Ultrafiltration is a size-based membrane separation process that is used routinely for protein concentration and buffer exchange during the purification of biologics. Ideal ultrafiltration membrane structures consist of high porosity, highly interconnected uniform pores in order to display a sharp molecular weight cut off (MWCO) as well as high permeate flux. In this work, uniform pore size, high-porosity ultrafiltration membranes were developed using three dimensionally-ordered macroporous templates. A membrane casting cell was designed for self-assembly of silica spheres into a colloidal crystal template. The resulting close-packed colloidal crystal was infiltrated with a reactive monomer solution. After polymerization, the silica spheres were etched away, resulting in an inverse colloidal crystal (ICC) membrane with high porosity and uniform pores that are highly interconnected. Atom transfer polymerization was used to tailor the membrane pore size. Poly[(polyethylene glycol) methacrylate] (PPEGMA) chains were grown from the outer and internal (pore) membrane surface. The resulting ultrafiltration membranes were characterized using FESEM, ATR-FTIR, XPS, and water contact angle measurements. PPEGMA chains were grown successfully from the membrane surface. Membrane performance was evaluated using direct flow filtration experiments. Dextran rejection and the variation of permeate flux with degree of modification were determined. Permeate flux decreased monotonically with increasing polymerization time, as the average pore size decreased. Surface modification may be used to convert a microporous ICC membrane into an ultrafiltration membrane. (C) 2012 Elsevier By. All rights reserved.