Cells grow out of osteogenic differentiated cellular-microspheres

The use of acellular bone substitutes is frequently insufficient in critical size defects. Hence there is a demand for scaffolds with outgrowing cells. Furthermore, artificial scaffolds have partially negative influences on the complete regeneration. Thus the aim of the current work was it to investigate whether cells grow out of stem cell based microspheres, while at the same time these microspheres adopt scaffold like characteristics by mineralisation. Microspheres were produced from unrestricted somatic stem cells (USSCs) or embryonic stem cells (ESCs) and were incubated with osteoinductive medium. After osteoinduction for different time periods, outgrowth distances of cells out of microspheres were evaluated and histology was performed for microsphere sections. Staining with alisarin red showed that microspheres were strongly mineralised after seven days osteoinduction. In contrast, controls only start to mineralise after this time, but resulted in completely mineralised spheres after 28 days. Significant reductions (P ≤ 0.01) in sprouting distances were found during increasing time of osteogenic induction for both USSC- and ESC-microspheres. However, the average outgrowth distances of USSCs were much higher than of ESCs. Massońs trichrome staining revealed a time-dependent and DAG (dexamethasone, ascorbic acid and beta-glycerolphosphate)-induced increase in extracellular matrix proteins of USSC microspheres. It was shown that cells migrate out of the microsphere and spread into the surrounding, while at the same time the microspheres incorporate calcium. Thus microspheres are the scaffold and the source of cells with osteogenic potential at the same time. Furthermore, microspheres permit the precise administration of large amount of cells into an area of interest.