Magnesium Alloy Implants Research Articles

Structure design, preparation and performance of a novel composite coating on medical magnesium-zinc alloy

Magnesium alloy is a promising implant material, but its inherent defects limit its clinical application. In this article, the CaP pre-coating and polycaprolactone (PCL) composite coatings doped with different hydroxyapatite (HA) and zinc oxide (ZnO) nanoparticles were successively prepared on the surface of Mg6Zn alloy using hydrothermal method and dip coating technique.Results show that ZnO compounds was formed in the CaP pre-coating on the solution treated Mg6Zn alloy, which can enhance the bonding strength of CaP compounds with alloy substrate. Comparing with the PCL coating on bare alloy, the bond strength of the PCL coating on CaP pre-coating was increased by about 5 times. Therefore, the preparation of CaP pre-coating is necessary because it can help to improve the bonding strength of the PCL coating on the substrate, and effectively avoid the peeling, blistering and loss of the barrier effect of the PCL coating. The nanoparticles in the composite coating play important roles for fabricating multifunctional coating. Firstly, doping HA and ZnO nanoparticles help to increase surface roughness of the composite coating, which is beneficial to cell attachment and proliferation. Secondly, the formation of porous structure in the composite coating enable it the ability to control the degradation rate of the matrix by adjusting the porosity. Thirdly, the composite coating doped with ZnO nanoparticles brings better antibacterial properties for magnesium alloy implants. The alloy coated with CaP pre-coating and (2wt.%nHA + 2wt.%nZnO)/PCL composite coating has antibacterial rate of over 90 % and cell proliferation rate of about 90 %, demonstrating it can be used as a potential multifunctional medical implant material.

Corrosion, stress corrosion cracking and corrosion fatigue behavior of magnesium alloy bioimplants

Abstract The use of magnesium and its alloys as temporary implants has gained interest in the last two decades due to their good mechanical properties and bio-degradability in the in-vivo conditions. However, the issues of higher corrosion rate and stress corrosion cracking persist, which are responsible for the implants’ early failure. This review paper focuses on the challenges involved in the use of magnesium-based implants and the advancements in mitigating the corrosion-related issues for in-vivo use of biodegradable magnesium alloy implants. Herein we review the degradation behavior of three groups of magnesium alloys, i.e., aluminum-containing Mg alloy, rare earth element (REE) containing Mg alloy, and aluminum-free Mg alloy in a variety of testing media. We also review various surface modification techniques such as mechanical methods, physical methods, and chemical methods adopted to address the shortcomings of the Mg alloys. Furthermore, recent developments in Mg based bioimplants such as Mg-based open porous scaffolds, nanostructured Mg alloys and Mg based bulk metallic glasses are reviewed. In the end, recent clinical trials of the Mg-based implant were reported in detail.

A Computational Pitting Corrosion Model of Magnesium Alloys.

Controlling the corrosion rate of implants to maintain mechanical properties during tissue healing is significant in developing magnesium alloy implants. In addition to surface treatment and material properties, the study of geometric alteration and mechanical strength are also vital for implant development. In this study, we developed a three-dimensional model for semi-autonomous computational pitting corrosion. It is based on the Monte Carlo method, modeling magnesium alloy implants toward clinical application. The corrosion probability is based on the number of exposed surfaces to saline and the oxidation characteristics of the elements. The computational results are well compared with the experimental measurement using micro-computed tomography (micro-CT) in 500 h. Subsequently, the computational analysis is extended to 3,000 h of corrosion analysis. The 3D model appears promising to assist the development of biodegradable implants.

