Biocompatibility Of Magnesium Alloys Research Articles

One-Pot but Two-Step Vapor-Based Amine- and Fluorine-Bearing Dual-Layer Coating for Improving Anticorrosion and Biocompatibility of Magnesium Alloy.

Hydrophobic coating is of great interest to enhance the corrosion resistance of magnesium alloy implants, which always suffer from rapid corrosion that leads to the failing application under physiological conditions. Plasma-polymerized fluorocarbon (C-F) coating has been widely studied as a substrate protection layer; however, the precise control of the deposition rate of C-F coating with fluorinated alkanes has been a challenge. In this study, a thin, uniform, pinhole-free, polymerlike, and hydrophobic C-F coating was successfully prepared using acetylene (C2H2) as a cross-linking agent, which endows the coating with tunable properties of deposition rate by incorporation of unsaturated bonds. Electrochemical corrosion and in vitro immersion test demonstrated that the C-F coating significantly slows down the corrosion rate of MgZnMn in phosphate-buffered saline solution at 37 °C. Furthermore, an additional layer of PPAam was deposited on the C-F coating to eliminate the adverse effect of C-F surface on cytocompatibility. Thus, such a stacked coating imparts MgZnMn with a significantly improved corrosion resistance and promotes cell adhesion and viability. Therefore, the strategy of acetylene-mediated C-F-based coating shows a great potential for tailoring ideal surface functionalities of magnesium-based medical devices.

Fabrication of chitosan/heparinized graphene oxide multilayer coating to improve corrosion resistance and biocompatibility of magnesium alloys.

Due to its good biodegradability and mechanical properties, magnesium alloys are considered as the ideal candidate for the cardiovascular stents. However, the rapid degradation in human physiological environment and the poor biocompatibility seriously limit its application for biomaterials. In the present study, a chitosan/heparinized graphene oxide (Chi/HGO) multilayer coating was constructed on the AZ31B magnesium alloy surface using layer-by-layer (LBL) method to improve the corrosion resistance and biocompatibility. The results of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectrum (RAMAN), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) showed that a dense and compact Chi/HGO multilayer coating was fabricated on the magnesium alloy surface. The results of potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), pH value changes and magnesium ion release suggested that the multilayer coating can significantly enhance the corrosion resistance of the magnesium alloy. Moreover, the Chi/HGO multilayer coating could not only significantly reduce the hemolysis rate and platelet adhesion, but also promote the adhesion and proliferation of endothelial cells. Therefore, the Chi/HGO multilayer coating can simultaneously improve the corrosion resistance and biocompatibility of the magnesium alloys.

Hydroxyapatite Coating on Fluorine-treated Magnesium Alloy by Hydrothermal Method and Its Electrochemical Corrosion Behaviour in Hank’s Solution

In order to improve the corrosion resistance and biocompatibility of magnesium alloys, hydroxyapatite (HA) coating with an outer chrysanthemum-like crystals layer and an inner needle-like crystals layer was successfully prepared on fluorine-treated AZ31 magnesium alloy by hydrothermal treatment. The needle-like crystals was about 1 μm long and grew almost vertically from fluoride conversion film. The inner layer arranged orderly and compactly, while the outer layer was thick but loose. The HA coating increased the open circuit potential, decreased the corrosion current density and improved the Rf and Rct of fluoride coated sample, indicating that the HA coating can delay the degradation of fluoride conversion film and postpone the corrosion of AZ31 alloy in Hank’s solution.

