Effect of varying physical properties of porous, surface modified bioactive glass 45S5 on osteoblast proliferation and maturation

The objective of this study was to determine the effect of porous bioactive glass (45S5) substrate characteristics on the expression and maintenance o f the osteoblastic phenotype. We cultured ROS 17/2.8 cells on substrates wi th different pore size and porosity for periods up to 14 days and analyzed the characteristics of the cells and extracellular matrix. Results of the s tudy show that the glass substrates supported the proliferation and growth of osteoblast-like cells. Although the morphologies of the cells differed o n the various substrates, their shape and the extent of membrane ruffling s uggested that they maintained high levels of metabolic activity. Cells on a ll substrates expressed high levels of alkaline phosphatase activity and pr oduced extracellular matrices that mineralized to form nonstoichiometric, c arbonated, calcium-deficient apatites. An important finding was that at a g iven porosity of 44%, the Fore size neither directed nor modulated the in v itro expression of the osteoblastic phenotype. In contrast, porosity did af fect cellular function. We noted that at an average pore size of 92 mu m, a s the porosity increased from 35 to 59%, osteoblast activity was reduced. A s designed in this experiment, an increase in the porosity led to a corresp onding increase in total surface area of the specimens. With increasing por osity and surface area, glass reactions in the media may persist for longer durations at higher intensities, thereby affecting local media composition . As such, we suggest that extensive conditioning treatments before cell se eding can reduce this effect. Our results also revealed that the expression of the osteoblastic phenotype is enhanced by the ongoing glass dissolution . The reaction pathway at the origin of this effect still needs to be eluci dated. Taken together, the findings support the overall hypothesis that in vitro cell activity can be controlled by a careful selection of substrate p roperties. (C) 2000 John Wiley & Sons, Inc.