Development of an injectable, in situ crosslinkable, degradable polymeric carrier for osteogenic cell populations. Part 3. Proliferation and differentiation of encapsulated marrow stromal osteoblasts cultured on crosslinking poly(propylene fumarate)

This study investigated the effect of temporary encapsulation of rat marrow stromal osteoblasts in crosslinked gelatin microparticles on long-term cell proliferation and phenotypic expression for microparticles placed on crosslinking poly(propylene fumarate) (PPF) composites using N-vinyl pyrollidinone (N-VP) as a crosslinking agent over a 28 day time period. Encapsulated cells (ECs) were seeded on actively crosslinking PPF composites 6 min after initiation of the crosslinking reaction, and also on fully crosslinked PPF composites and tissue culture polystyrene controls, with a cell seeding density of 5.3×104 cells/cm2. Composites prepared with three PPF:N-VP ratios were examined: 1:0.5, 1:0.1, and 1:0.05. Samples were taken at specified time points and analyzed by DNA, 3H-thymidine, alkaline phosphatase, osteocalcin, and calcium assays, and the measurements were compared with those for nonencapsulated cells (NCs). The results showed that encapsulated marrow stromal cells exhibited much higher viability, proliferation, and phenotypic expression when placed on crosslinking PPF composites than NCs. The assay results for ECs on crosslinking PPF composites were also similar to those on fully crosslinked PPF composites. The data further demonstrated that the PPF:N-VP ratio had no effect on the viability, proliferation, or phenotypic expression of the ECs. These results suggest that cells encapsulated in crosslinked gelatin microparticles may be part of an injectable, in situ crosslinkable, biodegradable polymeric composite for bone tissue engineering applications.