In vitro osteogenic differentiation of marrow stromal cells encapsulated in biodegradable hydrogels.

Novel hydrogel materials based on oligo(poly- (ethylene glycol) fumarate) (OPF) crosslinked with a redox radical initiation system were recently developed in our laboratory as injectable cell carriers for orthopedic tissue engineering applications. The effect of OPF hydrogel mate- rial properties on in vitro osteogenic differentiation of encap- sulated rat marrow stromal cells (MSCs) with and without the presence of osteogenic supplements (dexamethasone) was investigated. Two OPF formulations that resulted in hydrogels with different swelling properties were used to encapsulate rat MSCs (seeding density 13 million cells/ mL, samples 6 mm diameter 0.5 mm thick before swell- ing) and osteogenic differentiation in these constructs over 28 days in vitro was determined via histology and biochem- ical assays for alkaline phosphatase, osteopontin and cal- cium. Evidence of MSC differentiation was apparent over the culture period for samples without dexamethasone, but there was large variability in calcium production between constructs using cells of the same source. Differentiation was also seen in samples cultured with osteogenic supplements, but calcium deposition varied depending on the source pool of MSCs. By day 28, osteopontin and calcium results sug- gested that, in the presence of dexamethasone, OPF hydro- gels with greater swelling promoted embedded MSC differ- entiation over those that swelled less (43.7 16.5 g calcium/sample and 16.4 2.8 g calcium/sample, respec- tively). In histological sections, mineralized areas were ap- parent in all sample types many microns away from the cells. These experiments indicate that OPF hydrogels are promising materials for use as injectable MSC carriers and that hydrogel swelling properties can influence osteogenic differentiation of encapsulated progenitor cells. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 70A: 235-244, 2004