Enhancing chondrogenesis and mechanical strength retention in physiologically relevant hydrogels with incorporation of hyaluronic acid and direct loading of TGF-beta

摘要

Cell-loaded hydrogels are frequently applied in cartilage tissue engineering for their biocompatibility, ease of application, and ability to conform to various defect sites. As a bioactive adjunct to the biomaterial, transforming growth factor beta (TGF-beta) has been shown to be essential for cell differentiation into a chondrocyte phenotype and maintenance thereof, but the low amounts of endogenous TGF-beta in the in vivo joint microenvironment necessitate a mechanism for controlled delivery and release of this growth factor. In this study, TGF-beta 3 was directly loaded with human bone marrow-derived mesenchymal stem cells (MSCs) into poly-D,L-lactic acid/polyethylene glycol/poly-D,L-lactic acid (PDLLA-PEG) hydrogel, or PDLLA-PEG with the addition of hyaluronic acid (PDLLA/HA), and cultured in vitro. We hypothesize that the inclusion of HA within PDLLA-PEG would result in a controlled release of the loaded TGF-beta 3 and lead to a robust cartilage formation without the use of TGF-beta 3 in the culture medium. ELISA analysis showed that TGF-beta 3 release was effectively slowed by HA incorporation, and retention of TGF-beta 3 in the PDLLA/HA scaffold was detected by immunohistochemistry for up to 3 weeks. By means of both in vitro culture and in vivo implantation, we found that sulfated glycosaminoglycan production was higher in PDLLA/HA groups with homogenous distribution throughout the scaffold than PDLLA groups. Finally, with an optimal loading of TGF-beta 3 at 10 mu g/mL, as determined by RT-PCR and glycosaminoglycan production, an almost twofold increase in Young's modulus of the construct was seen over a 4-week period compared to TGF-beta 3 delivery in the culture medium. Taken together, our results indicate that the direct loading of TGF-beta 3 and stem cells in PDLLA/HA has the potential to be a one-step point-of-care treatment for cartilage injury.