Influence of Bioactive Glass Ions on Osteoblast Response During Mineralization

Introduction: Direct bone bonding occurs between implanted bioactive glasses and bone matrix. Corrosion products of bioactive glasses may play an active role in enhanced osteoblast matrix mineralization. (Hench et al; Foppiano et al.). Objective: To determine if these corrosion products enhance osteogenic marker expression and mineralized tissue production. Methods: Bioactive glass (53 wt.% SiO₂, 6P53-b) and Bioglass^TM (45 wt.% SiO₂, 45S5) were soaked in a-MEM (48h) and sterilized (0.2 µm filter) to produce an ion extract. These extracts were supplemented (10% FBS, 1% pen strep, 50 mg/L ascorbic acid, 10 mM glycerol-2-phosphate) to produce glass conditioned media (GCM) (6P53-b and 45S5), which were analyzed using Inductively Coupled Plasma Mass Spectrometry (ICPMS). GCM and control media were added to differentiated (21d) MC3T3-E1.4 osteoblast cultures for an additional 30d. Osteoblasts were assayed for production of alkaline phosphatase, osteocalcin, and studied for mineralization using histology and atomic force microscopy (AFM). Results: Ion concentrations (Si: 13.2±2.0 ppm for 45S5; Si: 32.0±4.5 ppm, Mg: 25.1±0.8 ppm for 6P53 b) were higher in GCM compared to controls (Si: < 0.1 ppm, Mg: 18.1 ppm in a-MEM). Akaline phosphatase expression was similar for GCM and control treated cultures. Osteocalcin expression was 2x higher in 45S5 GCM treated cells versus 6P53-b and control treated cells after 2 d in culture and this trend continued throughout mineralization (ANOVA, p < 0.05). Von Kossa staining showed mineralization tissue with evidence of cells surrounded by pericellular space within mineralized matrix. Results of AFM analysis showed mineralized fiber formation. Conclusions: Bioactive glass coating corrosion products in general enhance intracellular levels of osteogenic markers, however, overall mineralization was not altered. Support: NIH/NIDCR Grants 1K25DE018230-01, R01DE11289, and T32DE07306