Obtaining of light biocompatible magnesium alloys using levitation equipment under controlled argon atmosphere

The use of resorbable materials to make orthopedic implants is a new direction, with major benefits for both the patient and the surgeon. The purpose of a bioresorbable implant is to support the regeneration and healing of tissues, followed by completely dissolving after its purpose is achieved, being characterized by the biodegradability and biocompatibility capability. Magnesium is a natural element of the human body, the magnesium-based implant having the ability to be fully resorbed without inducing local or systemic toxic effects. Experimental alloys were obtained from 99.5% pure magnesium powders in which alloying elements (Ca) or micro-alloying (La, Ce) were added in the 0.5-5% range to identify the best bio-compatible alloy recipes. The metallurgical process was conducted in an induction melting equipment under a controlled atmosphere of argon, through levitation. The melting time for each alloy weighing 15 g was about 3 minutes, and the electrical parameters varied in the range: Voltage Umf = 480 - 500 V; Current Imf = 55 - 65 A; Frequency fmf = 60 - 70 kHz; Power Pmf = 20 - 35 kW. Following the process, about 10% magnesium losses were obtained, due to the vaporization process. The samples obtained were characterized in terms of chemical composition, microstructure and micro-hardness. The micro-hardness values were ranging from 49 to 87.4 HV0.2.

Microstructure and Corrosion Properties of Calcium Phosphate Coating on Magnesium Alloy Prepared by Hydrothermal Treatment at Various pH Values

Calcium phosphate (Ca-P) coatings were deposited on AZ31 magnesium by hydrothermal treatment at various pH values to improve the corrosion resistance and biocompatibility of magnesium alloys. The crystal phase, morphology and composition of the coatings were investigated by XRD, SEM and EDS, respectively. Electrochemical measurements and immersion tests were performed in Hank's solution to examine the bio-corrosion behaviors of the coated specimens. The results show that the pH value of solutions influences the phase composition and microstructure of the coating. And the degree of protection provided by the Ca-P coating varies with its microstructure. The deposited Ca-P coating treated at pH=6 is composed of OCP (Ca8H2(PO4)6·5H2O). When the pH value increases to 8 and 10, only the HA is formed. The HA coating with nano-scale and rod-like crystals prepared at pH=10 can prevent the penetration of solution more effectively than the OCP coating at pH=6 and the honeycomb-like HA coating at pH=8.

Comparison of calcium phosphate coatings on AZ31 and fluoride-treated AZ31 alloy prepared by hydrothermal method and their electrochemical corrosion behaviour

HA (hydroxyapatite) coating was deposited on AZ31 and the fluoride-treated AZ31 magnesium by hydrothermal treatments in EDTA-Ca and KH2PO4 aqueous solution to improve the corrosion resistance and biocompatibility of magnesium alloys. Crystal phase, morphology and composition of the coatings were investigated by XRD, SEM and EDS, respectively. The electrochemical measurements and immersion tests were carried out in Hank's solution to examine and compare the corrosion behaviours of the coated specimens. HA coating formed on AZ31 alloy consisted of flake-like crystallites, while the coating on fluoride-treated AZ31 magnesium consisted of needle-like crystallites. The HA coatings have two layers. The inner layer is dense and fine-grained, while the outer layer is loose and well-crystallized. Fluoride conversion film with high resistance and low capacitance is more effective than HA coating on delaying the degradation of magnesium alloy. HA coating further increased the open circuit potential and decreased the corrosion current densities of MgF2 coated AZ31, but the Rp of HA/MgF2 coated specimen is a little lower than that of MgF2 coated specimen due to a slight dissolution of fluoride conversion layer during the hydrothermal treatment process. Reducing the dissolution or keeping enough thickness of fluoride conversion film during the hydrothermal treatment could improve the quality of the coating and further postpone the degradation of magnesium alloy.

Effects of nanofeatures induced by severe shot peening (SSP) on mechanical, corrosion and cytocompatibility properties of magnesium alloy AZ31.

A major challenge for most commonly used metals for bio-implants is their non-biodegradability that necessitates revision surgery for implant retrieval when used as fixation plates, screws, etc. Magnesium is reported among the most biocompatible metals that resorb over time without adverse tissue reactions and is indispensable for many biochemical processes in human body. However, fast and uncontrolled degradation of magnesium alloys in the physiological environment in addition to their inadequate mechanical properties especially under repeated loading have limited their application in the biomedical field. The present study providesdata on the effect of a relatively simple surface nanocrystallziation method with high potential to tailor the mechanical and chemical behavior of magnesium based material while maintaining its cytocompatibility.

