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Although widely used in blood-contacting devices, polypropylene (PP) membranes are prone to biofouling by plasma proteins and blood cells. The present study explores the effect of a surface zwitterionization process on the improvement of the biofouling resistance of PP membranes for leukocyte reduction filters. The modification strategy consists in forming an interpenetrating network of poly(glycidyl methacrylate-co-sulfobetaine methacrylate) (poly(GMA-co-SBMA) around the fibers of coated PP membranes, using a cross-linking agent: ethylenediamine (EDA). It is shown that with EDA, a range of poly(GMA-co-SBMA) concentration (1-5 mg/mL) leads to a 0°-water contact angle and high hydration of the networks without affecting the intrinsic porous structure of the material. Besides, the related membranes show excellent resistance to biofouling by Escherichia coli, fibrinogen, leukocytes, erythrocytes, thrombocytes and cells from whole blood with reductions in adsorption of 97%, 86%, 90%, 95%, 97% and 91%, respectively, compared to unmodified PP. Used in whole blood filtration, it is demonstrated that in the best conditions (5 mg/mL copolymer, with EDA), leukocytes can be efficiently removed (> 99.99%) without altering the erythrocytes concentration in the permeate, and that leukodepletion is more efficient than that measured with a commercial hydrophilic PP blood filter (about 50% retention). Physical retention of leukocytes is only efficient if the membrane material is anti-biofouling, and so, does not interact with other blood components able to trigger leukocyte attachment/deformation.

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Poly(ethylene terephtalate) (PET)-based materials face general biofouling issues that we addressed by grafting a copolymer of glycidyl methacrylate and sulfobetaine methacrylate, poly(GMA- r-SBMA). The grafting procedure involved a dip-coating step followed by UV-exposure and led to successful grafting of the copolymer as evidenced by X-ray photoelectron spectroscopy and zeta potential measurements. It did not modify the pore size nor the porosity of the PET membranes. In addition, their surface hydrophilicity was considerably improved, with a water contact angle falling to 30° in less than 20 s and 0° in less than 1 min. The effect of copolymer concentration in the coating bath (dip-coating procedure) and UV exposure time (UV step) were scrutinized during biofouling studies involving several bacteria such as Escherichia coli and Stenotrophomonas maltophilia, but also whole blood and HT1080 fibroblasts cells. The results indicate that if all conditions led to improved biofouling mitigation, due to the efficiency of the zwitterionic copolymer and grafting procedure, a higher concentration (15 mg/mL) and longer UV exposure time (at least 10 min) enhanced the grafting density which reflected on the biofouling results and permitted a better general biofouling control regardless of the nature of the biofoulant (bacteria, blood cells, fibroblasts).

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This study introduces a zwitterionic material to modify polysulfone (PSf) membranes formed by a dual bath procedure, in view of reducing their fouling propensity. The zwitterionic copolymer, derived from a random polymer of styrene and 4-vinylpyrridine and referred to as zP(S-r-4VP), was incorporated to the PSf solution without any supplementary pore-forming additive to study the effect of the sole copolymer on membrane-structuring, chemical, and arising properties. XPS and mapping FT-IR provided evidence of the modification. Macrovoids appeared and then disappeared as the copolymer content increased in the range 1–4 wt%. The copolymer has hydrophilic units and its addition increases the casting solution viscosity. Both effects play an opposite role on transfers, and so on the growth of macrovoids. Biofouling tests demonstrated the efficiency of the copolymer to mitigate biofouling with a reduction in bacterial and blood cell attachment by more than 85%. Filtration tests revealed that the permeability increased by a twofold factor, the flux recovery ratio was augmented from 40% to 63% after water/BSA cycles, and irreversible fouling was reduced by 1/3. Although improvements are needed, these zwitterionic PSf membranes could be used in biomedical applications where resistance to biofouling by cells is a requirement.

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