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Constructing a functional hybrid coating appears to be a promising strategy for addressing the poor corrosion resistance and insufficient endothelialization of Mg-based stents. Nevertheless, the steps for preparing composite coatings are usually complicated and time-consuming. Herein, a novel composite coating, composed of bioactive magnesium thioctic acid (MTA) layer formed by deposition and corrosion-resistant magnesium hydroxide (Mg(OH)2) layer grown in situ, is simply fabricated on ZE21B alloys via one-step electrodeposition. Scanning electron microscopy (SEM) shows that the electrodeposited coating has a compact and uniform structure. And the high adhesion of the MTA/Mg(OH)2 hybrid coating is also confirmed by the micro-scratch test. Electrochemical test, scanning kelvin probe (SKP), and hydrogen evolution measurement indicate that the hybrid coating effectively reduces the degradation rate of Mg substrates. Haemocompatibility experiment and cell culture trial detect that the composite coating is of fine biocompatibility. Finally, the preparation mechanism of MTA/Mg(OH)2 hybrid coatings is discussed and proposed. This coating shows a great potential application for cardiovascular stents.

In this study, the effects of intermetallic compounds (Mg17Al12 and Al8Mn5) on the Mg-Al layered double hydroxide (LDH) formation mechanism and corrosion behavior of an in-situ LDH/Mg(OH)2 steam coatings on AZ80 Mg alloy were investigated. Citric acid (CA) was used to activate the alloy surface during the pretreatment process. The alloy was first pretreated with CA and then subjected to a hydrothermal process using ultrapure water to produce Mg-Al-LDH/Mg(OH)2 steam coating. The effect of different time of acid pretreatment on the activation of the intermetallic compounds was investigated. The microstructure and elemental composition of the obtained coatings were analyzed using FE-SEM, EDS, XRD and FT-IR. The corrosion resistance of the coated samples was evaluated using different techniques, i.e., potentiodynamic polarization (PDP), electrochemical impedance spectrum (EIS) and hydrogen evolution test. The results indicated that the CA pretreatment significantly influenced the activity of the alloy surface by exposing the intermetallic compounds. The surface area fraction of Mg17Al12 and Al8Mn5 phases on the surface of the alloy was significantly higher after the CA pretreatment, and thus promoted the growth of the subsequent Mg-Al-LDH coatings. The CA pretreatment for 30 s resulted in a denser and thicker LDH coating. Increase in the CA pretreatment time significantly led to the improvement in corrosion resistance of the coated AZ80 alloy. The corrosion current density of the coated alloy was lower by three orders of magnitude as compared to the uncoated alloy.

Layered double hydroxide (LDH) coatings on magnesium (Mg) alloys shine brightly in the field of corrosion protection because of their special ion-exchange function. State-of-the-art steam coating as a type of LDH film preparation technique has emerged in recent years because only pure water is required as the steam source and its environmentally friendly LDH coating fits the current need for green development. Moreover, this coating can effectively inhibit the corrosion of the Mg alloy substrate due to the chemical bonding between the coating and the Mg alloy substrate. This review systematically explains cutting-edge advancements in the growth mechanism and corrosion behavior of LDH steam coatings, and analyzes the advantages and limitations of the steam-coating method. The influencing factors including pressure, CO2/CO32−, aluminum content of the substrate alloy, solution type, and acid-pickling pretreatment, as well as the post-treatment of steam-coating defects, are comprehensively elucidated, providing new insights into the development of the in situ steam-coating technique. Finally, existing issues and future prospects are discussed to further accelerate the widespread application of Mg alloys.

Superhydrophobic coatings have been considerably used in corrosion and its protection of metallic Mg. And the comprehensive performance (hydrophobicity, bonding strength, and corrosion resistance, etc.) of the top coating may be highly dependent on the physical and chemical properties of the primer or under coat. Herein, an integrated superhydrophobic polypropylene (PP) coating was fabricated on the micro-arc oxidized Mg substrate via one-step dipping. Surface morphologies and chemical compositions of the composite coating were examined through Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and field-emission scanning electron microscopy (FE-SEM) together with X-ray photoelectron spectroscopy (XPS). The surface wettability of the coating was determined by contact angle and sliding angle. The corrosion-resistant performance was evaluated via electrochemical and immersion measurements. The results showed that the hybrid coating possessed micron-scaled granular structure on the surface with a high water contact angle of 167.2 ± 0.8° and a low water sliding angle of 2.7 ± 0.5°. The corrosion resistance of superhydrophobic coating was obviously enhanced with a low corrosion current density of 8.76 × 10−9 A/cm2, and the coating still maintained integrity after 248 h of immersion in 3.5 wt% NaCl aqueous solution. The MAO coating provides better adhesion of PP to the surface. Hence, the superhydrophobic coating exhibited superior bonding strength, corrosion resistance and durability.

The clinic applications of bioabsorbable magnesium (Mg) and its alloys have been significantly restricted owing to their poor corrosion resistance. Besides elemental alloying, surface modification and functionality is a major approach to increasing corrosion resistance for magnesium alloys. This article reviews the cutting-edge advances and progress of biodegradable surface coatings upon Mg alloys over the last decades, aims to build up a knowledge framework of surface modification on biodegradable Mg alloys. A considerable number of conversion, deposition, mechanical and functional coatings and their preparation methods are discussed. The emphasis has been placed on the composition of chemical conversion and deposited coatings to overcome the disadvantages of adhesion, corrosion resistance and biocompatibility of a single coating for biomedical materials. The issues have been addressed on the integration of the structural and functional factors of the composite coatings. Keywords: Magnesium alloy, Biomaterial, Corrosion resistance, Coating, Biodegradability

Bioinspired coatings with decreased corrosion rate and enhanced bond strength are at the core of future clinic applications on degradable magnesium (Mg)-based implants. The hybrid of organic and inorganic compounds offers a strategy to fabricate biodegradable, biocompatible and compact coatings on biomedical Mg alloys. Hereby, a comparison with and without DNA addition was made on the corrosion resistance and adhesion strength of Ca–P coatings fabricated on AZ31 alloy via hydrothermal deposition. The morphology, chemical composition, and crystallographic structure of the coatings were investigated by means of SEM, EDS and FTIR as well as XRD before and after corrosion tests. Corrosion resistance was evaluated via potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS) and hydrogen evolution tests in Hank's solution. Results show that the coatings are mainly characterized by tricalcium phosphate (TCP), dicalcium phosphate anhydrous (DCPA) and calcium-deficient hydroxyapatite (CDHA). The presence of DNA leads to the formation of Ca–P coating with improved corrosion resistance and adhesion strength. Additionally, the formation mechanism for DNA-induced Ca–P coating is proposed. The DNA-induced Ca–P coating exhibits a promising future for controlling the corrosion rate of biodegradable Mg alloys. Keywords: DNA, Corrosion resistance, Biodegradability, Magnesium alloys, Coatings