Degradation Of Magnesium Alloy Research Articles

Enhanced corrosion resistance and cytocompatibility of biodegradable Mg alloys by introduction of Mg(OH)2 particles into poly (L-lactic acid) coating

A strategy of suppressing the fast degradation behaviour of Mg-based biomaterials by the introduction of one of Mg degradation products Mg(OH)2 was proposed according to the following degradation mechanism, Mg + 2H2O ⇋ Mg(OH)2 + H2↑. Specifically, Mg(OH)2 submicron particles were mixed into poly (L-lactic acid) (PLLA) to synthesize a composite coating onto hydrofluoric acid-pretreated Mg-Nd-Zn-Zr alloy. The in vitro degradation investigations showed that the addition of Mg(OH)2 particles not only slowed down the corrosion of Mg matrix, but also retarded the formation of gas pockets underneath the polymer coating. Correspondingly, cytocompatibility results exhibited significant improvement of proliferation of endothelial cells, and further insights was gained into the mechanisms how the introduction of Mg(OH)2 particles into PLLA coating affected the magnesium alloy degradation and cytocompatibility. The present study provided a promising surface modification strategy to tailor the degradation behaviour of Mg-based biomaterials.

In vivo degradation of magnesium alloys and poly (lactic-co-glycolic acid) and degradation evaluation of magnesium alloys using micro-ct

?To explore the degradation of AZ31 magnesium alloy and poly (lactic-co-glycolic acid) (PLGA) in the femoral condyle, and then evaluate the laws of degradation of AZ31 magnesium alloy by Micro-CT images and data. ?Forty 3-month-old male New Zealand white rabbits (weighing, 2.5 kg) were randomly divided into 4 groups, 10 rabbits each group. Forty micro-arc-oxidized AZ31 magnesium alloy pins and 40 PLGA pins were implanted into the right and left femoral condyle, respectively. Micro-CT images and data analysis were used to evaluate the degradation at 4, 8, 12, and 16 weeks after operation (n=10). Degradation was evaluated by weight difference between pre-and post-implantation. The inflammatory response was observed around the implants by HE staining. The weight loss of magnesium alloy and Micro-CT results were compared. ?The Micro-CT images showed that PLGA pins had gray low signal, which was similar to the soft tissue around. At 4 weeks after operation, no signs of degradation were observed, and there were little corrosion pitting on the magnesium alloy. At 8 weeks, corrosion pitting gradually expanded, the boundary between the longitudinal axis and the cross section became blurred; at 16 weeks, corrosion pitting became bigger, and the boundary was discontinuous. Micro-CT quantitative analysis showed that the volume fraction of magnesium pins decreased slowly at 4 and 8 weeks; it was significantly lower at 12 and 16 weeks than 4 and 8 weeks (P<0.05). The magnesium cylinder mineral density continuously decreased during the study period, it had a rapidly speed from 12 to 16 weeks (P<0.05). However, the magnesium CT image density showed a slight change (P>0.05). The surface-to-volume ratio of the pins constantly increased, and the ratio was significantly larger at 12 and 16 weeks than 4 and 8 weeks, and at 16 weeks than 12 weeks (P<0.05). There was more and more corrosion pitting on the surface with time, which resulted in a decrease in the radius that mean trabecular thickness gradually decreased, showing significant difference between different time points after 8 weeks (P<0.05). The weight loss detection showed that the degradation of magnesium pin and PLGA gradually increased with time (P<0.05), and the degradation rate of magnesium pin was significantly lower than that of PLGA at 8-12 weeks (P<0.05), but the degradation rate of magnesium pin was higher than that of PLGA at 16 weeks. At each time point, the weight loss of magnesium alloy was similar to that by Micro-CT, but mass fraction was lower than volume fraction and had significant differences at 8, 12, and 16 weeks (P<0.05). HE staining revealed that slight inflammatory response was observed around the magnesium pins at 4 weeks, and inflammatory reaction gradually reduced with time and disappeared at 16 weeks, but no inflammatory reaction was seen around PLGA. ?Micro-CT has the advantages of non-trauma, in vivo detection, quantitative analysis, and precise data in evaluating the degradation of AZ31 magnesium alloy. Regarding the degradation of the magnesium alloy and PLGA in vivo, the degradation rate is slow in the early stage, and then increases with time. The degradation of PLGA is faster and earlier but it is then overtaken by AZ31 magnesium alloy at 16 weeks. During the degradation, the density of the magnesium has almost no change. The biomaterials can not firmly attach to the surrounding tissues due to inadequate holding forces.

