The feasibility of culturing osteoblasts on biodegradable poly($\alpha$-hydroxy esters) to form new bone was investigated through a series of five studies. The first study demonstrated that rat calvarial osteoblasts attached, proliferated, and functioned equally well on all the biodegradable polymer substrates studied (poly(L-lactic acid) (PLLA), 75:25 poly(DL-lactic-co-glycolic acid) (PLGA), 50:50 PLGA, and poly(glycolic acid) (PGA)) throughout the 14 day study, even though the polymer films were continuously degrading.
The second study showed that osteoblast migration occurred as a monolayer of individual osteoblasts and not a calcified tissue front on poly($\alpha$-hydroxy ester) films. Copolymer ratio in the polymer films did not affect the rate of increase in culture area covered by the growing cell colony; however, the rate of increase in culture area was lower for cell colonies formed with a lower osteoblast seeding density. The proliferation rate for the osteoblasts arising from bone chips was lower than either of the isolated cell colonies.
Bone formation in vitro was investigated in the third and fourth study by culturing stromal osteoblasts or rat calvarial osteoblasts in three-dimensional (3-D), biodegradable 75:25 PLGA foams. The polymer foams supported the growth of seeded osteoblasts as well as their differentiated function. Cell number, alkaline phosphatase activity, and mineralized tissue deposition increased significantly over time for all the polymer foams. Osteoblasts seeded at a lower cell density proliferated more rapidly, reaching comparable cell numbers at later culture times, but pore size over the range tested did not affect cell proliferation or function.
In the final study, porous biodegradable poly(DL-lactic-co-glycolic acid) foams were seeded with rat stromal osteoblasts and implanted into the rat mesentery for up to 49 days to investigate in vivo bone formation using this osteoblast transplantation method. An organized and mineralized bone-like tissue was formed in all the constructs as early as 7 days post-implantation. Foam pore size did not affect the penetration depth of mineralized tissue or mineralized tissue volume per surface area found within the constructs at any time during the study.