Corrosion behaviour and biocompatibility of boron containing titanium alloys in simulated physiological environments

The corrosion behaviour of cast and hot isostatically pressed Ti-6Al-4V-B alloys was studied for several compositions in the <0.001-1.09 wt-% B range. Passivity and corrosion resistance were observed in all of the alloys subjected to cyclic potentiodynamic polarisation (CPP) in phosphate buffered saline. The CPP tests were also conducted in 0.9 wt-% sodium chloride (saline) over a wide potential range. The pitting potentials generally decreased with increasing boron content with the notable exception of the 0.01B alloys, which did not pit. The repassivation potentials generally increased with increasing boron content. When osteoclast precursor cells (macrophages) and osteoclast activating cells (fibroblasts) were cultured on Ti-6Al-4V-B alloy discs, higher levels of macrophage receptor activator of nuclear factor kappa B (RANK) and fibroblast RANK ligand were expressed in comparison with CP Ti, 316L and Ti-6Al-4V. This suggests that boron containing alloys may facilitate differentiation of osteoclasts derived from macrophages that interact with the prosthetic surface. However, it is not yet known whether the upregulation of RANK or RANK ligand is sustainable over longer periods of time.