Degradation Of Mg Alloys Research Articles

Honeycomb Bionic Graphene Oxide Quantum Dot/Layered Double Hydroxide Composite Nanocoating Promotes Osteoporotic Bone Regeneration via Activating Mitophagy.

Abnormal osteogenic and remodeling microenvironment due to osteoblast apoptosis are the primary causes of delayed fracture healing in osteoporotic patients. Magnesium (Mg) alloys exhibit biodegradability and appropriate elastic moduli for bone defects in osteoporosis, but the effect on the local bone remodeling disorder is still insufficient. Inspired by the "honeycomb," layered double hydroxide (LDH) with regular traps with graphene oxide quantum dots (GOQDs) inlayed is constructed by pulsed electrodeposition to generate GOQD/LDH composite nanocoatings on the surfaces of Mg alloy substrates. The honeycomb bionic multi-layer stereoscopic structure shows good regulation of the degradation of Mg alloy for the support of healing time required for osteoporotic bone defect. Within its lattice, the local microenvironment conducive to osteogenesis is provided by both the rescue effect of GOQD and LDH. The osteoblast apoptosis is rescued due to the activation of mitophagy to clear dysfunctional mitochondria, where the upregulation of BNIP3 phosphorylation played a key role. The osteoporotic rat model of femoral defects confirmed the improvement of bone regeneration and osseointegration of GOQD/LDH coating. In summary, honeycomb bionic composite nanocoatings with controllable degradation and excellent pro-osteogenic performance demonstrated a promising design strategy on Mg alloy implants in the therapy of osteoporotic bone defects.

Improvement of Mg alloy corrosion resistance and apatite formation ability via PEO/Alginate/Akermanite hybrid coatings for biomedical purposes

The rapid degradation of Mg alloys in biodegradable orthopedic applications is a significant concern to be investigated. In this study, a bilayer composite coating based on alginate/akermanite and plasma electrolytic oxidation (PEO/ALG-AK) on the AZ31 Mg alloy was intended to enhance its corrosion resistance. For this purpose, akermanite nanopowder was synthesized using the sol-gel method and characterized by TEM and XRD. The influence of the PEO/ALG-AK coating layer on the physicochemical properties, electrochemical, and immersion behaviors in simulated body fluid (SBF) was compared to that of uncoated and PEO-coated samples. The AFM images revealed that the bilayer coating exhibited the highest average roughness (Ra = 781 ± 49.3 nm) among the other samples. The EIS test was conducted after 2, 72, and 168 h of immersion in SBF. The bilayer coatings on Mg alloy consistently demonstrated the highest corrosion resistance due to the ALG/Ak layer covering the PEO coating pores. The results of the polarization test also confirmed the achieved results. Furthermore, the implementation of the coatings, particularly the PEO/ALG-AK coating, illustrated a significant reduction in the release of Mg2+ ions and hydrogen bubbles, resulting in corrosion resistance improvement. Finally, the ability of samples to induce apatite formation was also assessed. The results displayed that the deposits on the bare Mg alloy, PEO, and PEO/ALG-AK coatings exhibited Ca/P ratios of 0.83, 1.11, and 1.57, respectively, which closely resembled the natural bone in the PEO/ALG-AK sample. Hence, this developed bilayer coating can be a suitable candidate for enhanced corrosion resistance and bioactivity (apatite formation ability) in the field of Mg biodegradable implants.

Strontium-zinc-based phosphate coatings fabricated in situ on the zinc-pretreated magnesium alloy for degradation control and cytocompatibility enhancement

