Preparation Of Chitin/Chitosan Based Nanogels And Their Applications In Biomaterials

As natural polymers,chitin and chitosan have good biocompatibility and biodegradability.Therefore,a series of nanomaterials constructed by chitin/chitosan have attracted extensive attention from researchers.Chitin and chitosan nanogels have the advantages of both nanoparticles and gels,and show great potential applications in biomedical fields such as drug delivery,antimicrobial materials,biological imaging and tissue engineering.In this paper,chitin and chitosan were used as raw material,dissolved in alkali/urea aqueous solvent system,and then regeneratd into chitin nanogels and chitosan nanogels by one-step stirring method.On this basis,a series of chitin or chitosan nanogels based functional biomedical materials were constructed.The structures and properties of the materials were characterized by various characterization methods,such as scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),infrared spectroscopy(FTIR),thermogravimetric analysis(TG),ultraviolet visible spectroscopy(UV-Vis),rheometer and so on.At the same time,the cytology and zoology experiments were used to evaluate the application prospect of chitin and chitosan nanogels in the biomedical field,which opened a new way for the research,development and application of chitin and chitosan materials.The main research contents and results are as follows:1 Chitin nanogels were prepared by one-step stirring method in NaOH/urea system for the first time,and the charge on the nanogel surface was regulated by simple chemical modification.Chitin nanogels with size of 20-30 nm was obtained by dissolving chitin in NaOH/urea solution and subsequently stirring the solution(8000-12000 rpm).The stirring speed,the concentration of chitin,and other conditions on the size and dispersion of chitin nanogels(CNGs)were studied.The results showed that under different conditions of preparation the particle size of the nanogels was basically as the same,but nanogels with higher concentration were more likely to gather.The chitin nanogels morphology and properties were investigated by FTIR,SEM,TEM,XRD,rheometer,and the biocompatibility of nanogels was studied by MTT cytotoxicity test and cell adhesion test.The results showed that the preparation process of chitin nanogel was physical change and the dispersion had the property of shear thinning.Cell experiments showed that the nanogels had good biocompatibility.Amino and carboxylated nanogels with positive and negative surface charges were prepared by deacetylation and oxidation under Tempo.of chitin nanogels.The effects of different preparation conditions on amino and carboxylated nanogels were investigated.Finally,the antibacterial properties of chitin nanogels,amino and carboxyl nanogels were studied.the aminated nanogels showed excellent antibacterial properties against E.coli and S.aureus.2 Rectorite/chitin nanocomposites with high hemostatic performance were prepared.By mixing chitin solution with layered silicate rectorite,chitin nanogels and rectorite nanocomposites with special structure were prepared by one step stirring.The properties and morphology of the obtained nanocomposites were investigsted by SEM,TEM,FTIR,TG,XRD,Zeta potential.The bibulous rate of material,hemolysis rate in vitro blood,coagulation time,clotting mechanism,biocompatibility of the materials were also studied.The results showed that some chitin molecular chains could insert into the layer of the rectorite during the preparation process,and most of the chitin self-assembled into nanoparticles,which were attached to the surface of the rectorite to form a special interlayer structure.The zeta potential of pure rectorite was negative,while the composites zeta potential was positive.At the same time,the liquid absorption rate of the pure rectorite was only 200%,and the liquid absorption rates of the compound material with chitin were greatly increased,both above 1000%.Cell experiment and hemolysis experiment proved that the composites had good biocompatibility.The clotting experiment revealed that the main clotting mechanism of the composite material was that rectorite activated endogenous clotting factors,thus promoting clotting.At last,the hemostasis effect was studied by tail cutting experiment in rats and femoral artery cutting experiment in rabbits.The results showed that chitin/rectorite nanocomposites had better hemostatic effect than the commercial hemostatic material Celox,which could of severed tail in rats around 121 s,and stop the bleeding of hemorrhage of rabbit femoral artery around 140 s.The results proved that the nanocomposites had significant hemostatic effect.3 In situ synthesis of gold nanoparticles(AuNPs)using chitin nanogel as template was carried out to prepare composite materials(CNGs@AuNPs)with good photothermal properties.AuNPs with particle size of 2.5 nm?90 nm were prepared by adjusting reaction temperature and the concentration of HAu Cl₄,the results showed that under the 120?gold and chloride acid concentration of 1 mg/m L,the temperature of obtained CNGs@AuNPs can increase 30?within 10 min under the power of 2 W/cm².DOX was loaded on CNGs@AuNPs to investigate the release behavior of the materials under different p H,temperature and NIR power.The results showed that CNGs@AuNPs was p H responsive,low p H and high temperature can promote drug release.In addition,NIR stimulation also could speeds up drug release.The synergistic effect of CNGs@AuNPs loaded DOX with chemotherapy and photothermia under NIR irradiation was confirmed by cell assay4 Chitosan nanogels(CSNGs)obtained by self-crosslinking molecular chains of chitosan were used as templates to prepare chitosan nanogels and silver nanoparticles composites with excellent antibacterial properties.Chitosan nanogels with particle size of about 40 nm were prepared by high speed agitation of chitosan dissolved in KOH/Li OH/urea system,and then characterized by FTIR,XRD,TEM and rheometer.The results showed that the preparation of chitosan nanogels was a physical process,and the chitosan nanogels had the property of shear thinning.Chitosan nanogels/AgNPs composites were prepared by in situ reduction of Ag NO₃ by chitosan nanogels.The particle size of AgNPs can be regulated by changing the ratio of chitosan nanogels to Ag NO₃.The samples that were prepared under the condition that the ratio of chitosan nanogels to Ag NO₃was 18/1,the average AgNPs particle size was only 4 nm.The biological properties of the materials were studied by MTT cytotoxicity assay and in vivo and in vitro antibacterial assay.The results showed that the chitosan nanogels and the composite had good cellular compatibility.In vitro and in vivo antibacterial experiments showed that chitosan nanogels/AgNPs composite had excellent antibacterial properties.