Use of synergistic mixture of chelating agents for in situ LDH growth on the surface of PEO-treated AZ91.

The principal possibility to grow layered double hydroxide (LDH) at ambient pressure on plasma electrolytic oxidation (PEO) treated magnesium alloy AZ91 in the presence of chelating agents is demonstrated for the first time. It avoids hydrothermal autoclave conditions, which strongly limit wide industrial application of such coating systems, and the presence of carbonate ions in the electrolyte, which lead to the formation of "passive" non-functionalizable LDH. A combination of chelating agents (sodium diethylenetriamine-pentaacetate (DTPA) and salicylate) were introduced to the treatment solution. The role of each additive and the influence of treatment bath composition on the LDH formation processes are discussed. A synergistic effect of DTPA and salicylate during LDH formation is discovered and its possible explanation is proposed.

PEO coatings design for Mg-Ca alloy for cardiovascular stent and bone regeneration applications.

Four bioactive PEO (plasma electrolytic oxidation) coatings were generated on Mg0.8Ca alloy using a Ca/P-based electrolyte and adding Si or Fas necessary. Surface characteristics, chemical composition and ion liberation of the coatings were characterized using SEM/EDS (Scanning Electron Microscopy/Energy Dispersive X-ray spectroscopy), X-ray diffraction, optical profilometry and ICP-OES (inductively coupled plasma optical emission spectrometry). Direct biocompatibility studies were performed by seeding premyoblastic, endothelial and preosteoblastic cell lines over the coatings. Biocompatibility of the coatings was also evaluated with respect to murine endothelial, preosteoblastic, preosteoclastic and premyoblastic cell cultures using extracts obtained by the immersion degradation of the PEO-coated specimens. The coatings reduced the degradation of magnesium alloy and released Mg Ca, P, Si and F. Of all the studied compositions, the Si-containing PEO coating exhibited the optimal characteristics for use in all potential applications, including bone regeneration and cardiovascular applications. Coatings with high F content negatively influenced the endothelial cells. RAW 264.7, MC3T3 and co-culture differentiation studies using extracts of PEO coated Mg0.8Ca demonstrated improved osteoclastogenesis and osteoblastogenesis processes compared to bare alloy.

Electrochemical surface engineering of magnesium metal by plasma electrolytic oxidation and calcium phosphate deposition: biocompatibility and in vitro degradation studies.

In this study, the surface of magnesium metal was electrochemically engineered for enhanced biocompatibility and controlled degradation in body fluid. Firstly, a plasma electrolytic oxidation (PEO) coating was formed on magnesium, followed by electrochemical deposition of calcium phosphate (CaP) using an unconventional electrolyte. Cytocompatibility tests using L929 cells revealed that the PEO-CaP coating significantly improved the biocompatibility of magnesium. In vitro electrochemical degradation experiments in simulated body fluid (SBF) showed that the PEO-CaP coating improved the degradation resistance of magnesium significantly. The corrosion current density (i corr) of the PEO-CaP coated magnesium was ∼99% and ∼97% lower than that of bare magnesium and the PEO-only coated magnesium, respectively. Similarly, electrochemical impedance spectroscopy (EIS) results showed that the polarisation resistance (R P) of the PEO-CaP coated magnesium was one-order of magnitude higher as compared to the PEO-only coated magnesium and two-orders of magnitude higher than the bare magnesium, after 72 h immersion in SBF. Scanning electron microscopy (SEM) analysis revealed no localized degradation in the PEO-CaP coated magnesium. The study demonstrated that the PEO-CaP coating is a promising combination for enhancing the biocompatibility and reducing the degradation of magnesium for potential biodegradable implant applications.

Influence of circumferential notch and fatigue crack on the mechanical integrity of biodegradable magnesium-based alloy in simulated body fluid.

Applications of magnesium alloys as biodegradable orthopaedic implants are critically dependent on the mechanical integrity of the implant during service. In this study, the mechanical integrity of an AZ91 magnesium alloy was studied using a constant extension rate tensile (CERT) method. The samples in two different geometries that is, circumferentially notched (CN), and circumferentially notched and fatigue cracked (CNFC), were tested in air and in simulated body fluid (SBF). The test results show that the mechanical integrity of the AZ91 magnesium alloy decreased substantially (∼50%) in both the CN and CNFC samples exposed to SBF. Fracture surface analysis revealed secondary cracks suggesting stress corrosion cracking susceptibility of the alloy in SBF.

Magnesium alloys as implant materials--principles of property design for Mg-RE alloys.

Magnesium alloys have attracted increasing interest in the past years due to their potential as implant materials. This interest is based on the fact that magnesium and its alloys are degradable during their time of service in the human body. Moreover magnesium alloys offer a property profile that is very close or even similar to that of human bone. The chemical composition triggers the resulting microstructure and features of degradation. In addition, the entire manufacturing route has an influence on the morphology of the microstructure after processing. Therefore the composition and the manufacturing route have to be chosen carefully with regard to the requirements of an application. This paper discusses the influence of composition and heat treatments on the microstructure, mechanical properties and corrosion behaviour of cast Mg-Gd alloys. Recommendations are given for the design of future degradable magnesium based implant materials.