Preparation And Characterization Of Chitosan/Silver Nano Microspheres

The chitosan, with excellent properties such as biocompatibility and biodegradability, is a typical biomedical materials. The nano-silvers are embedded with chitosan to further enhance the anti-bacterial properties of chitosan.Chitosan was dissolved in 2 wt% hexanoic acid solution, which is as the medium. The stable silver nanoparticles were prepared by the reduction of silver nirtrate using sodium borohydride as reducing agent. and factors affecting silver nanoparticles such as the concentration ratio of AgNO3 and reducing agent, AgNO3 concentration, reaction time were studied. The results indicated that chitosan/silver colloidal sol can be prepared under such conditions that: the concentration ratio of AgNO3 and sodium cirtate was 1:3, the concentration of AgNO3 was 0.30 mol·L-1, and reaction time was 60 min. The morphology of the silver nanoparticles in chitosan/silver colloidal sol was characterized by TEM, which positively evidenced that silver nanoparticles in chitosan/silver colloidal sol are all spherical with mean diameters in the range 5~10 nm. The X-ray diffraction (XRD) pattern of the sample showed that silver nanoparticles was face–centered cubic silver.The CS/Ag microspheres were prepared by emulsion cross-linking method. The chitosan/silver colloidal sol was as dispersed phase, liquid paraffin was as continuous phase, and glutaraldehyde was as crosslinking agent. The factors affecting CS/Ag microspheres such as the amount of glutaraldehyde, composite emulsifier type, the amount of emulsifier, and the amount of liquid paraffin were studied. The results showed that CS/Ag nanoparticles microspheres can be prepared under such conditions that: the concentration ratio of Span80 and OP-10 was 13:7, the concentraion of liquid paraffin, emulsifier, chitosan/silver colloidal sol and glutaraldehyde were 83.55 wt%, 6.06 wt%, 6.85 wt%, 3.54 wt %.The morphology of CS/Ag nanoparticles microspheres was characterized by SEM, which positively evidenced that the morphology of sample all spherical with mean diameters about 98 nm. The SEM showed tha nano-silvers are spherical with mean diameters about 5~20 nm, The X-ray diffraction (XRD) pattern of the sample showed that chitosan is amorphous crystal and silver nanoparticles was face–centered cubic silver. Comparing the FTIR absorption spectra, we can know that silver nanoparticles were embedded in CS/Ag microspheres. TGA-DSC showed that conformation of chitosan molecules were changed,crystallization of chitosan was decreased, so the heat was low when CS/Ag microspheres were decomposition. The antimicrobial ability of CS/Ag microspheres on Escherichia coliand, rhizopus, Staphylococcus aureus, and mucor were studied. The result showed that CS/Ag composite microspheres were more efficient anti-bacterial properties than the CS microspheres. The antimicrobial ability of the CS/Ag microspheres was enhanced as silver of CS/Ag microspheres increased.The small size of the CS/Ag microspheres was much stronger than the large size of CS/Ag microspheres. We speculated that the CS/Ag microspheres antimicrobial mechanisms. The result showed that silver nanoparticles killed the bacteria or fungus,and chitosan played a synergistic role in antibacterial.