Surface modification of silicon nitride ceramics by secondary phase removal for improved biomedical performance

Silicon nitride (Si 3 N 4 ) is considered a potential material for biomedical implants due to its mechanical strength and biocompatibility. However, the presence of a glassy phase may affect osseointegration by potentially leading to ion release and altered surface wettability, among other effects. In this study, a surface modification method using molten NaOH was employed to remove the secondary phase and improve surface characteristics. The treated samples (N-SN) showed increased surface roughness and exposure of crystalline planes, which are associated with enhanced cell adhesion. In vitro experiments indicated that N-SN supported the proliferation and osteogenic differentiation of MC3T3-E1 preosteoblasts, with up-regulated expression of osteogenic marker genes such as ALP, Col-1, OPN, and Runx-2. In a Beagle dog mandible model, N-SN implants formed direct bone contact and newly formed bone tissue without evident inflammatory response, suggesting improved osseointegration. This surface treatment approach may provide a practical option for enhancing the bioactivity of Si 3 N 4 ceramics in orthopedic and dental applications.