Preparation Of PH Responsive Multilayers Based On LBL Self-assembly Technique For Smart Antibacterial Materials

The pathogenic bacteria attached to medical instruments and implants can form biofilms in the extracellular matrix secreted by themselves,which is the reason of treatment failure of many bacterial infections.Researchers have tried to develop effective antibacterial materials in the recent years.Strategies utilizing specific microenvironments as a cue in the treatment of diseases have attracted increased attention.Different from normal tissues,the pH of acute infection sites is always slightly lower because of the acid substance produced by bacteria metabolism.Thus,the switching of material functions triggered by pH variations of bodily fluids owing to bacterial growth can be realized during the development of wounds.In this study,the pH responsive intelligent antibacterial materials was prepared by layer-by-layer(LBL)assembly technology and the relationship between multilayer structure and bacterial behavior was studied.1.Multilayers composed of dopamine-anchored poly(acrylic acid)(PAA-dopa)and chitosan quaternary ammonium salt(Q-CS)were deposited onto silicon via LBL assembly technology.The multilayer was crosslinked through the reaction of catechol moieties.The properties of multilayers were characterized by contact angle analysis,zeta potential measurement and atomic force microscopy(AFM).The results showed that the multilayers have good wettability and pH sensitivity.The surface charge of the multilayer reversibly shifted from positive(+30 mV at pH=5.0)to negative(-60 mV at pH=7.4)as the pH increased without influencing the chemical composition and wettability of the top layer.The bactericidal efficiency increased 15 times for E.coli.and 2 times for S.aureus when the pH changed from 7.4 to 5.0,while almost 90% dead S.aureus and 100% E.coli.were released from the surface when the pH increased from 5.0 to 7.4.2.Several types of cationic polymers(poly(allylamine hydrochloride)?chitosan quaternary ammonium salt ? branched polyethylenimine ? linear polyethylenimine ? poly(diallyldimethylammonium chloride)?polylysine)were selected to obtain multilayers by LBL assembly with PAA.Then photosensitive cross-linking agent 4,4'-hediazostilbene-2,2'-disulfonic acid disodium salt was used to crosslink the multilayer under UV irradiation.The multilayers composed of different cationic polymers have different pH transition behavior and isoelectric point.Furthermore,the structure of multilayer was regulated by changing the number of layers,molecular weight of polymer,concentration of cationic polymer and pH of polyelectrolyte solution.The influence of multilayer structure to the isoelectric point was studied.The number of multilayer has little effect on the isoelectric point,but top layer has a significant impact on the isoelectric point.An increasing isoelectric point of multilayers can be achieved by increasing the concentration of cationic polymer.And higher assembly pH results in less negative charges,or a higher isoelectric point of multilayer film.Three multilayers with different isoelectric point were selected for the study of antibacterial capabilities.When the pH was lower than the isoelectric point,the surface charge of the multilayer film is positive and the bacteria could adhere to the surface causing a higher antibacterial efficiency.On the contrary,when the pH was lower than the isoelectric point,the multilayers show high bacterial-adhesion resistance and good biocompatibility owing to the negative charge of the surface.