Owing to the good mechanical support, degradability, and biocompatibility, magnesium (Mg) alloys have large potential in medical applications such as guided bone regeneration membranes. However, the rapid degradation of Mg alloys under physiological conditions hinders many clinical applications. Herein, strontium-zinc-based phosphate (SZP) coatings are fabricated in situ on the zinc (Zn)-electrodeposited WE43 Mg alloy for corrosion protection, degradation control, and cytocompatibility enhancement. The Zn coating acts as a protective cathode for the Mg alloy substrate and provides a stable environment to foster the growth of the SZP coating in comparison with direct deposition onto the Mg alloy surface. The virtues are verified by the smaller corrosion current density, corrosion of the Zn coating instead of the Mg alloy substrate after soaking in artificial saliva, as well as good adhesion provided by the Zn-incorporated transition layer of SrZn2(PO4)2 between the Zn coating and SZP coating. The dense and inert SZP coating mitigates degradation as shown by a decrease in the corrosion current density of 44 times to 0.21 uA cm−2 in the simulated oral environment with artificial saliva. Furthermore, the coating resistance and charge transfer resistance increase by more than one order of magnitude compared to the Zn-treated Mg alloy, and there is no obvious degradation after immersion for 7 days. The Zn coating shows adverse effects on the attachment, spreading, and proliferation of MC3T33-E1 pre-osteoblasts, but the SZP coating providing a higher level larger than 100% of the cell viability after incubation with its extract for 3 days is more compatible with cells because of the retarded dissolution and bio-friendly chemical compositions of SrHPO4 and SrZn2(PO4)2. The hybrid coating has excellent prospects in biomedical products such as biodegradable Mg-based guided bone regeneration membranes.

Degradation protection and enhanced biocompatibility of Mg alloys pretreated with plasma proteins.

After implantation of the Mg alloy in the human body, the adsorption of plasma protein on surface will cause a series of cell reactions and affect the degradation of Mg alloys. Herein, in vitro biological reactions of the ZK60 and AZ31 Mg alloys are analyzed in plasma protein environment. Combined with mass spectrometry analysis of the type of adsorbed proteins, it is shown that proteins such as fibrinogen, vitronectin, fibronectin, and prothrombin are prone to get adsorbed on the surface of the alloys than other proteins, leading to the promotion of MG63 cell adhesion and proliferation. The effect of selected proteins (fibrinogen, fibronectin, and prothrombin) on degradation of ZK60 and AZ31 Mg alloys is investigated using immersion tests. The degradation of AZ31 Mg alloy is significantly restrained with the presence of proteins. This is due to the protein adsorption effect on the sample surface. The molecular dynamics simulation results indicate that both fibrinogen and fibronectin tend to adsorb onto the AZ31 rather than ZK60, forming a stable protein layer on the AZ31 Mg alloy retarding the degradation of the samples. As to ZK60 alloy, the addition of protein inhibits the degradation in the short term, however, the degradation increases after a long time of immersion. This phenomenon is particularly pronounced in fibronectin solution.

Poly(l-lactide)/polycaprolactone based multifunctional coating to deliver paclitaxel/VEGF and control the degradation rate of magnesium alloy stent

Despite significant advancements made in cardiovascular stents, restenosis, thrombosis, biocompatibility, and clinical complications remain a matter of concern. Herein, we report a biodegradable Mg alloy stent with a dual effect of the drug (Paclitaxel) and growth factor (VEGF) release. To mitigate the fast degradation of Mg alloy, inorganic and organic coatings were formed on the alloy surface. The optimized hierarchal sequence of the coating was the first layer consisting of magnesium fluoride, followed by poly(l-lactide) and hydroxyapatite coating, and finally sealed by a polycaprolactone layer (MgC). PLLA and HAp were used to increase the adhesion strength and biocompatibility of the coating. Paclitaxel and VEGF were loaded in the final PCL layer (Mg-C/PTX-VEGF). As compared to bare Mg alloy (28 % weight loss), our MgC system showed (3.1 % weight loss) successful decrease in the degradation rate. Further, the in vitro biocompatibility illustrated the highly biocompatible nature of our drug and growth factor-loaded system. The in vivo results displayed that the drug loading decreased the inflammation and neointimal hyperplasia as indicated by the α-SMA and CD-68 antibody staining. The growth factor helped in the endothelialization which was established by the FLKI and ICAM antibody staining of the tissue.

Recent advances in the development of Mg-Ca-Zn alloys as biodegradable orthopedic implants

Development of biodegradable orthopedic implants has gathered significant attention around the globe as it eliminates the second implant removal surgery after bone healing. Mg based alloys are most sought-after materials for these applications however the imbalance between the rate of bone healing and rate of degradation of Mg alloys poses a main challenge for their clinical success. Mg-Ca-Zn alloys possess potential properties to be adopted as biodegradable orthopedic implants. This review presents an overview on the properties and performance of Mg-Ca-Zn alloys. First, Mg-Ca and then Mg-Ca-Zn system is discussed. The effects of manufacturing processes, alloying elements, heat treatments on microstructure, mechanical and corrosion properties of these systems are presented. The effects of surface modification on the corrosion behavior of Mg-Ca-Zn alloys are also discussed in this review. The aim of this review is to coherently present the various scattered results on the development of Mg-Ca-Zn alloys for orthopedic implant applications.