Improving Corrosion Resistance and Biocompatibility of Magnesium Alloy by Combining Chemical Treatment with Biomolecules Immobilization

Improving Corrosion Resistance and Biocompatibility of Magnesium Alloy by Combining Chemical Treatment with Biomolecules Immobilization

Fracture Properties of Mg-Alloys Assessed with Nanoindentation

This paper deals with micromechanical properties of biocompatible magnesium alloys MgCa0.8 prepared by extrusion. At first, the microstructure, elastic and hardness properties are assessed at the scale of one micrometer by means of a nanoindenter. Further, determination of fracture mechanism, fracture area and fracture toughness of the alloy is studied with sharp indentation, optical microscopy and SEM and by means of energetic methods. Based on the examination of optical images it was concluded that the Mg matrix is not vulnerable to distinct cracking around indents even for high indentation loads. By computations, it was found the fracture area is very small, about 0.7-3% of the tip contact area based on the assumption of limit values of the target fracture toughness 10-20 MPa·m1/2.

Improving Corrosion Resistance and Biocompatibility of Magnesium Alloy by Sodium Hydroxide and Hydrofluoric Acid Treatments

Owing to excellent mechanical property and biodegradation, magnesium-based alloys have been widely investigated for temporary implants such as cardiovascular stent and bone graft; however, the fast biodegradation in physiological environment and the limited surface biocompatibility hinder their clinical applications. In the present study, magnesium alloy was treated by sodium hydroxide (NaOH) and hydrogen fluoride (HF) solutions, respectively, to produce the chemical conversion layers with the aim of improving the corrosion resistance and biocompatibility. The results of attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) indicated that the chemical conversion layers of magnesium hydroxide or magnesium fluoride were obtained successfully. Sodium hydroxide treatment can significantly enhance the surface hydrophilicity while hydrogen fluoride treatment improved the surface hydrophobicity. Both the chemical conversion layers can obviously improve the corrosion resistance of the pristine magnesium alloy. Due to the hydrophobicity of magnesium fluoride, HF-treated magnesium alloy showed the relative better corrosion resistance than that of NaOH-treated substrate. According to the results of hemolysis assay and platelet adhesion, the chemical surface modified samples exhibited improved blood compatibility as compared to the pristine magnesium alloy. Furthermore, the chemical surface modified samples improved cytocompatibility to endothelial cells, the cells had better cell adhesion and proliferative profiles on the modified surfaces. Due to the excellent hydrophilicity, the NaOH-treated substrate displayed better blood compatibility and cytocompatibility to endothelial cells than that of HF-treated sample. It was considered that the method of the present study can be used for the surface modification of the magnesium alloy to enhance the corrosion resistance and biocompatibility.

Enhanced Corrosion Resistance and Biocompatibility of Magnesium Alloy by Mg-Al-Layered Double Hydroxide.

Magnesium (Mg) and its alloys have been suggested as revolutionary biodegradable materials. However, fast degradation hinders its clinic application. To improve the corrosion resistance and biocompatibility of Mg-Nd-Zn-Zr alloy (JDBM), magnesium-aluminum-layered double hydroxide (Mg-Al LDH) was successfully introduced into Mg(OH)2 coating by hydrothermal treatment. The anions in the interlayer of Mg-Al LDH can be replaced by chloride ions, resulting in a relatively low chloride ion concentration near the surface of the coating. The favorable corrosion resistance of the coating was proved by polarization curves and hydrogen collection test. The Mg-Al LDH significantly promoted cell adhesion, migration and proliferation in vitro. In addition, the coating almost fulfilled the request of the clinical application in the hemolysis ratio test. Finally, in vivo results indicated that the coating offered the greatest long-lasting protection from corrosion and triggered the mildest inflammation comparing to the pure Mg(OH)2 coatings and untreated magnesium alloy. Mg(OH)2 coating containing Mg-Al LDH in the present study shows a promising application in improving anticorrosion and biocompatibility of Mg alloys, and might act as a platform for a further modification of Mg alloys ascribed to its special layer structure.

