Synthesis And Properties Of Silver Loaded Chitosan/Alginate Composite Antibacterial Material

In this thesis, chitosan microspheres （CSM） were prepared by using the emulsioncross-linking method through orthogonal experimental design. The effects of various preparationfactors suah as chitosan concentration, chitosan molecular weight, ratio of oil to water （O:W）,and glutaraldehyde （GD） content on the morphology and particle size distribution properties ofchitosan microspheres were investigated systematically by using Scanning ElectronicMicroscopy （SEM）, Fourier Transformed Infrared Spectroscopy （FTIR）, Dynamic LightScattering （DLS）, Transmission Electron Microscopy （TEM） and Thermogravimetric Analysis（TG） so as to determine the optimal conditions for preparing CSM. Furthermore, silver nitratewas added during CSM preparation followed by reduction with sodium borohydride, to obtainchitosan microspheres loaded with nano silver particles （AgCSM）. The morphology andstructural characteristics of the AgCSM microspheres thus obtained were also investigatedsystematically by using the above-mentioned analitical methods along with X-ray diffraction（XRD）, and Atomic Force Microscopy （AFM）. In the meantime, the silver-loaded chitosanmicrospheres without adding the reducing agent of sodium borohydride were prepared（AgNO₃CSM）. The antimicrobial abilities of microspheres were compared by using theshaking-flask method, bacteriostatic ring experiments and colony counting method. And finallythe cytotoxicity of those microspheres was also measured by MTT assay.The main conclusion ofthe study may be given as follows:The optimum conditions for preparing CSM are: chitosan used had a molecular weight of98000, and its mass concentration of acetic acid solution is0.75%, the volume ratio of oil towater is5:1, and the amount of glutaraldehyde was3mL. Stirring rate is1500r·min-1, thetemperature of water bath was40oC and reaction time was1.5h. Our results show that chitosanconcentration, molecular weight of chitosan, oil-water ratio and GD amount affected themorphology of microspheres strongly, while the GD amount、stirring rate and oil-water ratiocould influnce the particle size of CSM microspheres.By exploring the influences of chitosan concentration, the amount of silver nitrate and thatof sodium borohydride on both silver loading and encapsulation efficiency of microspheres, theoptimum preparation conditions for AgCSM can be concluded as follows: chitosan used has amolecular weight of98000and its mass concentration is1.25%, AgNO₃has a concentration of0.75mol/L, and the molar ratio of AgNO₃to NaBH4is1:5. Under the optimal condition, theAgCSM microspheres had a silver loading of186mg/g, and the encapsulation efficiency is66.7%.FTIR spectra show that there is the absorption peak of the amide bond for crosslinkedmicrospheres, indicating that Schiff base crosslinking may occur by the reaction of amino groups of chitosan and aldehyde groups of GD. For the AgNO₃CSM and AgCSM, the infraredabsorption peak is partially blue-shifted, indicating that certain interactions between Ag⁺and CSor Ag and CS may exist. XRD patterns show that silver nano partices in AgCSM wereface-centered cubic crystals, and it might have a particle size of about10nm as calculated by theScherrer equation.Chitosan microspheres are observed to have obvious effect on sustained release of silvernanoparticles. By means of correlating the sustained-release profiles with mathematical modelscommonly used, it can be found that in vitro release behavior of Ag⁺from AgNO₃CSMmicrospheres could be basically consistent with First Order release kinetic models while that ofsilver nanopaticles from AgCSM microspheres comply with the Ritger-Peppas model.The antibacterial performance test shows that the addition of silver has greatly improved theantimicrobial properties of the chitosan microspheres. The cytotoxicity test results show thatwhen the AgCSM microsphere concentration reaches the desired sterilization effect, almost notoxicity role on mouse epithelial cells （L929） could be observed, but at the same concentrationAgNO₃CSM had obvious cytotoxic with increase of extraction time. These results suggest thatchitosan microspheres may have obvious effect on sustained release of silver nanoparticles, andthen greatly improved the biosatety and safety of silver loaded chitosan microspheres.Finally, alginate films containing AgCSM were prepared by CaCl₂crosslinking. Theantibacterial rates of alginate films on three kinds of common bacteria were all above99.9%when preparation parameters of films are3.5%mass concentration of sodium alginate,1:10massratio of AgCSM to sodium alginate,3.5%volume fraction of glycerin, and3%massconcentration of CaCl2.