Enhanced degradation performance and promoted bone regeneration of novel CaCO3-based hybrid coatings on magnesium alloy as bioresorbable orthopedic implants

Fast degradation of Mg alloys and slow bone regeneration process largely impede their clinical applications as one kind of degradable metallic orthopedic implants. In current study, novel calcium carbonate (CaCO3) coatings are prepared via the hydrothermal method and optimized via the addition of glutamate acid (Glu) or dopamine (DOPA) to improve the degradation and biological performance of the MgZnCa alloy. The results revealed that the CaCO3 coating was mainly composed of rhombohedral calcite aggregates and deposited rod-like aragonite. Whereas, the introduction of Glu or DOPA stabilized plate-like vaterite via the adsorption or incorporation of organic molecules, and suppressed the deposition of rod-like aragonite on CaCO3 hybrid coating with lower roughness, higher adhesion strength and thickness. Thus, CaCO3 hybrid coatings endowed the MgZnCa alloy with more favorable in vitro degradation resistance. Furthermore, all CaCO3-based coatings showed good in vitro cytocompatibility, while CaCO3@Glu hybrid coating exhibited the best in vitro osteogenic activity of osteoblasts, attesting the synergistic effect of Glu and vaterite on the biological activity of the MgZnCa alloy. In vivo results verified the significantly inhibited degradation and promoted osteogenesis of the CaCO3@Glu hybrid coating. These results provide important guidelines and rationality for the further application of the CaCO3-based coatings on orthopedic implants towards more excellent clinical performance.

Utilizing Computational Modelling to Bridge the Gap between In Vivo and In Vitro Degradation Rates for Mg-xGd Implants

Magnesium (Mg) and its alloys are promising materials for temporary bone implants due to their mechanical properties and biocompatibility. The most challenging aspect of Mg-based implants involves adapting the degradation rate to the human body, which requires extensive in vitro and in vivo testing. Given that in vivo tests are significantly more labour-intensive than in vitro and ethics prohibit direct experiments on animals or humans, attempts are commonly undertaken to infer conclusions on in vivo degradation behavior from in vitro experiments. However, there is a wide gap between these tests, and in vitro testing is often a poor predictor of in vivo outcomes. In the development of biodegradable Mg-based implants, considerable efforts are being made to reduce the overall time and cost of in vitro and in vivo testing. Finding a suitable alternative to predict the degradation of Mg alloys, however, remains challenging. We present computational modelling as a possible alternative to bridge the gap between in vitro and in vivo testing, thus reducing overall cost, duration and number of experiments. However, traditional modelling approaches for complex biodegradable systems are still rather time-consuming and require a clear definition of the relations between input parameters and the model result. In this study, Kriging surrogate models based on the peridynamic in vitro degradation model were developed to simulate the degradation behavior for two main alloys, Mg-5Gd and Mg-10Gd, for both in vitro and in vivo cases. Using Kriging surrogate models, the simulation parameters were calibrated to the volume loss data from in vitro and in vivo experiments. In vivo degradation of magnesium has one order of magnitude higher apparent diffusion coefficients than in vitro degradation, thus yielding the higher volume loss observed in vivo than in vitro. On the basis of the diffusivity of the Mg2+ ions modeled under in vitro degradation, Kriging surrogate models were able to simulate the in vivo degradation behavior of Mg-xGd with a ratio between 0.46 and 0.5, indicating that the surrogate-modelling approach is able to bridge the gap between in vitro and in vivo degradation rates for Mg-xGd implants.

