Effect of Borate Glass Composition on Its Conversion to Hydroxyapatite and on the Proliferation of MC3T3-E1 Cells

Glasses containing varying amounts of B ₂ O ₃ were prepared by partially or fully replacing the SiO ₂ in silicate 45S5 bioactive glass with B ₂ O ₃ . The effects of the B ₂ O ₃ content of the glass on its conversion to hydroxyapatite (HA) and on the proliferation of MC3T3-E1 cells were investigated in vitro . Conversion of the glasses to HA in dilute (20 m M ) K ₂ HPO ₄ solution was monitored using weight loss and pH measurements. Proliferation of MC3T3-E1 cells was determined qualitatively by assay of cell density at the glass interface after incubation for 1 day and 3 days, and quantitatively by fluorescent measurements of total DNA in cultures incubated for 4 days. Higher B ₂ O ₃ content of the glass increased the conversion rate to HA, but also resulted in a greater inhibition of cell proliferation under static culture conditions. For a given mass of glass in the culture medium, the inhibition of cell proliferation was alleviated by using glasses with lower B ₂ O ₃ content, by incubating the cell cultures under dynamic rather than static conditions, or by partially converting the glass to HA prior to cell culture.