Chlorine Rechargeable Biocidal N-Halamine Nanofibrous Membranes Incorporated with Bifunctional Zwitterionic Polymers for Efficient Water Disinfection Applications

Fighting against biofilm: The antifouling and antimicrobial material

Biofilms are groups of microorganisms protected by self-secreted extracellular substances. Biofilm formation on the surface of biomaterial or engineering materials becomes a severe challenge. It has caused significant health, environmental, and societal concerns. It is believed that biofilms lead to life-threatening infection, medical implant failure, foodborne disease, and marine biofouling. To address these issues, tremendous effort has been made to inhibit biofilm formation on materials. Biofilms are extremely difficult to treat once formed, so designing material and coating bearing functional groups that are capable of resisting biofilm formation has attracted increasing attention for the last two decades. Many types of antibiofilm strategies have been designed to target different stages of biofilm formation. Development of the antibiofilm material can be classified into antifouling material, antimicrobial material, fouling release material, and integrated antifouling/antimicrobial material. This review summarizes relevant research utilizing these four approaches and comments on their antibiofilm properties. The feature of each method was compared to reveal the research trend. Antibiofilm strategies in fundamental research and industrial applications were summarized.

Self-healing and durable antifouling zwitterionic hydrogels based on functionalized liquid metal microgels

Hydrogels are a promising new class of antifouling materials. But their utility is constrained by low mechanical strength and unsatisfactory antifouling performance over the long term. Herein, we successfully prepared zwitterionic polymer PEIS cross-linked gallium-based liquid metal microgels-based (PEIS-Gel@PMPC-GLM) hydrogels via UV-curing and amidation reaction. The as-prepared hydrogels showed preferable mechanical properties and superior hydrophilicity to the original hydrogels. The PEIS-Gel@PMPC-GLM hydrogels could prevent the adhesion of more than 90 % of microalgae and nearly 100 % of bacteria in a short-term antifouling test. PEIS-Gel@PMPC-GLM hydrogels also performed exceptionally well in the high concentration antibacterial test and the long-term antifouling test (remove more than 90 % bacteria and 80 % microalgae). In addition to releasing a high concentration of gallium ions, as shown by the ICP-OES test, PEIS-Gel@PMPC-GLM hydrogels also exhibitedexcellent lubrication performance, as demonstrated by the friction test (coefficient of friction as low as 0.023). Therefore, the antifouling effect of gallium ions combined with the strong hydration ability of the surfaces endowed the hydrogels remarkable antibacterial and antifouling properties. As a result of the exposed gallium atoms inducing further crosslinking of residual vinyl monomer in hydrogels, PEIS-Gel@PMPC-GLM hydrogels revealed certain self-healing performance.

High-strength hydrophilic N-halamines chitosan and cellulose nanofibers membranes with repeated bactericidal properties

Direct addition of disinfectants and membrane separation techniques have been common methods to address microbial contamination in water. However, disinfectants may generate toxic by-products, and even minor damage or biofilm formation on filtration membranes can lead to a heightened risk of microbial contamination. Consequently, how to quickly and safely disinfect microbial contaminated water sources remains a huge challenge. In this study, the high-strength broad-spectrum antibacterial CNF/CS composite membrane was fabricated by utilizing cellulose nanofibers (CNF) to reinforce the structure of chitosan (CS). The resulting CNF/CS composite membrane exhibits an impressive tensile strength of 148 MPa and boasts an active chlorine content of 5.29 %. Notably, even after undergoing 50 washing cycles and 10 repeated chlorination procedures, the structural integrity and high active chlorine content of the composite membrane remain preserved, validating its exceptional strength, stability, and chlorine rechargeability. Additionally, the CNF/CS antibacterial materials demonstrate remarkable attributes in terms of rapid sterilization, sustained and consistent release of active chlorine, and efficient inhibition of biofilm formation, demonstrating great potential in efficient, green, and safe sterilization.

Preparation of Rechargeable Antibacterial Polypropylene/N-Halamine Materials Based on Melt Blending and Surface Segregation

Polypropylene (PP) has been widely used in health care and food packaging fields, however, it lacks antibacterial properties. Herein, we prepared the polymeric antibacterial agents (MPP-NDAM) by an in situ amidation reaction between 2,4-diamino-6-dialkylamino-1,3,5-triazine (NDAM) and maleic anhydride grafted polypropylene (MPP) using the melt grafting method. The effects of reaction time and monomer content on the grafting degree of N-halamine were investigated, and a grafting degree of 4.86 wt % was achieved under the optimal reaction conditions. PP/MPP-NDAM composites were further obtained by a melt blending process between PP and MPP-NDAM. With the adoption of surface segregation technology, the content of N-halamine structure on the surface of PP/MPP-NDAM composites was significantly increased. The antibacterial tests showed that the PP/MPP-NDAM composite could achieve 99.9% bactericidal activity against 1.0 × 107 CFU/mL of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) within 10 and 5 min of contact, respectively. The antibacterial effect became more pronounced with the prolongation of chlorinated time, and it could achieve 99.9% bactericidal activity against E. coli within merely 1 min of contact.

