| Trauma has become the third leading cause of death after cancer and cardiovascular and cerebrovascular diseases.As an important branch of trauma,skin trauma has attracted more and more attention.According to the type of wound,skin trauma can be roughly divided into two categories: chronic wound and acute wound.The treatment of chronic wounds,such as burns,scalds,diabetes and some pathological ulcers,are aimed at preventing wound infection and promoting tissue regeneration.Acute wound mainly refers to massive hemorrhage,and its primary treatment goal is rapid hemostasis.At present,the main method to treat skin trauma is to use some dressing products.The ideal wound healing material must have a series of significant characteristics,such as rapid coagulation,maintaining a suitable moist environment,allowing oxygen exchange,absorbing wound exudate,accelerating wound closure,reducing pain and preventing infection.In addition to the traditional sterile gauze and absorbent cotton,many functional materials have been developed for trauma treatment,such as silver nano particle,chitosan,alginate,collagen and polyurethane.Although these materials play a positive role in the treatment of trauma,the application of these dressing products is limited by many factors,such as single function,complex preparation process,high cost,poor physical and chemical properties and potential toxicity.Therefore,the exploration and development of ideal wound healing materials are always the hotspot and difficulty in this field.Bacterial nano-cellulose(BNC)is a kind of natural polymer synthesized by some microorganisms.BNC has a nano-fibril network,high chemical purity,high water holding capacity and good biocompatibility,which has great potential in the area of biomaterial.To be used as a wound dressing is one of the most potential applications of BNC,and has attracted the attention of many researchers in the world.However,BNC itself does not have antibacterial properties,and the ability to promote healing needs to be improved.The antibacterial properties and healing promoting ability of BNC have been endowed and improved by introducing functional materials,and its application potential in trauma treatment has been evaluated.BNC materials produced from different strains often have different physico-chemical and biological properties,which may have an impact on the therapeutic effect of trauma,but these have not attracted enough attention of researchers.In addition,the selection of different antibacterial agents and healing promoting factors,as well as the exploration of efficient preparation methods of composite materials play a direct role in the practical application of materials.Moreover,the preparation of BNC-based functional materials for acute bleeding wounds has not been found,especially for absorbable hemostatic materials in vivo.These studies are of great significance to the preparation,optimization and application of BNC based functional materials.In this dissertation,three different strains of Komagataeibacter xylinus(DHU-WX-1,DHUATCC-1and ATCC 23770)were selected to evaluate and compare the microstructure,physicochemical properties and biocompatibility of BNC from different strains,so as to explore the influence of these differences on the wound healing effect,and to screen out the best producing strain of BNC as wound dressing.On this basis,lactoferrin and collagen were compounded with BNC through an electric field driven method;additionally,pseudo protein and hyaluronic acid were compounded with BNC through the electrostatic self-assembly method.A variety of BNC based composite materials with antibacterial and healing promoting functions were prepared,and their wound healing effects were evaluated in a rat animal model.Finally,an oxidized bacterial nanocellulose(OBC)was prepared by selective oxidation,and then an OBC/collagen/chitosan composite sponge was obtained by using electrostatic self-assembly.The therapeutic effect of the composite sponge as absorbable hemostasis in vivo was evaluated in the rat model of liver hemorrhage,and therefore the application scope of BNC based wound healing materials was widened.The major contents and results of the dissertation are summarized as follows:1.The effects of BNC from different strains on wound healing were evaluated and compared,and the best producing strain of the BNC as wound dressing was selected.The results found that the BNC from different strains had various physical and chemical properties,which were embodied in different fiber density and fiber diameter,resulting in different water holding,water vapour permeability and mechanical properties.The upper surface of BNC from different strains was denser than the lower surface,and the loose lower surface had better biocompatibility than the dense upper surface.Moreover,the upper surface of the three BNC had no significant difference in biocompatibility,while the lower surface had significant difference.The results of animal experiments showed that the three BNC had different effects on wound healing.In a word,BNC from different strains had different physical and chemical properties and cell compatibility,which