Bioactive Glass Corrosion Enhances Osteocalcin and Collagen Type 1 Expression

Objective: Direct bone bonding occurs between implanted bioactive glasses and bone matrix collagen (Hench and colleagues). We tested the hypothesis that bioactive glass corrosion products enhance collagen and osteocalcin expression and mineralized tissue formation by osteoblasts.

Methods: Bioactive glass (53 wt. % SiO₂, 6P53-b) and commercial Bioglass (45S5) specimens were soaked in cell culture medium (α-MEM, 10% FBS, 1% pen-strep, control medium) for 48 h to make glass conditioned medium (GCM) and analyzed by Inductively Coupled Plasma Mass Spectrometry (ICPMS) for their ion concentrations. GCM and control medium were added along with ascorbate (50 mg/L) and β-GP (10 mM) for differentiation and mineralization studies. Osteoblasts were assayed for protein and gene expression using sandwich ELISA and quantitative PCR (qPCR). Histology and atomic force microscopy (AFM) were used to image mineralized tissue formation.

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 (control: Si: < 0.1 ppm, Mg: 18.1 ppm). Collagen type 1 gene expression increased 3-fold after 1 day and osteocalcin increased 1.5- to 2-fold after 10 d GCM exposure. For mineralization, osteocalcin expression was 1.1- to 1.3-fold higher in GCM treated cells versus control after 2 d in culture, and this trend continued throughout mineralization (ANOVA, p < 0.05). Von Kossa staining showed evidence of cells surrounded by pericellular space and further surrounded by mineralized tissue. Results of AFM analysis showed mineralized fiber formation.

Conclusions: Bioactive glass corrosion enhanced collagen type 1 and osteocalcin expression in osteoblasts; however, there was no enhanced impact on matrix formation.

Support: NIH/NIDCR Grants 1K25DE018230-01, R01DE11289 T32DE07306, R01 DE015633, and Michelle Gras, Joel Commisso, and Dr. Peter Green (UC Davis) for ICPMS analysis.