Cell-matrix gel and membrane pore size are the two factors relevant to the limited mass transfer by diffusion in such gel entrapment of mammalian cell culture.

Rat hepatocytes were cultured in three polysulfone, hollow-fiber cartridges, characterized by two membrane variables: pore size and inner diameter (ID). Hepatocytes entrapped in a micro-filtration (MF) cartridge with the membrane pore size 0.1 microm had twice the production of urea and 4-fold the amount of albumin in comparison to the control cartridge, a ultra-filtration (UF) cartridge with a molecular weight cut-off (MWCO) of 100 kDa. Hepatocytes entrapped in a UF cartridge with ID of 0.5 mm secreted twice the amount of urea and 10-fold the amount of albumin compared with the control UF cartridge.

Opposite to the established view that collagen is an extracellular substratum for only dispersed hepatocyte culture, hepatocyte spheroids were directly formed within hollow fibers by addition of moderate concentrations of soluble collagen. Morphologically, these spheroids indicated a close relationship with their in vivo structure of liver. The albumin and urea synthetic profiles confirmed that those spheroids maintained liver-specific functions for at least 8 days. Spheroid formation by addition of collagen not only presents a potential methodology for clinical use of spheroids in bioartificial liver device but also indicates a likely function of collagen for self-assembly of primary cells in tissue engineering.