| Device-associated infections(DAIs)caused by bacterial adhesion have become the main type of nosocomial infections.In order to solve the problem of DAIs,antibacterial coatings have been extensively researched.For example,coatings can eliminate bacteria in situ by loading with antibiotics,but the antibacterial properties of such coatings lack long-term stability and risk antibiotic resistance.Antimicrobial peptides(AMPs)have also been loaded onto the surface as an alternative to antibiotics.The AMPs coating exhibits good antibacterial activity,but the high toxicity,high cost of AMPs and the adhesion of dead bacteria on the coating also hinder its development.Multifunctional coatings with antibacterial,antifouling and biocompatibility can be constructed by combining hydrophilic polymers or zwitterionic polymers with cationic polymers,but polymer segments with different functions often interfere with each other,which affect the coating properties.Responsive coatings are constructed by introducing stimuli-responsive groups or polymer segments,which can activate different medical functions on demand under the stimulation of external conditions.This method can reduce the mutual interference between functional segments,which can help improve the coating performance.antibacterial and antifouling properties.The main research contents of this thesis are as follows:In Chapter 1,firstly expounds the significance of studying the problem of countering DAIs and analyzes the reasons for the emergence of DAIs.Secondly,the advantages and research progress of responsive antibacterial coatings in solving the problem of DAIs are introduced.Finally,the characteristics,preparation methods and potential applications of polypeptide materials in the field of antibacterial materials are introduced.In Chapter 2,a single-component anionic polypeptide coating based on sulfonate is designed,which has different medical functions such as sterilization or antifouling at different pH.The preparation reaction of this polypeptide includes the ring-opening polymerization and side chain modification of S-(2-allyloxycarbonyl)ethyl-L-cysteine-Namic acid anhydride(ALC-NCA).Polypeptide modified polydimethylsiloxane(PDMS)surfaces were prepared by dipping method with polydopamine as the adhesion layer.After the surface is treated with an acidic solution,the side chain of the polypeptide generates a sulfonic acid group,and the surface can form a high acid microenvironment,thereby killing bacteria in contact with the surface.After the surface is treated with a weak base,the side chain of the polypeptide generates a sodium sulfonate group.At this time,the surface has excellent antifouling performance and good biocompatibility.The results of in vivo experiments showed that the coating with anionic polypeptides had good antibacterial properties and histocompatibility.In Chapter 3,a star-shaped imidazolium-based polypeptide(S4-PIL-FS)containing fosfomycin counteranion was designed and prepared.The surface bactericidal mechanism of this polypeptide coating combines the membrane breaking mechanism of cationic polymers and inhibit cell wall synthesis of fosfomycin sodium.The surface bactericidal activity of the coating in vitro and in vivo is higher than that of the coating using cationic polypeptide or fosfomycin sodium alone,so the coating exhibits a synergistic bactericidal effect and enhances the surface bactericidal activity.Fosfomycin counter-anion effectively reduced the cytotoxicity and hemolysis rate of star-shaped imidazolium-based polypeptide coatings.In addition,the S4-PIL-FS coating also possesses biofilm-responsive properties,which originate from the cleavage of polymer side chain ester bonds induced by bacterially secreted esterases,facilitating the peeling of biofilms from the surface.In Chapter 4,we summarized the full thesis and looked forward to the relevant research work that can be improved and developed in the future.In this thesis,anionic polypeptides,star-shaped imidazolium-based polypeptides and their coating materials were prepared by combination of ring-opening polymerization and side-chain modification.The research results with certain innovative significance were obtained,which provided a certain reference for the structural design of antibacterial coatings and the development of new antibacterial materials. |
