Machinable diopside-lanthanum phosphate composite ceramics for fabricating load bearing bone implants

Bioceramic-based composites are extensively being used in orthopedics for decades due to their excellent biocompatibility and osteoconductivity. However, the inherent brittleness and high hardness of ceramics heavily impact their machinability, thus restricting their use as bone fixation devices. In this study, Mg-doped calcium silicate ceramic diopside (DI) has been employed as a ceramic matrix material owing to its superior mechanical properties in comparison to hydroxyapatite. To impart machinability in the diopside, rare earth lanthanum phosphate (LP) was introduced as a reinforcement. The indigenously synthesized and 800 °C calcined DI and LP powders were employed for composite fabrication by varying LP content (0–50% w/w). The composites were sintered at different temperatures (1000 °C, and 1200 °C) and sintering conditions (single sintered, and double sintered), and the 1200 °C double sintered (ds) composites were optimized due to their highest densification and mechanical properties. Among the optimized composites, ds-DI-LP (50:50, DL50) displayed the highest compressive strength (140 ± 5.21 MPa) compared to DL5 (121.16 ± 14.82 MPa) and DL10 (122.78 ± 28.74 MPa) composites. It was observed that the weak and layered LP interface in between the DI phase promoted machinability in the composites. Apart from being machinable, these ceramic composites were found to be bioactive, resulting in the formation of an apatite layer when immersed in simulated body fluid. Further, the optimized ceramic composites were found to be biocompatible and osteoconductive in nature on their functional assessment using primary rat calvarial osteoblast cells. Based on the results obtained, the ds-DL10 composites displayed considerable bioactivity and the highest ALP activity compared to ds-DL5 (p ≤ 0.01) and ds-DL50 (p ≤ 0.05) composites.