Membrane Stacks

A membrane stack, comprising:

• first and second membrane layers;
• and
• a spacer layer disposed between said first and second membrane layers;
• wherein
• said membrane stack is configured such that fluid passes through said membrane stack in a direction substantially perpendicular to the plane of said membrane layers and said spacer layer;
• the membrane layers and the spacer layer form alternating layers wrapped around a core;
• at least one of said membrane layers comprises a macroporous gel-filled membrane layer;
• the macroporous gel-filled membrane layer comprises a support member;
• the support member comprises a void volume;
• said void volume is substantially completely occupied by a macroporous gel;
• and
• the macroporous gel has macropores of average size between about 10 and about 3000 nm.