Green Construction and Application of Immobilized AgNPs/chitosan-based Antimicrobial Composites
Author:Wu Zheng Guo
Supervisor:wang xiao ying
Chitosan(CS)is a kind of good food packaging and medical hemostatic material,but its antibacterial activity is not high and durable enough.Silver nanoparticles(AgNPs)are the most widely used broad-spectrum antibacterial agents,which can be introduced into food packaging and medical materials to enhance the antibacterial activity of proto-biomass polysaccharide materials.However,a large amount of AgNPs release from the materials in a short time will produce cumulative toxicity to human body in the antibacterial process.Therefore,it is one of the urgent problems to search for green and efficient immobilization technology and develop safe and non-toxic immobilized AgNPs antibacterial agent in the field of nano-antibacterial.Based on toxicity problem of AgNPs,safe and non-toxic polysaccharide/AgNPs composite antibacterial agent were synthesized green and efficiently by using biomass polysaccharide or active substances as reductants and stabilizer,as well as liposome,liponite(LAP)and modified carbon spheres as carriers.Subsequently,with the help of physical and chemical methods,immobilized or embedding technology of AgNPs was analyzed.In addition,its immobilized mechanism,antibacterial mechanism and functional application were also explored.These not only realized the high-value utilization of biomass resources,but also provided a new idea and method for expanding the safe application of nano-silver antibacterial agent in food packaging and medical materials.The main contents of this work are as follows:(1)Hydrophilic lignin-AgNPs was synthesized by using lignin as reductant,which could make it easier to be encapsulated into liposomes.Subsequently,liposomes were used to encapsulate laurel essential oil(LEO)and AgNPs(Lip-LEO-AgNPs),and mixed with chitosan to coat polyethylene(PE)films(PC-Lip/LEO/AgNPs)to package pork.The results show that only about 29.30%of LEO and 11.79%of AgNPs were released from the liposome.Nevertheless,Lip-LEO-AgNPs showed good antioxidant properties.Moreover,PC-Lip/LEO/AgNPs films had good antimicrobial activity.Evaluation tests on pork indicate that PC-Lip/LEO/AgNPs films could keep the quality of pork at 4 ~oC for 15 days while pure PE film only kept it for 9 days,and that the coating films had no cytotoxicity.PC-Lip/LEO/AgNPs films exhibited significant combined action in functional packaging to extend storage period.(2)Utilized confinement effect of laponite(LAP),LAP immobilized AgNPs(LAP@AgNPs)was synthesized with quaternized chitosan as reductant and LAP as immobilization agent.The results show that only about 5.6%of AgNPs were released from the films with laponite,which were much lower than those films without laponite,and physicochemical properties of the films were improved due to the suitable addition of laponite.Furthermore,although the films showed very low toxicity to cells,they exhibited good antimicrobial activity and effectively extended the storage life of litchi as a packaging comparing with commercial preservative film.(3)Chitosan was modified by mercaptosuccinic acid to obtain the thiol-modified chitosan(TMC),which was used as a carrier to prepare immobilized AgNPs/TMC composite sponges(TMC/AgNPs)for the hemostasis of medical wounds.The results show that good softness and high absorption chitosan-based hemostatic sponges had complex interlaced tubular porous structure with high porosity(99.42%)and low density(0.4037 g/cm~3).Mercaptochitosan has good immobilization efficiency for AgNPs,and its release rate is14.35%.TMC/AgNPs has excellent antibacterial activity against S.aureus,E.coli and P.aeruginosa.In addition,in vitro and in vivo hemostasis experiments have confirmed that TMC/AgNPs had rapid and efficient hemostatic performance,and its hemostasis mechanism was the synergistic effect of high blood absorption capacity,the interaction between amino and sulfydryl and blood cells.Moreover,TMC/AgNPs hemostatic sponge had good safety due to the immobilization of mercaptochitosan for AgNPs.(4)Subsequently,in order to further reduce the release of AgNPs from TMC,it was pre-hydrothermal carbonized to obtain carbon nanospheres(SMCS).Carbon nanospheres immobilized silver nanoparticles(AgNPs-SMCS)were prepared due to the interaction between abundant active groups and silver ions,and then mixed with chitosan to prepare composite films(CS/AgNPs-SMCS).The results showed that though the release of AgNPs from the films decreased to 5.0%,it possessed good and endurance antibacterial activity.Moreover,in order to simplify the preparation process,the TMC was direct mixed with silver ions to prepare carbon encapsulated AgNPs(SMCS-Ag)by one-step hydrothermal method,and then blend with chitosan to produce composite films(CS/SMCS-Ag).The results showed that the release rate of AgNPs from CS/SMCS-Ag film was 9.03%,and it had antibacterial activity but weaker due to the effect of the outer carbon matrix.