Size-dependent degradation and bioactivity of borate bioactive glass

Borate bioactive glass has been shown to convert faster and more completely to hydroxyapatite and enhances new bone formation in vivo when compared to silicate bioactive glass. In this work, bioactive borate glass scaffolds, with a grid-like microstructure having different filament diameters (130±10 µm to 300±20 µm), were prepared by a robotic deposition technique. In vitro degradation and hydroxyapatite formation on borate bioactive glass scaffolds were investigated in a simulated body fluid (SBF) at 37 °C under static conditions. Mineralization of borate and silicate bioactive glass powders was also tested under the same conditions. When immersed in SBF, degradation rate of the scaffolds and conversion to a hydroxyapatite-like material showed dependence on filament diameter. Similarly, conversion of bioactive glass particles to calcium phosphate phase strongly depends on the particle size and the sample/SBF ratio of the system. Large particles and scaffolds composed of thick struts formed less apatite and degraded less completely compared with smaller particles and thinner struts. Results showed that it is possible to tailor the degradation rate and bioactivity by changing the filament diameter of the borate bioactive glass scaffolds produced by robocasting.