In vitro corrosion behaviour of Mg alloys in a phosphate buffered solution for bone implant application

The corrosion behaviour of Mg–Mn and Mg–Mn–Zn magnesium alloy in a phosphate buffered simulated body fluid (SBF) has been investigated by electrochemical testing and weight loss experiment for bone implant application. Long passivation stage and noble breakdown potential in the polarization curves indicated that a passive layer could be rapidly formed on the surface of magnesium alloy in the phosphate buffered SBF, which in turn can protect magnesium from fast corrosion. Surfaces of the immersed magnesium alloy were characterized by SEM, EDS, SAXS and XPS. Results have shown that Mg–Mn and Mg–Mn–Zn alloy were covered completely by an amorphous Mg-containing phosphate reaction layer after 24 h immersion. The corrosion behaviour of magnesium alloys can be described by the dissolving of magnesium through the reaction between magnesium and solution and the precipitating of Mg-containing phosphate on the magnesium surface. Weight loss rate and weight gain rate results have indicated that magnesium alloys were corroded seriously at the first 48 h while Mg-containing phosphate precipitated fast on the surface of magnesium alloy. After 48–96 h immersion, the corrosion reaction and the precipitation reaction reach a stable stage, displaying that the phosphate layer on magnesium surface, especially Zn-containing phosphate layer could provide effective protection for magnesium alloy.     

Improve corrosion resistance of magnesium in simulated body fluid by dicalcium phosphate dihydrate coating

A dicalcium phosphate dihydrate (DCPD) coating composed of bar-shaped crystals was deposited on the surface of magnesium in order to slow down the corrosion rate of the substrate. The corrosion resistance of the DCPD-coated specimens was evaluated in a simulated body fluid (SBF) with uncoated specimens as a control. Time-dependent characteristics of specimens and the corresponding SBF were analyzed at 3, 5, 7, 14 and 21 days of immersion. Less weight loss and pH increase were observed for the coated group than the uncoated group. The coating was intact after 3 days of immersion although its dissolution was manifested by XRD examination. Noticeable DCPD dissolution occurred at the 5th day accompanied by a temporary increase in Ca and P concentrations in SBF which otherwise kept decreasing. Despite the dissolution of the coating, some DCPD particles were still observed on the surface of the substrate after 21 days of immersion. In contrast to the coated specimens, a porous layer of Mg(OH)₂ was formed on the surface of uncoated specimens at the 5th day of immersion. It was found that the corrosion rate of the coated group was substantially lower than that of the control.     

Role of biomineralization on the degradation of fine grained AZ31 magnesium alloy processed by groove pressing

Groove pressing (GP) has been successfully adopted to achieve fine grain size up to 7 μm in AZ31 magnesium alloy with an initial grain size of 55 μm. The effect of microstructural evolution and surface features on wettability, corrosion resistance, bioactivity and cell adhesion were investigated with an emphasis to study the influence of deposited phases when the samples were immersed in simulated body fluid (SBF 5 ×). The role of microstructure was also evaluated without any surface treatments or coatings on the material. GPed samples exhibit improved hydrophilicity compared to the annealed sample. After immersion in SBF, specimens were characterized using scanning electron microscopy (SEM), energy dispersive X-ray (EDAX) analysis and X-ray diffraction (XRD) methods. More amount of white precipitates composed of hydroxyapatite and magnesium phosphate along with magnesium hydroxide was observed on the surfaces of groove pressed specimens as compared to the annealed specimens with an increase in immersion time in SBF. Corrosion behavior of the samples estimated using potentiodynamic polarization curves indicate good corrosion resistance for GPed samples before and after immersion in SBF. The MTT assay using rat skeletal muscle (L6) cells revealed that both the processed and unprocessed samples are nontoxic and cell adhesion was promising for GPed sample.     

Microstructure evolution and corrosion mechanism of dicalcium phosphate dihydrate coating on magnesium alloy in simulated body fluid

Dicalcium phosphate dihydrate (DCPD) coating was deposited on the substrate surface of magnesium alloy with solution treatment. The microstructures and corrosion behaviors of the DCPD-coated samples before and after immersion in simulated body fluid (SBF) for different times were investigated. It is important to note that DCPD was not only transformed into hydroxyapatite (HA) but also induced HA precipitation after immersion in SBF. An HA-like coating was generated on the substrate surface in a two step process involving an initial coating with DCPD, resulting in the corrosion resistance increasing along with the corrosion mechanism changing with increase to soaking time.     

