Platelet Lysate–Enriched Human Induced Pluripotent Stem Cell–Derived Chondrocyte Sheets for Bone Defect Repair via Endochondral Ossification

Bone defects are a major clinical challenge, primarily owing to the limited self-healing capacity of bones and the high risk of complications associated with conventional treatment strategies. Traditional tissue engineering approaches typically rely on intramembranous ossification for bone repair however, this method often yields suboptimal results. In this study, we found that chondrocyte sheets derived from human induced pluripotent stem cells (iPSCs) can be activated through immune stimulation to initiate endochondral ossification in vivo. Based on these findings, we hypothesized that cartilage-based materials might be more effective in inducing osteogenesis during bone defect repair. Human platelet lysate (HPL) is a cost-effective and readily available source of bioactive molecules. It is rich in various growth factors and functional proteins and has shown significant application potential in regenerative medicine. In this study, we developed a novel method for preparing iPSC-derived chondrocyte sheets augmented with HPL (iCDCHs). Experimental results revealed that HPL treatment significantly enhanced endochondral ossification within chondrocyte sheets and accelerated bone regeneration. Compared with allogeneic bone grafts, iCDCHs resulted in improved bone repair outcomes, with notably lower immunogenicity. Further analysis revealed that chondrocyte sheets promoted M2 macrophage polarization by activating the PI3K/Akt signaling pathway, thereby generating various pro-regenerative metabolic factors and establishing a microenvironment conducive to effective bone repair. These findings suggest that iPSC-derived chondrocyte sheets hold promise in the repair of bone defects and serve as a valuable alternative to allogeneic bone grafts in tissue engineering.