Antibacterial Properties Of Alkyl-substituted Imidazolium-based Poly(Ionic Liquid)s

Poly(ionic liquid)s(PILs)are a class of polymers whose repeating units consist of anionic and cationic groups,and combine the antimicrobial potency of ILs and the processability of polymers,and thus they have received a great deal of attention in antibacterial applications.As a kind of cationic antibacterial materials,PILs normally kill bacteria by physically destroying the cell membrane structure.In this case,the likelihood of drug resistance is severely reduced since bacteria can hardly repair their physically damaged cell membranes.The factors affecting the antibacterial properties of PILs are complicated,the interaction between PILs and bacterial is not clear currently.It is interesting that self-assembled cationic polymer nanoparticles display a better antibacterial performance than the individual polymer molecule because their local mass and cationic charges in this nanostructure are highly concentrated.As reported in our previous work,imidazolium-based PILs can self-assemble into polymeric nanoparticles with highly ordered inner structures when they are dissolved in aqueous solutions or organic solvents.However,few reports focus on the antibacterial application of self-assembled PIL nanoparticles.In addition,PILs are used to construct a variety of antibacterial materials such as films and coatings because of their excellent antibacterial properties,and accordingly have a variety of applications including food,medical and other fields.These PILs antibacterial materials can effectively kill live bacteria adhering to the material surface.However,they usually suffer from the accumulation of dead bacteria and debris,which not only shield the functional groups,thereby reducing the bactericidal efficacy,but also cause an immune response or inflammation that harms human health.Therefore,there is an urgent need to construct a multifunctional antibacterial material that can kill live bacteria and resist the adhesion of dead bacteria as well.In this work,a series of poly[CnVIm+][Br-](n=8,10,12,16)were synthesized via radical polymerization,the effect of alkyl chain length and anion species on the antibacterial properties of PIL nanoparticles were systemically investigated.The antibacterial mechanism was also revealed by scanning electron microscopy(SEM)and fluorescence microscopy.In addition,we blended P(C,VIm BF4'-MMA-PEGMA)with PES,and systematically studied the antibacterial and anti-adhesion properties of the blend membranes.The results are shown as follows:(1)we synthesized ionic liquids homopolymers poly[C.VIm+][Br](n=8,10,12,16)via radical polymerization,and investigated the antibacterial activities of the obtained PIL nanoparticles against both E.coli and S.aureus.There was a clear dependence of antibacterial efficacy on the alkyl chain length,and the antibacterial activities of those PIL nanoparticles follow an order of Poly[C12VIm+][Br]>Poly[C16VIm+][Br']>Poly[C10VIm+][Br-]>Poly[C8VIm+][Br'].PIL nanoparticles exhibit the best antibacterial properties when the alkyl side chain length is 12.(2)We introduced Trp' to PILs in view of the certain antibacterial activity of tryptophan(Trp).The poly[C.VIm+][Trp-](n?8,12,16)were prepared via anion exchange reaction.Both polyfCsVIm][Trp-]and poly[C12VIm][Trp-]nanoparticles exhibit higher antibacterial activities when compared with their corresponding PIL-Br nanoparticles,but for PILs with longer alky1 side chins,the antibacterial efficacy is reduced after the anion exchange reaction.For example,poly[C16VIm+][Trp-]display lower antibacterial properties than poly[C16VIm+][Br-].Therefore,the synergistic effect of anions was dependent on the alkyl chain length of PILs.To further study the synergistic interactions between bacteria and the anions,the morphologies of E.coli and S.aureus labeled with poly[C12VIm+][Flu-]were observed by the fluorescence microscopy.The fluorescence images clearly showed that the bacteria cells incubated with PIL-flu exhibited bright green fluorescence.This indicated that PIL nanoparticles have dual functions of bacteriostatic and biological imaging,their antibacterial process can be monitored by fluorescent labeling.(3)An three-component random copolymer P(C.VIm+BF4'-MMA-PEGMA)(n=4,8,12)was prepared by free radical polymerization,and then blended with polyethersulfone(PES).The effect of the length of the alkyl side chain on the imidazolium moieties on the antibacterial properties of the blend membranes were investigated,the antibacterial property of P(CnVIm+ BF4--MMA-PEGMA)/PES blend membranes decreased gradually with the increase of the length of the carbon chain substituted to the imidazolium rings.When the carbon chain length is 4,the blend membrane exhibits the best antibacterial activity relative to the carbon chain length of 8 and 12,which is very different from PIL nanoparticles.(4)P(C.VIm+BF4'-MMA-PEGMA)/PES membranes exhibited excellent anti-bacterial adhesion properties.It was found that an increase of IL unit content in P(C.VIm+BF4'-MMA-PEGMA)would lead to a higher anti-adhesion efficiency probably due to the enhanced hydrophilic properties.In addition,after sterilization,the blend membranes can regain its antibacterial activity simply by cleaning the membranes with PBS.It should be pointed out that the antibacterial properties still maintain after these blend membranes were used 5 recycles.(5)The prepared PIL nanoparticles and P(C.VIm+BF4'-MMA-PEGMA)/PES films have excellent selectivity,and have almost no significant cytotoxicity to mouse fibroblasts L929 and 3T3.In this thesis,the antibacterial activities of the corresponding PILs were systemically investigated.The results provide a theoretical basis for the structural design and performance optimization of new anti-multidrug resistant bacteria antibacterial material,and also provide guidance for the development of other bio-antibacterial materials.