Effect of corrosion on mechanical behaviors of Mg-Zn-Zr alloy in simulated body fluid

The main purpose of this paper is to investigate the effect of corrosion on mechanical behaviors of the Mg-Zn-Zr alloy immersed in simulated body fluid （SBF） with different immersion times. The corrosion behavior of the materials in SBF was determined by immersion tests. The surfaces of the corroded alloys were examined by SEM. The tensile samples of the extruded Mg-2Zn-0.8Zr magnesium alloy were immersed in the SBF for 0, 4, 7, 10, 14, 21 and 28 d. The tensile mechanical behaviors of test samples were performed on an electronic tensile testing machine. SEM was used to observe the fracture morphology. It was found that with extension of the immersion time, the ultimate tensile strength （UTS）, yield strength （YS） and elongation （EL） of the Mg-2Zn-0.8Zr samples decreased rapidly at first and then decreased slowly. The main fracture mechanism of the alloy transformed from ductile fracture to cleavage fracture with the increasing immersion times, which can be attributed to stress concentration and embrittlement caused by pit corrosion.     

微波辅助法制备镁合金的植酸镁/羟基磷灰石复合涂层及其耐蚀性能

采用微波辅助法在AZ31镁合金表面制备了植酸镁/羟基磷灰石(PA/HA)复合涂层。利用FESEM、EDS、XRD和电化学性能测试等方法表征涂层的表面形貌、物相组成以及耐蚀性能,探究了植酸溶液的pH值对PA/HA复合涂层形貌及耐蚀性能的影响,并通过浸泡实验研究了镁合金及PA/HA复合涂层在模拟体液(SBF)中的降解矿化行为。结果表明:在植酸预处理中,植酸溶液的pH=5.0时制备得到的PA/HA复合涂层表面均匀、无裂纹,与镁合金基底的界面结合良好;并且在此pH值下PA/HA复合涂层包覆镁合金样品的交流阻抗最大,自腐蚀电流密度最小,说明其耐蚀性最好。在SBF中,PA/HA复合涂层能够快速诱导磷灰石的生成,并显著提高镁合金基底的耐蚀性能。     

In vitro degradation behavior of M1A magnesium alloy in protein-containing simulated body fluid

Magnesium alloys possess unique advantages to be used as biodegradable implants for clinical applications. In this study, in vitro cells responses and degradation behaviors of magnesium alloy M1A in simulated body fluid (SBF) and albumin-containing SBF (A-SBF) were systematically investigated. Cell responses, in terms of Cell morphology and cell proliferation, imply that M1A possesses good viability for MG63 cells. The corrosion behaviors of M1A are strongly affected by the addition of albumin through the combined effects of adsorption and chelation. Electrochemical testing indicates that such an absorbed albumin layer makes M1A to be more noble with a smaller corrosion current. Corrosion rate monitored by hydrogen evolution rate suggests that the quickly adsorbed albumin serves as an effective protective layer, resulting in a much slower hydrogen release rate at initial stage. With increasing immersion time, a higher corrosion rate is observed since the chelation effect exerts more significant acceleration effects on the removal of the passivation layer. The corrosion mode evaluated by surface morphology of the samples changes from a nonuniform-anisotropic mode for M1A in SBF to a uniform-isotropic mode for M1A in A-SBF.     

Biodegradable behaviors of AZ31 magnesium alloy in simulated body fluid

Magnesium alloys have unique advantages to act as biodegradable implants for clinical application. The biodegradable behaviors of AZ31 in simulated body fluid (SBF) for various immersion time intervals were investigated by electrochemical impedance spectroscopy (EIS) tests and scanning electron microscope (SEM) observation, and then the biodegradable mechanisms were discussed. It was found that a protective film layer was formed on the surface of AZ31 in SBF. With increasing of immersion time, the film layer became more compact. If the immersion time was more than 24 h, the film layer began to degenerate and emerge corrosion pits. In the meantime, there was hydroxyapatite particles deposited on the film layer. The hydroxyapatite is the essential component of human bone, which indicates the perfect biocompatibility of AZ31 magnesium alloy.     

