Biomimetic epiphysis inspired by natural developmental mechanisms promote the repair of large-scale epiphyseal defects

Epiphysis is an organized and dynamically evolving developmental tissue that is susceptible to physical damage. At present, significant challenges in developing complex and controllable substitutes for epiphyses persist. In this study, human bone marrow mesenchymal stem cell (hBMSC) microspheres and recombinant human Indian hedgehog (IHH) were used to simulate the key mechanisms of bone development: mesenchymal condensation and biochemical signaling. The results showed that hBMSC microspheres self-assembled into cartilage-like blocks (SAB) under chondrogenic induction. In addition, the ex vivo regulatory effect of recombinant IHH was related to the concentration and treatment time. Notably, 100 ng/mL IHH significantly enhanced the chondrogenic differentiation efficiency of hBMSC microspheres while shortening the induction period. The internal cells of SAB-100 were in a dynamic balance of proliferation and differentiation, and its matrix morphology was similar to those of natural epiphyses. Therefore, SAB-100 was regarded as a biomimetic epiphysis (BME). In a large-scale epiphyseal defect model, SAB-100 showed superior chondrocyte regeneration potential. Additionally, elevated thrombospondin-2 (THBS2) expression significantly suppressed angiogenesis and bone bridge formation at the defect site, while partially restoring the cellular and matrix homeostasis of adjacent undamaged epiphyses. Ultimately, SAB-100 effectively prevented angular deformities and reduced limb length discrepancies. These findings suggest that exogenous IHH has the potential to reconstruct the IHH regulatory network ex vivo, and SAB-100 is expected to partially restore the developmental function of damaged epiphyses.