Study of antibacterial performance of Mg-Cu alloy on Porphyromonas gingivalis

Event Abstract Back to Event Study of antibacterial performance of Mg-Cu alloy on Porphyromonas gingivalis Xue Zhao1*, Peng Wan2*, Ke Yang2* and Yaping Pan1* 1 China Medical University, School of Stomatology, China 2 Chinese Academy of Sciences, Institute of Metal Research, China Introduction: Bone grafts are widely used in periodontal surgery, such as periodontal regeneration, socket preservation, peri-implant defects, and alveolar bone augmentation. The possibility to reconstruct an infrabony periodontal defect or a resorbed edentulous ridge, or to prevent the resorption of the extraction socket, represents a significant improvement in the treatment of clinical conditions. An ideal bone graft material should be biocompatible, biosafe, non-allergenic, non-toxic, and no risk of disease transmission. It should also have enough mechanical strength for space maintenance and be easy to manipulate during surgical phases. Magnesium alloys are presently investigated as potential implant materials for their good biocompatibility, osteogenesis and biodegradability[1]. More importantly, magnesium has been reported to have antibacterial activity and could therefore be used to prevent implant infections. Degradation of magnesium alloys in the body can locally produce alkaline environment to kill bacteria. But the body fluid will soon neutralize the alkaline and thus reduce the antibacterial effect. Hence a novel Mg-Cu alloy is designed to combine the favorable properties of magnesium with the well-known antibacterial performance of copper ions[3]. Porphyromonas gingivalis is one of the most important periodontal pathogen bacteria. Periodontal doctors can only rely on a large number of antibiotics to prevent postoperative infections[2]. However, the abuse of antibiotics has become a worldwide problem. Therefore, Mg-Cu alloy as a new type of antibacterial bone graft has great research value. In this study, three Mg-Cu alloys with different Cu content, Mg-0.05Cu, Mg-0.2Cu and Mg-0.5Cu, respectively, were studied in order to provide relevant experimental evidence for future application. Methods: Materials: Material extract solution was made according to ISO10993-5. Mg-Cu alloys were immersed separately in brain-heart infusion broth (BHI) for 3h, 6h, 12h, 24h and 48h, and then the alloy extract solution was obtained. Antibacterial test: The strain used in this study was Porphyromonas gingivalis ATCC33277. Bacterial suspension (1×109CFU/ml) was added to material extract solution in a proportion of 1:100, and the mixture was incubated anaerobically for 24h. Then the cell suspension was cultivated on a BHI agar plate. The bacteria cells were enumerated after incubation for 7-10 days. Real-time quantitative PCR (qPCR) analysis was performed to enumerate the definitive qualification of bacteria DNA, and then to calculate the concentration of bacteria in the material extract solution through the standard curve. Results: The antimicrobial activities of Mg-Cu alloys were compared with pure Mg (Fig 1). The 3h extract solution of Mg-Cu alloy showed fast killing rate, and the 24h extract solution achieved nearly 100% killing. While the 12h extract solution of pure Mg showed fast killing rate. In the study of the inhibitory abilities of Mg-Cu alloy and Mg through Real-time PCR, the bacterial concentration through standard curve was calculated (Fig 2). The results showed that the ability of Mg-Cu alloy to inhibit bacteria growth was much stronger than that of pure Mg. But the difference among three Mg-Cu alloys was not much obvious. Conclusion: Mg-Cu alloy has stronger antiseptic effect to Porphyromonas gingivalis than pure Mg, which will have more value in dental application.

