||During the past decade, injectable hydrogels hold great promise as a carrier for cells and bioactive molecules in tissue engineering application. Our laboratory has developed a novel biodegradable polymer, oligo(PEG fumarate) (OPF), as a carrier for cells and growth factors. OPF was combined with a PEG-diacrylate crosslinker and the radical initiator to form a hydrogel encapsulating rabbit MSCs. Here, gelatin microparticles (MPs) loaded with TGF-b1 were also co-encapsulated with rabbit MSCs to provide localized delivery of growth factors. After 14 days of in vitro culture, results indicated that MSCs in hydrogel composites were viable during the culture period and only hydrogel composites containing TGF-b1-loaded MPs had a significant increase in collagen type II gene expression, a marker of the chondrocytic phenotype, thus suggesting the potential of OPF hydrogel composites as part of a novel tissue regeneration strategy involving localized delivery of cells and bioactive molecules.