High strength and rapid solution Mg alloy by adding Fe element fabricated by binder jetting additive manufacturing

The effects of Fe addition on the mechanical properties and corrosion behaviors of AZ91D alloys prepared by binder jetting additive manufacturing have been investigated. The results show that the constitution of the second phase is large dependence on Fe content. With the Fe content increasing, the second phase can transform AlFe phase to Fe and AlFe phase. In addition, with increasing Fe content, the content of second phase increases gradually, while the content of pores also increases. We believe that with the Fe content increasing, the content of second phase with Fe element increases which the melt temperature is higher than sintering temperature, and the content of liquid phase decreases, that leading the high-viscosity liquid alloy cannot fill the pores fully and the more pores will remain and causes the relative density reduces. The compressive strength shows a parabola relationship with Fe content. Furthermore, adding Fe can accelerate the degradation of Mg alloys owing to the galvanic corrosion. The sample with 5 wt% Fe content shows the highest ultimate compressive strength (440 MPa) and fast degradation rate (9091 mm/Y), which meets the soluble Mg alloy with rare earth but cost much lower.

The deteriorated degradation resistance of Mg alloy microtubes for vascular stent under the coupling effect of radial compressive stress and dynamic medium

The degradation of Mg alloys relates to the service performance of Mg alloy biodegradable implants. In order to investigate the degradation behavior of Mg alloys as vascular stent materials in the near service environment, the hot-extruded fine-grained Mg-Zn-Y-Nd alloy microtubes, which are employed to manufacture vascular stents, were tested under radial compressive stress in the dynamic Hanks’ Balanced Salt Solution (HBSS). The results revealed that the high flow rate accelerates the degradation of Mg alloy microtubes and its degradation is sensitive to radial compressive stress. These results contribute to understanding the service performance of Mg alloys as vascular stent materials.

Advances in bioorganic molecules inspired degradation and surface modifications on Mg and its alloys

Mg alloys possess biodegradability, suitable mechanical properties, and biocompatibility, which make them possible to be used as biodegradable implants. However, the uncontrollable degradation of Mg alloys limits their general applications. In addition to the factors from the metallic materials themselves, like alloy compositions, heat treatment process and microstructure, some external factors, relating to the test/service environment, also affect the degradation rate of Mg alloys, such as inorganic salts, bioorganic small molecules, bioorganic macromolecules. The influence of bioorganic molecules on Mg corrosion and its protection has attracted more and more attentions. In this work, the cutting-edge advances in the influence of bioorganic molecules (i.e., protein, glucose, amino acids, vitamins and polypeptide) and their coupling effect on Mg degradation and the formation of protection coatings were reviewed. The research orientations of biomedical Mg alloys in exploring degradation mechanisms in vitro were proposed, and the impact of bioorganic molecules on the protective approaches were also explored.

Biodegradable magnesium alloys for orthopaedic applications.

ABSTRACTThere is increasing interest in the development of bone repair materials for biomedical applications. Magnesium (Mg)-based alloys have a natural ability to biodegrade because they corrode in aqueous media; they are thus promising materials for orthopaedic device applications in that the need for a secondary surgical operation to remove the implant can be eliminated. Notably, Mg has superior biocompatibility because Mg is found in the human body in abundance. Moreover, Mg alloys have a low elastic modulus, close to that of natural bone, which limits stress shielding. However, there are still some challenges for Mg-based fracture fixation. The degradation of Mg alloys in biological fluids can be too rapid, resulting in a loss of mechanical integrity before complete healing of the bone fracture. In order to achieve an appropriate combination of bio-corrosion and mechanical performance, the microstructure needs to be tailored properly by appropriate alloy design, as well as the use of strengthening processes and manufacturing techniques. This review covers the evolution, current strategies and future perspectives of Mg-based orthopaedic implants.

The effect of enzymes on the in vitro degradation behavior of Mg alloy wires in simulated gastric fluid and intestinal fluid

With an upsurge of biodegradable metal implants, the research and application of Mg alloys in the gastrointestinal environment of the digestive tract have been of great interest. Digestive enzymes, mainly pepsin in the stomach and pancreatin in the small intestine, are widespread in the gastrointestinal tract, but their effect on the degradation of Mg alloys has not been well understood. In this study, we investigated the impacts of pepsin and pancreatin on the degradation of Mg-2Zn alloy wires. The results showed that the pepsin and pancreatin had completely different even the opposite effects on the degradation of Mg, although they both affected the degradation product layer. The degradation rate of Mg wire declined with the addition of pepsin in simulated gastric fluid (SGF) but rose with the addition of pancreatin in simulated intestinal fluid (SIF). The opposite trends in degradation rate also resulted in completely different degradation morphologies in wires surface, where the pitting corrosion in SGF was inhibited because of the physical barrier effect of pepsin adsorption. In contrast, the adsorption of pancreatin affected the integrity of magnesium hydrogen phosphate film, causing a relatively uneven degraded surface. These results may help us to understand the role of different digestive enzymes in the degradation of magnesium and facilitate the development and clinical application of magnesium alloy implanted devices for the digestive tract.

