A tough polysaccharide-based cell-laden double-network hydrogel promotes articular cartilage tissue regeneration in rabbits

Hydrogels used for cartilage tissue engineering purposes must be designed to mimic the biological and physical features of the native extracellular matrix (ECM). Here, we developed three different types of physical and chemical chondro-inductive hydrogels with the controlled drug release ability based on sulfated alginate (SAlg) and chitosan (CS). Bioconjugation of catechol to SAlg (SAlg-Cat) resulted in formation of SAlg-Cat/CS hydrogels with higher mechanical stability than physical SAlg/CS hydrogel. In the chemical double-network hydrogel (DN/ SAlg-Cat), the presence of catechol and amine groups within the network resulted in dynamic and reversible bonding with energy dissipation. Our DN/SAlg-Cat hydrogel with initial compressive modulus of 34.86 kPa exhibited adequate compressive strength (421.45 kPa), toughness (89.69 kJ/m3), ability to self-heal and recoverability, which could be exceptional for utilizing in a load-bearing tissue like cartilage. Among hydrogels, the DN/SAlg-Cat hydrogel displayed less degradation rate (6.81%) and higher mechanical stability (81% retention of stiffness) in the presence of lysozyme (15 mu g/mL) during 21 days. Incorporation of the sulfate and catechol groups within these hydrogels mediated the sustained release of TGF-beta 1 and kartogenin (KGN) chondrogenic agents, and resulted in proper chondrogenesis of the encapsulated mesenchymal stem cell (MSC) and chondrocyte (CH) co-culture. The catechol-enriched hydrogels (SAlg-Cat/CS and DN/SAlg-Cat) showed better regeneration of full-thickness articular defects in rabbits after 12 weeks due to the high affinity of the catechol group for cell adhesion, tissue integration, and immobilization of the biological factors. Our results demonstrated a role for a biomimetic microenvironment in efficient chondrogenesis.