A robustly adhesive hydrogel with enhanced osteogenic properties for cartilage defect repair

Cartilage defects are a common joint disorder. Current hydrogels used for cartilage repair and bone regeneration at defect sites suffer from inadequate adhesive properties and inferior mechanical performance in the early repair stage. Additionally, a lack of bioactive ion supply in the later stage impairs new bone formation. To address these issues, β-TCP/BN/P(AM-PEG) (TBPAP) hydrogels with BN serving as the bridging structures were synthesized by in situ growth of P(AM-PEG) on the β-TCP and BN via ionic cross-linking. A key innovation lies in the exceptional adhesive properties of TBPAP, synergistically achieving through covalent bonding, ionic interactions, and electrostatic adsorption. Specifically, the interfacial adhesive strength between TBPAP and bone sheets reached a remarkable 1.59 ± 0.04 MPa, which is significantly higher than that of many existing hydrogels. Meanwhile, the bridging-structured BN and coordinate bond formation between β-TCP and the hydrogel enhanced its compressive properties. Another innovation of TBPAP hydrogel is the precise quantification of its expansion stress, which ranged between 0.15 MPa and 0.24 MPa. Cell pressurization cultures revealed that an expansion stress of 0.21 MPa optimally promoted osteoblast adhesion, proliferation, and early differentiation. Furthermore, TBPAP enabled sustained release of calcium ions through ionic cross-linking and electrostatic attraction. These findings demonstrate that TBPAP effectively overcomes the limitations of current hydrogels, showing significant potential for clinical applications in cartilage repair and bone regeneration.