Antimicrobial function of yeast against pathogenic and spoilage microorganisms via either antagonism or encapsulation: A review

Contaminations of pathogenic and spoilage microbes on foods are threatening food safety and quality, highlighting the importance of developing antimicrobial agents. According to different working mechanisms, the antimicrobial activities of yeast-based agents were summarized from two aspects: antagonism and encapsulation. Antagonistic yeasts are usually applied as biocontrol agents for the preservation of fruits and vegetables via inactivating spoilage microbes, usually phytopathogens. This review systematically summarized various species of antagonistic yeasts, potential combinations to improve the antimicrobial efficiency, and the antagonistic mechanisms. The wide applications of the antagonistic yeasts are significantly limited by undesirable antimicrobial efficiency, poor environmental resistance, and a narrow antimicrobial spectrum. Another strategy for achieving effective antimicrobial activity is to encapsulate various chemical antimicrobial agents into a yeast-based carrier that has been previously inactivated. This is accomplished by immersing the dead yeast cells with porous structure in an antimicrobial suspension and applying high vacuum pressure to allow the agents to diffuse inside the yeast cells. Typical antimicrobial agents encapsulated in the yeast carriers have been reviewed, including chlorine-based biocides, antimicrobial essential oils, and photosensitizers. Benefiting from the existence of the inactive yeast carrier, the antimicrobial efficiencies and functional durability of the encapsulated antimicrobial agents, such as chlorine-based agents, essential oils, and photosensitizers, are significantly improved compared with the unencapsulated ones.

A Polysiloxane Delivery Vehicle of Cyclic N-Halamine for Biocidal Coating of Cellulose in Supercritical CO2

Cyclic N-halamines are highly antimicrobial, very stable, and not susceptible to bacterial resistance. A polysiloxane delivery vehicle was synthesized to deliver cyclic imide N-halamine onto cellulose via a benign and universal procedure that does not require a harmful solvent or chemical bonding. In brief, Knoevenagel condensation between barbituric acid and 4-hydroxybenzaldehyde furnished 5-(4-hydroxybenzylidene)pyrimidine-2,4,6-trione, whose phenolic O-H was subsequently reacted with the Si-H of poly(methylhydrosiloxane) (PMHS) via silane alcoholysis. The product of silane alcoholysis was interpenetrated into cellulose in supercritical CO₂ (scCO₂) at 50 °C, to form a continuous modification layer. The thickness of the modification layer positively correlated with interpenetration pressure in the experimental range of 10 to 28 MPa and reached a maximum value of 76.5 nm, which demonstrates the ability for tunable delivery, to control the loading of the imide N-H bond originating from barbituric acid unit. The imide N-H bonds on cellulose with the thickest modifier were then chlorinated into N-Cl counterparts using tert-butyl hypochlorite, to exert a powerful biocidability, providing ~7 log reductions of both S. aureus and E. coli in 20 min. The stability and rechargeability of the biocidability were both very promising, suggesting that the polysiloxane modifier has a satisfactory chemical structure and interlocks firmly with cellulose via scCO₂ interpenetration.

Hydrophilic tyrosine-based phenolic resin with micro-ripples morphology for marine antifouling application

Since biofouling challenges negatively influence the marine and transportation industries, developing effective antifouling materials have attracted extensive concern. A tyrosine-based antifouling phenolic resin (TPP resin) was synthesized using tyrosine as a natural phenol source. TPP exhibited shell-like surface morphology with micro-ripples and excellent anti-adhesion properties against bacteria and diatom. The micro-ripples surface might be caused by the strong hydrogen bonding or ionic interaction among tyrosine units resulting in microphase separation during the curing process. Tyrosine content in TPP resin has a great influence on the surface properties, morphology and antifouling characteristics. The higher the tyrosine content, the higher is the surface hydrophilicity, the denser and more regular is the micro-ripples morphology, and the stronger is the antifouling performance. TPP-60 % exhibited the best antifouling performance. Combination of the surface hydrophilicity and regular micro-ripples surface morphology afford TPP excellent antifouling performance. TPP resins offer a broad prospect for developing phenolic resin in the antifouling field.

Improving the Sensitivity of Nanofibrous Membrane-Based ELISA for On-Site Antibiotics Detection

An ultrasensitive and portable colorimetric enzyme-linked immunosorbent assay (ELISA) sensor for antibiotics was fabricated by immobilizing antibodies inside the largely porous and highly hydrophilic nanofibrous membranes. Different from regular electrospun nanofibrous membranes where antibodies may frequently be blocked by the heterogeneous porous structure and sterically crowded loaded on the surface, the controlled microporous structure and increased hydrophilicity of nanofibrous membranes could improve the diffusion properties of antibodies, reduce the sterically crowding effect, and dramatically improve the sensitivity of the membrane-based ELISA. The limitation of detection (LOD) for chloramphenicol (CAP) reached 0.005 ng/mL, around 200 times lower than the conventional paper-based ELISA, making quantitative analysis and portable on-site detection achievable via the use of smartphones. The successful design and fabrication of the nanofibrous membrane-based ELISA with novel features overcome the structural drawbacks of regular electrospun nanofibrous membranes and provide new paths to develop highly sensitive on-site detection of hazardous chemical agents.

