this has an adverse effect on the elastic modulus. Small amounts of Fe (0-2 wt.%) and Si (0-1 wt.%) were added to Ti-35Nb-7Zr-6Ta (TNZT) biocompatible alloy to increase its strength in beta solution treated condition. Fe and Si additions were shown to cause a significant increase in tensile strength and also in the elastic modulus (from 65 GPa to 85 GPa). However, the elastic modulus of TNZT alloy with Fe and Si additions is still much lower than that of widely used Ti-6Al-4V alloy (115 GPa), and thus closer to that of the bone (10-30 GPa). Si decreases the elongation to failure, whereas Fe increases the uniform elongation thanks to increased work hardening. Primary human osteoblasts cultivated for 21 days on TNZT with 0.5Si+2Fe (wt.%) reached a significantly higher cell population density and significantly higher collagen I production than cells cultured on the standard Ti-6Al-4V alloy. In conclusion, the Ti-35Nb-7Zr-6Ta-2Fe-0.5Si alloy proves to be the best combination of elastic modulus, strength and also biological properties, which makes it a viable candidate for use in load-bearing implants.

A Review of Metastable Beta Titanium Alloys

“…However, α + β Ti alloys generally have lower notched fatigue resistance and poorer wear characteristics compared to metastable beta Ti alloys [75]. Another consideration is the modulus of elasticity mismatch between α + β Ti alloys, which is approximately between 110 GPa and 115 GPa, and cortical bone, which is approximately 30 GPa [11,30]. The stiffer implant carries the load rather than the bone, which atrophies and loses density (osteopenia) due to lack of functional stimulation in a process known as stress shielding [77].…”

“…More recently, several new experimental metastable beta Ti alloys have been developed including Ti-35Nb-7Zr-6Ta-(0-2)Fe-(0-1)Si (wt. %) [30], Ti-8Mo-(4-6)Nb-(2-5)Zr (wt. %) [31], Ti-33Nb-4Sn (wt.…”

Novel Ti-Ta-Hf-Zr alloys with promising mechanical properties for prospective stent applications

“…Considering the biocompatibility and the stability of β phase, β stabilizers such as Mo, Ta, Nb, Hf, Pd and Fe are usually selected as primary additive elements in the design of a β-type biomedical Ti alloy. Moreover, Zr can be used as a β stabilizer when used with combination of other β stabilizers such as Ta and Nb, and improve the performance of the Ti alloys202122232425. In this study, Ta, Zr and Hf were selected as the β stabilizers in order to achieve improved performance of the Ti alloys.…”

Cytocompatibility assessment of Ti‐Zr‐Pd‐Si‐(Nb) alloys with low Young's modulus, increased hardness, and enhanced osteoblast differentiation for biomedical applications

“…In addition, our earlier study, also performed on β‐Ti alloys, showed that the adhesion and proliferation of human osteoblast‐like U‐2 OS cells and primary human osteoblasts on Ti–35Nb–7Zr–6Ta (TNZT) with various small additions of Fe and Si (particularly those with 0.5 wt % of Si+ 2 wt % of Fe) were higher than on the Ti‐6Al‐4 V alloy. At the same time, the number of U‐2 OS cells on Ti‐6Al‐4 V was significantly lower than in control tissue culture polystyrene wells (by about 25%), and the number of human osteoblasts on Ti‐6Al‐4 V was even ∼8.5 times lower than on polystyrene wells . The TNZT alloys also better promoted the production of collagen I, that is, an early marker of osteogenic differentiation, in primary human osteoblasts than the Ti‐6Al‐4 V alloy and standard cell culture polystyrene dishes .…”