Patent ID: 8596467

Claim:
A semipermeable hollow fiber membrane comprising: an outer wall surface, an inner wall surface, and an interior lumen extending along the length thereof and having a selective layer on the outer wall surface, characterized by having a smallest pore size on the outer wall surface, and wherein the outer wall surface is smooth, continuous and homogeneous in a nanoscopic scale, being virtually devoid of roughness with roughness parameters R a and R q of not more than 10 nm, a roughness being measured with an atomic force microscope (AFM), and calculating the roughness parameters R a and R q using the following equations: R a = 1 N ⁢ ∑ i = 1 N ⁢  Z i  R q = 1 N ⁢ ∑ i = 1 N ⁢ Z i 2 with N being the total number of data points and Z i being the height of a data point above an average picture level, and wherein a membrane wall between the outer wall surface and the inner wall surface has at least four layers with different pore sizes and mass densities, and wherein a layer positioned closest to a middle of the membrane wall has a smaller pore size and a higher mass density than the two layers directly adjacent on each side of said layer positioned closest to the middle of the membrane wall.