| Harmful microorganisms have always been the main factor that affects the quality of human life.Around the world,the infection of pathogenic bacteria(such as E.coli,Pseudomonas aeruginosa,Staphylococcus aureus)and fungi(such as Monilia albicans)is one of the major causes of death amongst patients with burn injury and amongst intensive care unit(ICU)patients with non-cardiac death.Although antibiotics are used in clinic for prevention and treatment of burn infection,excessive dose of antibiotics will lead to the increase of drug-resistant strains and may also cause the changes of patients'autologous antibacterial spectrum.At present,there are many shortcomings of the drugs which are commonly used for treating burnt injury,such as short antibacterial efficacy,narrow antimicrobial spectrum and many side effects(e.g.,causing human pain,allergy and metabolic acidosis).Therefore,research and development of inorganic nano-antimicrobial material with broad antimicrobial spectrum,good biocompatibility,fast killing harmful microbes and long term inhibiting microbes' growth is a critical agenda for the future development of clinical medicine.Chitosan(CTS)is a biodegradable,biocompatible and nontoxic aminopolysaccharide obtained by partial deacetylation of chitin which can be widely found in the natural world(e.g.,crustacean shell).This thesis takes the carboxyl-chitosan as supporting layer for synthesizing three kinds of biopolymer-inorganic nanocomposites,such as chitosan-silver(CTS-Ag),chitosan-copper(CTS-Cu)and chitosan-titanium dioxide(CTS-TiO2)nanocomposites.The structures,surface state,composition,and other physicochemical properties of nanocomposites were characterized by X-ray diffraction(XRD),transmission electron microscopy(TEM),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),UV-Vis diffuse reflectance spectroscopy(UV-Vis DRS),Fourier-transform infrared spectroscopy(FT-IR)and Raman spectroscopy.Besides,the antimicrobial efficacy and potency of nanocomposites were measured by Kirby-Bauer disk diffusion test,log-killing rate test and minimum inhibitory concentration(MIC)method.The MTT colorimetric method was used to evaluate the cytotoxicity of nanocomposites on immortalized mouse fibroblast cell lines(L-929).The main contents of the thesis and innovative conclusions are as follows:(1)Silver nanoparticles(Ag NPs)with different surface states were synthesized by changing dispersants.Immobilized chitosan-Ag nanocomposites(CTS-Ag)with special surface state show better antimicrobial efficacy than several other reported monodisperse colloidal Ag NPs.Due to the synergetic effect of CTS and Ag NPs,the immobilized CTS-Ag nanocomposites present a broader antimicrobial spectrum and a more effective antifungal activity against Monilia albican.Furthermore,the experiment found that the precursors exhibit a great influence on the antibacterial properties of the products.(2)Highly stable dispersion of nanosized copper particles were synthesized through immobilizing Cu NPs on the amino-enriched surface of CTS by reducing Cu(II)in situ with the assistance of microwave irradiation,for which NaBH4 was used as reduction agent and nontoxic L-ascorbic acid acted as stabilizer.The CTS-Cu nanocomposites were found to exhibit high antimicrobial activity against Gram-positive bacterial pathogen Staphylococcus aureus and fungal pathogen Monilia albican.In addition,CTS as an environment friendly dispersant can help to reduce the cytotoxicity of Cu on higher organisms.The CTS-Cu nanocomposites were stable and maintained good disinfection potential even after 90-day shelf-time under ambient conditions.Then,the mixing ratio of CTS-Ag and CTS-Cu was optimally designed in order to broad antimicrobial spectrum,enhance the antimicrobial properties and reduce the production cost.(3)CTS-TiO2 nanocomposites were synthesized via low temperature hydrothermal method and calcination method.A series of reactantratio and react temperature were investigated in detail.The product CTS-TiO2 nanocomposites are anatase-TiOI2,which has visible-light absorption(420 nm<?<800 nm)and show better antibacterial activity than nitrogen-doped of TiO2(N-TiO2).Meanwhile,CTS-TiO2 nanocomposites exhibit high photocatalytic activity and photo-stability in the photocatalytic degradation of rhodamine B(RhB)and 4-chlorophenol(4-CP).Finally,this thesis investigated the relation between structure and photocatalytic activity of nanocomposites,and elucidated the mechanism of photocatalytic sterilization. |
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