| The drug resistance in bacteria increasingly threatens people health due to the abuse of antibiotics.The infection resulted from the multidrug-resistant bacteria kill more than 700,000 people each year.Therefore,it is urgent to develop new antibacterial materials without antibiotic resistance.Generally,the cationic antibacterial agents fight against bacteria following a membrane-disruption mechanism.In this case,the drug resistance is severely restricted since this mechanism can induce physically damage of cell membrane instead of gene mutation.Poly(ionic liquid)s(PILs)is a new class of cationic antibacterial materials that combine the structural designability of IL with improved processability of polymers.Through combination of anion and cation,the molecular structure of PILs can be adjusted,which endow PILs with a variety of functions.The factors influencing the antibacterial properties of cationic antimicrobials are very complex.It has been found that the length of N-alkyl chains and charge density play a vital role in antibacterial properties through the surface/interface structures of cationic antimicrobials.Obviously,understanding of surface/interface structures of cationic antimicrobials is of particularly importance for optimizing their antibacterial performance.Many common characterization techniques,unfortunately,cannot provide the structural information at the outer-layer of material surface.Frequency vibration spectrum(SFG)vibrational spectroscopy is a desirable technique with intrinsic submonolayer surface sensitivity based on the second-order nonlinear optical principle.More importantly,SFG vibrational spectroscopy has been emerged as a powerful technique for detecting in-situ surface/interface structures.Fabricating PIL brushes is an important way for achieving surface functionalization of materials.In this paper,well-defined PDMAEMA based PIL brushes was prepared via a controllable polymerization technique,activators regenerated by electron transfer-ATRP(ARGET ATRP).ATRP initiators were firstly immobilized to silicon wafer surfaces,and then DMAEMA was polymerized,finally the resultant PDMAEMA was quaternized with an alkyl halide to obtain a series of quaternary ammonium PIL brushes.The obtained PIL brushes with different alkyl chain length were denoted as PIL-C4,PIL-C8,PIL-C12,PIL-C16.The in-situ surface/interface structures of those PIL brushes in the acting against bacteria were explored through SFG vibrational spectroscopy,and the relationship between those interface structures and antibacterial activities of the prepared PIL brushes was examined in detail.The main conclusions are as follows:(1)The antibacterial activities of PIL brushes are closely related to N-alkyl chain lengths.The antibacterial efficacies of PIL brushes with different alkyl chain lengths increase following the order of PIL-C16<PIL-C12<PIL-C8<PIL-C4,which means that a shorter alkyl chain facilitates the enhancement of antibacterial activity.(2)As revealed by SFG spectra,for PIL brushes with shorter alkyl chains,both N+groups and alkyl chains were exposed to water.Such interfacial characterization facilitates the absorption of bacteria and the insertion of the extended alkyl chains into cell membranes,and thus the PIL-C4 brushes exhibit the highest antibacterial activities.On the other hand,longer alkyl chains tended to fold back at the interfaces due to their higher hydrophobicity and more conformational flexility,keeping the charged nitrogen atoms exposure to water.In this case,long alkyl chains migrate hardly toward water,enabling them difficult accessible to bacteria.Therefore,PIL-16 brushes display a lower antibacterial efficacies and slower bactericidal behavior.(3)The density of ATRP initiators was changed by using tetrabutyl ammonium fluoride(TBAF)to degraft initiator from the substrate,by which the grafting density of PIL-C4 brushes was controlled.It was shown that the antibacterial potency is enhanced as increasing grafting density.SFG spectra indicate that,in case of lower grafting density,both the extended alkyl chains and charged nitrogen atoms dominate the polymer/PBS interfaces.The shift of peaks at 3200 and 3400 cm-1 to higher frequency range suggests that the hydrogen-bonded water molecules become weaker.Traditional antibacterial materials fighting against bacteria generally accompany with the absorption of the dead bacteria on substrates.If the surface is covered in debris,the substance will be buried,which can lead to a loss of function and can serve as a conditioning layer for further bacterial attachment.Herein,the amphiphilic ternary copolymers P(ILC4-PEGMA-HEMA)were synthesized by free-radical polymerization.Then the polyurethane copolymer coatings containing ILC4 and PEGMA moieties were cross-linked with polymeric phenyl methanediisocyanate.In particular,the relationship between interface structures and protein adsorption resistance of polyurethane copolymer coatings was examined.The main conclusions are as follows:(1)In air,the hydrophobic methoxyl end group tends to move toward the surface of polyurethane copolymer coatings.In PBS,the polyurethane copolymer coatings interfaces also show a good ordering of the PEGMA at the interfaces as well.PEGMA can form strongly and weakly hydrogen-bonded water molecules with water molecular,which provide a strong barrier to prevent approaching proteins from being adsorbed on the surface.Therefore,the higher the PEGMA content is,the better the protein adsorption resistance the coating has.However,when the content of PEGMA is too high,PEGMA will cover ILC4 to a certain degree.This greatly reduces the sterilization rate of the polyurethane copolymer coatings.(2)The bacteria and protein adhering to the surface can be easily removed by washing the polyurethane coating with PBS buffer solution,and thus the antibacterial properties are readily recovered.When the polyurethane coating with PEGMA content of 55.8%is recycled for 5 times,the antibacterial rate can still reach about85 %. |
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