Ultrafiltration membranes and methods of making

A virus removal methodology comprising:

• providing a filtration device comprising a housing having a fluid inlet and a filtrate outlet, and containing at least one two-layered membrane having one asymmetric ultrafiltration layer in which particles having a 20 to 100 nanometer (nm) diameter are retained and one microporous asymmetric layer in which particles larger than 0.1 μm are retained, wherein the membrane is produced from two polymer solutions and the membrane has an integral transition zone between the ultrafiltration layer and the microporous layer, wherein the transition zone is a region where the pore size transitions from the ultrafiltration layer to the microporous layer, wherein:
• the layers of the membrane are each substantially hydrophilic,
• at least one of the layers of the membrane is capable of substantially preventing the passage therethrough of a virus and both layers are capable of substantially permitting the passage therethrough of a protein,
• the layers of the membrane each having a tight-side and an open-side, the average surface pore size of said tight-side being less than the average surface pore size of said open-side to form the asymmetric layers, and
• a first layer of the membrane being oriented such that fluid introduced into said housing through the fluid inlet commences passage through said first layer through the open-side;
• providing a manufactured protein-containing solution comprising a predominant solute, wherein the predominant solute in the solution is said protein, and wherein the solution is prone to contamination by said virus;
• and
• flowing the solution through the filtration device under conditions sufficient to effect substantial passage of the protein through each layer of the membrane and out of the housing through the filtrate outlet, whereby any virus contaminating the manufactured protein-containing solution is substantially prevented from passage through the membrane, and is substantially removed from the solution.