Patent ID: 8118176

Claim:
A method for extracorporeal treatment of a fluid comprising the steps of: manufacturing a filtration device for extracorporeal treatment of a fluid, said fluid being blood or plasma, the filtration device comprising a first internal compartment and a second external compartment separated by a semipermeable membrane mounted in a casing, said first internal compartment being configured to circulate blood or plasma and said second external compartment being configured to circulate filtrate, wherein the semipermeable membrane comprises a bundle of hollow fibres manufactured according to the steps of: preparing a polymer solution containing a copolymer of acrylonitrile and at least one of an anionic comonomer and an ionizable comonomer, extruding the prepared polymer solution through a die having two concentric nozzles, a fluid being injected in the internal nozzle to form the lumen of the hollow fiber, thereby forming a gel fiber, and thermomechanically treating the gel fiber leaving the die, and placing the bundle of hollow fibers in a tubular enclosure secured at both ends by a potting compound for binding the fibers together and for tightly sealing in the tubular enclosure the first internal and second external compartments, the first internal compartment being an inner space between each potting compound and a corresponding end-fitting enclosing a corresponding end of the tubular enclosure and the inner space inside the hollow fibers, the second external compartment being the space between an inner side of the tubular enclosure and an external side of the hollow fibers, wherein the method further comprises the steps of: coating the external side of the hollow fibers by circulating, in said second external compartment, a polymer solution containing at least one cationic polymer or a mixture of polymers of which at least one polymer is cationic and is a hydrophilic polymer selected from the group comprising a polyamine, a diethylaminoethyldextran, and a polymer and copolymer containing one or several quaternary ammonium groups; circulating the blood or plasma in the first internal compartment; circulating the filtrate in the second external compartment, the circulating of the blood or plasma in the first internal compartment and the circulating of the filtrate in the second external compartment generating a pressure crossing in the filtration device causing a backfiltration, wherein during the back filtration, molecules contained in the filtrate are filtered to blood or plasma; and preventing endotoxins to pass from the filtrate to blood or plasma during backfiltration.