OSTEOBLAST MIGRATION ON POLY(ALPHA-HYDROXY ESTERS)

We investigated the migration of rat calvaria osteoblast populations o n poly(cr-hydroxy ester) films for up to 14 days to determine effects of substrate composition and culture conditions on the migratory chara cteristics of osteoblasts. Initial osteoblast culture conditions inclu ded cell colonies formed by seeding a high (84,000 cells/cm(2)) or low (42,000 cells/cm(2)) density of isolated osteoblasts on the polymer f ilms, and bone tissue cultures formed by plating bone chips directly o n the substrates. High density osteoblast colonies cultured and allowe d to migrate and proliferate radially on 85:15 poly(DL-lactic-coglycol ic acid) (PLGA) films, 75:25 PLGA films, and tissue culture polystyren e controls demonstrated that the copolymer ratio in the polymer films did not affect the rate of increase in substrate surface area (or cult ure area) covered by the growing cell colony. However, the rate of inc rease in culture area was dependent on the initial osteoblast seeding density. Initial cell colonies formed with a lower osteoblast seeding density on 75:25 PLGA resulted in a lower rate of increase in culture area, specifically 4.9 +/- 0.3 mm(2)/day, versus 14.1 +/- 0.7 mm(2)/da y for colonies seeded with a higher density of cells on the same polym er films. The proliferation rate for osteoblasts in the high and low d ensity seeded osteoblast colonies did not differ, whereas the prolifer ation rate for the osteoblasts arising from the bone chips was lower t han either of these isolated cell colonies. Confocal and light microsc opy revealed that the osteoblast migration occurred as a monolayer of individual osteoblasts and not a calcified tissue front. These results demonstrated that cell seeding conditions strongly affect the rates o f osteoblast migration and proliferation on biodegradable poly(rr-hydr oxy esters). (C) 1996 John Wiley & Sons, Inc.