Influence of Surrounding Cations on the Surface Degradation of Magnesium Alloy Implants under a Compressive Pressure.

The effect of cations in the surrounding solutions on the surface degradation of magnesium alloys, a well-recognized biodegradable biomaterial, has been neglected compared with the effect of anions in the past. To better simulate the compressive environment where magnesium alloys are implanted into the body as a cardiovascular stent, a device is designed and employed in the test so that a pressure, equivalent to the vascular pressure, can be directly applied to the magnesium alloy implants when the alloys are immersed in a medium containing one of the cations (K(+), Na(+), Ca(2+), and Mg(2+)) found in blood plasma. The surface degradation behaviors of the magnesium alloys in the immersion test are then investigated using hydrogen evolution, mass loss determination, electron microscopy, pH value, and potentiodynamic measurements. The cations are found to promote the surface degradation of the magnesium alloys with the degree decreased in the order of K(+) > Na(+) > Ca(2+) > Mg(2+). The possible mechanism of the effects of the cations on the surface degradation is also discussed. This study will allow us to predict the surface degradation of magnesium alloys in the physiological environment and to promote the further development of magnesium alloys as biodegradable biomaterials.

Influence of Magnesium Alloy Degradation on Undifferentiated Human Cells.

BackgroundMagnesium alloys are of particular interest in medical science since they provide compatible mechanical properties with those of the cortical bone and, depending on the alloying elements, they have the capability to tailor the degradation rate in physiological conditions, providing alternative bioresorbable materials for bone applications. The present study investigates the in vitro short-term response of human undifferentiated cells on three magnesium alloys and high-purity magnesium (Mg).Materials and MethodsThe degradation parameters of magnesium-silver (Mg2Ag), magnesium-gadolinium (Mg10Gd) and magnesium-rare-earth (Mg4Y3RE) alloys were analysed after 1, 2, and 3 days of incubation in cell culture medium under cell culture condition. Changes in cell viability and cell adhesion were evaluated by culturing human umbilical cord perivascular cells on corroded Mg materials to examine how the degradation influences the cellular development.Results and ConclusionsThe pH and osmolality of the medium increased with increasing degradation rate and it was found to be most pronounced for Mg4Y3RE alloy. The biological observations showed that HUCPV exhibited a more homogeneous cell growth on Mg alloys compared to high-purity Mg, where they showed a clustered morphology. Moreover, cells exhibited a slightly higher density on Mg2Ag and Mg10Gd in comparison to Mg4Y3RE, due to the lower alkalinisation and osmolality of the incubation medium. However, cells grown on Mg10Gd and Mg4Y3RE generated more developed and healthy cellular structures that allowed them to better adhere to the surface. This can be attributable to a more stable and homogeneous degradation of the outer surface with respect to the incubation time.

The effect of anodized Ti on output performance of biomedical compatible triboelectric nanogenerators used for controlling the degradation of Mg-3wt%Zn-0.8wt%Zr

Triboelectric nanogenerators (TENGs) can convert amorphous mechanical energy into electrical energy and solve the issue of source power for biological electronics implanted in the human body. Biomedical metal Ti was selected as the bottom plate, to fabricate a TENG with a poly-L-lactic-acid (PLLA) Ti structure. The Ti sheets were treated with a two-step anodization method, and the growth of titanium dioxide nanotube arrays (TNTAs) was controlled by variation in anodic oxidation time. The results showed that the output voltage and current of the PLLA-TNTAs biocompatible triboelectric nanogenerator (BCTENG), prepared by the two-step anodization method under 60 V for 6 h, can reach 220.6 V and 15.1 μA, respectively. The output voltage and current increased by 96.3% and 91.1%, respectively, compared with TENGs prepared without using the anode oxidation method. The choice of materials and modification of the surface morphology of the TENG components was found to be critical for increasing the triboelectrically generated surface charge. The output of the BCTENG can regulate degradation of magnesium alloys freely by using cathodic protection.

