Construction And Application Of Chitosan-based Multifunctional Materials

In recent years,the construction of new multi-functional materials and the relationship between their structures and properties have attracted much attention and become a research hotspot in the field of materials research.The unique advantage of composite material is that it can give play to the structure and performance characteristics of each components,and presents the performance that single component material is difficult to obtain.Thus,it broadens the application scope of material,and can be widely used in following fields biomedicine,new energy and environmental protection,etc.Facing the increasing consumption of non-renewable fossil resources and the increasingly serious environmental pollution caused by non-degradable plastics,renewable biomass resources show great application prospects,especially the research and development of natural polymers.Chitosan,a derivative of chitin deacetylation,is the only natural polysaccharide with carrying positive charge in nature.It exhibits good biocompatibility,biodegradability and non-toxicity,and becomes appending to more and more researchers and scientists.In this work,chitosan was used as a raw material and dissolved in the“green”solvent system developed by our laboratory at low temperature,and a series of chitosan-based multi-functional composites were formed.The relationship between the structure and properties of the materials were characterized by using scanning electron microscope(SEM),transmission electron microscope(TEM),atomic force microscopy(AFM),optical microscope(OM),solid-state nuclear magnetic resonance spectroscopy(¹³C NMR),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),thermogravimetric analysis(TGA),ultraviolet-visible spectroscopy(UV),N₂adsorption,and mechanical properties tests.At the same time,the application prospects of these materials in many fields such as biomedicine,wastewater treatment,analysis and detection,intelligent response and so on were evaluated.The main innovations of this work include as follow:(1)based on the electroneutral behavior of chitosan in alkali/urea aqueous solvent system,a new type of chitosan polyelectrolyte composite hydrogel with high strength and toughness was constructed by chemical cross-linking.That hydrogel was proved to be beneficial to cartilage repair in biomedical area;(2)based on the homogeneous blend solution of chitosan and carrageenan in alkali/urea aqueous solvent system,the amphiphilic composite microsphere was constructed by emulsion method.That microsphere had strong adsorption ability to anionic and cationic dyes as well as metal ions;(3)based on the unique pH-sensitive swelling behavior of chitosan microspheres,the composite microsphere with functional wrinkle structure was constructed by depositing Ag nanoparticles(Ag NPs)on the surface of the microspheres through electrostatic layer-by-layer(LBL)self-assembly,and it was proved that it can be used in surface enhanced Raman spectroscopy(SERS);(4)nanofibrous chitosan microsphere was constructed by thermally induced self-assembly of chitosan chains in alkali/urea aqueous solvent system,and could be used as 3D cell carriers;(5)chitosan/poly(N-isopropylacrylamide)bilayer hydrogel was created,and it was proved that the bilayer hydrogel had dual response in intelligence behavior of temperature and pH and could be designed as bionic manipulator.The main research contents and conclusions of this thesis is summarized five parts below.By using the alkali/urea aqueous solvent as cosolvent,the chitosan/carrageenan composite hydrogel with high strength and toughness was prepared by chemical crosslinking,due to the electroneutral behavior of chitosan in the solvent.Due to the electrostatic interaction and chemical cross-linking between chitosan and carrageenan,the composite hydrogel exhibited multiple cross-linking network structure,and had excellent mechanical properties and stability.The porous structure,hydrophilicity,light transmittance and mechanical properties of the composite hydrogel could be effectively regulated by changing the composition ratio of chitosan and carrageenan,which is of great significance in practical application.The biological experiment results showed that the composite hydrogel has good cell compatibility,which not only promoted the adhesion,proliferation and growth of the cartilage cell ATDC5,but also helped the chondrogenesis differentiation of the ATDC5 cells in vitro and enhanced the expression of the cartilage-related genes.This chitosan/carrageenan composite hydrogel is expected to be used as scaffold material for in cartilage repair.Therefore,it has potential application in biomedical field.The magnetic chitosan/carrageenan composite microsphere was prepared by emulsion method with using chitosan and carrageenan homogeneous blend solution in alkali/urea aqueous solvent system.The SEM and TEM results showed that the magnetic Fe₃O₄ nanoparticles with diameter of about 180 nm were closely embedded in the network structure of the microsphere,which made the microsphere has good magnetic responsiveness and is easy to be recycled and reused.The results of adsorption experiments showed that the composite microsphere exhibits high adsorption capacity for anionic and cationic dyes as well as metal ions,and had good recycling reusability.It is proved that the microspheres can effectively adsorb and separate out pollutants by using it