Biomechanically inspired composite hydrogel bioink enhances engineered cartilage formation

Current therapies for articular cartilage defects or degeneration, such as osteoarthritis, remain largely unsatisfactory. There are significant clinical demands for the development of more efficient approaches to enhance the repair or regeneration of articular cartilage lesions. In this study, a newly defined alginate- gelatin (A-G) composite bioink was synthesized using the carbodiimide chemistry crosslinking method. Then, the dual-crosslinking (DC) bioscaffolds containing both chemical and ionic networks were fabricated by 3D-bioprinting technique and Ca2+ treatment. Mimicking the mechanical properties of the pericellular matrix of native articular cartilage, the optimized networks formed in the DC bioscaffolds provided a desirable Young’s modulus and geometric constraints, which were superior to that of the single-crosslinking control group. Chondrocytes encapsulated in the 3D printed A-G-DC bioscaffolds exhibited above 95% viability and higher proliferation rate compared to those in the alginate-only group after 7 days of in vitro culture. Chondrogenic differentiation in vitro was improved in the A-G-DC bioscaffolds compared to that of the alginate-only group, indexed by upregulation of chondrogenic marker gene expression, including SOX9, COL2A1, COMP, and ACAN. In subcutaneous transplantation and osteochondral defect models in severe combined immunodeficiency mice, the A-G-DC bioscaffolds exhibited superior chondrogenesis and repair capacity compared to the alginate-only or no-implant control groups. This was evidenced by increased expression of SOX9 and collagen type II (Col II) and higher ICRS II scores. These findings demonstrate that the biomechanically inspired A-G composite bioink and the 3D-printed A-G-DC bioscaffolds possess excellent cell biocompatibility, satisfactory biomechanical properties, and the ability to promote chondrogenesis, making them a promising candidate for enhancing cartilage regeneration in patients with articular cartilage lesions.