Bone Tissue Condition during Osteosynthesis of a Femoral Shaft Fracture Using Biodegradable Magnesium Implants with an Anticorrosive Coating in Rats with Experimental Osteoporosis

Today, osteoporosis has become a major global health issues. The World Health Organization declares that 320 billion people have osteoporosis now, and more than 1.5 billion osteoporosis traumatic events occur every year. Bones become fragile and fracture risk is high; thus, it is crucial to choose the right biodegradable implants in order to minimize reoperations of patients with systemic osteoporosis. This investigation aimed to carry out a morphological assessment of the state of bone tissue with osteosynthesis of a femoral fracture in rats, using a model of osteoporosis with the installation of magnesium alloy implants coated with hydroxyapatite and sealed with polytetrafluoroethylene. According to this study, the indicators of angiogenesis and bone formation in experimental animals were significantly higher when an implant coated with hydroxyapatite sealed with polytetrafluoroethylene was used, compared to an implant coated only with hydroxyapatite and in rats without an implant. Based on the data obtained, it is possible to consider a magnesium implant coated with hydroxyapatite and sealed with polytetrafluoroethylene as a promising material for fracture therapy in patients with reduced bone density.

Micro-arc oxidation-assisted sol-gel preparation of calcium metaphosphate coatings on magnesium alloys for bone repair

Calcium phosphate coating is an attractive surface modification strategy for magnesium alloys, since it can increase their corrosion resistance and endow them with osteogenic function simultaneously. Herein, a calcium metaphosphate (CMP) coating was fabricated on magnesium alloy by using sol-gel approach assisted with micro-arc oxidation pre-treatment. Scanning electron microscopy showed that the micro-pores and cracks in micro-arc oxidation inner layer generated during the pre-treatment process were sealed by the grainy sol-gel outer layer. Energy dispersive spectrometry and X-ray diffraction results demonstrated the identity of the coating as CMP. The cross-cut test showed that the adhesion of CMP coating was strong. Applying bare magnesium alloy substrate as a control, the CMP coating surface was rougher and more hydrophilic. The potentiodynamic polarization test demonstrated that the corrosion resistance was significantly improved by using CMP coating. Hydrogen evolution in immersion test further confirmed that the degradation rate was decelerated within 14 days. Moreover, CMP coating facilitated the adhesion speed, spreading area, and focal adhesion formation of bone marrow stem cells. The number of cells in the active proliferating state and proliferated cells present on the CMP coating also increased. Additionally, CMP coating upregulated alkaline phosphatase activity and osteogenic gene expression in cells. In summary, the micro-arc oxidation assisted sol-gel CMP coatings increased the corrosion resistance and promoted the interfacial cell behavior for magnesium alloy implants, which might inform the further development of surface modifications on magnesium alloys for bone related applications.

Multimodal ex vivo methods reveal that Gd-rich corrosion byproducts remain at the implant site of biodegradable Mg-Gd screws

Extensive research is being conducted on magnesium (Mg) alloys for bone implant manufacturing, due to their biocompatibility, biodegradability and mechanical properties. Gadolinium (Gd) is among the most promising alloying elements for property control in Mg alloy implants; however, its toxicity is controversial. Investigating Gd behavior during implant corrosion is thus of utmost importance. In this study, we analyzed the degradation byproducts at the implant site of biodegradable Mg-5Gd and Mg-10Gd implants after 12 weeks healing time, using a combination of different imaging techniques: histology, energy-dispersive x-ray spectroscopy (EDX), x-ray microcomputed tomography (µCT) and neutron µCT. The main finding has been that, at the healing time in exam, the corrosion appears to have involved only the Mg component, which has been substituted by calcium and phosphorus, while the Gd remains localized at the implant site. This was observed in 2D by means of EDX maps and extended to 3D with a novel application of neutron tomography. X-ray fluorescence analysis of the main excretory organs also did not reveal any measurable accumulation of Gd, further reinforcing the conclusion that very limited or no removal at all of Gd-alloy happened during degradation. Statement of significanceGadolinium is among the most promising alloying elements for property control in biodegradable magnesium alloy implants, but its toxicity is controversial and its behavior during corrosion needs to be investigated. We combine 2D energy dispersive x-ray spectroscopy and 3D neutron and x-ray tomography to image the degradation of magnesium-gadolinium implants after 12 weeks of healing time. We find that, at the time in exam, the corrosion has involved only the magnesium component, while the gadolinium remains localized at the implant site. X-ray fluorescence analysis of the main excretory organs also does not reveal any measurable accumulation of Gd, further reinforcing the conclusion that very limited or no removal at all of Gd-alloy has happened during degradation.