Enhanced corrosion resistance and biocompatibility of AZ31 Mg alloy using PCL/ZnO NPs via electrospinning

In the efforts to improve corrosion resistance and biocompatibility of magnesium alloys, polycarprolactone (PCL) and zinc oxide nanoparticles (ZnO NPs) composite coatings were applied onto AZ31 Mg alloys via electrospinning technique in this study. The PCL/ZnO composite coatings on Mg alloys were characterized by using FE-SEM, EDX, XPS, and FT-IR. Moreover, coating adhesion test, electrochemical corrosion test, and biocompatibility test in vitro were performed to measure coating performance. Our results revealed that the increase in the content of ZnO NPs in the composite coatings not only improved the coating adhesion of composite coatings on Mg alloys, but also increased the corrosion resistance. Furthermore, the biocompatibility of MC3T3-E1 osteoblasts of the PCL/ZnO composite coated samples was superior to the biocompatibility of the bare samples. Such data suggest that applying PCL/ZnO composite coating to the magnesium alloys has suitable potential in biomedical applications.

Novel biocompatible magnesium alloys design with nutrient alloying elements Si, Ca and Sr: Structure and properties characterization

Magnesium has been widely studied as a biodegradable material, where its mechanical property and biocompatibility make it preferred candidate for orthopedic implant. Proper alloying can further improve the properties of Mg. First and foremost, to guarantee the biosafety for biomedical application, the alloying element should be toxic free. To address this point, nutrient elements including Si, Sr and Ca were selected due to their biological functions in human body, especially in bone regeneration and repair. In this study, 0.5–1.0wt% Sr and Ca were used to refine and modify the morphology of coarse Mg2Si in Mg-1.38wt% Si to obtain an uniform microstructure. Microstructure, mechanical and degradation properties of as-cast and homogenizing-annealed quaternary Mg-1.38Si-xSr-yCa (x,y=0.5–1wt%) alloys were investigated by optical microscopy, scanning electronic microscopy, X-ray diffraction, tensile and electrochemical measurement. Addition of Sr and Ca element cause a morphological change in Mg2Si particles from coarse Chinese script shape to small polygonal type. The presences of intermetallic phases, such as Mg2Si, CaMgSi and Mg17Sr2, were confirmed in quaternary alloys, of which content was applied to interpret the results for the quaternary system. Compared with the as-cast state, fewer, finer and homogenized microstructure were observed after an anneal heat treatment under 500°C. The mechanical properties were improved with increase of Ca and Sr additions, which was related to the evolution of the microstructure and second phases, however, also causing an increase of corrosion rate due to the galvanic-corrosion at the same time. The cytocompatibility results revealed that the Mg-Si-Sr-Ca alloys promote the proliferation of preosteoblasts and exhibit cytotoxicity of Grade 0–1, indicating their acceptable biosafety and potential for the orthopedic applications.

MgNd2 alloy in contact with nasal mucosa: an in vivo and in vitro approach.

Biodegradable and biocompatible magnesium alloys appear to be very promising not only for temporary clinical application but also for developing deformable and degradable medical implants. This study analyzes the in vivo degradation behavior and the impact on the paranasal sinuses of the highly ductile Mg-2wt%Nd alloy (MgNd2) in order to provide a basis for a satisfying stent system for the therapy of a chronic sinusitis. Moreover, in vitro tests were carried out on primary porcine nasal epithelial cells (PNEC). For the in vivo tests, cylindrical MgNd2 specimens were implanted into the sinus' mucosa of minipigs. During and after a total period of 180days the long-term biodegradation and biocompatibility properties after direct contact with the physiological tissue were analyzed. Biodegradation was investigated by measuring the mass and volume losses of the MgNd2 specimens as well as by performing element analyses to obtain information about the degradation layer. The influence on the surrounding tissue of paranasal sinuses was evaluated by endoscopic and histopathological examinations of the mucosa. Here, only a locally unspecific chronic infection was found. The degradation rate showed a maximum after 45days postsurgery and was determined to decrease subsequently. In vitro experiments using PNEC showed adequate biocompatibility of MgNd2. This study demonstrates a good in vivo biocompatibility for MgNd2 in the system of paranasal sinuses and underlines the promising properties of alloy MgNd2 for biodegradable nasal stent applications.

