Claire Roulin
Virus filtration by size exclusion is a robust means of eliminating viruses in blood or pharma products. Porous polymer membranes with a narrow size distribution are used to allow passage of the protein product but retain viruses. The chosen polymer must resist process-induced physical and chemical wear and is therefore generally inert and hydrophobic material. When filtrating potentially heterogeneous products such as IgG from pooled blood samples, protein adsorption on the polymer surface causes high fouling. This eventually blocks the filter and reduces total filtration volume. A solution to this adsorption problem is to graft a hydrophilic gel-like polymer layer on the membrane inner surface to reduce protein adsorption. The surface properties are thus changed while retaining the stability of the bulk polymer. The grafting was initiated with an electron beam, which creates free radicals by unspecific scission of the polymer backbone through electron irradiation. Two acrylate monomers were used for polymerization, a monofunctional monomer and a bifunctional one, used as a crosslinker to form the gel structure. Two different grafting method were tested. The first grafting method is simultaneous grafting, where the membrane is impregnated with the monomer solution then irradiated. Initiation and polymerization thus occur almost simultaneously. The grafted membrane properties were assessed using flow measurements, protein adsorption tests, FTIR absorbance measurements, virus retention tests and filter integrity tests. Comparing the various grafting approaches, it can be seen that simultaneous grafting lowers considerably protein adsorption, to the price of a highly reduced buffer flow. These filters therefore run slowly but can process more volume before fouling. The sequential grafting method using peroxides as initiators did not show significant filtration improvements compared to the reference membrane when the solution with monomer and crosslinker was used. However, when only monofunctional monomer was used for peroxidation grafting, the protein filtration capacity was increased with limited buffer flow loss. Generally, the sequential method is interesting for graft polymerization of porous membranes because it allows higher degree of grafting and the versatile grafting parameters involved give many development options depending on the application
2010