as column fillers and the adsorption properties of the microspheres were investigated.Moreover,the composite microsphere exhibited good biodegradability and can be completely biodegraded in soil without causing harm to environments.This chitosan/carrageenan magnetic composite microsphere is a kind of wide spectrum adsorbents with showing excellent performance and environmental protection,which exhibited potential application value in the field of wastewater treatment.Based on pH-sensitive chitosan microsphere prepared in alkali/urea aqueous solvent system,the composite microsphere with functional wrinkle structure was constructed by depositing Ag nanoparticles on the surface of the microspheres through electrostatic layer-by-layer(LBL)self-assembly.The SEM and TEM results showed that the surface of the microsphere had uniform multi-scale wrinkled structure,and the significant difference in swelling ratio between the rigid Ag NPs layer and the elastic chitosan microspheres substrate which had provided sufficient driving force for the formation of surface micro/nano-scale wrinkled structure.By adjusting the number of LBL self-assembly,the thickness of Ag NPs coating on the surface of microsphere can be adjusted,and the morphology of the surface wrinkle structure can be effectively controlled.At the same time,the formation of wrinkled structure much increased the specific surface area and surface hydrophobicity of microspheres.Moreover,the application of composite microsphere as a 3D SERS substrate for analysis and detection was evaluated.The results showed that the formation of wrinkled structure can effectively enhance the SERS signal of the analyte and has a good reproducibility.Therefore,chitosan microsphere with multi-scale controllable wrinkled structure had potential applications in molecular detection,electronic sensing,optical devices,cell recognition and self-cleaning coating.Based on the mechanism of chitosan dissolving at low temperature in alkali/urea aqueous solvent system,the sheath-like structure formed by hydrogen bonding around chitosan molecular chain was destroyed by increased temperature.Thus,the chitosan molecular chains were arranged in parallel to form nanofibers,and the high strength nanofibrous chitosan were further constructed by emulsion method.The SEM results showed that the surface and interior of the microsphere exhibited uniform nanofiber structure(about 30 nm in diameter)and a high specific surface area(395m² g^-1).The formation of nanofibers in heat was characterized by AFM and TEM,which further confirmed the formation of nanofibers from self-assembly of chitosan chains in parallel.The size of the microsphere and the diameter of the nanofibers can be controlled by changing the experimental parameters,temperature and concentration of the solution.Biological experiments showed that the chitosan nanofibrous microspheres can effectively support the growth of osteoblast MC3T3-E1 and promote the three-dimensional adhesion and proliferation of MC3T3-E1 cells,which has good biocompatibility.Therefore,chitosan nanofibrous microspheres can be used as an excellent 3D cell microcarrier for bone repair and has potential application value in the field of tissue engineering materials.Based on the chitosan hydrogel prepared in alkali/urea aqueous solvent system,bilayer hydrogel composed of chitosan and poly(N-isopropylacrylamide)(PNIPAM)with temperature and pH response was successfully prepared.The SEM results displayed that the chitosan hydrogel layer and PNIPAM hydrogel layer formed a semi-interpenetrating polymer network(semi-IPN)structure between the interface,which made the bilayer hydrogel stick closely together and had a good interfacial adhesion force.Based on the temperature sensitivity of PNIPAM hydrogel,the bilayer hydrogel exhibited rapid self-deformation behavior at high temperature and recover to its initial shape at low temperature,showing reversible temperature response.Moreover,based on the difference of swelling ratio between chitosan hydrogel and PNIPAM hydrogel under different pH conditions,the bilayer hydrogel also exhibited bidirectional reversible self-deformation behavior and excellent cyclic stability.Due to the sensitivity of bilayer hydrogels to both temperature and pH,a bionic manipulator for grabbing objects was designed and prepared.Cytotoxicity test also showed that the bilayer hydrogel was safe and non-toxic,and had good cell compatibility.This kind of bilayer hydrogel with multiple response has broad application prospects in biomedicine,soft robots and so on.In this thesis,the alkali/urea aqueous solvent system was used to dissolve chitosan and construct several multi-functional composite materials.Taking advantage of the unique advantages of chitosan in the formation of nanofibers in this solvent system,a series of multi-functional composite materials with high strength including hydrogel,microsphere,etc were successfully constructed.A large number of experimental results showed that these materials had potential applications in biomedical,water treatment,analysis,detection and intelligent response.These basic research results have obvious innovation and scientific value,and provide fresh ideas and new methods for designing unique chitosan multi-functional composite materials,and are consistent with the strategy of sustainable development at the same time.Therefore,this thesis has important scientific significance and feasible application prospect.