Magnesium Modeling Using SolidWorks

Increased cost and complexity associated with orthopaedic surgeries has led to advancements in degradable materials. Degradable metals like magnesium have shown great promise as magnesium based alloys provide the strength of metals but the degradability of polymers. As the development of degradable magnesium alloys expands there is a significant need for simplified computational models that can account for the numerous mechanical changes associated with degradation. The current study examined initial in silico models of Magnesium samples to gain insight on how degradation impacts mechanical performance over time. Models of magnesium rods were created and analyzed using the finite element analysis functionality in a commercially available software package.  SolidWorks is widely known for its design capabilities and generation of 3D solid models; however its analyses capabilities would be useful for such a smart material, like magnesium.  Therefore, this work explores the analysis capabilities of SolidWorks, for degradable magnesium in a skeletal environment.

In vitro and in vivo studies of biodegradable fine grained AZ31 magnesium alloy produced by equal channel angular pressing

The objective of the present work is to investigate the role of different grain sizes produced by equal channel angular pressing (ECAP) on the degradation behavior of magnesium alloy using in vitro and in vivo studies. Commercially available AZ31 magnesium alloy was selected and processed by ECAP at 300°C for up to four passes using route Bc. Grain refinement from a starting size of 46μm to a grain size distribution of 1–5μm was successfully achieved after the 4th pass. Wettability of ECAPed samples assessed by contact angle measurements was found to increase due to the fine grain structure. In vitro degradation and bioactivity of the samples studied by immersing in super saturated simulated body fluid (SBF 5×) showed rapid mineralization within 24h due to the increased wettability in fine grained AZ31 Mg alloy. Corrosion behavior of the samples assessed by weight loss and electrochemical tests conducted in SBF 5× clearly showed the prominent role of enhanced mineral deposition on ECAPed AZ31 Mg in controlling the abnormal degradation. Cytotoxicity studies by MTT colorimetric assay showed that all the samples are viable. Additionally, cell adhesion was excellent for ECAPed samples particularly for the 3rd and 4th pass samples. In vivo experiments conducted using New Zealand White rabbits clearly showed lower degradation rate for ECAPed sample compared with annealed AZ31 Mg alloy and all the samples showed biocompatibility and no health abnormalities were noticed in the animals after 60days of in vivo studies. These results suggest that the grain size plays an important role in degradation management of magnesium alloys and ECAP technique can be adopted to achieve fine grain structures for developing degradable magnesium alloys for biomedical applications.

The influence of storage and heat treatment on a magnesium-based implant material: an in vitro and in vivo study.

BackgroundMagnesium alloys are recommended as a potential material for osteosynthesis. It is known that storage-induced property modifications can occur in materials like aluminum. Thus the aim of this study was to analyze the influence of storage durations of up to 48 weeks on the biomechanical, structural, and degradation properties of the degradable magnesium alloy LAE442.MethodsExtruded implants (n = 104; Ø 2.5 mm × 25 mm) were investigated after storage periods of 0, 12, 24, and 48 weeks in three different sub-studies: (I) immediately after the respective storage duration and after an additional (II) 56 days of in vitro corrosion in simulated body fluid (SFB), and (III) 48 weeks in vivo corrosion in a rabbit model, respectively. In addition, the influence of a T5-heat treatment (206 °C for 15 h in an argon atmosphere) was tested (n = 26; 0 week of storage). Evaluation was performed by three-point bending, scanning electron microscopy, radiography, µ-computed tomography, evaluation of the mean grain size, and contrast analysis of precipitations (such as aluminum or lithium).ResultsThe heat treatment induced a significant reduction in initial stability, and enhanced the corrosion resistance. In vivo experiments showed a good biocompatibility for all implants. During the storage of up to 48 weeks, no significant changes occurred in the implant properties.ConclusionsLAE442 implants can be safely used after up to 48 weeks of storage.

