Patent ID: 8663780

Claim:
A polymeric membrane having a tapered pore and comprising (n+2) polymeric layers wherein said tapered pore is formed by (n+2) apertures of differing diameter within said (n+2) polymeric layers, n being an integer from 0 to 10, said n+2 apertures being aligned with each other to form said tapered pore, wherein said tapered pore, at its smallest diameter, has a ratio of diameter of said pore to height of said polymeric layer at said smallest diameter of said pore of ≧3, wherein the aperture at an end layer of the membrane has the smallest diameter, and the diameters of the apertures in other layers gradually increase from the end layer to present the tapered pore, and wherein the diameter of the tapered pore is between 1 μm and 30 μm.