A New Subpopulation of Extracellular Vesicles Harvested from Osteogenically Induced Mesenchymal Stromal Cells of Surgical Site-Released Tissue

Impaired bone healing is a major challenge in orthopedic and trauma surgery, often causing long-term disability and high costs. While autologous bone grafting is the gold standard, it is limited by donor site morbidity, low availability, and surgical risks. As an alternative, surgical site-released tissue (SSRT) collected intraoperatively offers a readily available source of regenerative cells and bioactive factors. This study investigates the potential of SSRT-derived mesenchymal stromal cell (MSC)-like cells and their extracellular vesicles (EVs) to support bone healing in a cell-free approach. SSRT samples from 30 patients undergoing elective hip replacement were collected using a surgical vacuum filter. MSC-like cells were isolated and characterized based on International Society for Cellular Therapy (ISCT) criteria. Interestingly, many SSRT-derived MSC-like cells expressed CD34, a marker typically absent in cultured MSCs but linked to tissue-resident stromal cells, suggesting distinct regenerative properties. These cells also showed slow proliferation rates (P1: 8.7 ± 3.2 days; P2: 8.2 ± 5.4 days). EVs were isolated from osteogenically stimulated (EVs^MSC/O+) and unstimulated (EVs^MSC/O-) MSCs over three weeks. Antibody profiling revealed distinct cargo compositions, with a notable enrichment of CD13+ EVs in the stimulated group. Further in vivo and functional studies are needed to clarify underlying mechanisms and confirm therapeutic efficacy.