Corrosion behavior, biocompatibility and biomechanical stability of a prototype magnesium-based biodegradable intramedullary nailing system

Implants made of degradable magnesium alloys are a potential alternative to conventional orthopaedic implant materials, e.g. stainless steel or titanium. Intramedullary nails made of the magnesium alloy LAE442 were subjected to cyclic fatigue tests in both distilled water and Hank's Balanced Salt Solution (HBSS) at 37.5°C until implant failure or a limit of 500,000cycles was reached. In distilled water, four of the five nails were still intact after the end of the biomechanical test. In HBSS, a breakage within the first 70,000 bending cycles was observed. Additionally, the degradation rate of this alloy was determined in HBSS according to the weight loss method (0.24±0.12mmyear−1) and based on gas release (0.21±0.03mmyear−1) with a standard eudiometer. A cytotoxicity test with L929 cells was carried out in accordance with EN ISO 10993-5/12. This test demonstrated sufficient cell viability of the diluted extracts (50%, 25% and 12.5%). The relative metabolic activity of the 100% extract was reduced slightly below 70%, which is classified as a threshold value for cytotoxicity. In conclusion, this in vitro study indicates that intramedullary nails made of LAE442 may not have the required fatigue resistance for load-bearing applications and the development of a corrosion-protective coating may be necessary to prevent early failure of the implant.

Effects of extracellular magnesium extract on the proliferation and differentiation of human osteoblasts and osteoclasts in coculture

Coculture of osteoblasts and osteoclasts is a subject of interest in the understanding of how magnesium (Mg)-based implants influence the bone metabolism and remodeling upon degradation. Human telomerase reverse transcriptase (hTERT) transduced mesenchymal stem cells (SCP-1) were first differentiated into osteoblasts with osteogenic supplements and then further cocultured with peripheral blood mononucleated cells (PBMC) without the addition of osteoclastogenesis promoting factors. Concomitantly, the cultures were exposed to variable Mg extract dilutions (0, 30×, 10×, 5×, 3×, 2× and 1×). Phenotype characterization documented that while 2× dilution of Mg extract was extremely toxic to osteoclast monoculture, monocytes in coculture with osteoblasts exhibited a greater tolerance to higher Mg extract concentration. The dense growth of osteoblasts in cultures with 1× dilution of Mg extract suggested that high concentration of Mg extract promoted osteoblast proliferation/differentiation behavior. The results of intracellular alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP) activities as well as protein and gene expressions of receptor activator of nuclear factor kappa-B ligand (RANKL), macrophage colony-stimulating factor (M-CSF), and osteoclast-associated receptor (OSCAR) revealed significantly enhanced formation of osteoblasts whereas decreased osteoclastogenesis in the cultures with high concentrations of Mg extract (2× and 1× dilutions). In conclusion, while an increased osteoinductivity has been demonstrated, the impact of potentially decreased osteoclastogenesis around the Mg-based implants should be also taken into account. Cocultures containing both bone-forming osteoblasts and bone-resorbing osteoclasts should be preferentially performed for in vitro cytocompatibility assessment of Mg-based implants as they more closely mimic the in vivo environment. Statement of SignificanceAn attractive human osteoblasts and osteoclasts cocultivation regime was developed as an in vitro cytocompatibility model for magnesium implants. Parameters in terms of cellular proliferation and differentiation behaviors were investigated and we conclude that high concentration of magnesium extract could lead to a promotion in osteoblastogenesis but an inhibition in osteoclastogenesis. It could contribute to the repeated observations of enhanced bone growth adjacent to degradable magnesium alloys. More interestingly, it demonstrates that compared to monoculture, osteoclasts in cocultures with osteoblasts exhibited higher tolerance to the culture environment with high magnesium extract. It might attribute to the neutralization process of the alkaline medium by acid generated by increased amount of osteoblasts in the condition with high concentration of Mg extract. The submitted work could be of significant importance to other researchers working in the related field(s), thus appealing to the readership of Acta Biomaterialia.

