Bone Marrow Cell Colonization Of, and Extracellular Matrix Expression On, Biodegradable Polymers

Poly(DL-lactide-co-glycolide)s (PLGAs) have been proposed as substrata for bone tissue engineering. In the experiments reported herein, we sought to identify the optimum lactide to glycolide ratio, from the series 85:15, 75:25, 50:50, or poly-(DL-lactide) (PLA), for the elaboration of bone matrix by cultured rat bone marrow cells (RBMC) on two-dimensional substrates. Having identified PLGA 75:25 as the optimum for bone matrix elaboration by RBMC, we produced three dimensional foams from this copolymer. For the two dimensional substrata, glass coverslips were spin-coated with one of the PLGAs, or PLA. Cultures were maintained for two weeks. We employed a new technique to label the elaborated bone matrix with the fluorescent antibiotic tetracycline. Bone matrix was present to a varying degree dependent on substrate composition: PLGA 75:25 = TCP > PLGA 85:15 > > PLA. No bone matrix was observed on PLGA 50:50 or on uncoated glass coverslips. Cell proliferation was similar on each surface except PLA on which they did not proliferate. Cell morphology was assessed by scanning electron microscopy. Based on these results, three dimensional devices were produced from PLGA 75:25. Our results demonstrate that the copolymer ratios that maximize cell proliferation are not identical to the that optimize bone matrix elaboration. Furthermore, despite the intended use of three dimensional matrices for connective tissue engineering applications, bone marrow-derived cells produced only a superficial matrix layer that did not invade the scaffold, whether produced by either the salt leaching or freeze-drying procedures employed.