Research On The Fabrication And Performance Of Bacterial Cellulose-based Electroconductive Tissue Engineering Materials

Bacterial cellulose(BC)synthesized from Acetobacter xylinum has drawn an increasing attention and interest in the field of biomedical device due to its unique structure and properties.It exhibits attractive properties such as high purity and crystallinity in chemical composition,a high degree of polymerization(2,000-8,000),excellent biocompatibility and biodegradability.Since the bioelectric activity of BC is poor,BC nanofiber is difficult to meet the diversified demands on the material properties in the field of tissue engineering.In particular,it cannot be used for tissue engineering of electroactive material field.In recent years,the flexible neural electrodes provides a new technical in the treatment of diseases of the nervous system.Therefore,developing high bioelectricity flexible nanomaterials in the field of tissue engineering has important practical application value.There is a unique choice to integrate electro activity with the inherent properties of BC nanofibers including the flexibility,large length diameter ratio,and high specific surface.It may assist in building biocompatible scaffolds by mimicking the native extracellular matrix(ECM)and interfacing the cells better for biomedical research or tissue engineering.The BC-based electroconductive nanofibers composite combines the properties of BC nanofibers and conductive systems,and it may potentially be used for flexible displays,biosensors,and platfonn substrates to study the effect of electrical signals on cell activity,and to direct desirable cell function for tissue engineering applications.Integrated in this paper,the main contributions of this dissertation are described as follows:1.Three-dimensional BC/PEDOT composite nanofibers with high performance for electrode-cell interfaceWe developed a facile approach to prepare electroactive and flexible three-dimensional(3-D)nanostructured biomaterials with high performance based on bacterial cellulose(BC)nano fibers.Our approach can coat BC nanofibers with poly(3,4-ethylenedioxythiophene)(PEDOT)by in situ interfacial polymerization in a controllable manner.The PEDOT coating thickness is adjustable by the monomer concentration or reaction time during polymerization,producing nanofibers with a total diameter ranging from 30 to 200 nm.This fabrication process also provides a convenient method to tune different parameters such as the average pore size and electrical conductivity on the demands of actual applications.Our experiments have demonstrated that the 3-D BC/PEDOT nanofibers exhibit high specific surface area,excellent mechanical properties,electroactive stability,and low cell cytotoxicity.With electrical stimulation,calcium imaging of PC 12 neural cells on BC/PEDOT nanofibers has revealed a significant increase in the percentage of cells with higher action potentials,suggesting an enhanced capacitance effect of charge injection.As an attractive solution to the challenge of designing better electrode-cell interfaces,3-D BC/PEDOT nanofibers promise many important applications such as bio-sensing devices,smart drug delivery systems,and implantable electrodes for tissue engineering.2.The preparation of PSS doped BC/PEDOT conductive composite nanofibers and its biocompatibility evaluationA high-performance 3-D electro-conductive nanomaterial was templated synthesized by biocompatible bacterial cellulose(BC)nanofibers.PSS(poly(styrene sulfonate))was doped to improve its conductivity in a controlled way.Mechanical performance and electrochemical measurements showed that the composite possess excellent electroactive and mechanical stability.Especially,evidence was provided that the BC/PEDOT nanofibers with moderate PSS doped had excellent biocompatibility,from the results of the cellular morphology and proliferation of human mesenchymal stem cells(hMSCs)cultured on the BC/PEDOT/PSS nanofibers.As a 3-D conductive nanomaterial with flexibility,it shows potential application in electroactive substrates/scaffolds for tissue engineering,cell culture,biosensors,drug delivery,and implanted electrodes.3.Biointerface by cell growth on graphene oxide decorated bacterial cellulose/poly(3,4-ethylenedioxythiophene)nanofibersA bacterial cellulose/poly(3,4-ethylene dioxythiophene)/graphene oxide(BC/PEDOT/GO)composite nano fibers was synthesized through the in situ polymerization of PEDOT with the decoration of GO.The abundant free carboxyl and hydroxy groups offer the BC/PEDOT/GO film active functional groups for suxface modification.We demonstrate the use of this composite nanofibers for the electrical stimulation of PC 12 neural cells as this resultant nanofiber scaffold could closely mimic the structure of the native extracellular matrix(ECM).With a promoting cell orientation and differentiation after electrical stimulation of PC12 cells,it is expected that this biocompatible BC/PEDOT/GO material will find potential applications in biological and regenerative medicine.4.Electrically-responsive core-shell hybrid microfibers for controlled drug release and cell cultureWe report the development of the multifunctional core-shell hybrid microfibers with excellent mechanical and electrical performance as a new smart biomaterial.The microfibers was synthesized using a combination of co-axial spinning with a microfluidic device and subsequent dip-coating,containing a hydrogel core of bacterial cellulose(BC)and a conductive polymer shell layer of poly(3,4-ethylenedioxythiophene)(PEDOT).The hybrid microfibers were featured with a well-controlled microscopic morphology,exhibiting enhanced mechanic properties.A model drug,diclofenac sodium,can be loaded in the core layer of the microfibers in situ during the process of synthesis.Our experiments suggested that the releasing behaviors of the drug molecules from the microfibers were enhanced by external electrical stimulation.Interestingly,we demonstrated an excellent biocompatibility and electroactivity of the hybrid microfibers for PC12 cell culture,thus promising a flexible template for the reconstruction of electrically-responsive tissues mimicking muscle fibers or nerve networks.5.Bacterial cellulose-mimicking extracellular matrix-hybrided graphene foam for conductive neural stem cells scaffoldSelectively guide the differentiation of neural stem cells into mature cells is very useful in tissue engineering.In this work,we add the 3D graphene into fermentation solution during Acetobacter xylinum dynamic fermentation to prepared bacterial cellulose-mimicking extracellular matrix-hybrided graphene foam.We found that the adding graphene has no affection in growth and metabolism of Acetobacter xylinum.The as-prepared material shows 3 d macroporous with BC nanofibers dopant,resulting in positive impact on promoting cell proliferation and differentiation.Furthermore,calcium imaging of neural stem cell verified that 3D-G/BC was an efficient conductive platfornn to mediate electrical stimulation for neural cells featuring an enhancement of double-layer charging capacitance.Therefore,the as-prepared material is expected to become a potential nerve scaffold material.To sum up,we have studied the preparation methods of flexible BC-based electroactive composite materials and evaluated their performance as biological electrodes in regulating cell behavior,the result proves that it is expected to become a new kind of flexible neural interface material in nerve repair,angiogenesis and muscle reconstruction.