In vivo chondrogenesis of mesenchymal stem cells in a photopolymerized hydrogel

Background: Surgical options for cartilage reconstruction can be significantly improved through advances in cartilage tissue engineering, whereby functional tissue replacements are created by growing cells on polymer scaffolds. The objective of this study was to use a photopolymerizable hydrogel to implant bone marrow-derived mesenchymal stem cells subcutaneously in a minimally invasive manner and promote cartilage tissue formation by the cells in vivo. Methods: Athymic nude mice were injected subcutaneously with polymer solutions of poly(ethylene) oxide diacrylate containing mesenchymal stem cells and placed under a UVA lamp to transdermally photopolymerize (solidify) the injected liquid. Experimental groups included polymer solutions with hyaluronic acid (HA), transforming growth factor (TGF)-beta 3, or both. After 3 weeks of implantation, cartilage formation was evaluated by gene expression analysis and histologic techniques. Results: Hyaluronic acid increased the viscosity of the polymer solutions, which helped maintain the injections at the desired site during photopolymerization. Mesenchymal stem cells in hydrogels containing both HA and TGF-beta 3 produced the highest quality cartilage, based on expression of the cartilage-specific genes and production of proteoglycan and collagen II. When used independently, TGF-beta 3 and HA alone induced cartilage-specific gene expression and collagen type 11 production; however, TGF-beta 3 was essential for proteoglycan production. HA enhanced proteoglycan production when combined with TGF-beta 3 and reduced expression and production of collagen I. Conclusions: This study is the first to demonstrate the minimally invasive implantation and subsequent chondrogenic differentiation of mesenchymal stem cells in the subcutaneous environment. This lays the foundation for further optimization of a novel and practical technology for cartilage reconstruction.