Patent ID: 8197745

Claim:
A method for the preparation of a permselective asymmetric hollow fiber membrane by solvent phase inversion spinning, the membrane being for the separation of toxic mediators from blood, the membrane comprising at least one hydrophobic polymer and at least one hydrophilic polymer, the membrane permitting passage of molecules having a molecular weight of up to 45,000 Daltons in presence of whole blood, the membrane having a molecular weight exclusion limit in water of about 200,000 Daltons, the method comprising: a) dissolving the at least one hydrophobic polymer and the at least one hydrophilic polymer in a solvent to form a polymer solution, b) extruding the formed polymer solution through an outer ring slit of a nozzle with two concentric openings, the nozzle having a temperature between about 30° C. and about 80° C. such that the temperature of the formed polymer solution at the outlet of the nozzle is between about 30° C. and about 80° C., c) exposing the formed polymer solution emerging from the outer slit opening to a humid steam/air mixture with a solvent content between about 0.5 weight % and about 5 weight % related to the water content of the humid steam/air mixture, d) extruding a center fluid through the inner opening of the nozzle such that the temperature of the center fluid at the outlet of the nozzle is between about 30° C. and about 80° C., and e) subsequently washing and optionally drying the membrane, wherein dissolving the at least one hydrophobic polymer and the at least one hydrophilic polymer in a solvent to form a polymer solution comprises dissolving the at least one hydrophobic polymer and the at least one hydrophilic polymer in a solvent to form a polymer solution comprising about 10 weight %-about 20 weight % hydrophobic polymer and about 2 weight %-about 11 weight % hydrophilic polymer.