Biodegradable Materials for Clinical Applications: A Review

This review article focuses on mechanical properties and composition of degradable polymer, metal (magnesium), ceramic and composite materials with respect to clinical application involving cortical/cancellous bone, dentin and enamel, and ligament, tendon and fascia. On the basis of mechanical property comparison, each class of densified material may be used to substitute cortical bone, may not be used to substitute cancellous bone, may be used to substitute enamel and dentin, may be used to substitute lower limb ligaments and tendons, and may be used to substitute selected upper limb and trunk ligaments and associated tissues. For relatively longer times of recovery from more severe orthopedic trauma, PLLA (poly L-lactic acid) and TMC (trimethyl carbonate) polymers, selected Mg alloys containing zinc (Zn), calcium (Ca) and/or rare-earth (RE) elements, or hydroxyapatite (HA) and tricalcium phosphate (TCP) as crystalline bioceramics apparently are most suitable. Mg alloys or composites have significant potential for clinical application where the ability to bear appropriate load at least in the initial stages of recovery prior to significant resorption and load transfer to new tissue is critical. However, there is no clear opinion at present regarding the toxicity levels of many alloying elements in Mg alloys, particularly concerning RE elements. There is also the potential issue of nanoparticle cytotoxicity concerning alloy nanocomposite degradation invivo. Compared to crystalline bioceramics, the higher index of bioactivity (IB) of amorphous glasses and glass ceramics reflects their superior ability to form a dense interphase and bond strongly with bone, despite their mechanical inferiority. The combination of bioceramic and biodegradable polymer is synergistic based on direct improvement of mechanical property and degradation resistance of the polymer, indirect reduction of foreign body interactions, and direct increase in toughness of the ceramic. Future directions of this field regarding developments on cellulose as a biodegradable material, bone tissue regeneration and engineering, stronger and more corrosion resistant and biocompatible magnesium alloy systems, applicable nanoparticles and nanotechnology, and soft tissue engineering such as vascular tissue engineering are also addressed.

In vitro and in vivo studies on biodegradable magnesium alloy

The microstructure, mechanical property, electrochemical behavior and biocompatibility of magnesium alloy (BioDe MSM™) were studied in the present work. The experimental results demonstrated that grain refining induced by extrusion improves the alloy strength significantly from 162MPa for the as-cast alloy to 241MPa for the as-extruded one. The anticorrosion properties of the as-extruded alloy also increased. Furthermore, the hemolysis ratio was decreased from 4.7% for the as-cast alloy to 2.9% for the as-extruded one, both below 5%. BioDe MSM™ alloy shows good biocompatibility after being implanted into the dorsal muscle and the femoral shaft of the New Zealand rabbit, respectively, and there are no abnormalities after short-term implantation. In vivo observation indicated that the corrosion rate of this alloy varies with different implantation positions, with higher degradation rate in the femur than in the muscle.

Influence of shot peening on corrosion properties of biocompatible magnesium alloy AZ31 coated by dicalcium phosphate dihydrate (DCPD)

Magnesium alloys are promising materials for biomedical applications because of many outstanding properties like biodegradation, bioactivity and their specific density and Young's modulus are closer to bone than the commonly used metallic implant materials. Unfortunately their fatigue properties and low corrosion resistance negatively influenced their application possibilities in the field of biomedicine. These problems could be diminished through appropriate surface treatments. This study evaluates the influence of a surface pre-treatment by shot peening and shot peening+coating on the corrosion properties of magnesium alloy AZ31. The dicalcium phosphate dihydrate coating (DCPD) was electrochemically deposited in a solution containing 0.1M Ca(NO3)2, 0.06M NH4H2PO4 and 10mL/L of H2O2. The effect of shot peening on the surface properties of magnesium alloy was evaluated by microhardness and surface roughness measurements. The influence of the shot peening and dicalcium phosphate dihydrate layer on the electrochemical characteristics of AZ31 magnesium alloy was evaluated by potentiodynamic measurements and electrochemical impedance spectroscopy in 0.9% NaCl solution at a temperature of 22±1°C. The obtained results were analyzed by the Tafel-extrapolation method and equivalent circuit method. The results showed that the application of shot peening process followed by DCPD coating improves the properties of the AZ31 surface from corrosion and mechanical point of view.

