Regeneration of full-thickness cartilage defects using small umbilical cord-derived fast proliferating cells combined with magnesium in a rat model.

The effective application of allogeneic mesenchymal stem cells (MSCs) has the potential to enhance cartilage regeneration. This study aimed to evaluate the therapeutic efficacy of intra-articular (IA) injections of small umbilical cord-derived fast proliferating cells (smumf cells) combined with magnesium (Mg2+) in a rat model of full-thickness cartilage defects (FTDs). Adhesion of smumf cells was assessed on type I collagen-coated surfaces in vitro, in an uncontained ex vivo model, and via cell tracking in a rat FTD model. Therapeutic efficacy was evaluated using histological analyses of macroscopic and microscopic in vivo (at 4 and 8 weeks, n = 6). Mg2+ improved the adhesion of smumf cells by up to 1.89-fold in the ex vivo model, and by 2.80-fold in cell tracking. A single injection of smumf cells alone improved histological scores by 2.33-fold at 4 weeks, whereas the combination with Mg2+ resulted in further improvements in both macroscopic (1.30-fold) and microscopic (1.26-fold) scores at 8 weeks. Moreover, the smumf cells + Mg2+ group showed significant increases in tissue thickness (1.40-fold), safranin O-positive area (2.88-fold), and type II collagen synthesis (1.22-fold) in rat model. This study demonstrates that a single IA injection of smumf cells combined with Mg² enhances cell homing and functional adhesion at the defect site, thereby promoting superior cartilage regeneration compared with smumf cells alone.