CSBD Healing in Rats after Application of Bovine Xenogeneic Biomaterial Enriched with Magnesium Alloy.

Xenogeneic biomaterials Cerbone® and OsteoBiol® are widely used in oral implantology. In dental practice, xenogeneic biomaterial is usually combined with autologous bone to provide bone volume stability needed for long-term dental implants. Magnesium alloy implants dissolve and form mineral corrosion layer that is directly in contact with bone tissue, allowing deposition of the newly formed bone. CSBD heals by intramembranous ossification and therefore is a convenient model for analyses of ostoconductive and osteoinductive properties of different type of biomaterials. Magnesium alloy-enriched biomaterials have not yet been applied in oral implantology. Therefore, the aim of the current study was to investigate biological properties of potentially new bovine xenogeneic biomaterial enriched with magnesium alloy in a 5 mm CSBD model. Osteoconductive properties of Cerabone®, Cerabone® + Al. bone, and OsteoBiol® were also analyzed. Dynamics of bone healing was followed up on the days 3, 7, 15, 21, and 30. Calvary bone samples were analyzed by micro-CT, and values of the bone morphometric parameters were assessed. Bone samples were further processed for histological and immunohistochemical analyses. Histological observation revealed CSBD closure at day 30 of the given xenogeneic biomaterial groups, with the exception of the control group. TNF-α showed high intensity of expression at the sites of MSC clusters that underwent ossification. Osx was expressed in pre-osteoblasts, which were differentiated into mature osteoblasts and osteocytes. Results of the micro-CT analyses showed linear increase in bone volume of all xenogeneic biomaterial groups and also in the control. The highest average values of bone volume were found for the Cerabone® + Mg group. In addition, less residual biomaterial was estimated in the Cerabone® + Mg group than in the Cerabone® group, indicating its better biodegradation during CSBD healing. Overall, the magnesium alloy xenogeneic biomaterial demonstrated key properties of osteoinduction and biodegradidibility during CSBD healing, which is the reason why it should be recommended for application in clinical practice of oral implantology.

The influence of alternating cyclic dynamic loads with different low frequencies on the bio-corrosion behaviors of AZ31B magnesium alloy in vitro

The real physiological environment of human body is complicated with different degrees and forms of dynamic loads applied to implanted medical devices due to the daily activities of the patients, which would have impacts on the degradation behaviors of magnesium alloy implants. In this work, the bio-corrosion behaviors of AZ31B magnesium alloy under alternating cyclic dynamic loads with different low frequencies (0.1–2.5 Hz) were specially investigated. It was found that the bio-degradation performances under external dynamic stressed conditions were much severer than those under unstressed conditions and static loads. The corrosion rates were generally accelerated as the rise of cyclic frequency. Hereby a numerical model for the degradation process of Mg alloy was established. The corrosion current density icorr of Mg alloy and the applied loading frequency f matches a linear relationship of ln icorr∝ f, which is the result of interactions between the cyclic alternating load and corrosive environment. This work could provide a theoretical reference and an experimental basis for further researches on the biodegradation behaviors of biomedical materials under dynamic conditions.

Microstructure, mechanical properties and corrosion fatigue behaviour of biodegradable Mg–Zn–Y–Nd alloy prepared by double extrusion

ABSTRACT The application of biodegradable Magnesium (Mg) alloy implants is limited due to their insufficient corrosion fatigue resistance. This work investigated the influence of double extrusion on the microstructure, mechanical properties and corrosion fatigue behaviour of Mg–Zn–Y–Nd alloy. The results showed that, after double extrusion, the texture intensity was significantly weakened and a more uniform microstructure with fine grain size was obtained. The double extruded alloy showed improved mechanical properties with a yield strength of 196.5 MPa, an ultimate tensile strength of 241.8 MPa and an elongation up to 29.7%. As compared to that of single extruded Mg–Zn–Y–Nd alloy, the fatigue tests indicated that double extrusion improved the fatigue strength of the alloy by 23% in air and 20% in simulated body fluid. Based on the results, the mechanisms of fatigue and corrosion fatigue of double extruded Mg–Zn–Y–Nd alloy were presented.

