Background:

With the development of tissue engineering and regenerative medicine, engineered tissue constructs have become more prevalent and are now used as substitutions of patients’ damaged organs or tissues. To date, a scaffold-free cell transplantation technique based on cell sheets have been widely used in clinic. While poor vascularization and adverse immune reactions to biomedical devices remain crucial challenges in tissue engineering. The inflammatory response represents one of mainly and important regulators of vascularization and engineered tissue function restoration. This study investigated the effect of macrophage secretion on the formation of microvascular-like structures of human umbilical vein endothelial cells (HUVECs) in the bone marrow mesenchymal stem cell (BMSC) sheets. Methods Researchers differentiated the human monocytic leukemia cell line (THP-1) cells into the resting state of macrophage (M0) by phorbol 12-myristate 13-acetate (PMA) and further activated them into pro-inflammation and pro-healing states with the use of various cytokines. Condition media derived from kinds of macrophages were used to investigate the impact of macrophage on the viability and arrangement of HUVECs on BMSC sheets. Cytokines related to angiogenesis were detected in the culture supernatant of HUVECs, BMSC sheets, and pre-vascularized sheets. Results Results indicated that macrophages may guide the arrangement of endothelial cell through the paracrine pathway. The cell sheets that were cultured in the microenvironment with pro-inflammatory macrophages had fewer cell layers compared to those generated in other media. Furthermore, after experiencing high levels of vascular endothelial growth factor (VEGF) and tumor necrosis factor alpha (TNF-α) in the first 3 days while high level of platelet-derived growth factor (PDGF)-BB but low TNF-α and VEGF concentration in the next 4 days, pre-vascularized sheets had the most significant micro-vessel network. Conclusions The fates of pre-vascularized sheets regulated by macrophages secreted factors in microenvironment and sequential released cytokines could even promote neovascularization and angiogenesis.