Electrochemical characterization and in-vitro bio-assessment of AZ31B and AZ91E alloys as biodegradable implant materials.

The degradation of magnesium alloys, AZ31B and AZ91E, are under review due to a their ability to degrade under physiological conditions and successively yield an oxidized biocompatible by-product which can safely be absorbed by the body. By exploiting the biodegradability of magnesium alloys, the prospects of developing an unprecedented class of implant are at hand. To do so however, the rate of corrosion of the alloys must be modified in order to better suit physiological conditions. Therefore, anodization was carried out on AZ31B and AZ91E specimens to alter the surface chemistry to reduce the corrosion rates and improve biocompatibility. Scanning electron microscopy, energy dispersive spectroscopy, atomic force microscopy and contact angle meter, were used to characterize and compare the surfaces of untreated and anodized magnesium alloys. Corrosion behavior was evaluated by electrochemical tests using potentiodynamic polarization and electrochemical impedance spectroscopy, to verify changes in corrosion rates as a result of anodization. Finally, a bio-assessment using MTS assays and fluorescent microscopy were carried out to ensure that the anodization process had no compromise on the biocompatibility of the magnesium alloys. The study indicated that the anodization process did alter the surface chemistry of the alloys, yielding slower corrosion rates, while causing no adverse effects in regards to biocompatibility.

Corrosion Effects of Electrolytic Biocomposites Coated Magnesium on Endolithial Cell Viability

Though the degradable magnesium alloy used to construct an absorbable stent could be another candidate, its poor corrosion resistance is relatively a serious impediment against wider applications of magnesium alloy[1]. In this study, the coatings of zirconia (ZrO2) bottom layer and calcium phosphate (CaP) top layer are carried out on pure magnesium specimens by electrolytic deposition and subsequent annealing, leading to the corrosion current density reduced from 13.3 to 3.86 μA/cm2 derived by potentiodynamic polarization tests in artificial blood plasma at 37 °C. Furthermore, calcium phosphate (CaP), gelatin (Gel) and heparin (Hep) are co-deposited on post CaP/ZrO2 coated specimens in order to fabricate the heparin sustaining release system for promoting the hemocompatibility of magnesium. Heparin loaded composite coatings are analyzed by X-Ray diffractometry (XRD), field emission scanning electron microscope (FESEM), focused ion beam (FIB) system, toluidine blue colorimetric assay, UV-visible spectrometer, and indirect endothelial cell viability tests. The drug content increases from 243.56±55.18 μg/cm2 for single layer (CaP-Hep) to 484.19±19.26 μg/cm2 for multilayer (CaP-Gel-Hep/CaP-Hep/CaP/ZrO2) and the sustaining release of the latter lasting for more than 28 days compared with that of the former for 1 day in PBS solution. The cell viability, related to Mg2+ ions in medium extracts which are still toxic to endothelial cells at high concentrations, is 63 % for the uncoated, 97 % for the ZrO2 coated, and 110 % for the CaP/ZrO2 and CaP-Gel-Hep/CaP-Hep/CaP/ZrO2 coated specimens compared with 100 % for the negative control. All results indicate that ZrO2 coated, CaP/ZrO2 coated, and CaP-Gel-Hep/CaP-Hep/CaP/ZrO2coated magnesium specimens are potential for biodegradable cardiovascular stents. Acknowlegement The authors are grateful for the support of this research by the National Science Council,Republic of China (Taiwan) under contract No. NSC 102-2221-E-005-027-MY3. [1]M.J. Wang, C.F. Li, S.K. Yen, Electrolytic MgO/ZrO2 duplex-layer coating on AZ91D magnesium alloy for corrosion resistance, Corrosion Science, 76 (2013) 142-153.