In vitro degradation,hemolysis and MC3T3-E1 cell adhesion of biodegradable Mg–Zn alloy

In this study a kind of patent binary Mg–6 wt.%Zn magnesium alloy was investigated as degradable biomedical material. The results of in vitro degradation including electrochemical measurements and immersion tests in simulated body fluid (SBF) revealed that zinc could elevate both the corrosion potential and Faraday charge transfer resistance of magnesium and thus improve the corrosion resistance. XRD and EDS analysis proved that the corrosion products on the surface of Mg–Zn contained hydroxyapatite (HA), Mg(OH)₂ and other Mg/Ca phosphates, which could reduce the degradation rate. The degradation process of magnesium alloy and the mechanism of corrosion layer formation were also discussed in this work, i.e. the byproducts of degradation of magnesium, Mg²⁺ and OH^?, reacted with the phosphate and Ca²⁺ in the SBF, thus the corrosion layer containing HA, Mg(OH)₂ and other magnesium-substituted apatite precipitated in corrosion pits and covered the surface of magnesium alloy.The hemolysis test found that the hemolysis rate of Mg–Zn was 3.4%, which is lower than the safe value of 5% according to ISO 10993-4. For the cell culture experiments, after 2 h incubation the pre-osteoblastic cell MC3T3-E1 was able to adhere and spread on the corrosion layer of Mg–Zn alloy, indicating that despite the fluctuation of pH value of DMEM culture solution, Mg–Zn alloy could still support the earlier adhesion of pre-osteoblastic cells on the surface. Hemolysis and adhesion of cells display good biocompatibility of Mg–Zn alloy in vitro.     

Development and evaluation of a magnesium–zinc–strontium alloy for biomedical applications — Alloy processing,microstructure, mechanical properties,and biodegradation

A new biodegradable magnesium–zinc–strontium (Mg–Zn–Sr) alloy was developed and studied for medical implant applications. This first study investigated the alloy processing (casting, rolling, and heat treatment), microstructures, mechanical properties, and degradation properties in simulated body fluid (SBF). Aging treatment of the ZSr41 alloy at 175 °C for 8 h improved the mechanical properties when compared to those of the as-cast alloy. Specifically, the aged ZSr41 alloy had an ultimate tensile strength of 270 MPa, Vickers hardness of 71.5 HV, and elongation at failure of 12.8%. The mechanical properties of the ZSr41 alloy were superior as compared with those of pure magnesium and met the requirements for load-bearing medical implants. Furthermore, the immersion of the ZSr41 alloy in SBF showed a degradation mode that progressed cyclically, alternating between pitting and localized corrosion. The steady-state average degradation rate of the aged ZSr41 alloy in SBF was 0.96 g/(m²·hr), while the pH of SBF immersion solution increased. The corrosion current density of the ZSr41 alloy in SBF solution was 0.41 mA/mm², which was much lower than 1.67 mA/mm² for pure Mg under the same conditions. In summary, compared to pure Mg, the mechanical properties of the new ZSr41 alloy improved while the degradation rate decreased due to the addition of Zn and Sr alloying elements and specific processing conditions. The superior mechanical properties and corrosion resistance of the new ZSr41 alloy make it a promising alloy for next-generation implant applications.     

Comparison of the Corrosion Behavior of Coated and Uncoated Magnesium Alloys in an In Vitro Corrosion Environment

The in vitro degradation of magnesium alloys with various alloying elements, the effect of coatings, and the impact of an altered experimental environment are investigated. LANd442 and Nd2 alloys are subjected to a continuously moving environment during an immersion test allowing flowing SBF. Applying an MgF₂ coating to the alloys increases the corrosion resistance of LANd442 but has no effect on the corrosion rate of Nd2 within the period of investigation. It leads to a more‐even degradation with less pitting corrosion in the early stages of corrosion. A bioglass coating on Nd2 increases the corrosion rate. The mass loss, volume loss, and loss in maximum force all show the same trends as the specimens degrade over time.     

XPS Studies of Magnesium Surfaces after Exposure to Dulbecco's Modified Eagle Medium,Hank's Buffered Salt Solution,and Simulated Body Fluid

Magnesium‐based biomaterials are gaining increasing interest, while in vitro corrosion tests are not standardized yet. Moreover, the effects of different corrosion media on the corrosion products are still not fully understood. To compare and evaluate the three main corrosion media applied in most in vitro studies, an XPS investigation of magnesium surfaces was carried out after exposure of the specimens to Dulbecco's modified eagle medium (DMEM), Hank's buffered salt solution (HBSS), and simulated body fluid (SBF). The effects of rinsing the specimens after immersion were also determined. XPS investigations especially on the Mg 2p state showed that MgO, Mg(OH)2, and MgCO3 species were the dominant corrosion products presenting in all specimens despite of the different corrosion media. However, the ratio of corrosion products depends on the medium composition. It was also shown that rinsing specimens after immersion experiments is a necessary procedure when surface analysis is employed afterward.     

