Scaffold-Based Delivery of Bone Marrow Mesenchymal Stem Cell Sheet Fragments Enhances New Bone Formation in Vivo

PURPOSE:Stem cell therapy is becoming a potent strategy to shorten the consolidation time and reduce potential complications during distraction osteogenesis (DO). However, the conventional local injection or scaffold-based delivery of bone marrow mesenchymal stem cell (BMSC) suspension deprives the cells of their endogenous extracellular matrix, which might dampen cell differentiation and tissue regeneration after implantation. Therefore, in our study, a BMSC sheet was established and was then minced into fragments and loaded onto a hydroxyapatite (HA) scaffold for grafting.MATERIALS AND METHODS:The purified and characterized BMSCs were grown into a cell sheet, and bone formation and mineralization capacity, as well as the cell sheet composition, were analyzed. Afterward, the in vivo osteogenic ability of cell sheet fragments (CSFs) was evaluated in immunocompromised mouse and rabbit models of DO.RESULTS:The BMSC sheet exhibited higher alkaline phosphatase activity than osteogenic cell suspension cultures. Alkaline phosphatase activity and mineral particles in the cell sheet increased further after osteogenic induction. Moreover, calcium and phosphorus were present only in the osteogenic cell sheet, along with the common elements carbon, oxygen, chlorine, sodium, and sulfur, as indicated by x-ray photoelectron spectroscopy analysis. In a mouse model, the CSF-HA complex was injected subcutaneously. Micro-computed tomography analysis showed that the osteogenic CSF-HA complex led to a considerably higher bone volume than the BMSC-HA or CSF-HA complex. The osteogenic CSF-HA specimens showed increased angiogenesis and deposition of type I collagen compared with the non-osteogenic CSF-HA or BMSC-HA specimens. Moreover, the osteogenic CSF-HA markedly improved bone consolidation and increased bone mass in DO rabbits.CONCLUSIONS:Collectively, the incorporation of osteogenic BMSC sheets into HA particles greatly promoted bone regeneration, which offers therapeutic alternatives for DO.