FEM‐BEM Code for the Multiscale Modeling and Computer Aided Design of Wire Drawing Technology for Magnesium Alloys

The purpose of the paper is the problem of determination of parameters of hyperfine wire drawing process of biocompatible magnesium alloys. The originality of the considered alloys is the intergranular fracture mechanism associated with small strains (0.07–0.09) in macro‐scale. It was proven that the material state just before appearance of the meso‐cracks is the optimal state of material from the point of view of the restoration of the plasticity by annealing. The forecasting of this material state during drawing process requires the development of the model of intergranular fracture. In this case, new BEM model of the cracks initiation in meso‐scale is proposed. The in situ tests, which allowed observation of the microstructure during deformation, are used for the calibration and validation of the present model. The empirical parameters of the fracture model in micro‐scale for MgCa0.8 and Ax30 magnesium alloys are obtained using tensile and share tests. The developed model was implemented to the Drawing 2d software. The results of meso‐scale simulation were verified by using the experimental drawing process of the hyperfine wires (diameter 70 µm) according to developed technology.

Numerical and Experimental Analysis of Wire Drawing for Hardly Deformable Biocompatible Magnesium Alloys / Numeryczna I Doswiadczalna Analiza Ciagnienia Drutu Z Trudno Odkształcalnych Biozgodnych Stopów Magnezu

In the present paper the drawing processes of thin wire of biocompatible magnesium alloys in heated die was investigated. Due to the hexagonal close packet structure magnesium alloys have low plasticity. In order to design the technological parameters the FEM model of wire drawing process in heated die and models of yield stress and ductility were developed. The relationship between technological parameters of drawing and fracture parameters was obtained based on developed models. The maps of possible elongation for MgCa0.8 and Ax30 magnesium alloys were developed using simulations. The draft schedule for final wire diameter 0.1 mm was design assisted with FEM model in experimental part of work. Based on this draft plan the drawing process from initial diameter 1.0 mm to final diameter 0.1 mm in heated die was performed in designed by author’s device.

The Physical and Numerical Mesoscale Modeling of Cold Wire Drawing Process of Hardly Deformable Biocompatible Magnesium Alloys / Fizyczne I Numeryczne Modelowanie W Mezo Skali Procesu Ciągnienia Na Zimno Trudno Odkształcalnych Stopów Magnezu O Podwyższonej Biozgodności

The problem of determination of the cold low diameter wire (diameter less than 0.1mm) drawing process parameters for hardly deformable biocompatible magnesium alloys by using the mathematical mesoscale model is described in the paper. The originality of the considered alloys (MgCa0.8, A×30) is the intergranular fracture mechanism associated with small strains (0.07-0.09). In previous authors works it was proven that the material state directly before appearance of the microcracks is in the optimal state from the point of view of the recovery of the plasticity by annealing. The forecasting of this material state in drawing process requires the development of the model of intergranular fracture initiation and using this model in two cases: - modeling of the in-situ tests, what allows calibrating and validating of the model; - modeling of the drawing process, what allows optimizing of the drawing parameters. A new model of the microcracks initiation in mesoscale using the boundary element method is proposed. The in-situ tests, which allowed observing the microstructure evolution during deformation, are used for the calibration and validation purpose. The model was implemented into self-developed FE software Drawing2d, which is dedicated to the drawing process. The results of mesoscale simulation were verified by the experimental drawing process of 0.07 mm diameter wires according to developed technology. It was shown by analysis of microstructure that the model allows forecasting the microcracks initiation during the wire drawing process.