Antifouling Microfiltration Membranes Modified By Antimicrobial Peptides:Performance And Mechanisms

The world is currently facing critical issues,such as water scarcity and severe water pollution.Membrane separation technology is considered as one of the main technical approaches to control water pollution and alleviate the water resource crisis,due to its simple process and high treatment efficiency.However,membrane fouling,particularly membrane biofouling caused by microorganisms’attachment and settlement on the membrane surface,is a primary factor that restricts the development of membrane technology.Therefore,developing highly efficient antifouling membrane materials is an essential strategy to mitigate membrane biofouling.In this study,we focused on the need for antifouling membranes and prepared composite microfiltration membranes incorporating antimicrobial peptides（AMPs）using electrostatic adsorption self-assembly and grafting polymerization.We optimized the preparation methods to investigate the effect of AMPs on the basic properties and antifouling performance of membranes.We also analyzed the antibacterial and antifouling mechanisms of the antimicrobial peptides composite microfiltration membrane,providing theoretical and technical support for the development of novel and efficient antifouling membrane materials.Firstly,AMPs/alginate multilayers with controllable thickness at nanometer scale on a poly（vinylidene fluoride）（PVDF）microfiltration membrane were constructed via electrostatic adsorption induced layer-by-layer self-assembly.Utilizing the three-dimensional network formed by alginate hydrogel,the release of AMPs was delayed,thereby improving the long-term antimicrobial efficiency of the composite membrane.The results showed that when the number of AMPs/alginate layers was greater than or equal to 5,the composite membrane exhibited good antibacterial efficiency against both Escherichia coli（E.coli）and Staphylococcus aureus（S.aureus）.As the number of layers increased from 0 to 10,the hydrophilicity of the AMPs/alginate multilayers modified membrane significantly enhanced,with a water contact angle of 26.5±1.7°compared to 90.2±1.3°of the pristine membrane,while the water flux did not altered.When the number of layers increased to 15,the pore size of the membrane decreased from 98.5 nm to 72.3 nm and the membrane flux decreased from 29.28±0.84 L/m²h k Pa to 15.54±1.22 L/m²h k Pa,indicating that the assembly layers significantly affected the basic properties of the membrane.The impact of assembly layers on the release rate of AMPs was further studied.The results showed that with an increasing number of sodium alginate layers,the initial and stable release rates of Ponericin G1（a kind of AMP used in this study）continually decreased.The AMPs/alginate multilayers modified membrane with 15 layers(MSA₁₅)had the lowest release rate(initial release rate of 1.79±0.07μg/cm²d and stable release rate of 0.55±0.03μg/cm²d.In contrast,the AMPs/alginate multilayers modified membrane with 5 layers（MSA₅）exhibited an initial release rate of 2.07±0.15μg/cm²d and a stable release rate of 0.74±0.02μg/cm²d.Molecular dynamics simulations were conducted to elucidate the mechanism underlying the effect of alginate on the release rate of AMPs.The results demonstrated that a Ponericin G1molecule and several alginate molecules could form a more stable gel network than that and one alginate molecule,maindly due to the stronger affinity of Ponericin G1towards alginate surrounded.Long-term antibacterial contamination tests showed that the MSA₁₀exhibited high antibacterial performance and stability,with a significantly reduced membrane fouling rate compared to that of the pristine membrane,indicating that the AMPs/alginate-modified membrane possessed excellent long-term antibiofouling performance.In order to enhance the stability of antimicrobial peptides on the composite membranes,grafting polymerization method was employed to immobilize antimicrobial peptides molecules onto the membrane surface via acylation reaction,thus constructing a composite membrane with a stable and efficient antibacterial layer.The results showed that with the increase of the amount of AMPs,the content of characteristic surface elements of the modified membrane increased continuously,indicating the successful grafting of AMPs onto the membrane surface.Antibacterial experiments demonstrated that when the addition of AMPs was not less than 0.4mg/m L,the modified membranes exhibited significant antibacterial effect against E.coli and S.aureus,with a inhibition rate up to 90%.Furthermore,the E.coli attached to the membranes showed a loss in the morphological integrity.Batch antibiofouling test showed that the membrane had a higher recovery flux（80.1±3.5%）and a lower total flux decline ratio（16.0%）when the amount of the AMPs was 0.4 mg/m L.However,when the amount of the AMPs exceeded 0.7 mg/m L,the antibiofouling performance was deteriorated,since positively charged surfaces of them might easily adsorb negatively charged foulants and thus negatively affect the antibiofouling performance.When surffered from bacterial fouling and chemical cleaning,the modified membranes still maintained stable antibacterial performance.In addition,the membrane functional structure was not destroyed,indicating that the process of fouling and cleaning did not compromise antibacterial and antibiofouling properties imparted by the immobilized AMPs,revealing a potential for long-term operation.