Preperation Of Electroactive Anticorrosion Coatings On Magnesium Alloy Surface Based On Self-assembled Nanoparticles

Biomedical metal materials are widely used in clinical medicine,because of the excellent mechanical properties?such as high mechanical strength and fatigue resistance?,processability and reliability.Biomedical metal materials can be divided into two main categories:traditional biomedical metals?such as titanium,stainless steel,cobalt-based alloys?and biodegradable metals such as magnesium-based metal,zinc and iron.Magnesium-based metal implants are widely used as bone repair materials and other implant materials due to their good biodegradability and biocompatibility.However,Mg-based implants degrade rapidly and the degradation rate is uncontrollable in aqueous solution.In this case,the mechanical properties are destroyed prematurely which could even lead to implant failure finally.Presently,surface-treatment is the most common method for improving above problems.Among the coatings,natural macromolecule coatings have become a research hotspot due to their excellent biocompatibility and biodegradability.However,natural macromolecule coatings have poor anti-corrosion effect and single anti-corrosion mechanism.Fortunately,the electro-active anti-corrosion coating with redox properties can achieve better protective performance through multiple anti-corrosion mechanisms.Thus,in this paper,the electroactive self-assembled colloidal particles were prepared by combining natural macromolecules and electroactive tetraaniline.Anticorrosion coating was prepared on the surface of AZ31 magnesium alloy from self-assembled colloidal particles through electrodeposition and the cytocompatibility of the coating was investigated.The main research contents are as follows:1.Preparation and properties of Dex-CA/TANi composite anti-corrosion coatingFirstly,the polysaccharide dextran?Dex?was modified by hydrophobic caffeic acid?CA?via esterification reaction to obtain dextran-caffeic acid?Dex-CA?.Tetraaniline?TANi?was synthesized from N-phenyl-p-phenylenediamine?4-ADPA?.The structures of Dex-CA and TANi were characterized by ¹H NMR.Then Dex-CA/TANi composite colloidal particles were obtained by the self-assembly of Dex-CA and TANi in DMSO/EtOH mixed solvent.The size,structure and morphology of the composite colloidal particles were studied through EDS,UV-vis and TEM.The electrochemical activity of the colloidal particles was investigated by cyclic voltammetry.Finally,anti-corrosion coating was prepared on the surface of magnesium alloy by cathode electro-deposition technology with the colloidal solution as the electrophoretic medium.The corrosion resistance and cytocompatibility in simulated body fluid were studied.The results indicated that the Dex-CA and electro-active TANi were synthesized successfully.The modification rate of CA to Dex was 30%.The size of spherical electro-active Dex-CA/TANi particles was about 150 nm and the loading rate of TANi was more than 75%.More importantly,the corrosion test showed that the Dex-CA/TANi coating had better corrosion resistance compared with Dex-CA coating,and the composite coating still had good cell compatibility.2.Preparation and properties of?-PGA-TANi anticorrosion coatingThe amount of TANi introduced by self-assembly with macromolecules was small,and the structure of Dex was too rigid,and the charge of the system was too low to form ideal coating.Therefore,we selected the natural polypeptide?-polyglutamic acid??-PGA?with a large amount of carboxyl groups in the side chain as the raw material,and?-PGA-TANi was prepared through amidation reaction between?-PGA and TANi.The structure of?-PGA-TANi was characterized by ¹H NMR.Then the?-PGA-TANi self-assembled into colloidal particles in DMSO/Et OH mixed solvent.The size and morphology of the colloidal particles were characterized through TEM and SEM.Electrochemical activity of colloidal particles was investigated by UV-vis and electrochemical workshop.Electro-deposition technique was used to immobilize the?-PGA-TANi particles on the surface of magnesium alloy under the optimal preparation conditions.The corrosion resistance,anti-corrosion mechanism and cytocompatibility of?-PGA-TANi coating were dicussed by corrosion test and cell experiments in vitro.The results showed that the modification rate of TANi on?-PGA was up to 27%(?-PGA-TANi₂₇)and the electro-active?-PGA-TANi colloidal particles were spherical by self-assembly.The size of particles was about 100 nm.The optimal preparation conditions of?-PGA-TANi₂₇7 were 150 V?deposition voltage?,15 min?deposition time?,and 8 mg/mL?concentration?.The anti-corrosion performance was significantly improved compared with the?-PGA coating and the Dex-CA/TANi coating,due to the electrochemical activity?redox properties?and physical shielding effect of?-PGA-TANi coating,while L929 cells could effectively adhere and growth on the coating.3.Preparation and properties of?-PGA-TANi/?-PGA-DDA hydrophobic coatingA coating based on hydrophilic macromolecules have a low contact angle and the corrosive medium can easily penetrates through the coating to contacts with the magnesium substrate.Eventually,the coating peels off and loses the anti-corrosion effect.In this case,the moderate hydrophobic component is necessary.In this chapter,hydrophobic long-chain dodecylamine?DDA?was further introduced based on the previous chapter.Firstly,?-PGA-DDA was obtained by amidation reaction.The structure of?-PGA-DDA was characterized by ¹H NMR.Then?-PGA-TANi/?-PGA-DDA colloidal particles were prepared by?-PGA-DDA self-assembled with?-PGA-TANi in DMSO/Acetone mixed solvent.TEM and SEM were used to characterize the particles.Finally,the colloidal particles reassembled on the surface of AZ31 magnesium alloy through electrodeposition.The preparation of the coating and the change of surface wettability were confirmed by FT-IR and contact angle test.Electrochemical Workshop,Immersion Test and Cell Experiment were used to explore the anticorrosion and cytocompatibility.The results showed that?-PGA-DDA was successfully synethised and the modification rate was 40%.The?-PGA-TANi and?-PGA-DDA co-assembled into spherical particles with about 150 nm.Addition of dodecylamine effectively improved the hydrophobicity of the coating,the contact angle was up to 100^o,and the long-term corrosion resistance was further improved compared with?-PGA-TANi coating.The suitable contact angle provided by the coating and the control of the corrosion rate of the magnesium substrate were favorable to the adhesion,growth and proliferation of L929 cell.