Self-assembly Of Hydroxyapatite On Carbon Nanotubes And Related Composite

Carbon nanotubes (CNTs) have perfect structure and very high aspect ratio (length-to-diameter ratio), as well as excellent mechanical property and good electrical property, so, they are considered to be the utmost type of fiber-like reinforcement. Carbon nanotube composite is an important branch of the application research of CNTs. In recent years, research on carbon nanotubes/ hydroxyapatite (HAp) has been conducted on CNTs/ HAp powder. Through traditional technics, the optimum content of carbon nanotues in CNTs/ HAp composites is 5%, but, on this degree, we cannot get perfect thermal property. This problem must be overcome to get CNTs/ HAp composites. According to the philosophy mentioned above, self-assembly technology is introduced with the aim of improving the properties of CNTs/HAp composites. We systematically studied the fabrication process, mechanical properties, microstructure, strengthening mechanism, in vitro cytocompatibility and dissolution of CNTs/HAp composite. On the basis of the results above, antibacterial HAp and CNTs/HAp ceramics were prepared via ion diffusion method, the antibacterial was characterized by pilot study.Multi-walled carbon nanotubes (MWCNTs) were oxidized by concentrated nitric acid, aqua fortis and Fenton reagent separately, and the first means was selected as the final method. The structure of oxidized MWCNTs was examined by TEM, FTIR, thermal analysis and XRD. UV-vis spectrophometric measurement was used to quantitatively characterize colloidal stability of the dispersions as a firstly new method. A general thermodynamic driving force for such wrapping and highâ–³G_sp⁰ value and intense adsorbability in this study are considered as evidences for the interaction between sodium dodecyl sulfate (SDS) and MWCNTs. The stabilization mechanisms of the MWCNTs suspension are discussed by XPS, zeta potential and FTIR studies. The detailed description of the surface chemistry can be used as a guide for designing efficient dispersant.HAp nanoparticles were densely decorated on MWCNTs successfully by a simple and effective self-assembly technology. During preparation, the effect of pH value, calcium concentration, aging temperature, aging time and heat treatment on the property of composite powder was studied systematically. And it found that in the course of coating MWCNTs with HAp, the surface modification of MWCNTs by dispersing MWCNTs in SDS solution is effective for imparting a negative charge. The Ca²⁺ ions then can be absorbed onto the surface of MWCNTs due to the electrostatic attraction, and in situ react with PO₄^3- via electrovalent bond to form HAp precipitates.Different fabrication techniques such as hot press sintering in argon air and spark plasma sintering (SPS) are used to form the densely CNTs/HAp composites. The proper sintering technical parameters are: in hot press sintering, the sintering temperature 1100℃the pressure 30MPa, the time of heat preservation 20min; in SPS, the sintering temperature 950℃, the pressure 50MPa, the time of heat preservation 4min. The microstructure and mechanical properties of CNTs/HAp composites were investigated. If the CNTs distributes in the plane parallel with the hot press plane, the mechanical properties are the best in the plane normal to the hot press plane; the mechanical properties are the worst in the plane which is parallel with the hot press plane. The influence on microstructure and mechanical properties of CNTs content was studied. The experimental results show that the mechanical properties are the best when the volume content of CNTs is 15vol%, the bonding strength is 172.4MPa and the fracture toughness is 2.17MPa·m^1/2, increased 157% and 171% respectively compared with pure HAp. The difference between theoretical and experimental maybe resulted from the bridging and conglomeration of CNTs.The micro unit of HAp toughening by CNTs was analyzed, and the results show that the stress transfer between the CNTs and the matrix is the main manner to transfer stress. Therefore, the bonding strength between the CNTs tip and the matrix is the key factor that determines the mechanical properties of the composite material. Remainder stresses caused by the difference of expand modulus between matrix and CNTs intensified the interface, and improved the fracture strength. The expression to forecast the corporate toughening effect of CNTs bridging, CNTs evulsion and crackle deflexion was derived.Cytotoxicity of the samples was evaluated by MTT method, the results indicated that none of the sample had toxicity. The surface physicochemical changes of the ceramic soaked in a simulated body fluid (SBF) for various periods were determined by means of XRD, FTIR, SEM and EDX analysis. The results indicated that the composite surface transformed to a carbonated hydroxyapatite (CHA), which can support the bone mesenchymal stem cells (BMSCs) adhesion and spreading.The silver-supporting antibacterial HAp (CNTs/HAp) was prepared by the ion exchanging method with HAp ( CNTs/HAp) as the carrier and AgNO₃ solution as the exchanging solution. The influence of preparation process on exchanging ability of HAp (CNTs/HAp) was studied and the optimum preparation process was determined. The structure was characterized by XRD, FTIR, TEM, SEM, and the antibacterial ability was tested. The results show that the exchanging ability is greatly influenced by the concentration of exchanging solution, temperature, time, CNTs content, heat treatment temperature. The silver-supporting antibacterial composite has an excellent antibacterial performance against E.coli and S.aureus.