22 March 2022
Blood-compatible membranes are among the most effective and cost-saving tools used to separate blood components. However, polypropylene (PP) membranes currently used in blood-contacting devices are prone to biofouling by host blood cells, proteins, and bacteria. Host contamination is one of the most critical bottleneck factors that limit the usage of PP membranes in clinical microbiology. The development of a filtering membrane resistant to biofouling is essential not only in clinical microbiology but also in blood filtration processes, water treatment, and the food industry.
Biofouling resistance of PP membranes is significantly improved with surface zwitterionization for leukocyte reduction filters. Micronbrane enhanced this technique and developed zwitterionic interface ultra-self-assemble coating technology (global patent) used in Devin filter. The developed membrane can remove more than 95% of nucleated cells from whole blood samples within just 5 minutes. Let’s see how it works.
Why zwitterionic materials?
Compared to other types of materials, zwitterionic networks have higher stability in complex mediums. More importantly, zwitterions provide strong hydration, and the modification process results in better hydration of the membranes. This characteristic acts as an energetic barrier against adsorption and biofouling by proteins, bacteria, and blood cells. Essential advantages of developing the zwitterionic membranes are that the method does not involve irradiation, oxygen plasma treatment, or UV irradiation.
Protein, bacteria, and blood cell biofouling prevention
Protein biofouling observed in commercial membranes promotes the adsorption of bacteria and blood cells. One of the most essential proteins found in blood samples is fibrinogen, a vital plasma protein involved in the formation of clots. Fibrinogen adhesion during filtration processes leads to white blood cell adhesion, deformation, and cellular death. The results obtained from Zwitterionized membranes indicated a drastic decrease in fibrinogen adsorption from 6.4 to 0.9 μg/cm2.
Zwitterionized membranes were tested for resistance to Escherichia coli, a bacterium commonly responsible for medical infections such as urinary tract infections. The bacterial adherence value was set to 100%, and results revealed a decreased E.coli adherence to the lowest relative measured attachment of 3 ± 1%.
How modified PP membranes remove white blood cells from blood samples
Compared to the commercial membranes where the pore size is reduced, the method through which the membranes are developed preserves the large pore size and porosity (Fig.1). These traits are essential for blood filtration processes, red blood cell preservation, and retention of white blood cells.
Fig. 1. The effect of coating poly(GMA-co-SBMA) with/without cross-linking agent (EDA) on (a) the structure, (b) pore size, and (c) porosity of modified PP fibrous membranes.
When a blood sample is filtrated through the Devin filters, white blood cells remain in the retentate or the part that does not pass through the membrane. Not only this, as compared to other types of membranes, the shape of white blood cells remains unaltered, and cells are still viable.
Multiple tests revealed that the modified PP membranes were highly efficient in selectively removing 99.99% of white blood cells from the filtered blood sample without affecting the erythrocyte concentration (Fig. 2).
Fig. 2 Schematic presentation of leukocyte removal from whole blood during blood filtration using modified PP membranes with a cross-linked poly(GMA-co-SBMA) polymer
The permeate, or the part that passes through the membrane, revealed a concentration of 0.07 103 cells/μL after filtration, while the initial concentration was 9.39 103 cells/μL. In comparison, unmodified membranes do not permit blood flow, and the commercially available hydrophilic membranes are not suitable barriers for white blood cells (Fig. 3).
Another advantage of poly(GMA-co-SBMA)-coated membrane is that the red blood cell concentration remains unchanged after filtration. This result indicates that these filters can be used to prepare RBCs-rich blood fractions, essential to patients suffering from intense bleeding after physical trauma.
Fig. 3 Comparison of poly(GMA-co-SBMA)-coated membranes with virgin unmodified PP and 3 or 5 layers of commercial hydrophilic membranes. (a) Whole blood filtration; (b) Concentration of red blood cells and white blood cells in the permeate (dotted lines) and white blood cells removal ratio determined from the white blood cells concentration in whole blood
Overall poly(GMA-co-SBMA)-coated zwitterionic membranes showed a significant improvement in blood compatibility with all analyzed samples. Multiple tests showed that compared to commercial membranes poly(GMA-co-SBMA)-coated zwitterionic membranes proved higher resistance to biofoulants adsorption and ideal cell preservation proprieties. The results and characteristics of the modified zwitterionic membranes indicate that this technology effectively reduces leucocytes in blood samples and removes host contamination from body fluids like whole blood. Micronbrane holds patent for this unique technology and utilizes it in its novel Devin® filter. PaRTI-Seq® built upon Devin® filter can provide precise test results within less than 24 hours upon sample receival.
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