Blood triggered corrosion of magnesium alloys

Intravascular stents manufactured out of bioabsorbable magnesium (Mg) or Mg-alloys are considered as auspicious candidates for the next stent generation. However, before clinical application numerous physical and biological tests, especially to predict the clinically highly important degradation kinetics in vivo, have to be performed. In a Chandler-Loop model, the initial degradation of eight different magnesium alloys during 6 h in contact with human whole blood was investigated. The magnesium release varied between 0.91 ± 0.33 mg/cm² (MgAl9Zn1) and 2.57 ± 0.38 mg/cm² (MgZn1). No correlation could be found with Mg release data obtained after immersion in simulated body fluid (SBF). This pilot study showed that Mg corrosion is highly influenced by the biological test environment (SBF or blood, etc.) and that a modified Chandler-Loop model with human whole blood may be superior to predict corrosion of Mg alloys under clinical conditions than the SBF models presently used.     

Influence of Tris in simulated body fluid on degradation behavior of pure magnesium

In current paper, influence of tris-hydroxymethyl-aminomethane (tris) in simulated body fluid (SBF) on degradation behavior of pure magnesium is investigated using electrochemical tests as well as degradation measurement. Our results shows that tris mainly affects earlier degradation behavior of pure magnesium alloy. Tris and HCl used in preparation of SBF will form Tris–HCl which only lowers corrosion potential of magnesium slightly but accelerates degradation rates of pure magnesium by teens times. Consumption of OH^? generated during magnesium dissolution by Tris–HCl progressively promotes transformation from Mg to Mg²⁺, which is the main reason for quite high degradation rate of pure magnesium in SBF. Pure magnesium is also more sensitive to pitting corrosion due to inclusion of Tris–HCl in SBF. This study deepens the understanding on degradation mechanism of biomedical magnesium alloys.     

Corrosion of experimental magnesium alloys in blood and PBS: A gravimetric and microscopic evaluation

Corrosion tests for medical materials are often performed in simulated body fluids (SBF). When SBF are used for corrosion measurement, the open question is, how well they match the conditions in the human body. The aim of the study was to compare the corrosion behaviour of different experimental magnesium alloys in human whole blood and PBS^minus (phosphate buffered saline w/o Ca and Mg) as a simulated body fluid by gravimetric weight measurements and microscopic evaluation. Eight different experimental magnesium alloys, containing neither Mn nor other additives, were manufactured. With these alloys, a static immersion test in PBS^minus and a dynamic test using the Chandler-loop model with human whole blood over 6 h were performed. During the static immersion test, the samples were weighed every hour. During the dynamic test, the specimens were weighed before and after the 6 h incubation period in the Chandler-loop. From both tests, the total mass change was calculated for each alloy and the values were compared. Additionally, microscopic pictures from the samples were taken at the end of the test period. All alloys showed different corrosion behaviour in both tests, especially the alloys with high aluminium content, MgAl9 and MgAl9Zn1. Generally, alloys in PBS showed a weight gain due to generation of a microscopically visible corrosion layer, while in the blood test system a more or less distinct weight loss was observed. When alloys are ranked according to corrosion susceptibility, the results differ also between the test systems. The MgAl9 alloy, showing the most pronounced corrosion in PBS, was one of the least corroding alloys under simulated in vivo conditions in blood. Thus, the ranking concerning clinical suitability of the magnesium alloys tested in this study is different, depending on the used electrolyte and the kind of method. For a possible clinical use, the alloy MgAl9Zn1 might be preferable for further investigations.     

Biodegradable behaviour and fatigue life of ZEK100 magnesium alloy in simulated physiological environment

The fatigue life of ZEK100 magnesium alloy in the phosphate buffered solution for various immersion intervals was investigated by experiments and theoretical predictions. The biodegradable behaviours of ZEK100 magnesium alloy were also studied. Microstructure observation showed that the corrosion behaviours were characterized by pitting corrosion. The corrosion rate decreased a lot in the initial 7 d and then almost stayed unchanged. After 28 d immersion, the elastic modulus almost kept stable, while the yield strength and the ultimate strength decreased a lot, which indicated that corrosion had important effects on the tensile mechanical properties. It showed that the fatigue life of the samples under the same stress conditions decreased with increasing immersion time under the asymmetric stress‐controlled cyclic loading. Considering the effect of corrosion on the material failure, a modified fatigue life model was proposed for magnesium alloy under corrosion.     