Effect of Ni on the microstructure, mechanical properties and corrosion behavior of MgGd1Nix alloys for fracturing ball applications

The effects of Ni addition on the mechanical properties, corrosion behaviors, and corrosion mechanism of MgGd1Nix alloys have been investigated by compressive tests, weight loss, hydrogen evolution, and scanning electron microscopy. The results show that the constitution of the second phase is large dependence on Ni/Gd molar ratios, which can transform from LPSO(long-period stacking ordered)+Mg5Gd, LPSO to eutectic phase. In addition, with increasing Ni/Gd molar ratios, the content of second phase increases gradually, while the LPSO phase shows a parabola relationship. Furthermore, the formation of Ni-containing LPSO phase not only can improve the strength but also accelerate the degradation of Mg alloys owing to the galvanic corrosion. The optimal properties with ultimate compressive strength, degradation rate are 340 MPa, 2066 mm/y for MgGd1Ni0.75, respectively, which can meet the engineering application standard of fracturing ball and can be used as candidate materials for fracturing ball.

Titanate incorporated anodized coating on magnesium alloy for corrosion protection, antibacterial responses and osteogenic enhancement

The rapid degradation of Mg alloy was reduced by incorporating titanate on a fluorine-based anodized layer. The coating shows (i) excellent biomineralization ability, (ii) improved local and periodical corrosion behavior and (iii) enhanced expression of osteogenic factors (Runx2, Col 1, OCN and OPN) along with (iv) the antibacterial property. The fluoride and magnesium ions dissolution from the anodized layer is responsible for the better expression of osteogenic factors and antibacterial behavior. The preparation of the titanate incorporated anodized Mg alloy (Ti-AMg) is a facile solution to overcome the implant-associated bacterial infections with required biological functions including progression of bone ingrowth and biocompatibility.

Degradation Resistance and In Vitro Cytocompatibility of Iron-Containing Coatings Developed on WE43 Magnesium Alloy by Micro-Arc Oxidation

Iron (Fe) is an important trace element for life and plays vital functions in maintaining human health. In order to simultaneously endow magnesium alloy with good degradation resistance, improved cytocompatibility, and the proper Fe amount for the body accompanied with degradation of Mg alloy, Fe-containing ceramic coatings were fabricated on WE43 Mg alloy by micro-arc oxidation (MAO) in a nearly neutral pH solution with added 0, 6, 12, and 18 g/L ferric sodium ethylenediaminetetraacetate (NaFeY). The results show that compared with the bare Mg alloy, the MAO samples with developed Fe-containing ceramic coatings significantly improve the degradation resistance and in vitro cytocompatibility. Fe in anodic coatings is mainly present as Fe2O3. The increased NaFeY concentration favorably contributes to the enhancement of Fe content but is harmful to the degradation resistance of MAO coatings. Our study reveals that the developed Fe-containing MAO coating on Mg alloy exhibits potential in clinical applications.

The Influence of SMAT and Polishing on the Degradation of AZ31B Magnesium Alloy in 3.5 Wt.% NaCl Solution

Surface mechanical attrition treatment (SMAT) has been recognized as a potential surface treatment for improving the strength and the wear resistance of magnesium (Mg) and its alloy. However, this treatment potentially increases the degradation rate of these particular materials. Therefore, additional treatments might be needed to overcome such limitation of the SMAT. In this research, the influence of polishing on the degradation of the SMAT-processed AZ31B Mg alloy was investigated. Weight losses measurement and pH monitoring were carried out to determine degradation behavior of the Mg alloy during an immersion test in 3.5 wt.% NaCl solution. The results showed that the degradability of the Mg alloy decreased with the application of polishing to remove the rough surface layer and the Fe contaminant on the material surface generated by the SMAT. Based on all the findings in this work, it can be concluded that the SMAT is indeed a promising technique for lowering the degradability of AZ31B Mg alloy, but such an advantage was masked by the increased roughness and contamination of the alloy surface with this treatment.

