| BackgroundSince the late 20th century,the abuse of antibiotics has led to the continuous improvement of bacterial resistance,which has posed a serious threat to human health.Therefore,the development of new antimicrobial technology has become a research hotspot in the field of medicine.Since ancient times,sulfur and its sulfides have been playing an important role in people’s life as antibacterial and anti-inflammatory agents.However,due to the low solubility and dispersity of sulfur and its sulfides,the absorption efficiency and bioavailability of sulfur and its sulfides in antibacterial therapy are reduced.In addition,the antibacterial mechanism of sulfur has not been clearly explained due to its multiple valence states and abundant forms.Therefore,it is the basis and key to promote the development and application of sulfur-containing antimicrobial agents to develop nanometer antimicrobial agents based on sulfur and its sulfides by using synthetic technology and to further study their antimicrobial mechanism.One of the ways to improve the dispersibility of sulfur and its sulfides is to load it on a specific carrier and prevent the particles from agglomerating through the anchoring effect of the carrier.Among the many carriers,carbon materials have attracted widespread attention due to their unique physical and chemical properties,such as large specific surface area,good biocompatibility,non-covalent bond drug loading and its photothermal effect.Therefore,the sulfur and sulfide particles can be loaded on the carbon nanomaterial,and the interaction between the carbon material and the sulfur and sulfide particles can be used to improve the dispersibility and stability of the system.In addition,on the one hand,carbon materials can also be used to have high photothermal conversion efficiency in the near-infrared region,which can be used as an effective supplementary approach for antibacterial treatment of sulfur and its sulfides.On the other hand,carbon materials can be used as drug carriers to load other antimicrobial agents and play a combined effect of antimicrobial therapy with sulfur and its sulfides by taking advantage of their large specific surface area.Based on the above background,in this thesis we chose bletilla striata polysaccharide(BSP)and iron disulfide(FeS2)as the research objects.First,FeS2-modified carbon nano spheres(CNSs@FeS2)were synthesized by hydrothermal method to improve the dispersibility of FeS2.The morphology,structure,antibacterial activity,and mechanism of CNSs@FeS2 were studied in detail.The therapeutic effect of CNSs@FeS2 in acute peritonitis and wound infection models caused by bacteria was evaluated.Second,in order to further accelerate the healing of infected wounds,BSP was loaded into CNSs@FeS2,and the therapeutic effect of CNSs@FeS2 on wound infections in the presence or absence of BSP was evaluated.Through exerting the property of BSP with promoting proliferation and migration,the sulfur-containing antibacterial agent with the dual functions(sterilization and wound repair)can be obtained,thereby laying an experimental foundation for promoting the development of sulfur-containing antibacterial agents.Objectives(1)Through nano-synthesis technology,FeS2 is loaded on carbon balls to improve the dispersibility and bioavailability of FeS2.(2)The antibacterial activity and mechanism of CNSs@FeS2 were studied in detail,and the material basis for sulfide to exert antibacterial activity was clarified.(3)Integrating the characteristics of BSP in promoting cell proliferation and migration and the antibacterial activity of CNSs@FeS2,an antibacterial agent with dual effects was prepared to promote the development and application of sulfur and its sulfide antibacterial agents.MethodsChapter 1 Antibacterial activity and mechanism of FeS2 modified carbon nanospheresIn this chapter,first,hollow nanospheres(CNSs)were prepared by micellar template method,and then FeS2 was modified to carbon nanospheres(CNSs@FeS2)by hydrothermal method.The Physic-chemical properties of CNSs@FeS2 were characterized by SEM,TEM,HRTEM and other technologies.In addition,XRD and XPS are used to analyze the composition and structure of CNSs@FeS2.Second,we studied the antibacterial activity and mechanism of CNSs@FeS2,including the determination of glutathione levels in bacteria,lipid peroxidation levels,nucleic acid degradation in bacteria,and observation of bacterial morphology.Finally,after evaluating the biosafety of CNSs@FeS2,two animal models of acute peritonitis caused by Escherichia coli(E.coli)and wound infection caused by Staphylococcus aureus(S.aureus)were constructed to evaluate the therapeutic effects of CNSs@FeS2.Chapter 2 BSP-loaded FeS2 modified carbon nanospheres for bacteria-infected skin wound healingIn this chapter,the carbon nanospheres were used to load BSP,due to their large specific surface area,yielding of BSP/CNSs@FeS2.First,Fourier Transform Infrared spectroscopy(FTIR)was used to characterize BSP/CNSs@FeS2,and the drug loading capacity and drug loading efficiency were determined by the phenol-sulfuric acid method.Second,the effect of BSP on the HUVECs proliferation and migration were detected by MTT,cell scratch test and cell invasion test,and the antibacterial ability of BSP/CNSs@FeS2 was also measured.Finally,a wound infection model of S.aureus infection was constructed to evaluate the ability of BSP/CNSs@FeS2.ResultsChapter 1:The CNSs@FeS2 prepared in this chapter has a good degree of graphitization,the particle size is about 200 nm,the shell thickness is 10-20 nm,and the dispersion is good.Among them,it can be observed by HRTEM that C,N,Fe and S atoms are uniformly distributed throughout the sphere,and there are no obvious large-scale FeS2 particles.The effective inhibition on gram-positive bacteria(S.aureus and S.mutants),gram-negative bacteria(E.coli,S.typhimurium and P.aeruginosa),and fungi(M.albicans)indicated that CNSs@FeS2 could be a potential broad-spectrum antibacterial agent.This antibacterial ability was due to the slow release of Fe2+ ions from FeS2 nanoparticles through dissolution and disproportionation reactions,which caused lipid peroxidation and GSH depletion,thus triggering bacterial DNA degradation and death.Importantly,the released sulfur ions provided a protective effect on Fe2+ ions,ensuring the stable existence of Fe2+ to continuously kill bacteria.Moreover,the excellent photothermal conversion of carbon spheres helped to accelerate the release of Fe2+ ions,thus promoting the antibacterial activity through the synergism of hyperthermia and Fe2+ ions.The supernatant of CNSs@FeS2 exhibited a protective effect against the E.coli-induced acute peritonitis mouse model,extending the survival time of infected mice and down-regulating the production of cytokines,including TNF-α,IL-6,and IL-1 β.For the application of CNSs@FeS2 dispersion,the S.aureus-infected skin wound healing results revealed that the synergistic antibacterial system based on hyperthermia and Fe2+ ions expediently promoted wound disinfection in vivo.In the current study,we clarified the antibacterial mechanism of nano-FeS2 and proved that CNSs@FeS2,due to the synergic effect of Fe2+ ions and hyperthermia,may have great potential in various antibacterial applications.Chapter 2:In this chapter,FeS2 modified carbon nanospheres were used as a carrier to load and deliver BSP to obtain the BSP-loaded FeS2 modified carbon nanospheres(BSP/CNSs@FeS2).The drug loading capacity and drug loading efficiency of BSP/CNSs@FeS2 were determined to be 12%and 35%,respectively.In the FTIR spectra,the characteristic peaks of BSP/CNSs@FeS2 also proved that BSP molecules were successfully loaded into CNSs@FeS2.Cell experiments indicated that BSP could promote the proliferation and migration of HUVECs.Through antibacterial experiments,we found that although BSP had no antibacterial ability,the loading of BSP did affect the antibacterial ability of CNSs@FeS2.In the skin wound model of S.aureus infection,BSP/CNSs@FeS2 showed the best antibacterial performance,showing the fastest wound healing ability. |
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