Mechanism of Alginate-Collagen Hydrogel in the Repair of Rat Cartilage Injury

Background and Objectives Alginate and gelatin have biocompatibility and biodegradability for drug formulations or carriers, but the roles and mechanisms in cartilage injury (CI) repair remain unclear. This research investigated the application of alginate-collagen hydrogel (ACH) in rat CI repair and its related mechanisms through in vitro and in vivo experiments. Materials and Methods Alginate and modified collagen solutions were mixed to prepare the ACH. The obtained samples were characterized, and their sustained release properties were determined. L929 mouse fibroblasts were assigned into a blank control group (BC group, untreated), a positive control group (PC group, treated with 6.4% phenol), a negative control group (NC group, treated with tissue culture polystyrene), and an ACH group (treated with ACH). The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay assessed cell viability. Meanwhile, the cytotoxicity of the ACH and its impact on cell proliferation and cell attachment capabilities were analyzed. Thirty 4-week-old specific pathogen-free Sprague-Dawley rats were randomly grouped into a chondrocyte group (chondrocytes collected and cultured), a cPAGE group (chondrocytes treated with ACH), a model group (CI model), and an mPAGE group (CI model treated with ACH). The influence of ACH on chondrocyte proliferation and type II collagen (COL-II) expression were assessed via cell counting kit 8 (CCK-8) assay and immunofluorescence staining. Furthermore, the impacts of ACH on chondrocyte tissue and COL-II expression were analyzed using Safranin O-Fast Green staining, the International Cartilage Repair Society (ICRS) score, and COL-II tissue staining. Immunoblotting was utilized to detect tumor necrosis factor alpha (TNF-α), nuclear factor kappa-B (NF-κB), matrix metalloproteinase 13 (MMP-13), and COL-II proteins in cartilage tissue. Results The release rate of the constructed ACH reached over 85% within 72 h and achieved degradation equilibrium within 5 days with a weight loss rate of over 60%. L929 fibroblast culture results showed that the ACH posed no significant cytotoxicity, and cell attachment results were not obviously different from those on tissue culture plates ( p < .05). MTT assay results demonstrated that the ACH exerted no adverse effects on L929 cell proliferation and growth, indicating good biocompatibility. CCK-8 and COL-II results indicated that chondrocyte proliferation in the cPAGE group was markedly higher versus that in the chondrocyte group ( p < .05). Besides, animal experiments unveiled that, relative to the CI group, the mPAGE group had more chondrocytes, upregulated COL-II, and higher ICRS scores ( p < .05). MMP-13, NF-κB, and TNF-α were downregulated, and COL-II was upshifted in the mPAGE group, with remarkable differences ( p < .05). Conclusion ACH exhibited excellent biocompatibility and low cytotoxicity, promoted cell proliferation and growth, and facilitated chondrocyte proliferation in rat CI repair, offering a valuable research foundation for CI treatment.