Investigation of medium perfusion through scaffold-free tissue constructs using endothelial cell-covered spheroids in vitro

A scaffold-free tissue construct was formed by assembling endothelial cell-covered spheroids, and medium perfusion through the tissue construct was investigated using hydrostatic pressure-driven culture circuit. Primary rat hepatocyte spheroids covered by human umbilical vein endothelial cells (HUVECs) were assembled in culture chambers with a cylindrical culture space of 2 mm in diameter, and then medium was perfused through the assembled spheroids for 48 h. The medium flow rate through the culture chamber was measured over the perfusion culture time, which decreased during the first several hours, then increased or remained low depending on the amount of spheroids in the culture chamber. Histochemical analyses showed single tissue construct formation by spheroid fusion when cultured from 2 × 10⁵ nuclei spheroids, with the loss of boundaries between the spheroids. Moreover, a viable cell region was found at the center of the tissue construct in several locations. Poor adhesion was found between spheroids cultured from 4 × 10⁵ nuclei spheroids. The total nuclei density in cultured tissue constructs was estimated to be about half of that in HUVEC-covered hepatocyte spheroids. This study demonstrated the possibility of medium perfusion through scaffold-free tissue constructs by assembling endothelial cell-covered spheroids, promising for a large tissue construct culture in vitro.