Repair of a Meniscal Defect in a Rabbit Model Through Use of a Thermosensitive, Injectable, In Situ Crosslinked Hydrogel With Encapsulated Bone Mesenchymal Stromal Cells and Transforming Growth Factor β1.

Background: Meniscal injury repair with tissue engineering technique is promising. Among various scaffolds, the thermosensitive injectable hydrogel has recently attracted much attention. Purpose: (1) Evaluate the biocompatibility of thermosensitive, injectable, in situ crosslinked hydrogel and (2) determine whether the hydrogel with or without transforming growth factor beta 1 (TGF-beta 1) could support the fibrochondrogenic differentiation of bone mesenchymal stromal cells (BMSCs) and promote the repair of a critical-sized defect in rabbit meniscus. Study Design: Controlled laboratory study. Methods: The rheological and sustained release properties of the hydrogel were demonstrated. BMSCs were isolated and cultured. Cell viability, quantitative polymerase chain reaction (qPCR), and Western blot were tested in vitro. In vivo, a critical-sized defect was introduced into the meniscus of 30 rabbits. Each defect was randomly assigned to be implanted with either phosphate-buffered saline (PBS); BMSC-laden hydrogel; or BMSC-laden, TGF-beta 1-incorporated hydrogel. Histological and immunohistochemical analyses were performed at 8 weeks after surgery. The Ishida scoring system was adopted to evaluate the healing quantitatively. Results: The elastic modulus of the hydrogel was about 1000 Pa. The hydrogel demonstrated a sustained-release property and could promote proliferation and induce fibrochondrogenic differentiation of BMSCs after the incorporation of TGF-beta 1 (P < .001). At 8 weeks after surgery, a large amount of fibrocartilaginous tissue, which was positive on safranin-O staining and expressed strong type II collagen intermingled with weak type I collagen, was observed in the defect region of the BMSC-laden, TGF-beta 1-incorporated hydrogel group. In the BMSC-laden hydrogel group, the defect was filled with fibrous tissue together with a small amount of fibrocartilage. The mean +/- SD quantitative scores obtained for the 3 groups-PBS; BMSC-laden hydrogel; and BMSC-laden, TGF-beta 1-incorporated hydrogel-were 1.00, 3.20 +/- 0.84, and 5.00 +/- 0.71, respectively (P < .001). Conclusion: The hydrogel was biocompatible and could stimulate strong fibrochondrogenic differentiation of BMSCs after the incorporation of TGF-beta 1. The local administration of the BMSC-laden, TGF-beta 1-incorporated hydrogel could promote the healing of rabbit meniscal injury.