Intervertebral osteointegration and biomechanical performance of bioactive lithium disilicate glass-ceramic scaffold fabricated by digital light processing

The high strength of lithium disilicate (LD) glass-ceramic makes it difficult to form complex orthopaedic scaffolds using traditional methods. In addition, the osteointegration behavior of LD has also not been well studied in vivo. This study aimed to investigate the procedure of digital light processing (DLP) for fabricating porous LD glass-ceramic scaffolds and to assess the intervertebral osteointegration and biomechanical performance of the scaffolds. The phase formation, fracture morphology, flexural strength and density of LD glass-ceramics fabricated by DLP were evaluated to optimize the manufacturing process. Cell proliferation, cell differentiation and mineralization on the optimized glass-ceramics were recorded for comparison with traditional cast glass-ceramics (CG). The porous LD glass-ceramics scaffold was implanted into rabbits for 7 w and 14 w and then assessed using micro-CT and histological staining. Compression testing was also used to understand the scaffold's mechanical properties. Furthermore, the scaffold was inserted into a validated finite element model of a human lumbar spine to study the stress distribution during physiological motions. The results indicated that LD glass-ceramics with step-by-step crystallization formed principal phases of Li₂Si₂O₅ and Li₃PO₄, which had the highest flexural strength. Cell proliferation, cell differentiation and mineralization on the glass-ceramics formed by DLP were similar to the results of glass-ceramics formed by casting. The porous LD glass-ceramic scaffold promoted osseointegration in rabbits and was capable of withstanding physiological loads that would be experienced in a human lumbar spine. In conclusion, the bioactive LD glass-ceramic developed in this study showed good osteogenesis with sufficient mechanical performance, potentially making it suitable for applications in intervertebral fusion.