Visual Hydrogen Mapping Sensor for Noninvasive Monitoring of Bioresorbable Magnesium Implants In Vivo

The biodegradation process of Mg alloys (LAZ611 and WKX41) has been monitored transdermally by using a visual H2 mapping sensor. The visual mapping sensor changes color from gray to dark blue upon exposure to H2 permeating through the skin generated by the degradation of Mg alloys implanted subcutaneously in mice in vivo. The visual H2 mapping sensor can provide three-dimensional H2 permeation maps using a simple procedure that is less time consuming compared with point measurements with an electrochemical H2 sensor. The results of this study demonstrate that the visual H2 mapping sensor has the capability to monitor the different biodegradation rates of Mg alloys in vivo. This detection method is simple, noninvasive, and low cost, does not use energetic radiation such as x-ray imaging, and moreover, requires no specialty training for operating personnel.

In vitro corrosion of magnesium alloy AZ31 — a synergetic influence of glucose and Tris

Biodegradable Mg alloys have generated great interest for biomedical applications. Accurate predictions of in vivo degradation of Mg alloys through cost-effective in vivo evaluations require the latter to be conducted in an environment close to that of physiological scenarios. However, the roles of glucose and buffering agents in regulating the in vivo degradation performance of Mg alloys has not been elucidated. Herein, degradation behavior of AZ31 alloy is investigated by hydrogen evolution measurements, pH monitoring and electrochemical tests. Results indicate that glucose plays a content-dependent role in degradation of AZ31 alloy in buffer-free saline solution. The presence of a low concentration of glucose, i.e. 1.0 g/L, decreases the corrosion rate of Mg alloy AZ31, whereas the presence of 2.0 and 3.0 g/L glucose accelerates the corrosion rate during long term immersion in saline solution. In terms of Tris-buffered saline solution, the addition of glucose increases pH value and promotes pitting corrosion or general corrosion of AZ31 alloy. This study provides a novel perspective to understand the bio-corrosion of Mg alloys in buffering agents and glucose containing solutions.

In vivo quantification of hydrogen gas concentration in bone marrow surrounding magnesium fracture fixation hardware using an electrochemical hydrogen gas sensor

Magnesium (Mg) medical devices are currently being marketed for orthopedic applications and have a complex degradation process which includes the evolution of hydrogen gas (H2). The effect of H2 exposure on relevant cell types has not been studied; and the concentration surrounding degrading Mg devices has not been quantified to enable such mechanistic studies. A simple and effective method to measure the concentration of H2 in varying microenvironments surrounding Mg implants is the first step to understanding the biological impact of H2 on these cells. Here, the in vivo measurement of H2 surrounding fracture fixation devices implanted in vivo is demonstrated. An electrochemical H2 microsensor detected increased levels of H2 at three anatomical sites with a response time of about 30 s. The sensor showed the H2 concentration in the bone marrow at 1 week post-implantation (1460 ± 320 µM) to be much higher than measured in the subcutaneous tissue (550 ± 210 µM) and at the skin surface (120 ± 50 µM). Additionally, the H2 concentrations measured in the bone marrow exceeded the concentration in a H2 saturated water solution (∼800 µM). These results suggest that H2 emanating from Mg implants in bone during degradation pass through the bone marrow and become at least partially trapped because of slow permeation through the bone. This study is the first to identify H2 concentrations in the bone marrow environment and will enable in vitro experiments to be executed at clinically relevant H2 concentrations to explore possible biological effects of H2 exposure. Statement of SignificanceAn electrochemical H2 sensor was used to monitor the degradation of a Mg fracture fixation system in a lapine ulna fracture model. Interestingly, the H2 concentration in the bone marrow is 82% higher than H2 saturated water solution. This suggests H2 generated in situ is trapped in the bone marrow and bone is less permeable than the surrounding tissues. The detectable H2 at the rabbit skin also demonstrates a H2 sensor’s ability to monitor the degradation process under thin layers of tissue. H2 sensing shows promise as a tool for monitoring the degradation of Mg alloy in vivo and creating in vitro test beds to more mechanistically evaluate the effects of varying H2 concentrations on cell types relevant to osteogenesis.