Hierarchically structured injectable hydrogels with loaded cell spheroids for cartilage repairing and osteoarthritis treatment

The repair of cartilage lesions faces challenges in the integration of biological and mechanical cues into scaffolds. Herein, injectable hyaluronic acid (HA) hydrogels were developed with inoculation of bone marrow mesenchymal stem cell (MSC) spheroids and short fiber fillers. Kartogenin (KGN)-loaded short fibers (Fk) are assembled into cell spheroids (Fk-CS) as cell growth substrates and depots of cell differentiation modulators. Celecoxib (CXB)-loaded short fibers (FC) in HA hydrogels (HA-FC) benefit mechanical reinforcement and sustained release of anti-inflammatory agent. After inoculation in hydrogels, Fk-CS up-regulate differentiation-related gene expressions (aggrecan, collagen II, and Sox9) and the sustained release of KGN promotes chondrogenic differentiation and extracellular matrix (ECM) production in the entire spheroids. Osteochondral defects and osteoarthritis model are surgically created and treated with intraarticular injection of Fk-CS-loaded hydrogels. Osteochondral defects are fully repaired with integrated surrounding tissues, and the chondrocyte morphology, ECM (sulfated glycosaminoglycane and collagen II) deposition, and compressive moduli are comparable to those of normal cartilage. Osteoarthritis-derived cartilage lesions are repaired by regenerated ECMs, and osteoarthritis progression is retarded by downregulating pro-inflammatory cytokines and proteinase expressions. Thus, hierarchically structured injectable hydrogels and cell spheroids provide biochemical and mechanical cues for MSC differentiation, ECM deposition, cartilage regeneration, and inflammation removal in the treatment of osteochondral defects and osteoarthritis.