Anodization is known to be an effective way to slow down the initial corrosion rate of magnesium (Mg) and its alloys. Here, we investigated the specific use of oxy-salts to improve the corrosion resistance of anodizing coatings. Oxy-salts of silicate, phosphate, and carbonate were added separately to a sodium hydroxide alkaline electrolyte used to anodize Mg alloy AZ91D. The process was investigated in terms of anodizing behavior, the surface properties, and the corrosion behavior of AZ91D. Anodizing AZ91D using the silicate- containing electrolyte generated sparks, and produced a thicker and more corrosion-resistant layer than the other oxy-salts. In the process, MgO and SiO2 formed Mg2SiO4 at high temperatures. Coatings from the phosphate- and carbonate- containing electrolyte anodizations did not contain phosphorus or carbon. We also studied the effects of silicate concentration on the corrosion resistance and properties of the surface.

A water-based epoxy-resin-ester modified bis-[tri-ethoxy-silyl] ethane (BTSE) organosilane coated by electro-deposition was tried on hot-dipped galvanized (HDG) steel for corrosion protection. Various resin ratios were tested with different electro-deposition cathodic currents. FTIR showed a more cross-linked siloxane network (Si-O-Si) by electro-deposition than by immersion. AFM, SEM, EDX examined the morphology and interface between the coating and substrate. Performance tests of salt spray test (SST), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization showed the corrosion resistance of BTSE-resin film was dramatically increased by electro-deposition. A corrosion protection morphology was proposed according to the results in this work. (C) 2013 Elsevier B.V. All rights reserved.

Magnesium (Mg) and its alloys have numerous potential applications as biodegradable implants, but the fast degradation rate of Mg alloys at the initial implanted stage could be a problem. This paper describes the modification of the water-based bis-[triethoxysilyl] ethane (BTSE) silane applied to the surface of magnesium–yttrium (Mg–4Y) to increase its corrosion resistance. Surface characterization by SEM, FTIR, and EDX showed that the hydrolysis and condensation of the silane resulted in a covalent bonding to the Mg–4Y surface. Corrosion behavior of the uncoated and coated Mg–4Y alloy was evaluated in different environments by using a novel self-developed corrosion probe. Based on the electrochemical results of DC polarization and electrochemical impedance spectroscopy (EIS), we conclude that the epoxy-modified BTSE silane coating successfully increases the corrosion resistance at the initial stage of implantation. The corrosion rates in the flesh of dead mice environments such as body cavity and subcutaneous tissue of the mice were lower than the corrosion rates in in vitro environments.

The corrosion behavior of pure Mg, AZ31, and AZ91D were evaluated in various in vitro and in vivo environments to investigate the potential application of these metals as biodegradable implant materials. DC polarization tests and immersion tests were performed in different simulated body solutions, such as distilled (DI) water, simulated body fluid (SBF) and phosphate buffered solution (PBS). Mg/Mg alloys were also implanted in different places in a mouse for in vivo weight loss and biocompatibility investigations. The in vivo subcutis bio-corrosion rate was lower than the corrosion rate for all of the in vitro simulated corrosive environments. The Mg/Mg alloys were biocompatible based on histology results for the liver, heart, kidney, skin and lung of the mouse during the two months implantation. Optical microscopy and scanning electron microscopy were carried out to investigate the morphology and topography of Mg/Mg alloys after immersion testing and implantation to understand the corrosion mechanisms.

Electrochemical impedance spectroscopy (EIS), open circuit potential and pH changes were used to examine the corrosion of magnesium 4% yttrium alloy (Mg4Y) with and without a silane-epoxy-coating (SEC) in a stirred 0.154M NaCl solution at 37°C. For a good quality SEC we find a relatively low non-Faradaic resistance of 266Ωcm2. The quality of the SEC was affected by the curing temperature. In this article we compare the electrochemical measurements taken during corrosion of bare Mg4Y, Mg4Y with a SEC that remained intact, and a SEC that did not protect the Mg from corrosion.

Magnesium (Mg) and its alloys are emerging as a possible biodegradable implant material. However, Mg implants may degrade too quickly in the body, before the natural healing process is complete. In this work, anodization was investigated to slow down the initial corrosion of Mg in a simulated body corrosive environment. Pure Mg and AZ91D alloy were anodized and their corrosion resistance was compared in terms of anodization behavior and parameters such as applied voltage and current with different anodization time. Electrochemical impedance spectroscopy, DC polarization, and immersion testing were used to evaluate the corrosion resistance of Mg samples and further optimize anodization parameters. The results showed that anodization increased the corrosion resistance of both pure Mg and AZ91D samples. Further characterization showed the anodized layers on both pure Mg and AZ91D consisted of Mg, O and Si, in the mixture of MgO and Mg2SiO4.

A biosensor is an electronic device that measures biologically important parameters. An example is a sensor that measures the chemicals and materials released during corrosion of a biodegradable magnesium implant that impact surrounding cells, tissues and organs. A responsive biosensor is a biosensor that responds to its own measurements. An example is a sensor that measures the corrosion of an implant and automatically adjusts (slows down or speeds up) the corrosion rate. The University of Cincinnati, the University of Pittsburgh, North Carolina A&T State University, and the Hannover Medical Institute are collaborators in an NSF Engineering Research Center (ERC) for Revolutionizing Metallic Biomaterials (RBM). The center will use responsive sensors in experimental test beds to develop biodegradable magnesium implants. Our goal is to develop biodegradable implants that combine novel bioengineered materials based on magnesium alloys, miniature sensor devices that monitor and control the corrosion, and coatings that slow corrosion and release biological factors and drugs that will promote healing in surrounding tissues. Responsive biosensors will monitor what is happening at the interface between the implant and tissue to ensure that the implant is effective, biosafe, and provides appropriate strength while degrading. Corrosion behavior is a critical factor in the design of the implant. The corrosion behavior of implants will be studied using biosensors and through mathematical modeling. Design guidelines will be developed to predict the degradation rate of implants, and to predict and further study toxicity arising from corrosion products (i.e., Mg ion concentrations, pH levels, and hydrogen gas evolution). Knowing the corrosion rate will allow estimations to be made of implant strength and toxicity risk throughout the degradation process.

Development of biodegradable metal implants is a complex problem because it combines engineering and medical requirements for a material. This article discusses the development of sensing and corrosion control techniques that can help in the design of biodegradable metallic implants. Biodegradable metallic implants dissolve as new tissue is formed. One of the most important factors in the design of biodegradable implants is to study the active interface, which should be monitored and controlled to address the medical concern of biocompatibility. Thus miniaturized and nanotechnology-based sensors that measure the activities of the degradation process and the formation of tissue are discussed for use with in vitro and in vivo experiments. These sensors can monitor chemical components and also cell activity and can provide new knowledge about biodegradable interfaces and how to actively control the interface to provide the best bioactivity to regenerate new tissue in a short time. Development of new alloys, nano-materials, miniature sensors, corrosion control coatings, and auxiliary applications such as biodegradable drug delivery capsules is expected to open up a new era in the engineering of materials for medicine.