3-DIMENSIONAL CULTURE OF RAT CALVARIAL OSTEOBLASTS IN POROUS BIODEGRADABLE POLYMERS

Neonatal rat calvarial osteoblasts were cultured in 90% porous, 75:25 poly(DL-lactic-co-glycolic acid) (PLGA) foam scaffolds for up to 56 da ys to examine the effects of the cell seeding density, scaffold pore s ize, and foam thickness on the proliferation and function of the cells in this three-dimensional environment. Osteoblasts were seeded at eit her 11.1 x 10(5) or 22.1 x 10(5) cells per cm(2) onto PLGA scaffolds h aving pore sizes in the range of 150-300 or 500-710 mu m with a thickn ess of either 1.9 or 3.2 mm. After 1 day in culture, 75.6 and 68.6% of the seeded cells attached and proliferated on the 1.9 mm thick scaffo lds of 150-300 mu m pore size for the low and high seeding densities, respectively. The number of osteoblasts continued to increase througho ut the study and eventually leveled off near 56 days, as indicated by a quantitative DNA assay. Osteoblast/foam constructs with a low cell s eeding density achieved comparable DNA content and alkaline phosphatas e (ALPase) activity after 14 days, and mineralization results after 56 days to those with a high cell seeding density. A maximum penetration depth of osseous tissue of 220 +/- 40 mu m was reached after 56 days in the osteoblast/foam constructs of 150-300 mu m pore size initially seeded with a high cell density. For constructs of 500-710 mu m pore s ize, the penetration depth was 190 +/- 40 mu m under the same conditio ns. Scaffold pore size and thickness did not significantly affect the proliferation or function of osteoblasts as demonstrated by DNA conten t, ALPase activity, and mineralized tissue formation. These data show that comparable bone-like tissues can be engineered in vitro over a 56 day period using different rat calvarial osteoblast seeding densities onto biodegradable polymer scaffolds with pore sizes in the range of 150-710 mu m. When compared with the results of a previous study where similar polymer scaffolds were seeded and cultured with marrow stroma l cells, this study demonstrates that PLGA foams are suitable substrat es for osteoblast growth and differentiated function independent of ce ll source. (C) 1998 Elsevier Science Ltd. All rights reserved