Antibacterial Activity Of Chitosan Microspheres /nanoparticles In Dispersing State

Chitosan , a cationic polysaccharide in neutral, is obtained from the deacetylation of chitin. Chitosan is composed of 2-amino-2-deoxy-β-D-glucan combined with glyc- osidic linkages. The primary amine groups render chitosan some unique combination properties, such as antibacterial activity, biocompatibility, biodegradability, metal complexation, and so on. Investigations prove that chitosan has a natural and broad spectrum of antibacterial activities, that can inhibit a wide variety of microorganisms including bacteria and some fungi. At present, the antibacterial activity of chitosan has been widely explored, however, most of researches focused on chitosan solution and little focused on chitosan in solid phase. In this paper, chitosan microspheres/nanospheres are prepared and used to study the antibacterial activity of chitosan from a different perspective.Three kinds of chitosan microspheres(CMs) with different sizes are prepared and characterized prepared by emulsification cross-linking method, whose volume average particle size are 429.4μm, 134.4μm and 68.3μm. Biological microscope and scanning electron microscope (SEM) photographs show that CMs are smooth-surface, spherical shape, uniform size and well dispersed in aqueous solution. About the sterilization method, Ultraviolet sterilization is choosed in the following experiment. Because CMs are easy to gather after autoclaving and not easy to be well dispersed in solution.The chitosan nanoparticles (CNPs) are prepaerd by ionotropic gelation method. In this part,the influencing factors on particle size of CNPs are discussed,including the concerntration of chitosan solution,the mass ratio of chitosan and TPP and extraction time. Three different diameter range of chitosan nanoparticles are obtained by changing the reaction conditions, the average diameter of which are 541.28nm,237.74nm and 94.02nm, respectively. The photographs of SEM and TEM show that CNPs are spherical shape, uniform size and well dispersed in solution.CMs shows very strong inhibitory effect against E.coli and S.aureus.The antibacterial activities is enhanced with the increasing of concentration and the decreasing of diameter of CMs. To different strains,the antimicrobial activity of CMs are also different, the Gram-positive bacteria(S.aureus) are more sensitive to the CMs. SEM photographs exibit a series of morphological changes of the bacteria from integrity to damage completely, and show that the CMs can combine with the bacteria and inhibit their growth though interfacial interaction on the surface.The CNPs also has a strong growth inhibition against E.coli and S.aureus, whose antimicrobial activity is enhanced with the increase of the concentration. As to E.coli, the antimicrobial activity of CNPs increases with the decrease of the particle size. However, as to S.aureus, the particle size of CNPs can not make an obvious influence on its antimicrobial activity. It may be related with the different structures of the bacteria. According to the fluorescence emission spectrum diagrams and the Stern-Volmer equation, it can be figured out that the way of the Phe fluorescence quenching caused by CNPs is a kind of static quenching, that is to say, the CNPs can combine with the protein on the cell membrane, change their structure, and further affact their physical activities. In addition, through the comparison of the bacterial cell membrane permeability caused by CNPs and chitosan, it can be found that CNPs can more easily increase the permeability of the bacterial cell membrane and cause the bacterial death.Based on the above considerations, CMs and CNPs are both good antibacterial materials, and have a potentially practical application value.