Fabrication of superhydrophobic composite coating of hydroxyapatite/stearic acid on magnesium alloy and its corrosion resistance, antibacterial adhesion

The bacterial infection of bone implants is a vital factor leading to implant failure. Superhydrophobic surface with low adhesion can effectively enhance corrosion resistance and antibacterial adhesion properties of magnesium alloy. Herein, the superhydrophobic composite coating of hydroxyapatite (HA)/stearic acid was successfully prepared on magnesium alloy (AZ31B) using hydrothermal method and followed modification of stearic acid. The wettability, corrosion resistance and antibacterial adhesion capacity of the composite coating were studied. The composite coatings confer excellent superhydrophobicity with a contact angle about 152.52° and a sliding angle about 2°, and showed good long-term superhydrophobic stability in air. Meanwhile, during immersion in simulated body fluid (SBF), the superhydrophobic composite coating was converted to hydrophilicity in a short time and exposed the micro-/nano-scale structure surface of HA, which could induce the fast deposition of the mineralized apatite layer. The characteristics endowed the composite coating with the short-term antibacterial adhesion property and long-term corrosion resistance in SBF, which will afford a surface modification strategy for the application of magnesium alloy implants in orthopedics and dentistry.

Assessing the Corrosion Pattern of Magnesium Alloy Implants in Simulated Salivary Fluids at Different pH

Magnesium (Mg) alloy implants are formidable structural metals for biomedical applications, they are limited due to Mg chemical reactivity and its susceptible to corrosion. Efficient mitigation control toward Mg corrosion can only be proposed if its degradation kinetics are properly understood in various media. In the biomedical field, the auto-controlled degradation mechanism of orthopedic Mg implants eliminates repeated surgeries while also minimizing the risks associated with these medical procedures. However, their rapid degradation kinetics between living tissues contribute to sudden changes in local pH value, accumulation of unwanted hydrogen gas in bone cavities and subsequent mechanical failure. In this work, we have investigated the degradation pattern of Mg alloy implant in chloride-enriched simulated salivary fluids at different pH at room temperature. The implant demonstrated varying rates of corrosion and passivation within a range of pH of corrosion media. The effects of solution treatment on implant corrosion behavior was vividly studied and the trend of increasing corrosion was low pH > saline pH > high pH. Localized corrosion behavior has been observed by scanning electron microscopy evidence while electrochemical impedance spectroscopy and potentiodynamic polarization techniques revealed increased anodic polarization and charge transfer, respectively. The chemistry and diffraction phases of adhering corrosion products as well as their surface morphologies was also been identified. The implant must have uniformly corroded within the salivary fluids over an extended duration; however, the early corrosion stages reveal localized passivation of oxide films at grain boundaries at low pH.Most metallic implants made of corrosion-resistant alloys (e.g., cobalt, titanium and nickel) are excellent candidates for oral surgeries. However, most of them cannot serve as bone cements to stabilize dental implants during post-surgery tissue healing; a function that is possible with magnesium-based bone cement [1,2]. The use of these metal-type temporary implants in binding bone structures normally will require a secondary surgery operation to remove them, and this might lead to potential infections. This study features the analyses of the corrosion patterns of Mg alloy implants deployed in orthopedic applications. The salivary pH changes induce corrosion toward septic loosening prior to Mg implant degradation and dental implant infections.

Degradation and Biocompatibility of AZ31 Magnesium Alloy Implants In Vitro and In Vivo: A Micro-Computed Tomography Study in Rats.

