Fouling Reduction in Electrospun filter membrane

In water filtration, membrane fouling is a constant challenge as it results in significant drop in filtration performance and reduces its usage life. Such fouling comes from irreversible adhesion of substrates on the membrane surface, formation of biofilm or both. This is especially the case for membrane used in natural environment where there is a wide range of potential fouling agents. While electrospun membrane has been shown to exhibit good filtration performance, it must also demonstrate sufficient usage life before it is widely accepted. Therefore, the next stage in its development would be on its antifouling characteristic.

Materials exhibiting anti-fouling properties may be added to electrospun membrane. Goetz et al (2016) showed that electrospun cellulose acetate membranes surface coated with chitin nanocrystals effectively reduces the water contact angle to zero degrees. The resultant hydrophilic membrane demonstrated significantly reduced biofouling and biofilm formation. Similarly, Sun et al (2010) grafted poly(ethylene glycol) methyl ether methacrylate (PEGMA) to the surface of electrospun poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP) nanofiber membranes to improve hydrophilicity. The modified membrane was found to reduce protein adsorption and this removes one of the requirements for biofilm formation.

Apart from surface modifications, anti-microbial substances may be added to electrospun membrane to inhibit microbial growth on it. Dasari et al (2012) electrospun polylactic acid (PLA) membranes containing functionalized sepiolite fibrillar particles (5 wt. %) for anti-fouling membrane. Sepiolite is hydrophilic and its addition will improve hydrophilicity of the membrane. To reduce biofouling, sepiolite was functionalized with Cu and Ag. When tested with Saccharomyces cerevisiae and Pseudomonas putida, the membrane was able to reduce up to 85% of S. cerevisiae compared to neat PLA. The electrospun nanofiber structure may also help to enhance antibacterial property of the membrane compared to a film form of the same material. Samira et al (2020) constructed an electrospun membrane made of chitosan which is an antibacterial agent and PVA which helped to improve electrospinnability. Electrospun PVA/Chitosan membrane showed a higher antibacterial activity compared to polyvinyl alcohol (PVA) /Chitosan film cast based on colony forming unit (CFU) counts over 1 h, 8h and 24 h period. Electrospun PVA/Chitosan used in this study has an average diameter of 56.9 nm. Rod-shaped bacteria such as E. coli which was used in this study is in the micron size and its attachment to nanofiber structure in diameters smaller than its length may have led to conformational changes of the bacteria as it tries to wrap around each fiber. This may stress the bacteria and hence increases the antibacterial effect by nanofibers. In the study, the antibacterial effect on E. coli was stronger than S. aureus across all time points. Hydrophilicity of gram-negative bacteria made them more susceptible to damage by chitosan.

One way to reduce fouling is to use materials which shows resistance to it. Sulfobetaine methacrylate (SBMA) is a zwitterionic polymer has been shown to exhibit nonfouling properties. Emerick et al (2013) was able to electrospin SBMA by dissolving the polymer in NaCl solution (0.25M) at volume ratio of 1:1. After investigating the effect of SBMA molecular weight on the electrospinning outcome, they found that a molecular weight of ~420 kDa was able to produce uniform and smooth nanofibers.

▼ Reference

▼ Credit and Acknowledgement