P2O5 enhances the bioactivity of lithium silicate glass ceramics via promoting phase transformation and forming Li3PO4

Lithium silicate (LS) glass ceramic with excellent mechanical performance has been used in dental restoration but is seldom used in orthopedics due to its limited bioactivity. Given the osteoconductive features of calcium phosphate-based ceramics, optimizing the P2O5 content to adjust the ratio of CaO to P2O5 may improve the bioactivity of glass ceramics. The effect of P2O5 content on the phase formation, mechanical performance, cell proliferation, cell differentiation and mineralization of glass ceramics were investigated in this study. The results indicated that increasing the content of P2O5 increased the formation temperature of LiAlSi2O6 and provided nucleation sites for Li2SiO3 by forming Li3PO4 which, in turn, promoted the transformation from Li2SiO3 to Li2Si2O5. The phase morphology transformed from a lamellar shape to a columnar shape, and then formed an interlocking structure in the specific heat treatment. The phase transformation and formation of Li3PO4 improved cell proliferation, cell differentiation, and mineralization of the glass ceramics. In particular, the glass ceramic with 2.58 mol% P2O5 (LS3) and 4.12 mol% P2O5 (LS4) promoted the expression of alkaline phosphatase (ALP) and achieved the strength requirement of bone. In conclusion, the bioactivity of the glass ceramics was enhanced by increasing the P2O5 content, and the bone-like structure on the surface of the glass ceramic with 4.12 mol% P2O5 may make this material suitable for orthopedic applications.