Synergy effects of copper and silicon ions on stimulation of vascularization by copper-doped calcium silicate

Copper (Cu) has been reported to be able to stimulate vascularization/angiogenesis, which is critical for regeneration of vascularized tissue in tissue engineering. Silicate bioceramics have also been reported to have stimulatory effects on vascularization due to the silicon (Si) ions released from silicate biomaterrals. Therefore, we hypothesize that a combination of Cu and Si ions may show synergy effects on vascularization. Therefore, a copper-doped calcium silicate bioceramic (Cu-CaSiO3, Cu-CS) was designed and synthesized with the purpose to enhance the stimulatory effects of copper salts or pure silicate bioceramics on vascularization by combining the effects of Cu and Si ions. The cytocompatibility of Cu-CS was firstly assessed by testing the influence of Cu-CS ion extracts on proliferation of human umbilical vein endothelial cells (HUVECs). Thereafter, vascularization of HUVECs on ECMatrix (TM) gel or co-cultured with human dermal fibroblasts (HDFs) in Cu-CS extracts was evaluated and expression of angiogenic growth factors was analyzed. Results revealed that, as compared to CS extracts and media containing soluble CuSO4, Cu-CS extracts possessed stronger stimulatory effects on upregulation of angiogenic growth factors, which finally resulted in better stimulatory effects on vascularization. During the vascularization process, paracrine effects dominated in the co-culture system. In addition, lower concentrations of Cu and Si ions released from Cu-CS than those released from pure CS or CuSO4 were enough to stimulate vascularization, which indicated that there were synergy effects between Cu and Si ions during stimulation of vascularization by Cu-CS. Taken together, the designed Cu-CS may be suitable as a new biomaterial for regenerating blood vessels in tissue engineering.