Devitalized Stem Cell Microsheets for Sustainable Release of Osteogenic and Vasculogenic Growth Factors and Regulation of Anti-Inflammatory Immune Response.

The objective of this work was to investigate the effect of devitalized human mesenchymal stem cells (hMSCs) and endothelial colony-forming cells (ECFCs) seeded on mineralized nanofiber microsheets on protein release, osteogenesis, vasculogenesis, and macrophage polarization. Calcium phosphate nanocrystals were grown on the surface of aligned, functionalized nanofiber microsheets. The microsheets were seeded with hMSCs, ECFCs, or a mixture of hMSCs+ECFCs, cultured for cell attachment, differentiated to the osteogenic or vasculogenic lineage, and devitalized by lyophilization. The release kinetic of total protein, bone morphogenetic protein-2 (BMP2), and vascular endothelial growth factor (VEGF) from the devitalized microsheets was measured. Next, hMSCs and/or ECFCs were seeded on the devitalized cell microsheets and cultured in the absence of osteo-/vasculo-inductive factors to determine the effect of devitalized cell microsheets on hMSC/ECFC differentiation. Human macrophages were seeded on the microsheets to determine the effect of devitalized cells on macrophage polarization. Based on the results, devitalized undifferentiated hMSC and vasculogenic-differentiated ECFC microsheets had highest sustained release of BMP2 and VEGF, respectively. The devitalized hMSC microsheets did not affect M2 macrophage polarization while vascular-differentiated, devitalized ECFC microsheets did not affect M1 polarization. Both groups stimulated higher M2 macrophage polarization compared to M1.