In vitro bioactivity of S520 glass fibers and initial assessment of osteoblast attachment.

Bioactive glass fibers are attractive materials for use as tissue-engineering scaffolds and as the reinforcing phase for resorbable bioactive composites. The bioactivity of S520 glass fibers (52.0 mol % SiO(2), 20.9 Na(2)O, 7.1 K(2)O, 18.0 CaO, and 2.0 P(2)O(5)) was evaluated in two media, simulated body fluid (SBF) and Dulbecco's modified Eagle's medium (DMEM), for up to 20 days at 37 degrees C. Hydroxyapatite formation was observed on S520 fiber surfaces after 5 h in SBF. After a 20-day immersion, a continuous hydroxyapatite layer was present on the surface of samples immersed in SBF as well as on those samples immersed in DMEM [fiber surface area to solution volume ratio (SA:V) of 0.10 cm(2)/mL]. Backscattered electron imaging and EDS analysis revealed that the hydroxyapatite layer formation was more extensive for samples immersed in SBF. Decreasing the SA:V ratio to 0.05 cm(2)/mL decreased the time required to form a continuous hydroxyapatite surface layer. ICP was used to reveal Si, Ca, and P release profiles in DMEM after the 1st h (15.1, 83.8, and 29.7 ppm, respectively) were similar to those concentrations previously determined to stimulate gene expression in osteoblasts in vitro (16.5, 83.3, and 30.4 ppm, respectively). The tensile strength of the 20-microm diameter fibers was 925 +/- 424 MPa. Primary human osteoblast attachment to the fiber surface was studied by using SEM, and mineralization was studied by using alizarin red staining. Osteoblast dorsal ruffles, cell projections, and lamellipodia were observed, and by 7 days, cells had proliferated to form monolayer areas as shown by SEM. At 14 days, nodule formation was observed, and these nodules stained positive for alizarin red, demonstrating Ca deposition and, therefore mineralization.