A systematic investigation into β-phase Ti-alloys for biomedical applications

Melmoth, Lucie (2018) A systematic investigation into β-phase Ti-alloys for biomedical applications. Masters by Research thesis (MPhil), Manchester Metropolitan University.

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Abstract

Total hip replacement procedures are becoming increasingly common and often necessary due to injury in young patients. The materials currently utilised have a relatively short lifespan in comparison with the growing life expectancy of the population; this inherently results in the requirement of revision surgery continuing to rise. It is therefore imperative to develop a more suitable material, with greater durability and biological tolerance to reduce the number of complex, disruptive, and ultimately costly revision procedures. Currently, Ti-6Al-4V monopolises the metallic implant market; it has more desirable mechanical properties, including a relatively low elastic modulus (≈ 115GPa) and superior specific strength when compared to the cobalt-chromium and stainless steel alloys. However, in comparison to bone (≈ 30GPa) the elastic modulus is still too high. This leads to the bone remodelling, as a result of a changing stress/strain imposed, known as stress shielding; which could eventually lead to implant failure. In addition, efforts must be made to eliminate elements that have been associated with adverse reactions from the implant material. Recently, β-phase titanium alloys have shown promise; they have lower elastic modulus, more comparable to that of bone, than alloys in the α-β phase (such as Ti-6Al-4V) and the majority of alloying elements (such as tantalum and niobium) are currently believed to be non-toxic and highly biocompatible. Ultimately, the chosen biomaterial and implant design should possess all of the following attributes: excellent biocompatibility, high corrosion and wear resistance, suitable mechanical properties and osseo-integration. This thesis details a systematic approach, employed to develop and test a range of binary, titanium alloys, with alloying elements, niobium and molybdenum. The alloys were prepared via magnetron sputtering, before characterization and testing using techniques such as: X-ray diffraction; scanning electron microscopy; and energy dispersive X-ray spectroscopy. The alloys biocompatibility was also assessed using human mesenchymal stem cells, with alamarBlue® assay and scanning electron microscopy. The results obtained in this thesis using human mesenchymal stem cells, with alamarBlue® assay and scanning electron microscopy, suggested very little or no toxicity in binary Ti-Mo alloys with Mo content less than 25 at% and no toxicity in binary Ti-Nb alloys; therefore all the alloys investigated in this thesis show promise for biomedical applications with the exception of Ti-50Mo. The research completed in this thesis also suggests that this method of fabrication and analysis is a time, and cost efficient method that gives an initial indication of the most suitable alloy systems; it is important to note that the method proposed would not be employed to manufacture any part of the hip implant, its sole use is at the initial stage of alloy development.