In vivo study of magnesium plate and screw degradation and bone fracture healing

Each year, millions of Americans suffer bone fractures, often requiring internal fixation. Current devices, like plates and screws, are made with permanent metals or resorbable polymers. Permanent metals provide strength and biocompatibility, but cause long-term complications and may require removal. Resorbable polymers reduce long-term complications, but are unsuitable for many load-bearing applications. To mitigate complications, degradable magnesium (Mg) alloys are being developed for craniofacial and orthopedic applications. Their combination of strength and degradation make them ideal for bone fixation. Previously, we conducted a pilot study comparing Mg and titanium devices with a rabbit ulna fracture model. We observed Mg device degradation, with uninhibited healing. Interestingly, we observed bone formation around degrading Mg, but not titanium, devices. These results highlighted the potential for these fixation devices. To better assess their efficacy, we conducted a more thorough study assessing 99.9% Mg devices in a similar rabbit ulna fracture model. Device degradation, fracture healing, and bone formation were evaluated using microcomputed tomography, histology and biomechanical tests. We observed device degradation throughout, and calculated a corrosion rate of 0.40±0.04mm/year after 8weeks. In addition, we observed fracture healing by 8weeks, and maturation after 16weeks. In accordance with our pilot study, we observed bone formation surrounding Mg devices, with complete overgrowth by 16weeks. Bend tests revealed no difference in flexural load of healed ulnae with Mg devices compared to intact ulnae. These data suggest that Mg devices provide stabilization to facilitate healing, while degrading and stimulating new bone formation.

Tribocorrosion behaviors of AlN/MoS2–phenolic resin duplex coatings on nitrogen implanted magnesium alloys

Nitrogen ion implantation and AlN/MoS2–phenolic resin duplex coating are designed to improve wear and corrosion resistance of magnesium alloys. The microstructure and tribocorrosion behaviors of as-fabricated coatings are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), tribocorrosion and electrochemical tests. Studies show that Cl ions induce severe corrosion degradation of magnesium alloy during the tribocorrosion test. MoS2–phenolic resin coating has two phase composite structure consisting of MoS2 crystalline and phenolic resin, but this coating shows poor tribocorrosion resistance because force–corrosion synergy interaction accelerates the degradation process. The introduction of nitrogen ion implantation and AlN interlayer remarkably retards the corrosion degradation process of magnesium alloy. AlN/MoS2–phenolic resin duplex coating exhibits better tribocorrosion resistance. These present results indicating that gradient duplex coating might be a good candidate as protective coating in engineering applications of magnesium alloys.

Testing the in vitro performance of hydroxyapatite coated magnesium (AZ91D) and titanium concerning cell adhesion and osteogenic differentiation

AbstractIn the current study the in vitro outcome of a degradable magnesium alloy (AZ91D) and standard titanium modified by nanostructured-hydroxyapatite (n-HA) coatings concerning cell adhesion and osteogenic differentiation was investigated by direct cell culture. The n-HA modification was prepared via radio-frequency magnetron sputtering deposition and proven by field emission scanning electron microscopy and X-ray powder diffraction patterns revealing a homogenous surface coating. Human mesenchymal stem cell (hMSCs) adhesion was examined after one and 14 days displaying an enhanced initial cell adhesion on the n-HA modified samples. The osteogenic lineage commitment of the cells was determined by alkaline phosphatase (ALP) quantification. On day one n-HA coated AZ91D exhibited a comparable ALP expression to standard tissue culture polystyrene samples. However, after 14 days solely little DNA and ALP amounts were measurable on n-HA coated AZ91D due to the lack of adherent cells. Titanium displayed excellent cell adhesion properties and ALP was detectable after 14 days. An increased pH of the culture was measured for AZ91D as well as for n-HA coated AZ91D. We conclude that n-HA modification improves initial cell attachment on AZ91D within the first 24 h. However, the effect does not persist for 14 days in in vitro conditions.

