Combining polydioxanone-based scaffold and allogeneic adipose-derived mesenchymal stem cells enhances articular cartilage repair - a pre-clinical study.

Introduction: Articular cartilage exhibits limited intrinsic regenerative capacity, making its repair a persistent clinical challenge. Polydioxanone (PDO) scaffolds offer biocompatibility, tunable degradation, and structural support, whereas adipose-derived mesenchymal stem cells (AD-MSCs) possess chondrogenic, immunomodulatory, and regenerative potential. This study evaluated the biocompatibility of the PDO scaffold Methods: Twenty-four adult sheep were randomly allocated into six groups. Full-thickness chondral defects were created in the weight-bearing region of the medial femoral condyle and treated according to each group: Control (no treatment), MF alone, MF/COL, MF/PDO, SadMSC/COL, or SadMSC/PDO. SadMSCs were isolated, expanded, and characterized for viability, immunophenotyping, and trilineage differentiation. The biocompatibility of the PDO scaffold was assessed by cell adhesion and proliferation using Live/Dead staining and scanning electron microscopy. After 26 weeks, articular cartilage repair was evaluated macroscopically following ICRS scoring guidelines, histologically using the modified O'Driscoll score, and immunohistochemically for COL I, COL II, COL X, TGF-β2, and TGF-β3. Results: PDO scaffolds supported the survival, adhesion, and proliferation of SadMSCs. Clinically, animals showed good recovery without major complications. At necropsy, no residual membranes, inflammation, or adverse reactions were detected. Macroscopically, the PDO/MF group presented the best repair scores, significantly superior to the Control, MF alone, MF/COL, SadMSC/COL, and SadMSC/PDO groups. Microscopically, SadMSC/PDO achieved the highest O'Driscoll and immunohistochemistry scores, with strong expression of COL II and TGF-β, along with reduced COL I and COL X, indicating hyaline-like cartilage formation. Multivariate analysis confirmed a strong positive correlation between COL II, TGF-β expression, and histological scores. Conclusion: PDO scaffolds demonstrated excellent biocompatibility and, when combined with SadMSCs, promoted superior cartilage repair compared with COL scaffolds or MF alone. While PDO/MF achieved the best macroscopic outcomes, SadMSC/PDO provided the most favorable microscopic and molecular findings, suggesting that allogeneic AdMSCs seeded on PDO scaffolds enhance hyaline-like cartilage formation. These results highlight PDO and AD-MSC-based constructs as a promising alternative for translational strategies in cartilage repair. The translational potential of this article: This study demonstrated that the combination of PDO scaffold and allogeneic AD-MSCs significantly enhances the quality of stifle cartilage repair in a sheep model. Furthermore, the validation of this approach in an optimal large-animal model underscores its translational readiness for clinical application.