Preparation And Properties Of Chitosan-based 2D Hybrid Materials

Two-dimensional(2D)nanomaterials have found wide application in field of adsorption,and biomedical areas due to their high specific surface area.However,such materials suffer from aggregation and then poor performance.Stabilizing agents are conventionally used to meet such chanllenges for 2D nanomaterial applications.Traditional stabilizing agents for 2D nanomaterials suffer from drawbacks such as toxicity,environmental pollution and negative effects on material performance,which limit the processing of 2D nanomaterial and its biomedical application.Therefore,a major chanllenge for 2D nanomaterial industrial application is to develop a green and environment friendly method for facile and eff-icient 2D nanomaterials preparation.To meet this end and extend the applications of 2D nanomaterials,the fabrication of 2D hybrid materials is highly important.Chitosan is a green,environment friendly and biocompatible natural macromolecule bearing large amounts of hydroxyl and amino groups,which is a desired reducing and stabilizing agent for 2D nanomaterials.Chitosan and chitosan derivatives could be used for intercalation and exfoliation of 2D nanomaterials to prepare 2D hybrid materials.Importantly,the biocompatibility and biodegradability of chitosan can help extend the bioapplications of chitosan-based 2D hybrid materials.In this thesis,chitosan-based 2D hybrid materials,including chitosan/graphene,chitosan/layered silicate and graphene/chitosan/layered silicate,were synthesized by cation exchanges or electrostatic self-assembly.Novel techniques and methods were set up for fabrication of chitosan-based 2D functional hybrid materials.Novel application of such chitosan-based 2D hybrid materials as drug/gene carriers,adsorptive sponge,and polyelectrolyte hydrogels were explored.1.Fabrication and characterization of chitin/graphene nanocomposite sponges for hemostasisThe acetyl hydrophobic groups of chitosan can be absorbed onto surfaces of carbon materials as stabilizer for their better dispersity,so in this work chitin(with high degree of acetyl amino groups)was employed to help the exfoliation and stabization of graphene layers from graphite under ball-milling.The obtained chitin/graphene nanocomposite was dissolved in NaOH/urea solutions and cross-linked by epichlorohydrin to get chitin/graphene nanocomposite sponge(CG).This sponge can be applied to hemostasis due to the excellent adsorption capacity.The addition of graphene helped the activation of blood cells resulting in better hemostasis performance(the blood clotting index was decreased to 11.2 ± 1.6,lower than commercial PVF(?)sponge).The results indicate that the graphene/blood interactions can help improve the hemostasis performance of chitin sponge.2.Chitosan/holey graphene nanocomposite for reversal gene transfectionBased on the interaction between acetyl hydrophobic groups and graphene discussed in last experiment,herein,we employed the acetyl amino groups of chitosan to help the exfoliation of graphene within sonication bath.By the way,the high-power sonication treatment can perforate on graphene sheets to get stable chitosan/holey graphene nanocomposite.Importantly,the dropped components from the graphene sheets can be utilized as quantum dots.In this sonication exfoliation-etching method,holey graphene can be directly obtained from graphite,so the prepared holey graphene has a large lateral size(larger than 30 μm)with tunable pore diameters(40 nm to 300 nm)as well as high degree of graphitization.The prepared holey graphene showed high uptake capacity and protection effect towards dsDNA,and it can be used as reversal gene transfection substrate with similar efficiencyy to traditional gene transfection method.In addition,the obtained quantum dots can be used in cells imaging.This environmentally friendly etching method paves a way to fabricate holey two-dimensional materials for a wide range of structural and functional applications.3.Bioinspired maltose-like chitosan/rectorite nanocomposites with injectability for skin hemostasisAbove results indicate that chitosan can be used as exfoliation agents as well as stabilizer for graphene.The similar two-dimensional structure of layered silicate with graphene drives us to study the interaction between chitosan and layered silicate.Due to the excellent cation exchange capacity of layered silicate,herein we try to intercalate the chitosan derivatives(with different degree of carboxymethyl groups and quaternary ammonium groups)into interlayers of organic rectorite.The prepared nanocomposite was developed into a bioinspired maltose-like viscous nanocomposite for hemostasis.Through a hemostatic property of rectorite,the viscous nanocomposite decreased the in vitro clotting time by 43%.Moreover,an in vitro porcine skin model confirmed that the viscous nanocomposite can stably adhere on skin and impede the blood bleeding successfully.Importantly,the internal structure of the nanocomposites,chitosan intercalating into exfoliated rectorite interlayers,provided a physical cross-linked network to decrease the release of rectorite from the nanocomposite and its invasion in blood.Therefore,this viscous injectable nanocomposite provided a concept as a facile and sustainable biomaterial for skin hemostasis.The exfoliated rectorite particles confirmed the exfoliation and stabilization effect of chitosan towards two-dimensional nanomaterials.4.Self-assembly of graphene/chitosan/clay nanocomposites for dsDNA uptakeAbove results indicate the excellent absorption capacity of graphene and layered silicate towards biomolecules,so the combination of the two absorbers with chitosan of good biocompatibility will expand their application in biomedical fields.In this study,we prepared stable reduced graphene oxide(rGO)solutions with quaternized chitosan(QCS)and layered silicate as reducing and stabilizing agents.QCS was absorbed onto GO nanosheets through electro-static interaction,then clay was loaded over GO/QCS composite through cation exchange.During this process,GO was gradually reduced to rGO with QCS,and with the loading of OREC,we got the rGO/QCS/OREC nanocomposite.The nanocomposite showed high zeta potential(+38.5 mV)with high stability,as well as high uptake(425 μg/mg)toward double-stranded DNA(dsDNA).The self-assembly process developed through electro-static interactions can be applied to other two-dimensional nanocomposites fabrication.5.Drug-laden graphene/chitosan/clay injectable hydrogels for chemoembolizationHere,we fabricated the drug-laden graphene/chitosan/clay injectable hydrogels for chemoembolization.Combining the positively charged quaternized chitosan and negatively charged laponite to fabricate injectable shear-thinning hydrogels,and DOX-laden holey graphene oxide was encapsulated into this hydrogel.This injectable shear-thinning hydrogel can improve the embolization eff-iciency with easier injection,which are the problems happens in common embolization agents.The hydrogels can be facily injected through syringe and clinical catheters with human hands.The occluded hydrogels can undergo the high blood pressure with no break or move.In vitro 3D tumor model experiments indicate that the occluded hydrogels can decrease the cells growth with limited medium supply,also the released drug can enter cancer cells and then kill them.