Improvement of the cell-loading efficiency of biomaterials by inoculation with stem cell-based microspheres, in osteogenesis.

In critical-size bone defects, autologous or allogenic cells are required in addition to compatible biomaterials for the successful defect healing. State of the art inoculation methods of biomaterials are based on the application of cell suspensions to the biomaterial. However, only less amounts of cells can be applied and sufficient adhesion to the material is required. Therefore, it was investigated whether the advantages of stem cell-based microspheres and insoluble collagenous bone matrix (ICBM) scaffolds can be combined which can lead to an advancement in cell seeding on biomaterials. Microspheres were produced from unrestricted somatic stem cells from human umbilical cord blood and were mounted on ICBM scaffolds. Following the incubation with osteogenic or control medium, the constructs were analyzed histologically after 3, 7, 14, and 28 days. Alizarin Red S and von Kossa staining revealed microsphere mineralization after 3 days in osteogenic and after 14 days in control medium. Meanwhile, a time-dependent increase in tissue, growing out of the microspheres, was detected. Our results provide evidence that microsphere-ICBM constructs are promising candidates for approaches of bone regeneration. They allow the transfer of substantially high numbers of cells in partially mineralized constructs.