Green Construction And Antibacterial Application Of Chitosan/Metal Sulfide Nanocomposites

Wound tissue is susceptible to bacterial infection during the repair process,resulting in delayed healing.Conventional antibiotic therapies are prone to induced drug-resistance,so there is an urgent need to develop new antimicrobial materials.Currently,metal sulfide nanomaterials such as copper sulfide and molybdenum disulfide have arouse great attention due to unique physicochemical properties.They can kill bacteria through external photodynamic and photothermal effects,as well as exert intrinsic antibacterial effects through the release of metal ions,and thus replace antibiotics to control bacterial transmission and treat infectious wound diseases without causing bacterial resistance.However,metal sulfide nanomaterials suffer from complex and contaminated preparation,easy agglomeration leading to their reduced antibacterial activity,insufficient biocompatibility and lack of interaction toward bacteria,which limit their applications to some extent.Derived from shrimp and crab shells,chitosan has certain antimicrobial activity and good biocompatibility.Chitosan contains various reactive groups such as hydroxyl,acetylamino and amino groups as well as macromolecular network structure,making it unique advantages in the preparation of inorganic nanomaterials.In this paper,using the structural properties of chitosan as an exfoliator and stabilizer to prepare metal sulfide nanomaterials,we fully combined the advantages of chitosan and metal sulfide nanomaterials to prepare a series of chitosan/metal sulfide nanocomposite antimicrobial agents for bacterial killing and the treatment of infected wounds.The main research contents and results are listed as follows:1.Preparation of Mo S₂@quaternized chitosan/nanocellulose composite paper and its recyclable antibacterial propertiesUsing the reactive groups and macromolecular network structure of quaternized chitosan（QCS）to directly exfoliating and stabilizing Mo S₂nanosheets in the aqueous phase,the Mo S₂@QCS/CNF composite paper was further prepared by electrostatic attraction between QCS and cellulose nanofibers（CNF）.The results showed that the Mo S₂@QCS/CNF composite paper exhibited excellent photothermal and photodynamic activity,achieving over99.9%antibacterial efficacy against both E.coli and S.aureus within 12 min.The antibacterial mechanism suggested that the hyperthermia and reactive oxygen species（ROS）accelerated the glutathione（GSH）consumption and oxidative stress to destroy the bacteria membranes integrity,synergistically leading to the malondialdehyde（MDA）oxidation and protein leakage to inhibit the bacteria growth.Importantly,the self-assembled fibrous network incorporating with the photo-stable antibacterial Mo S₂enabled the flexible composite paper with excellent mechanical strength and recyclability for long-term antimicrobial,possessing over 99.5%inhibition even after five cycles.No cell cytotoxicity was observed for the Mo S₂@QCS/CNF composite paper,suggesting the potential application of composite paper for bacterial infection control.2.Quaternized chitosan/Cu S nanozyme with antibacterial activity for promoting infected wound healingThe last study was only applied for bacterial transmission control in the environment.This study combined catalytic,Cu²⁺release and QCS antibacterial activity for wound infection treatment.Herein,biocompatible QCS stabilized Cu S（Cu S@QCS）nanozyme was synthesized using QCS as a biotemplate through a green biomineralized strategy.The Cu S@QCS killed bacteria through positive charged QCS interacting with bacteria and releasing Cu²⁺to disrupt bacterial membrane.Importantly,Cu S@QCS nanozyme exhibited high intrinsic POD-like activity to convert low concentration of H₂O₂into highly toxic hydroxyl radical（·OH）,thereby eliminating bacteria.Through synergistic effect of nanozyme,Cu²⁺and QCS,this antibacterial nanoplatform exhibited excellent antibacterial efficacy of approximate 99.9%against E.coli and S.aureus within 30 min in vitro.In addition,the Cu S@QCS was successfully used to promote the healing of S.aureus infected wounds in vivo with minimal toxicity.In consequence,the present work suggests a synergistic strategy to enhance the antibacterial activity of nanozyme,especially reduce H₂O₂concentration（～0.027%）to avoid its harm.3.Cu S@chitin sponge with rapid antibacterial capacity for promoting healing of infected diabetic woundsIn the last study,the antimicrobial agent only treated wound infections.But for severe wound infections,the dressings are required to provides a closed environment to protect the wound.Herein,Cu S@Chitin（Cu S@CH）composite sponge was constructed by in situ green biomineralization of Cu S in chitin（CH）network and further crosslinked to promote diabetic skin wounds healing.The Cu S@CH sponge could trap bacteria on its surface through the electrostatic interaction and porosity.Meanwhile,the Cu S@CH sponge exhibited outstanding photothermal and photodynamic activity to generate localized heat and reactive oxygen species（ROS）upon NIR radiation as well as releasing of Cu²⁺,thus achieved predominant antibacterial behavior against E.coli（99.94%）and S.aureus（99.30%）within 8 min.The antibacterial mechanism suggest ED that the hyperthermia and ROS accelerated the glutathione（GSH）consumption and the damaged the integrity of bacteria membranes,which synergistically led to the malondialdehyde（MDA）oxidation,membrane permeation and finally caused the bacteria death.Via taking the synergistic action between the trapping effect and the NIR-activated antibacterial effect,Cu S@CH sponge killed infected bacteria on diabetic wounds and significantly promoted infected diabetic wound healing.The Cu S@CH sponge was further demonstrated to enhance collagen deposition and inflammation reduction.Therefore,this composite sponge with antibacterial and pro-healing capabilities may have great potential as diabetic wound dressings.4.Cu S&Mo S₂@QCS/PVA hydrogel eliminate MRSA and accelerate infected wound healingIn the last study,photothermal temperature and dry dressings may be detrimental to the treatment of wound tissue.So in this study we prepared moist dressings to reduce the effects of overheating for the treatment of drug-resistant bacterial wound infections.Herein,Cu S&Mo S₂@QCS nanocomposites were prepared by in situ green synthesis of Cu S loaded on Mo S₂@QCS nanosheet and further assembled into polyvinyl alcohol（PVA）.The Cu S&Mo S₂@QCS/PVA hydrogels was used for rapid and mild killing of methicillin-resistant Staphylococcus aureus（MRSA）and promoting wound healing of MRSA infections.The results showed that Cu S&Mo S₂@QCS/PVA hydrogel could produce more ROS and mild hyperthermia when the photothermal efficiency was increased to 39.83%,and the bactericidal rate of MRSA was more than 99.97%within 4 min.The results of in vivo experiments further confirmed that the composite hydrogel accelerated wound healing of MRSA infections without significant toxicity.This work presents a new way to fight against drug-resistant bacterial infections.