A macroencapsulation device for somatic cells using ultrapurified Na alginate and polysulfone hollow fibers of 30 kDa molecular weight cutoff. Ultrapurified Na alginate material is used which has a high `G` content, low endotoxin content, low divalent metal toxins and low protein impurities. Islet cells prior to being encapsulated, are irrigated with Hank's modified solution (without Ca and Mg) containing gentamycin, vancomycin and amphotericin B and then passed through a leukoabsorb filter to reduce the donor antigen load of passenger leukocytes and to reduce the bioburden of microorganisms including viruses. Encapsulation is done in RPMI 1640 tissue culture fluid containing necessary nutritional supplements and ATP source of energy. The open ends of the fiber are covered with a porous membrane. To further improve biocompatibility, the outer wall of the polysulfone is lightly gelled with alginate gel. Such double gelled, encapsulated fibers do not affect diffusion of glucose or insulin across the hollow fibers.