Bioceramics in the CaMgSi2O6-Li2O System: A Glass-Ceramic Strategy for Excellent Mechanical Strength and Enhanced Bioactivity by Spontaneous Elemental Redistribution

A novel glass-ceramic strategy for synthesizing mixed phase diopside (CaMgSi2O6)-lithium oxide (Li2O) bioceramics with excellent mechanical strength, superior biodegradation resistance, low environmental pH impact, enhanced bioactivity, and reasonable biocompatibility is developed for biomedical applications. The substitution of Li2O for MgO in CaMgSi2O6 stimulates the formation of secondary phases: CaSiO3, Li2Si2O5, SiO2, Li2SiO3, and Li2Ca2Si5O13. The evolution of CaSiO3 improves the surface hydroxyapatite (HAp) formation but lowers the mechanical strength and biological resistance, while the amorphous Li2Si2O5 phase tremendously reinforces the bioceramics by densifying the microstructure, indicating the simultaneous enhancement of bioactivity, mechanical strength, and durability. The promoted HAp formation is induced by the elemental redistribution where Mg elements are concentrated in large CaMgSi2O6 grains embedded in Li2Si2O5 amorphous matrix, which hinders the Mg2+ release and its readsorption by HAp. The cell viability is affected by Li2O substitution because of the high-dose Li+. In the current work, Li0.25 (25 mol% Li2O) has the highest hardness (700 Hv as sintered and 197 Hv after simulated body fluid soaking), lowest weight loss (approximate to 0.6 wt%), lowest pH variation (approximate to 8.1), efficient HAp formation, and reasonable cell viability (70.5%), demonstrating its remarkable potential for bone implant applications due to the synergistic structural densification and biological improvement.