Electrochemical Surface Construction And Optimization Of Biological Properties For Medical Titanium Metal

Surface modification and functional optimization of medical titanium(Ti) and its alloys are one of the most focal topics in biomaterials.Titanium and its alloys have no sufficient bioactivity themselves,it is necessary to conduct surface modifications to endow them with abilities of induction of bone tissue ingrowth and osseointegration at the implantation site.Preparing hydroxyapatite(HA) coating on titanium substrate is an important technology to improve the bioactivity,and plasma spraying technique has been commercially used to deposit HA coating on Ti surface.However the heat effect during the coating process unavoidably causes decomposition of HA,and the HA can not be uniformly coated on the Ti substrates with complicated shape.As a moderate non line coating technology,the electrodeposition method is proposed as one of the most promising alternatives.However,the HA coating obtained by electrodeposition remains loose structure and poor bonding with the substrate,and a great difference between the coefficients of thermal expansion(CTE) of Ti substrate and HA may result in sudden changes of physical property and stress concentration on their interface.The coefficient of thermal expansion of TiO₂ is 8.7×10^-6 K^-1,between Ti(8.2×10^-6 K^-1) and HA(15×10^-6 K^-1).So proper anodic oxidation or hydrothermal treatment for Ti has distinct advantages including simple and moderate preparation conditions,and facile to obtain a uniform coating on the substrates with complicated shape.The bonding strength between Ti substrate and prepared TiO₂ coating is high, ant it is able to resist its physiological corrosion in body fluids.On the other hand,the nano-structured TiO₂ derived form anodic oxidation or hydrothermal method on Ti is possible to provide oriented nucleation and growth template with an ordered structure for electrodeposition of HA.The main works in this thesis includes:a) development of anodic oxidation and hydrothermal method to construct nano-structured TiO₂ coatings on titanium substrate; b) controllable electrodeposition to prepare HA coating with ordered structure and definite composition on Ti-based TiO₂ film,and to obtain a biomimetic bone film of HA/TiO₂ with good mechanical properties and excellent biological properties,based on the views of bionics;c) the physicochemical,mechanical and biological characteristics of the coatings prepared by electrochemical methods were studied to learn the relationship of structure and properties of materials.The main findings and progresses are as follows:1.The hydroxyapatite nanocrystals were electrochemically-oriented deposited inside and onto the TiO₂ nanotubes by using the two-step electrodeposition for the first time.It is indicated that,thers is a large number of pure HA crystals deposited in TiO₂ nanotubes.At a lower cathodic current density,HA was mainly deposited between and on the walls of the TiO₂ nanotubes. Controlling electrochemical deposition parameters,the nano-HA coatings with different structures were prepared.And the morphology and structural changes of the nano-HA in the electrodeposition process was studied by SEM and XRD observations.The mechanical properties of the prepared materials were tested by the scratch analysis of nanoindentation.Tafel polarization and electrochemical impedance spectroscopy(EIS) were applied to study the electrochemical corrosion behavior of the modified medical titanium in Tyrode's physiological solution.2.Two different micro-nano structured anatase TiO₂ on medical titanium surface were prepared by hydrothermal method and post-treatment.The electrodeposition was developed to construct an orderly structured HA coating on the different TiO₂ films prepared by hydrothermal method.The effect of the deposition parameters on HA coating was studied.It is indicated, from in vitro cell culture,that the HA/TiO₂ composite is able to significantly enhance the ability of MG63 cell to adhere and grow on the coating,and its biocompatibility is superior to a single layer of TiO₂.And with increasing of HA in HA/TiO₂ composite coating,the biocompatibility and bioactivity are clearly improved.The HA grains has a significant impact on the extension of pseudopodia of cells.3.Using emulsion polymerization and dispersion polymerization,the monodisperse PS microspheres with different sizes of 0.1～5μm in diameter were prepared.Combination of anodic oxidation of titanium and sulfonation of the PS microspheres surface,the PS microspheres were successfully self-assembled on the prepared TiO₂ nanotube arrays surface.The uniform micro-nano structured interconnected porous HA was obtained by electrodepositing HA coating on TiO₂ nanotube arrays,through the templates of self-assembled and sulfonated PS(SPS) microspheres,and then annealing to remove the SPS microspheres and to further increase the bonding strength of the substrate and the coatings.The primary structure of prepared HA coating shows an ordered micron-scale pore structure derived from SPS microspheres,and the secondary structure is the HA nano-whisker formed from the electrodeposition of HA.And the HA coating has a completely interconnective structure,that is able to provide the geometric space and a relatively stable microenvironment for bioactive substances such as bone growth factors and osteoblasts.On the other hand,this structure is conducive to the flow of body fluids and nutrients within the material,and to increase the contact area between the material and the body fluids,which is helpful to accelerate the integration process of materials and organizations.The HA nanoparticles deposited inside and between the TiO₂ nanotubes will not only further improve the bonding strength at the interface,but also enhance the corrosion resistance of materials against the body fluids.In vitro cell culture showed that the prepared porous HA coatings are able to significantly enhance the ability of MG63 cell to adhere and grow on the surface.The biocompatibility and bioactivity of the porous HA coating is superior to the vertically oriented HA coating and TiO₂ nanotube arrays as well.This significant differences of biological activity is closely related to their unique two-level ordered structure of porous HA coating on medical Ti surfaces.