Bioactive Borate-Based Glass Coatings For Titanium Alloy Femoral Stems
thesisposted on 24.05.2021, 07:32 by Yiming Li
Hydroxyapatite (HA)-coated Ti6Al4V stems are currently used in total hip replacement (THR) surgeries. However, the residual stress in the HA coating due to mismatch in coefficient of thermal expansion (CTE) between HA and Ti6Al4V limits their application. Borate-based glasses can be promising alternatives to HA because of their similar CTEs to that of Ti6Al4V and excellent bioactivity that can promote bone repair. In this project, six borate-based glasses (Ly-B0, Ly-B1, Ly-B2, Ly-B3, Ly-B4, Ly-B5) from the B2O3-P2O5-CaO-Na2O-TiO2-SrO series were formulated by increasing the concentration of strontium oxide (SrO)from 0 to 25 in mol% at the expense of B2O3 in the glass series. Increased SrO content induced larger amounts of non-bridging oxygens and resulted in gradual increases in glass transition temperature (Tg). Discs of each glass powder were immersed in de-ionized water under 1, 7 and 30 days, and then the water extracts were used to determine the solubility and osteo-stimulatory effect of the glasses. Sr2+ doping retarded the dissolution rate of the glasses and the higher levels of Sr2+ doping (20 mol% and 25 mol%) promoted proliferation of osteoblasts. Except for Ly-B5 (containing 25 mol% SrO), discs of each glass powder exhibited bacteriostatic behavior against Staphylococcus aureus after 24 hours exposure. The glasses were enamelled onto Ti6Al4V substrates, and then bi-layer double cantilever beam (DCB) specimens were manufactured to measure the Mode I (GIC) and Mode II (GIIC) energy release rate of the glass coating/Ti6Al4V constructs. The mean GIC values increased from 6.56 ± 0.9 to 14.6 1 ± 2.1 J/m2 with increasing SrO content from Ly-B0 to Ly-B5, and the mean GIIC values increased from 36.07 ± 3.8 to 46.92 ± 3.3 J/m2 with increasing SrO content from Ly-B0 to Ly-B5, indicating that the incorporation of 15-25 mol% SrO significantly increased the fracture toughness of the construct. Moreover, the GIC and GIIC values of the coating/substrate system for all the six glasses significantly reduced (p ≤ 0.05) due to degradation in de-ionized water.