Methoxy polyethylene glycol-poly(3-caprolactone) (MPEG-PCL; MP) diblock copolymers undergo a solutionto-gel phase transition at body temperature and serve as ideal biomaterials for drug delivery and tissue engineering. Here, we examined the potential use of a chondrocyte-loaded MP solution as an injectable, in situ-forming hydrogel for cartilage regeneration. The chondrocyte-MP solution underwent a temperaturedependent solution-to-gel phase transition in vitro, as shown by an increase in viscosity from 1 cP at 20-30 C to 1.6 Â 10 5 cP at 37 C. The chondrocytes readily attached to and proliferated on the MP hydrogel in vitro.The chondrocyte-MP solution transitioned to a hydrogel immediately after subcutaneous injection into mice, and formed an interconnected pore structure required to support the growth, proliferation, and differentiation of the chondrocytes. The chondrocyte-MP hydrogels formed cartilage in vivo, as shown by the histological and immunohistochemical staining of glycosaminoglycans, proteoglycans, and type II collagen, the major components of cartilage. Cartilage formation increased with hydrogel implantation time, and the expression of glycosaminoglycans, and type II collagen reached maximal levels at 6 weeks post-implantation.Collectively, these data suggest that in situ-forming chondrocyte-MP hydrogels have potential as non-invasive alternatives for tissue-engineered cartilage formation.

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BackgroundHydrolyzed polyacrylonitrile (HPAN) has attracted much attention as a hydrogel for a broad range of biomedical applications. Therefore, in this study, we prepared HPAN derivatives with controllable compositions by the radical polymerization of acrylonitrile (AN), methacrylic acid (MAA) and N-isopropylacrylamide (NIPAM) monomers.ResultsThe prepared poly(AN-co-MAA-co-NIPAM) copolymers had different ratios of AN, MAA, and NIPAM and molecular weights ranging from 2000 to 50,000. The copolymers were prepared as films to examine their properties. The prepared copolymer films showed different solubilities, contact angles, and swelling ratios. The properties of the copolymer films were affected by the hydrophobic PAN segments and the hydrophilic PMAA or PNIPAM segments.ConclusionThus, we conclude that introducing PMAA and PNIPAM segments with different ratios and lengths into PAN segments could represent a method of controlling the hydrogel properties of copolymers.