Abstract: A novel hydrophilic composite porous membrane is obtained by applying a specific copolymer solution onto the overall surface of an oriented polyolefin membranous matrix comprising a plurality of microfibrils and a plurality of knotted portions cross-connected to the microfibrils, followed by drying. The copolymer is water-insoluble and is comprised of hydrophilic monomeric units and hydrophobic monomeric units in a specific ratio. In the obtained composite porous membrane, the microfibrils are bonded together by means of the copolymer, thereby forming bundles and a coat of the copolymer is formed on the overall surface of the bundles and knotted portions. The membrane has therewithin pores which are substantially elliptic in the cross section taken along the same direction as the longitudinal direction of the microfibril bundles and has on both surfaces thereof openings which are substantially elliptic as viewed against the surface of the membrane.

Abstract: A plasma separator containing porous hollow fibers composed of a polyolefin having elliptic pores defined by microfibrils and knotted portions, in which the pores of the hollow fibers, together with the spaces between the inner surface of the vessel and the fibers and between and inside the fibers, are filled with a sterile water or sterile solution and which has been sterilized with a sterilizing gas before the filling operation of the sterile water or solution. Incorporation of the water or solution into the pores is attained by applying a pressure to the water or solution. The incorporation of the water or solution causes the limiting pore diameter of the pores of the precursor hollow fibers to expand, thereby changing the pore characteristics of the precursor hollow fibers. The plasma separator, exhibiting high plasma component permeabilities, can be used safely, without troubles of hemolysis and residual chemical or solvents, and readily, without troubles of priming and washing.