Experimental research on degradation performance of magnesium alloy affected by mechanical environment

Objective To research the mechanical properties of magnesium alloy degradation affected by mechanical environment. Methods: After being divided into 4 groups randomly such as No.1, 2, 3 and 4,12 AZ31 magnesium alloy screws need suspending in the vessels containing 35ml simulated body fluid. No.1 was control group. Group 1 was under no load condition, experimental group 2, 3, and 4 were discontinuously applied fixed axial compression load of 30N, 60N, 90N respectively on time. The weight loss of magnesium alloy screws and the amount of gas generated were measured regularly. Results: From the cumulative amount of hydrogen production, group 1 and group 4 were relatively large, whereas group 2 and group 3 were relatively small. From the weight loss of magnesium alloy screws, group 3 > group 4 > group 2 > group 1. Conclusions: The general trend is the greater the load, the faster the degradation.

Fracture Healing Using Degradable Magnesium Fixation Plates and Screws

Internal bone fixation devices made with permanent metals are associated with numerous long-term complications and may require removal. We hypothesized that fixation devices made with degradable magnesium alloys could provide an ideal combination of strength and degradation, facilitating fracture fixation and healing while eliminating the need for implant removal surgery. Fixation plates and screws were machined from 99.9% pure magnesium and compared with titanium devices in a rabbit ulnar fracture model. Magnesium device degradation and the effect on fracture healing and bone formation were assessed after 4 weeks. Fracture healing with magnesium device fixation was compared with that of titanium devices using qualitative histologic analysis and quantitative histomorphometry. Micro-computed tomography showed device degradation after 4 weeks in vivo. In addition, 2-dimensional micro-computed tomography slices and histologic staining showed that magnesium degradation did not inhibit fracture healing or bone formation. Histomorphology showed no difference in bone-bridging fractures fixed with magnesium and titanium devices. Interestingly, abundant new bone was formed around magnesium devices, suggesting a connection between magnesium degradation and bone formation. Our results show potential for magnesium fixation devices in a loaded fracture environment. Furthermore, these results suggest that magnesium fixation devices may enhance fracture healing by encouraging localized new bone formation.

ChemInform Abstract: Surface Reactivity of Magnesium Alloys in Solid and Liquid States

AbstractReview: 14 refs.

Degradation of Magnesium Alloys in Artificial Urine Solution for Urological Device Applications

Magnesium-based alloys are promising for various biomedical applications due to their advantageous mechanical and biological properties. In this study, we investigated the potential use of magnesium-based alloys for urological device applications, e.g. a biodegradable and antibacterial ureteral stent. Previous studies showed that magnesium-based samples significantly inhibited bacterial growth and colony formation in artificial urine (AU) solution as compared with the polyurethane-based stent. This current study focuses on long-term magnesium-based sample degradation in AU solution and deionized water. We studied the effects of alloy composition (magnesium alloyed with yttrium or aluminum and zinc) and surface condition (oxide versus metallic surface) on the rate of degradation. Sample degradation was measured by the change in sample mass, pH of immersion solution, and magnesium ion concentration in the solution. Results showed that both alloy composition and surface condition affected the rate of degradation in the AU solution. For instance, magnesium-yttrium alloy degraded the fastest and the presence of the oxide layer increased its degradation rate in the AU solution. The overall degradation rate in the AU solution was in this order (fastest to slowest degrading): MgY_O &gt; MgY &gt; Mg_O &gt; AZ31. Further investigation is necessary to determine the efficacy and safety of magnesium-based biodegradable stents for urological applications.