Bioactive glass stimulates in vitro osteoblast differentiation and createsa favorable template for bone tissue formation

In this study, we have investigated the behavior of fetal rat osteoblasts c ultured on bioactive glasses with 55 wt% silica content (55S) and on a bioi nert glass (60S) used either in the form of granules or in the form of disk s, In the presence of Bioglass granules (55 wt% silica content), phase cont rast microscopy permitted step-by-step visualization of the formation of bo ne nodules in contact with the particles. Ultrastructural observations of u ndecalcified sections revealed the presence of an electron-dense layer comp osed of needle-shaped crystals at the periphery of the material that seemed to act as a nucleating surface for biological crystals. Furthermore, energ y dispersive X-ray (EDX) analysis and electron diffraction patterns showed that this interface contains calcium (Ca) and phosphorus (P) and was highly crystalline. When rat bone cells were cultured on 55S disks, scanning elec tron microscopic (SEM) observations revealed that cells attached, spread to all substrata, and formed multilayered nodular structures by day 10 in cul ture. Furthermore, cytoenzymatic localization of alkaline phosphatase (ALP) and immunolabeling with bone sialoprotein antibody revealed a positive sta ining for the bone nodules formed in cultures on 55S, In addition, the spec ific activity of ALP determined biochemically was significantly higher in 5 5S cultures than in the controls. SEM observations of the material surfaces after scraping off the cell layers showed that mineralized bone nodules re mained attached on 55S surfaces but not on 60S. X-ray microanalysis indicat ed the presence of Ca and P in this bone tissue. The 55S/bone interfaces al so were analyzed on transverse sections. The interfacial analysis showed a firm bone bonding to the 55S surface through an intervening apatite layer, confirmed by the X-ray mappings. All these results indicate the importance of the surface composition in supporting differentiation of osteogenic cell s and the subsequent apposition of bone matrix allowing a strong bond of th e bioactive materials to bone.