Background and objectives: The interaction of mesenchymal stromal cells (MSC) and endothelial cells (EC) hold a promising perspective for the revascularization of osteoconductive bone grafts in defect regeneration. Co-culture methods of MSC and ES are used to facilitate in vivo bone modeling. However, cell–cell interactions and cell-matrix integrations are not yet fully understood. Following the hypothesis that MSC and EC interactions can lead to an optimized revascularization of osteoconductive bone grafts we analyzed the interactions of MSC and EC in trans-well as well as direct co-culture in vitro. In addition we evaluated the integration and differentiation of MSC and EC co-cultures on osteoconductive bone grafts.

Methods: MSC and EC were labeled with fluorescent particles and seeded in monolayer and trans-well cultures. In addition MSC and EC co-cultures were established on two different osteoconductive bone grafts of different porosity and their differentiation analyzed using QT-PCR analysis for osteocalcin, vWf, VEGF as well as immunofluorecent labeling of CD31 and osteoprotegerin. Matrix integration was evaluated using 3D-imaging.

Results: Results indicated an endothelial and osteogenic interaction of MSC and EC leading to interdependent osteogenic and angiogenic differentiation in co-cultures in comparison to trans-well and singular cultures. 3D-imaging revealed an evenly distributed MSC and EC differentiation and integration in osteoconductive bone grafts of different porosity.

Conclusion: MSC and EC co-cultures can be used to create an osteo- and angio-inductive bone graft in vitro. Thus prevascularized, osteogenic cell-matrix-structures offer a promising stepping stone for future in vivo defect regeneration.