A cell-free composite hydrogel scaffold promotes in situ cartilage regeneration via adjusted stiffness

The repair of articular cartilage injuries is challenging due to their limited regenerative ability . Cell-based tissue engineering strategies are effective for cartilage repair. However, they are primarily in the preclinical stage and face challenges such as lengthy in vitro culture times, high costs, and regulatory restrictions. Cell-free scaffolds can recruit endogenous cells to the defect site to achieve in situ cartilage repair, and avoiding many complications related to cell use, and have therefore received increasing attention. In this study, we blended gellan gum (GG) and hyaluronic acid (HA) in a specific proportion to form an interpenetrating network , and then added cations (Ca 2+ ) for physical crosslinking to prepare a composite hydrogel with good biophysical and chemical properties. The stiffness of the hydrogel can be adjusted by changing concentrations of Ca 2+ . In vitro experiments, we evaluated the effect of hydrogels with different matrix stiffness on promoting the proliferation, migration and chondrogenic differentiation of bone marrow mesenchymal stem cells . In vivo experiments revealed that the hydrogel group achieved cartilage repair effect comparable to that of the group loaded with mesenchymal stem cells 12 weeks after surgery, without adding exogenous cells and growth factors. The composite hydrogel is an ideal cell-free scaffold material with good cartilage repair effect. Moreover, it is suitable for injection, easily translatable into clinical practice, and shows great potential for applications. • Simple mixing of two natural hydrogels to form an interpenetrating network. • The stiffness of the hydrogel can be adjusted by changing concentrations of Ca 2+ . • The composite hydrogel is an ideal cell-free scaffold material with good cartilage repair effect. • It is suitable for injection, easily translatable into clinical practice, and shows great potential for applications.