医用Mg-Zn-Ca-Mn合金在PBS模拟体液中的腐蚀行为

利用真空感应熔炼,采用金属模浇铸制备了Mg(100-x-y-z)-Znx-Cay-Mnz四元合金。使用光学显微镜、X射线衍射仪、扫描电镜及能谱仪对合金进行分析和表征。探讨了合金在PBS模拟体液中的腐蚀行为。结果表明,Ca、Zn及Mn原子的复合加入可显著细化合金的铸态显微组织;镁合金的腐蚀发生于晶粒内部,至晶界处终止;当加入2.0%的Zn和0.5%的Ca时,铸态合金的抗腐蚀性能最佳(平均腐蚀速率为0.77mm/a);当Zn、Ca含量均大于1%时,固溶时效态合金的腐蚀速率下降为铸态的1/2～1/4,表现出优异的耐蚀性;固溶时效处理可有效减少Mg2Ca相的体积分数,改善其分布,提高合金的耐蚀性能。     

Phosphating treatment and corrosion properties of Mg–Mn–Zn alloy for biomedical application

A phosphating treatment was applied to Mg–Mn–Zn alloy in order to improve the corrosion resistance. Surface morphology and phase constitute were observed and identified by SEM, EDS, SAXS, XRD and XPS. SEM observation showed that a rough and crystalline reaction layer was formed on the surface of Mg alloy. With the increasing of phosphating time, the layer became thicker and denser. It has been showed that the reaction layer was mainly composed of brushite (CaHPO₄ · 2H₂O). Small amount of Zn²⁺ was also detected by XPS and EDS. The corrosion resistance of the phosphated samples was measured by the electrochemical polarization and the immersion test in comparison with the bare alloy. The results manifested that the corrosion resistance of Mg alloy was improved by the phosphating treatment, and the corrosion resistance increased with the increase of the phosphating time within 50 min. Immersion tests showed that the phosphate layer could protect magnesium alloy from fast corrosion. The brushite layer has been transformed into hydroxyapatite (HA) during the immersion in the simulated body fluid (SBF) solution, which suggested the brushite layer could provide good biocompatibility.     

Corrosion behaviour of some vapour deposited magnesium alloys

Abstract

Binary magnesium alloys containing chromium, manganese, or titanium were made using a physical vapour deposition technique. The corrosion resistance of the alloys was assessed in aqueous chloride solutions using total immersion tests in quiescent 600 mmol L^?1 NaCI solutions. Alloying with manganese or titanium was found to lower the corrosion rate of magnesium over most of the compositional ranges of interest, whereas addition of chromium had a detrimental effect on the corrosion resistance of magnesium. The lowest corrosion rate was recorded for a Mg–Ti alloy where the value obtained was about 80 times lower than that found for vapour deposited pure magnesium. Open circuit corrosion potential measurements conducted in 600 mmol L^?1 NaCl solution showed that additions of chromium, titanium, and manganese also produced deposits which were significantly more noble than pure magnesium, suggesting that these alloys would be less susceptible to galvanic corrosion.

MST/3064     

Fabrication and corrosion behavior of HA/Mg-Zn biocomposites

The thermal-treated hydroxyapatite (HA) particles, Mg and Zn powders were used to prepare the HA/Mg-Zn composites with different HA contents by means of powder metallurgy technology. The microstructures, formation phases, and corrosion behaviors in simulated body fluid (SBF) were studied in comparison with pure magnesium and HA/Mg composites fabricated by the same preparation technology. As a result, no evident reaction happened between HA particles and Mg matrix during sintering process, and Zn atoms diffused into Mg matrix to form a single phase Mg-Zn alloy matrix. The addition of HA particles changed the corrosion mechanism of Mg matrix. During the corrosion process, HA particles would adsorb PO₄³⁻ and Ca²⁺ ions efficiently and induce the deposition of Ca-P compounds on the surface of composites. HA could improve the corrosion resistance of magnesium matrix composites in SBF and restrain the increase of pH of SBF. Furthermore, the addition of Zn was favorable to improve the corrosion resistance of HA/Mg composites due to the densification of composites and the formation of Mg-Zn alloy matrix.