Loading of EPO on hydroxyapatite/polyurethane composite scaffolds promotes osteogenesis and angiogenesis by regulating of HIF-1α/VEGF signaling.

Composite scaffolds composed of porous polyurethane (PU) block copolymer and nano-hydroxyapatite (n-HA) have demonstrated significant potential in bone defect repair. However, the co-effect of osteogenesis and angiogenesis during the process of large bone defect repair is still not yet fully understood. Recent research has found that erythropoietin (EPO) is essential for both osteogenesis and angiogenesis, offering a new research direction for bone regeneration strategies. In this study, a polydopamine (pDA)-modified, EPO-functionalized HA/PU scaffold was fabricated, and its physicochemical properties, release kinetics, and effects on bone repair were systematically investigated.In vitro, a co-culture system of human umbilical vein endothelial cells and rat bone marrow mesenchymal stem cells was used to evaluate the scaffold's effects on cell proliferation, osteogenic, angiogenic, and HIF-1α/ vascular endothelial growth factor (VEGF) pathway.In vivo, the modified composite scaffold was implanted onto the cranial bone defects of Sprague-Dawley rats to assess its efficacy in promoting bone repair and HIF-1α/VEGF pathway.In vitro, the EPO/pDA/HA/PU group showed more three-dimensional cell morphology with prominent pseudopodia, facilitating cell adhesion, and significantly increased mRNA expression of ALP, Runx2, CD31, CD34, HIF-1αand VEGF.In vivo, the EPO/pDA/HA/PU group exhibited the most significant bone regeneration, with micro- computed tomography analysis confirming a significantly higher the ratio of bone tissue volume to total tissue volume (BV/TV) compared to the blank and HA/PU control groups. These results indicated that the modified composite scaffold enabled sustained release of EPO, which upregulated the expression of HIF-1αand VEGF, thereby enhancing osteogenic and angiogenic capabilities bothin vitroandin vivo. Our research demonstrated that loading of EPO onto the HA/PU composite scaffold could effectively promote osteogenesis and angiogenesis. HIF-1α/VEGF signaling plays a crucial role in this process. This discovery provides novel insights and methods for using HIF-1α/VEGF as a regulatory target to advance the clinical translation of large bone defects repair.