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 orthopaedic applications.