Ion-Enriched Solution Improves the Adhesion of Freshly Thawed Umbilical Cord-Derived Mesenchymal Stem Cells and Supports Cartilage Repair in a Rat Full-Thickness Cartilage Defect Model

BACKGROUND: Freshly thawed umbilical cord-derived mesenchymal stem cells (FT-UC MSCs) often show reduced post-thaw functionality, limiting their use as off-the-shelf cell therapies. This study investigated whether an ion-enriched solution (IES) could improve FT-UC MSC adhesion and cartilage repair-associated outcomes. METHODS: UC MSCs were categorized as cryopreserved and culture-recovered UC MSCs (CP-UC MSCs) or FT-UC MSCs. Adhesion was assessed in vitro on type I collagen and ex vivo on human osteoarthritic cartilage using saline, IES, or magnesium chloride as carriers. In vivo, rats with full-thickness cartilage defects received intra-articular injections of IES alone, CP-UC MSCs in saline, or FT-UC MSCs in IES. Cartilage repair was evaluated by ICRS macroscopic and histological scoring, immunohistochemistry, and static weight-bearing. RESULTS: FT-UC MSCs showed reduced proliferation, metabolic activity, and adhesion compared with CP-UC MSCs. IES significantly enhanced FT-UC MSC adhesion in vitro and ex vivo , with magnesium chloride (MgCl 2 ) as the major contributor and sodium acetate (NaOAc) as a possible additional contributor. In vivo , FT-UC MSCs delivered with IES showed macroscopic and histological repair outcomes comparable to CP-UC MSCs delivered with saline, including lower subchondral abnormality and inflammation scores, lower type I collagen staining, and a favorable matrix profile at 8 weeks. CONCLUSION: FT-UC MSCs delivered with IES showed improved post-thaw adhesive function and repair-associated outcomes comparable to CP-UC MSCs delivered with saline in a rat full-thickness cartilage defect model. These findings support the potential utility of IES as a practical delivery carrier for freshly thawed UC-MSCs without an extended culture-recovery step, while further studies including an FT-UC MSCs + saline group are required to isolate the specific in vivo contribution of IES.