A Novel N-Halamine Biocidal Nanofibrous Membrane for Chlorine Rechargeable Rapid Water Disinfection Applications

Disinfecting pathogenic contaminated water rapidly and effectively on sites is one of the critical challenges at point-of-use (POU) situations. Currently available technologies are still suffering from irreversible depletion of disinfectants, generation of toxic by-products, and potential biofouling problems. Herein, we developed a chlorine rechargeable biocidal nanofibrous membrane, poly(acrylonitrile-co-5-methyl-5-(4'-vinylphenyl)imidazolidine-2,4-dione) (P(AN-VAPH)), via a combination of a free radical copolymerization reaction and electrospun technology. The copolymer exhibits good electrospinnability and desirable mechanical properties. Also, the 5-methyl-5-(4'-vinylphenyl)imidazolidine-2,4-dione (VAPH) moieties containing unique hydantoin structures are able to be chlorinated and converted to halamine structures, enabling the P(AN-VAPH) nanofibrous membrane with rapid and durable biocidal activity. The chlorinated P(AN-VAPH) nanofibrous membranes showed intriguing features of unique 3D morphological structures with large specific surface area, good mechanical performance, rechargeable chlorination capacity (>5000 ppm), long-term durability, and desirable biocidal activity against both bacteria and viruses (>99.9999% within 2 min of contact). With these attributes, the chlorinated P(AN-VAPH) membranes demonstrated promising disinfecting efficiency against concentrated bacteria-contaminated water during direct filtration applications with superior killing capacity and high flowing flux (5000 L m^-2 h^-1).

Incorporation of Antimicrobial Bio-Based Carriers onto Poly(vinyl alcohol-co-ethylene) Surface for Enhanced Antimicrobial Activity

A biobased rechargeable antimicrobial modification approach was developed using a covalent immobilization of food grade yeast cell wall particles on a model plastic film. We demonstrate the applications of this modification approach on poly(vinyl alcohol-co-ethylene) surface to inactivate inoculated bacteria with or without the presence of organic content, reducing the cross-contamination between food contact surface and model fresh produce, and inhibiting the growth of biofilms on the film surface. These biobased cell wall particle modified plastic films can enhance the binding of chlorine to the plastic surface in the form of N-halamine, extend the stability of chlorine against high organic content and ambient storage, and improve the rechargeability of the plastic films. Upon charging with chlorine, these modified plastic films inactivated 5 log of model Gram-negative bacteria (Escherichia coli O157:H7) and Gram-positive bacteria (Listeria innocua used as a surrogate of pathogenic Listeria monocytogenes) within 2 min of surface inoculation in water and within 20 min in an organic-rich aqueous environment. The modified plastic films prevented the transfer of bacteria and eliminated cross-contamination from the contaminated films to a spinach leaf surface, while 3 log CFU/leaf of bacteria were transferred from a contaminated native film to a noninoculated spinach surface. In addition, these modified plastic films reduced the adhesion of L. innocua cells by 2.7-3.6 log CFU/cm² compared with control films during extended incubation for biofilm formation. Overall, this study demonstrates the feasibility of this biobased food grade modification approach to reduce microbial contamination and improve produce safety in the food processing industry.

Mussel-inspired surface functionalization of polyamide microfiltration membrane with zwitterionic silver nanoparticles for efficient anti-biofouling water disinfection

Mature microfiltration (MF) membrane is a low-cost, effective, and promising technology to provide affordable purified water for people living in developing countries. However, the lack of disinfection ability and inherent membrane fouling problems have seriously restricted the large-scale application of conventional MF treatment system in producing safe drinking water. In this work, zwitterionic silver nanoparticles (AgNPs) with surface modification of poly(carboxybetaine acrylate-co-dopamine methacryamide) (PCBDA) copolymers were robustly immobilized onto commercial polyamide MF membrane via mussel-inspired chemistry for water disinfection. The designed microfiltration membrane, named as PCBDA@AgNPs-MF, exhibited integrated properties of high and stable payload of AgNPs, broad-spectrum anti-adhesive and antimicrobial activities, and easy removal of inactivated microbial cells from membrane surface. Ascribing to the synergetic effect of anti-adhesive and antimicrobial features brought by zwitterionic PCBDA@AgNPs, the biofilms growth on polyamide membrane surface was significantly inhibited, which showed potential access to achieve long-term biofouling resistance and maintain water flux for conventional MF membrane. As water disinfection device, these attributes enabled PCBDA@AgNPs-MF to effectively disinfect the model and natural bacteria-contaminated water.