Research On Mechanical-electrical Properties And Self-repair Mechanism Of Carbon Nanotube Concret

As the most abundant and widely distributed protein in mammals,collagen can spontaneously assemble in vivo into ordered collagen microfibrils and fibril bundles,which then form macroscopic network structures that provide the structural framework and mechanical support of many biological tissues.Through reasonable regulation of environmental conditions,collagen molecules can also self-assemble into ordered aggregates or supramolecular structures in vitro,and finally form fibrils.The formation of this supramolecular structure is due to the synergistic effect of various noncovalent interactions,mainly including hydrogen bonds,hydrophobic interactions,electrostatic interactions and van der Waals force.However,as a biomaterial,pure collagen has many disadvantages when used directly,such as poor water solubility,low mechanical strength,weak thermal stability and rapid biodegradation.In addition,the traditional preparation technology of collagen materials rarely considers the bottom-up hierarchical self-assembly behavior of collagen and the interaction between self-assemblies,and also cannot achieve the mutual adaptation of collagen materials in structure and function.Therefore,this work aims to develop collagen composites based on self-assembly behavior,systematically study the influence of in vitro incubation conditions during the collagen self-assembly process,demonstrate the relationship between molding conditions and the multi-level structure of collagen materials,and provide a theoretical basis for the design and development of collagen composites with self-assembly structure.The main findings and results of the study are as follows.The affecting factors of collagen self-assembly（collagen concentration,p H,temperature and ionic strength）in vitro were investigated in detail,and the kinetic behavior and morphology of collagen self-assembly in the presence of different transition metal ions and amino acids were compared by turbidity method and atomic force microscopy（AFM）.These results showed that when the collagen concentration is more than 200g/m L,the p H range is 5.0-7.0,and the temperature range is 25-37℃,the collagen can occur self-assembly behavior,and a two-phase kinetic process was provided that included the nucleation and propagation,which presents S-shape.The increase of ionic strength can promote collagen self-assembly behavior.The interaction between transition metal ions(Cu²⁺and Zn²⁺)and collagen molecules can enhance the instability of collagen molecules and promote the collagen self-assembly behavior.Amino acids can regulate collagen self-assembly behavior through electrostatic interaction between collagen molecules.Collagen/aspartic acid（Asp）composite fibers with self-assembly structure were prepared by wet-spinning technology based on the effect of Asp on the collagen self-assembly behavior.The effects of Asp on the self-assembly structure and properties of collagen composite fibers during fiber formation have been investigated.These results showed that the electrostatic interaction between collagen molecules and Asp can improve the self-assembly ability of collagen,enhance the mutual chimerism between molecules,and form a dense network structure.This network structure,based on self-assembly behavior made the composite fibers have excellent thermal stability,mechanical properties and enzymatic degradation resistance.The effects of different incubation conditions on the self-assembly structure and spatial distribution of collagen on the graphene oxide（GO）nanosheet surfaces were studied by AFM.Collagen/GO nanocomposite films with the layered structures were fabricated by vacuum-assisted self-assembly technique,and the influence of incubation conditions of collagen/GO dispersion on the interfacial interaction of the nanocomposite films was investigated.These results showed that the self-assembly process of collagen on GO nanosheet surfaces mainly depended on the collagen concentration,p H of dispersion and incubation time.Collagen concentration and incubation time mainly affect the size of the collagen fibrils,while the p H of the dispersion determines the self-assembly sites of collagen fibrils on the GO nanosheet surfaces.Structural studies of nanocomposite films have shown that there are strong interfacial interactions between GO nanosheets and collagen fibrils,which gives them excellent mechanical properties and thermal stability.In addition,the nanocomposite films have low cytotoxicity and can enhance the neuronal differentiation of SH-SY5Y cells.A solution casting-solvent evaporation and cation-specific effect approach are proposed to fabricate strong and tough collagen/cellulose nanofibril（CNF）composite films via the synergistic effect of hydrogen and metal-ligand bonds.The collagen/CNF composite films were first fabricated via solution casting-solvent evaporation induced collagen molecules self-assembly in CNF supramolecular network to form a high-density physical crosslinking supramolecular double network structure and then moved to inorganic saline solutions to induce the structure rearrangement and crosslinking of the composite films on the nanoscale through soaking.These results demonstrated that the collagen/CNF composite films with interpenetrating supramolecular double network structures significantly improved the crystallinity,dry and wet mechanical properties and thermal stability through the synergistic effect of hydrogen and metal-ligand bonds,and exhibited a good balance between cell compatibility and antibacterial activity.Using the TEMPO catalytic oxidation system and diethylenetriamine（DETA）to modify CNF by carboxylation and amination,and the p H-responsive collagen composite aerogels were prepared by directional freezing technology with modified CNF as the reinforcing component.The effects of different reinforcing components on the structures and properties of collagen composite aerogels were investigated.Taking5-fluorouracil（5-FU）as a model drug,the drug release performance of collagen composite aerogels was investigated,and the factors affecting the cumulative drug release rate and the drug release mechanism were analyzed.These results indicated that the collagen composite aerogels have a layered double network structure.The intermolecular interactions,such as chain entanglement and hydrogen bonds between the modified CNF and collagen fibrils,made the composite aerogels have good structural stability,excellent thermal stability and compression performance.The study of drug release behavior showed that the collagen composite aerogels had remarkable sustained release behavior and were p H-responsive.Collagen fibers with high orientation structure were prepared via the hydrodynamic focusing effect of microfluidic wet-spinning technology,and the optimal parameters of microfluidic wet-spinning technology were explored.Hydrodynamic focusing can induce collagen self-assembly in a microfluidic chip.Based on the self-assembly characteristics of collagen and cellulose nanocrystals（CNC）,the simultaneous preparation from collagen molecules to ordered microfibers and highly oriented fibers was realized by using the multichannel microfluidic chip.The effects of microfluidic spinning parameters and collagen/CNC co-assembly on the multi-level structure of fibers were studied.These results showed that the microfluidic wet-spinning technology based on the hydrodynamic focusing effect can achieve the assembly,arrangement and orientation of collagen microfibrils and CNC in the microchannel,and accurately regulate the collagen self-assembly behavior and the forming process of fibers in the micron scale.The orientation structure of the collagen/CNC composite fibers is more ordered and has an excellent crystal structure and thermal stability.The tensile strength of composite fibers is up to 642 MPa,which is 2.82 times that of pure collagen fibers.