Addition of Sn to TiNb alloys to improve mechanical performance and surface properties conducive to enhanced cell activity.

C Torres-Sánchez,L Zani,M Norrito,P.P Conway,J Wang

doi:10.1016/j.msec.2020.110839

Abstract

Titanium (Ti) alloys with Niobium (Nb) and Tin (Sn) were prepared in order to conduct a systematic study on the bulk and surface properties of as-cast c.p.Ti, binary Ti-40Nb and Ti-10Sn, and ternary Ti-10Nb-5Sn (at.%) to ascertain whether Sn content can be used as an enhancer for cell activity. From a metallurgy viewpoint, a range of binary and ternary alloys displaying distinctive Ti phases (i.e. β, α', α") were achieved at room temperature. Their surface (oxide thickness and composition, roughness, contact angle) and bulk (compressive stiffness, strength, elongation, microhardness, electrical resistance) features were characterised. The same surface roughness was imparted on all the alloys, therefore substrate-cell interactions were evaluated independently from this variable. The physico-mechanical properties of the ternary alloy presented the highest strength to stiffness ratio and thereby proved the most suitable for load-bearing orthopaedic applications. From a cellular response viewpoint, their cytotoxicity, ability to adsorb proteins, to support cell growth and to promote proliferation were studied. Metabolic activity using a mouse model was monitored for a period of 12 days to elucidate the mechanism behind an enhanced proliferation rate observed in the Sn-containing alloys. It was hypothesised that the complex passivating surface oxide layer and the bulk inhomogeneity with two dominant Ti phases were responsible for this phenomenon.

Highlights

Titanium (Ti) and its alloys attract much interest due to their low density, manufacturability, corrosion resistance, non-toxicity, bio-inertness and highly tuneable bulk mechanical properties arising from different approaches to alloying and thermal post-processing routines
Ti, intended for bioengineering applications [2,3], has been alloyed with elements such as Niobium (Nb), a beta stabiliser which suppresses the formation of equilibrium hexagonal closed-packed α,martensite hcp α’ and orthorhombic α” when quenching to room temperature, and Tin (Sn), a low-cost neutral stabiliser that diminishes the formation of the embrittling isothermal ω phase, stabilising the β phase and lowering the stiffness
Near the casting mould where rapid cooling occurs inducing constitutional supercooling, dendritic solidification with varying dendrite arms spaced at approximately 10 μm were observed (Supplementary S1)

Summary

Introduction

Titanium (Ti) and its alloys attract much interest due to their low density, manufacturability, corrosion resistance, non-toxicity, bio-inertness and highly tuneable bulk mechanical properties arising from different approaches to alloying and thermal post-processing routines. The use of alloying elements has permitted the modulation of a lower stiffness and a higher strength than pure Ti at room temperature. This is an attractive proposition when bone-mimicking properties are sought, because side effects such as stress shielding leading to osteopenia and implant loosening are undesirable [1]. Caution has been exercised when selecting relevant studies due to the different manufacturing processes, thermal/

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