Because of the limitations associated with biologic and synthetic grafts, we have pursued the idea of using in vitro synthesized bone as graft material. Procedures to synthesize bone tissue in vitro primarily relied on seeding various substrates with cells that have osteogenic capacity in culture.; The result of this research is a new, porous, surface modified, bioactive glass which acts as a scaffold stimulating bone formation in vitro. The porosity of the glass was 36.4%; the pore size ranged from 10 to 160 {dollar}mu{dollar}, and there was no incipient devitrification. Because BG undergoes corrosion in an aqueous environment, the effect of alkali ions released, in vitro, from the surface of porous bioactive glass (BG) on the cellular activity of neonatal rat calvaria osteoblasts was studied. At low tissue culture medium (TCM) volume to BG surface area (SA) (Vol/SA), the glass corrosion products shift the pH of the TCM to a value that adversely affects the cellular activity. Cells cultured on BG at low Vol/SA conditions produced non mineralized extracellular matrix (ECM). On the other hand, mineralized ECM was produced by cells seeded on BG and maintained at high Vol/SA.; We found it was necessary to condition the disks to be covered with a dual layer of calcium phosphate and serum protein, prior to seeding the glass with cells. We evaluated the importance of the presence of a surface crystalline versus amorphous calcium phosphate layer on the activity of osteoblasts seeded on bioactive glass. Furthermore, the effect on bone cell function of serum protein adsorbed on modified bioactive glass and hydroxyapatite ceramic was also studied. Optimum cellular activity was observed on BG conditioned to be covered with crystalline calcium phosphate-serum protein layer.; Immersing the glass in simulated body fluid for 180 h leads to the formation of a crystalline calcium phosphate layer at the glass surface. We found that the modified glass templates were rapidly invaded by cells which maintained the osteoblast phenotype; thus, they exhibited high alkaline phosphatase activity, they synthesized type I and III collagen, osteocalcin, osteopontin, and bone sialoprotein. SEM-EDAX showed that the cells elaborated substantial amounts of extracellular matrix and a bone-like tissue was present throughout the entire template thickness. FTIR analysis of material formed in the glass indicated that the mineral phase was a biological hydroxyapatite. In contrast a much smaller number of cells attached to the HA ceramic surface; although these cells synthesized similar profile of proteins, they produced a limited mineralized matrix. On the bioactive glass surface, the high selectivity of the calcium phosphate layer for fibronectin may be responsible for the bone cellular activity that is observed in vitro as well as when this material is implanted in vivo. (Abstract shortened by UMI.)
展开▼
