Stimulation of in vitro and in vivo osteogenesis by Ti-Mg alloys with the sustained-release function of magnesium ions.

Magnesium (Mg) is well-known for its bioactivity and degradability. However, due to its low evaporation temperature and limited solubility in titanium (Ti), the fabrication of Ti-Mg alloys remains a huge challenge. In this study, Ti-xMg (x = 0.312, 0.625, 1.25 and 2.5 wt.%) alloys were fabricated by the combination of mechanical alloying (MA) and spark plasma sintering (SPS). Mg mainly existed as a solid solute element in the Ti matrix, while it also existed as second-phase particles due to its precipitation and dispersion during the SPS process. At a low content of 0.625 wt.%, Mg could increase the mechanical strength of Ti by the solid solution strengthening. However, it was detrimental to material mechanical properties when the Mg content increased to 1.25 wt.%. Being immersed in phosphate buffered solution (PBS), Ti-Mg alloys exhibited a burst Mg2+ release behavior within the first day, and then the rates of Mg2+ release gradually decreased within the following 27 days. The results suggested that the cell viability was dependent on the content of Mg in the Ti-Mg alloys. The high Mg content (2.5 wt.%) in the Ti-Mg alloys could lead to significant cytotoxicity. However, appropriate Mg content (0.312∼0.625 wt.%) could promote cell attachment, proliferation and differentiation. The Ti-0.625Mg alloy exhibited the best in vitro biological performance among all groups. In vivo results obtained by implanting the Ti-0.625Mg alloy in the femurs of rats further revealed its enhanced regenerative potential and osteointegration compared to pure Ti implants.