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In the development of 3-dimensional cell-polymer matrices for tissue engineering, the ability of osteoblast cells to maintain their phenotypic properties and form a mineralized matrix while seeded on the polymer surface is very important. Osteoblast cell differentiation and bone formation using rat calvaria cells were studied on the surface of a porous poly(lactide/glycolide)/hydroxyapatite (PLAGA/HA) 3-dimensional polymer matrix. Cell adhesion and proliferation were determined at 24 hr, 3, 7, 14, and 21 days. Cell attachment and proliferation were observed to increase throughout the first two weeks of the study, followed by a period of gradual plateauing of cell numbers. Environmental scanning electron microscopy demonstrated that cells grown on the surface of the 3-dimensional porous PLAGA/HA matrix retained their characteristic morphology and grew in a multi-layer fashion. Light microscopy observations of experiment cultures revealed active osteoblastic cells forming a characteristic mineralized matrix in the presence of beta-glycerophosphate as a phosphate donor. Mineralization did not occur in media either not supplemented with beta-glycerophosphate or when the matrix without cells was incubated with the reagents, indicating that the mineralization was due to the cells and not the HA in the matrix. These results suggest that the 3-dimensional PLAGA/HA matrix could provide a matrix for bone cell differentiation and mineralization in vitro and, therefore, may be a candidate as a synthetic implant for bone regeneration.