led to different wound healing efficiency.Among them,BNC produced by DHU-WX-1 had the best wound healing effect due to its suitable water retention,permeability and cell compatibility,which would provide a theoretical basis for the selection of substrate materials in subsequent experiments.2.An electric field driven composite technology was creatively developed.By using the technology,a composite hydrogel material(BNC/LF/COL)with antibacterial and promoting function was prepared by compounding lactoferrin(LF)and collagen(COL)with BNC.The physical and chemical properties and biological properties of the composite hydrogel were studied,and its healing effect on the actual wound was evaluated in the rat model.The results found that the new technology had significant advantages in less consumption of time,greater protein loading,better homogeneity and less volume required of processing solution in comparison to traditional immersionadsorption method.BNC/LF/COL had suitable water retention and water vapour permeability,excellent broad-spectrum antibacterial properties and could significantly promote the adhesion and proliferation of fibroblasts.The results of animal experiments showed that BNC/LF/COL was able to significantly promote wound contraction and re-epithelialization.The average time of wound healing was 9 days,which was significantly shorter than that of the sterile gauze group(21 days),indicating the potential in the clinical treatment of chronic trauma.3.A safe and stable pseudo protein was used as antibacterial agent to self assemble with hyaluronic acid in the BNC network by electrostatic adsorption.Based on this strategy,a composite hydrogel material(BHAP)with antibacterial and promoting healing property was successfully prepared.The potential application of the material as a wound dressing for chronic trauma was evaluated both in vivo and in vitro.The results showed that the incorporation of pseudo protein and hyaluronic acid did not destroy the original nanofibril structure of BNC.By optimizing the composite ratio,the water holding capacity and water vapour permeability of BHAP were significantly improved compared with pure BNC.Depending on the polycation of pseudo protein,BHAP had a strong inhibitory effect on a variety of bacteria,but it had no significant toxicity on eukaryotic cells,showing a good cell compatibility.The results of animal experiments showed that BHAP could significantly promote wound contraction and re-epithelialization,and inhibit bacterial infection.The average time of wound healing was 10 days,significantly shorter than that of the sterile gauze group(21 days).4.The oxidized bacterial nanocellulose(OBC)was prepared by selective chemical oxidation.The polyanion of OBC and polycation of chitosan(CS)were used for electrostatic self-assembly of OBC/CS.In the process of assembly,collagen(COL)was cleverly bound to obtain a multifunctional nanocomposite(OBC/COL/CS).The effect of OBC/COL/CS as an absorbable hemostatic material for hemostasis in vivo was evaluated by using the liver hemorrhage model.The research found that the electrostatic force between OBC and CS can rapidly form the composite by self-assembly in a short time after mixing the two kinds of dispersion,and COL can be bound during the self-assembly process.This method may avoid the use of chemical cross-linking agents with certain toxicity,and would be suitable for the preparation of other biomacromolecule composite materials as a universal technology.OBC/COL/CS nanocomposite had suitable mechanical properties for operation,broadspectrum antibacterial properties,promoting the proliferation of fibroblast and excellent in vivo degradability.Animal experiments proved that OBC/COL/CS had better hemostatic effect than the current clinical hemostatic product Surgicel,which is manifested in better procoagulant properties and coagulation capacity,higher adhesion of red blood cells and platelets,and lower blood loss,greatly shortening the hemostatic time.In a word,OBC/COL/CS was a fast,efficient and safe procoagulant material,which has broad-spectrum antibacterial performance and cytocompatibility,and has a broad application prospect in the field of controlling internal bleeding.In this thesis,the physicochemical and biological properties of BNC from different strains were characterized,and the more suitable strain for producing the BNC as wound dressing was screened out,providing a theoretical basis for the selection of matrix materials in the development of BNC based functional dressing.A variety of BNC-based antibacterial and healing promoting materials with clinical application potential were prepared by electric field driving and electrostatic selfassembly technology.OBC/COL/CS was prepared by selective oxidation and electrostatic selfassembly technology.Finally,the potential of BNC-based materials for acute bleeding wound repair is greatly improved,and the application scope of BNC-based wound repair materials has been greatly widened.The whole dissertation has systematically evaluated and demonstrated the highefficiency of BNC in trauma treatment. |
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