Light-activated cartilage decellularised extracellular matrix hydrogels for engineering chondrogenic microenvironments with localised oxygen control

Cartilage tissue engineering requires biomaterials that can effectively maintain the tissue-specific functions of chondrocytes to enable the restoration of cartilage structure and function. Decellularised extracellular matrix (dECM)-derived hydrogels serve as tissue-specific biomaterials capable of preserving native biochemical cues and maintaining physiological chondrocyte phenotype in three-dimensional culture. However, their sol-gel transition relies heavily on collagen fibrillogenesis, a slow and poorly controllable process that limits mechanical tunability and suffers from inter-batch variability. Therefore, further efforts are required to functionalise cartilage dECM to achieve reproducible and controllable physicochemical properties. Here, we present a light-activated cartilage dECM hydrogel system based on ruthenium/sodium persulfate (Ru/SPS)-mediated dityrosine crosslinking, enabling rapid hydrogel formation under visible light irradiation while providing tunable mechanical properties and improved biological functionality. Comparison of the decellularisation protocols indicated that Triton X-100 combined with ammonium hydroxide efficiently eliminated residual DNA while preserving a substantial proportion of the native cartilage proteome. Pepsin-solubilised cartilage dECM hydrogels formed via dityrosine-based photo-crosslinking exhibited rapid gelation behaviour and superior mechanical characteristics compared to conventional thermally gelled dECM. The photo-crosslinked dECM hydrogels were cytocompatible, supported human bone marrow-derived mesenchymal stem cells (hBMSCs), and favoured cartilage-specific phenotypes, as demonstrated by chondrogenic genes upregulation, including COL2A1 and ACAN, compared with gelatin methacrylate (GelMA) hydrogels. Importantly, this photo-crosslinking strategy overcomes the incompatibility between oxygen-sensitive redox-based photochemistry and hypoxic culture conditions, enabling the incorporation of oxygen-scavenging microcapsules to establish low-oxygen microenvironments. Under hypoxia, the cartilage dECM hydrogels promoted a more articular-like phenotype in hBMSC-derived chondrocytes, with transcriptomic features associated with TGF-β/SMAD2/3 and IGF-1/2-IGF-1R signalling. Collectively, these findings establish photo-crosslinked cartilage dECM hydrogels as a biomaterial platform with tunable mechanical properties and favourable biological functionality for cartilage tissue bioengineering and biomimetic in vitro cartilage models.