(446d) Effect of Swelling Ratio of Injectable Hydrogel Composites on Chondrogenic Differentiation of Encapsulated Rabbit Marrow Mesenchymal Stem Cells In Vitro

During the past decade, cartilage tissue engineering that involving the use of cells, bioactive molecules and a three dimensional biodegradable scaffold material has received attention as a promising approach to aid regeneration of cartilage defects. In particular, injectable hydrogels hold great promise as a carrier for cells and bioactive molecules since constructs can be implanted minimally invasively and their high water content facilitates exchange of nutrients and waste.

Our laboratory has recently developed an injectable hydrogel composite consisting of oligo(poly(ethylene glycol) fumarate) (OPF) and gelatin microparticles (MPs) as a novel carrier system for cells and growth factors. In this study, hydrogel composites with different swelling ratios were prepared using OPF macromers with poly(ethylene glycol) repeating units of molecular weight 35,000 (OPF 35K), 10,000 (OPF 10K), 3,300 (OPF 3K) and 1,000 (OPF 1K). 250,000 rabbit marrow mesenchymal stem cells (MSCs) and MPs loaded with 25 ng transforming growth factor-β1 (TGF-β1) were encapsulated in each hydrogel composite to examine the effect of the swelling ratio of hydrogel composites on the chondrogenic differentiation of the cells. Hydrogel composites encapsulating rabbit marrow MSCs and blank MPs served as controls. Quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) results showed that rabbit marrow MSCs encapsulated in higher swelling ratio hydrogel composites (OPF 35K and OPF 10K) had a significant increase in the expression of chondrocyte specific genes such as collagen type II and aggrecan at day 28 compared with those encapsulated in low swelling ratio hydrogel composites (OPF3K and OPF 1K), both in the presence and absence of TGF-β1. Specifically, OPF 35K samples with TGF-β1-loaded MPs exhibited a 159 ± 95 fold increase of type II collagen gene expression and a 24 ± 12 fold increase of aggrecan gene expression after 28 days of in vitro culture as compared to controls at day 0. The results indicate that chondrogenic differentiation of rabbit marrow MSCs encapsulated within OPF hydrogel composites could be affected by the swelling ratio of the hydrogels, thus suggesting the potential of OPF composite hydrogels as part of a novel strategy for controlling the differentiation of stem cells.