Commonly used materials for the production of membranes include hydrogel polymers such as alginate, cellulose and thermoplastic polymers such as hydroxyethyl methacrylate-methyl methacrylate (HEMA- MMA), polyacrylonitrile-polyvinyl chloride (PAN-PVC), as well as variations of the above-mentioned. The material used determines the permeability of the cell membrane, which for polymer depends on the molecular weight cut off (MWCO). The MWCO is the maximum molecular weight of a molecule that may freely pass through the pores and is important in determining adequate diffusion of nutrients, waste and other critical molecules.