Directed Modification Of Bacterial Cellulose Nanofibers And Properties Of Their Functional Composites

As the hotspots in the field of new materials research,biopolymer is characterized by good biocompatibility,easy regulation of microstructure,stable chemical properties and environmental friendliness,which are widely used in biomedical and environmental sciences.Among them,Bacterial Cellulose(BC)secreted by microorganisms is currently widely studied due to its high crystallinity,high degree of polymerization,unique three-dimensional network structure,high elastic modulus and high tensile strength,and strong water-holding capacity and high biocompatibility.At present,the research on BC materials mainly focuses on the direction of bio-fermentation optimization to improve productivity.There are few reports on BC modified materials and related functional nano-materials with different structures and properties,and their application fields need to be further expanded.In this paper,the preparation and modification of bacterial cellulose nanofibers and the microstructure and physicochemical properties of several nanofiber-based composites were fully studied.Through the surface modification of BC nanofibers,the controllable design of BC surface active groups can be realized;and different methods can be used to construct new BC-based nanocomposites,thereby increasing BC added value and expanding BC in biomedical,drug carrier and environmental adsorption,and other applications in the field of materials.The details are as follows:(1)Scale regulation of bacterial cellulose nanofibers(BCN)and optimization of surface modification experimentsIn order to obtain BCN with high aspect ratio,excellent dispersibility and easy surface modification,the structural design of BCN was realized by catalytic hydrolysis using copper sulfate as cocatalyst and TEMPO(2,2,6,6-tetramethylpiperidine-1-oxyl)oxidation.The dispersibility was obviously improved with the fiber length of 200-500 nm and the diameter of20 nm.By studying the influence of the amount of cocatalyst on the structure and yield of BCN,it was proved that the addition of copper sulfate shortened the reaction time,improved the reaction efficiency and yield,the particle diameter of the product decreased,and the morphology of the nanofibers improved.Further,the TEMPO/laccase/O₂ oxidation system is used to introduce a large amount of carboxyl groups on the surface of BCN,which is more environmentally friendly and has fewer by-products than the conventional oxidation system.The effects of single factor reaction conditions and reaction system on the yield of carboxyl groups were discussed,and the oxidation reaction conditions were optimized.By interpreting the evolution of structure and properties of BCN in the above modification reaction process,it provides theoretical basis and technical support for the functional preparation of cellulose.(2)Research on the effect of BCN enhanced polyvinyl alcohol(PVA)hydrogelThe chemical nature of PVA has shown its important role in the field of medical scaffolds,but its molding structure and mechanical properties limit its application in this field.In order to solve the problem,BCN prepared by hydrolysis method are used as reinforcing materials,and the homogenization with PVA is improved by the addition of cross-linking agent and dispersing agent.PVA/BCN composite hydrogel material.The effects of the amount of BCN on the structure and properties of the composites were investigated.IR,XRD and SEM analysis showed that BCN were uniformly distributed in the PVA matrix and formed a three-dimensional porous structure;the determination of tensile strength,thermal stability and water absorption showed enhanced performance with the adding of BCN.Besides,when mass fraction of BCN reached 50%,the tensile stress is three times higher than that of PVA and is superior to many conventional polymers.At the same time,the biocompatibility of the material was evaluated by using 3T3 fibroblasts as seed cells.The results of MTT assay showed that the composite could effectively support cell growth and proliferation,which opens a new way for the preparation and performance enhancement of PVA-based medical scaffold materials.(3)Preparation of gradient mechanical structure PVA/BCN composite hydrogel and cell differentiationThe scaffold material of the gradient mechanical structure can achieve different guiding effects on cell differentiation.In this part,we prepared the PVA/BCN hydrogel by means of liquid nitrogen freezing method.The freezing process was regulated by temperature and time,and the physical freezing of molecules was further formed by cyclic freezing-thawing method to construct a structurally graded heterogeneous PVA/BC hydrogel.SEM showed that the composites presented porous microstructures arranged in the longitudinal direction.XRD analysis proved that the hydrogels showed a trend of gradient crystallization during the freezing process.The compression test results confirmed that the structural differences caused the mechanical strength of different cross-section layers.After culturing 3T3-L1 preadipocytes on different cross-section layers,the results of fluorescence staining showed that the number of cells differentiation and the average cell area increased with the mechanical strength of the cross-section of the material.When the mechanical strength of the material reaches 18 kpa,the influence of material rigidity on cell differentiation is gradually reduced.The preparation process of the gradient structure composite hydrogel material is simple and controllable,and different guiding effects on cell differentiation could be realized in the same material body,which has broad application prospects in the field of biological scaffold materials and biomedicine.(4)Study of polyethyleneimine(PEI)modified oxidized BCN composite aerogel and its drug controlled release propertiesThe existing drug sustained-release materials generally have a technical bottleneck with low adsorption capacity and poor controllable response means.The composite aerogel material was prepared by grafting BCN with PEI and crosslinking by ethyl carbodiimide hydrochloride(EDC)and N-hydroxysuccinimide(NHS).The adsorption kinetics and isothermal adsorption process of composite materials on aspirin,bovine serum albumin(BSA)and gentamicin were studied.The results showed that the materials showed good adsorption effect on these three drugs,and the maximum adsorption were 309 mg·g^-1,74.0 mg·g^-1 and 20.9 mg·g^-1,respectively.In the simulated intestinal fluid environment,the drug release of the sample reached 80.6%,much higher than the 52.3%release in the simulated gastric fluid environment.Therefore,PEI-BCN,as a biocompatible high prodrug sustained-release body,has the advantages of high drug-loading capacity,improved drug release route,and prolonged its effects,and has good development and application prospects.(5)Preparation and properties of magnetic attapulgite clay(ATP)/oxidized BCN/chitosan(CS)adsorbentsIn addition to excellent adsorption and release properties in the field of sustained drug release,BCN materials also present development potential in the field of environmental science.In this part,we prepared magnetic ATP@(BCN/CS)₇ adsorbent by blending CS and oxidized BCN on the surface of ATP modified by Fe₃O₄.The multilayer coating of CS and oxidized BCN was then realized by layer-by-layer electrostatic self-assembly to obtain.TEM analysis showed that the synthesized Fe₃O₄ nanoparticles were uniformly distributed on the surface of ATP with an average size of 80 nm.The effects of different p H values,adsorption time and initial ion concentration on the adsorption properties of Cu²⁺,Pb²⁺and Cr⁶⁺metal ions and anionic dyes were studied.The adsorption amount of Cr⁶⁺ions could reach 91 mg·g^-1and the adsorption amount of Congo red was 230 mg·g^-1.The adsorption-desorption experiment shows that the adsorption rate remains above 90%after 6 cycles of the material,ensuring its recycling in the environment,which provides a new idea for the development of low-cost and high-efficiency biomass-based adsorbent materials.