Electrical stimulation of adipose-derived mesenchymal stem cells and endothelial cells co-cultured in a conductive scaffold for potential orthopaedic applications

Electrical stimulation (ES) has emerged as a useful tool to regulate cell behaviour, but the effect of ES on mesenchymal stem cell (MSC)/vasculogenic cell co-culture has not been investigated. Herein, human adipose-derived MSCs (AD-MSCs) and umbilical vein endothelial cells (HUVECs) were co-cultured in an electrically conductive polypyrrole/chitosan scaffold. Compared with AD-MSC monoculture, calcium deposition in the co-culture without and with ES (200 mu A for 4 h/day) was 139% and 346% higher, respectively, after 7 days. As the application of ES to AD-MSC monoculture only increased calcium deposition by 56% compared with that without ES after 7 days, these results indicate that ES and co-culture with HUVECs have synergistic effects on AD-MSCs' osteogenic differentiation. ES application also significantly enhanced CD31 expression of HUVECs. In HUVEC monoculture, application of ES increased CD31 expression by 224%, whereas the corresponding increase in AD-MSC/HUVEC co-culture with ES application was 62%. The gene expression results indicate that ES enhanced the cellular functions in AD-MSC and HUVEC monoculture via autocrine bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF), respectively. In co-culture, crosstalk between AD-MSCs and HUVECs due to paracrine BMP-2 and VEGF enhanced the cellular functions compared with the respective monoculture. With application of ES to the AD-MSC/HUVEC co-culture, autocrine signalling was enhanced, resulting in further promotion of cellular functions. These findings illustrate that co-culturing AD-MSC/HUVEC in a conductive scaffold with ES offers potential benefits for bone defect therapy.