Construction And Application Of Free Radical Controlled-Release Antibacterial Nano-System

Although the use of antibiotics is currently the first choice for the treatment of bacterial infections,the abuse of antibiotics is constantly inducing the emergence of resistant bacteria.Therefore,it is necessary to develop new antibacterial agents or propose new antibacterial models to solve the current problem of low antibacterial efficacy.In recent years,as a new strategy for the treatment of bacterial infections,free radical release antibacterial systems have the potential to eliminate antibiotic resistance and biofilm formation.They are broadly divided into two groups:reactive oxygen species（ROS）and reactive nitrogen species（RNS）.However,free radicals are highly reactive and can react with any molecule in contact without distinction.Therefore,free radical-related treatments mainly focuses on how to achieve the effective precursor load for free radical release and how to target the site of bacterial infection.For it specifically releases toxic free radicals and effectively kills bacteria,and reducing the toxic side effects on normal tissue cells.Based on the special environment of the bacterial infection site and the inherent structure of the bacterial cell membrane,our aim is to construct two different free radical release systems for antibacterial and bacterial infection wound healing.The specific research contents are as follows:（1）Bacterial infections often create unique microenvironments,such as low p H（which can be as low as 5.5）.Therefore,these microenvironments can be used to achieve the release and accumulation of specific drugs at infected lesions and improve the availability of antibacterial agents.Metal peroxides（MPs）are composed of metal ions and peroxide groups,which can reversibly release metal ions and hydrogen peroxide（H₂O₂）under acidic conditions,and are considered to be a good substitute for exogenous H₂O₂ replenishment.In addition to the good Fenton reaction catalytic activity of Cu²⁺,low concentration Cu²⁺can promote wound healing.In the work,we successfully obtained nano copper peroxide（Cu O₂）by preparing Cu（OH）₂ nanowires as the material precursor,and then quickly reacting with H₂O₂.In order to reduce the infiltration of wound biological fluids into surrounding tissues,we use a biocompatible and biodegradable gelatin sponge（GS）as a carrier,and load Cu O₂ on the surface of the GS to prepare a degradable antibacterial wound dressing（GS-Cu O₂）.The results of in vivo and in vitro experiments show that this kind of wound dressing could be decomposed into Feton catalitic Cu²⁺and H₂O₂ in response to the weakly acidic environment,and followed by a Fenton-like reaction between them.The such p H-dependent Free radicals（·OH）production properties of GS-Cu O₂ can achieve effective local sterilization of infection without causing oxidative damage to surrounding normal tissues.In addition,the slow release of Cu²⁺from the dressing can stimulate the repair of epithelial tissues,promote angiogenesis and collagen deposition,thereby speeding up the wound healing process.We prepared the p H-responsive Fenton MP antibacterial wound dressing for the first time,and its successful application in antibacterial and promotion of wound healing provided new design ideas for MP-related antibacterial materials.（2）The lipopolysaccharide（LPS）in the cell membrane of gram-negative bacteria contains a large number of cis-glycol sugar structures,which can be covalently coupled with boric acid（BA）,providing a new targeting strategy for the treatment of gram-negative bacteria.In addition,bacteria have a large negatively charge at the outer membrane,which can be electrostatically combined with quaternary amine cations（QAS）,which is also commonly used as an antibacterial strategy to target bacteria.Based on the easy modification of cyclodextrin,we designed and synthesized two dual-targeting host molecules（CD-QAS-B₇ and CD-QAS-B₁）with 7 and 1 quaternary ammonium salt-phenylboronic acid functional groups at the 6 position of cyclodextrin respectively,and the guest molecule Ad-MH-NO,which is a nitric oxide（NO）donor based on the chain of maltoheptaose（MH）.Then they are coupling into amphiphilic supramolecules and self-assembled to form nanoparticles in water.In vitro antibacterial and intracellular NO fluorescence imaging experiments,showing that the prepared nanoparticles can increase the release concentration of NO near bacteria through the dual targeting mechanism of electrostatic interaction（QAS）and covalent coupling（BA）with bacterial membranes,which causes the bacteria to be quilkly killed.This multi-targeting mechanism and in-situ release of NO nanocarriers increase the utilization of NO gas antibacterial agents,which has great prospects in targeted antibacterial,and provides a new strategy for achieving precise release of NO to treat antibacterial infections.