In current orthodontic practice, miniscrew implants (MSIs) for anchorage and bone fixation plates (BFPs) for surgical orthodontic treatment are commonly used. MSIs and BFPs that are made of bioabsorbable material would avoid the need for removal surgery. We investigated the mechanical, degradation and osseointegration properties and the bone-implant interface strength of the AZ31 bioabsorbable magnesium alloy to assess its suitability for MSIs and BFPs. The mechanical properties of a Ti alloy (TiA), AZ31 Mg alloy (MgA), pure Mg and poly-L-lactic acid (PLA) were investigated using a nanoindentation test. Also, pH changes in the solution and degradation rates were determined using immersion tests. Three-dimensional, high-resolution, micro-computed tomography (CT) of implants in the rat femur was performed. Biomechanical push-out testing was conducted to calculate the maximum shear strength of the bone-implant interface. Scanning electron microscopy (SEM), histological analysis and an evaluation of systemic inflammation were performed. MgA has mechanical properties similar to those of bone, and is suitable for implants. The degradation rate of MgA was significantly lower than that of Mg. MgA achieved a significantly higher bone-implant bond strength than TiA. Micro-CT revealed no significant differences in bone density or bone-implant contact between TiA and MgA. In conclusion, the AZ31 Mg alloy is suitable for both MSIs and BFPs.

Preparation of vancomycin-loaded alginate hydrogel coating on magnesium alloy with enhanced anticorrosion and antibacterial properties

In this study, vancomycin (Van)-loaded sodium alginate (SA) hydrogel coating was fabricated on micro-arc oxidation (MAO)-treated magnesium alloy (MgA) surface via the electrostatic interaction between polyethyleneimine and SA to enhance anticorrosion, hemocompatibility, and antibacterial properties of MgA substrate. The surface morphology and chemical composition of the modified MgA substrate were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. The results showed the successful preparation of Van-loaded SA hydrogel coating on MgA/MAO substrate. Furthermore, the anticorrosion property of the coated MgA in simulated body fluids was also evaluated. The potentiodynamic polarization test indicated that corrosion resistance of MgA coated with the Van-loaded SA hydrogel was significantly improved. Biocompatibility of the modified MgA substrates was investigated by in vitro platelets adhesion assay, hemolysis ratio test, and dynamic coagulation time test. The results indicated that the modified MgA exhibited excellent antibacterial property and hemocompatibility. This study may provide an alternative pathway for surface modification of MgA implants to enhance their corrosion resistance and biocompatibility.

The influence of the crosslinking degree on the corrosion protection properties of chitosan coatings in simulated body fluid

This paper describes the protection of magnesium AZ31 alloy sheets in a simulated body fluid (SBF) medium provided by chitosan coatings. It demonstrates, by means of potentiodynamic polarization curves and electrochemical impedance spectroscopy, that chitosan coatings with a crosslinking degree of up to 42% are efficient in protecting the alloy in SBF, with a performance superior to similar coatings reported in the literature. With higher crosslinking degrees the coating becomes brittle and susceptible to cracks, decreasing its protective properties. The hydrogen evolution rate observed for the best coating complies with the acceptance level and further demonstrates its potential to control the degradation of magnesium alloy implants.

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.

Biodegradable magnesium alloys as temporary orthopaedic implants: a review.

The study of innovative biodegradable implant materials is one of the most interesting research topics at the forefront in the area of biomaterials. Biodegradable implant materials in the human body can be gradually dissolved, absorbed, consumed or excreted, so there is no need for the secondary surgery to remove implants after the surgery regions have healed. However, most of the biodegradable materials, usually polymers, do not have good mechanical properties to be reliable for bearing the load of the body. Magnesium and its alloys due to the excellent biodegradability and biocompatibility as well as the suitable mechanical compatibility with human bone are very promising candidates for the development of temporary, degradable implants in load-bearing applications. However, Mg alloys are corrosion susceptible in a biological environment. Besides, the high corrosion rate and the low bioactivity of magnesium implants are the challenging problems, which need to be resolved before employing them in clinical applications. This paper provides a review of state-of-the-art of magnesium alloy implants for orthopedic and tissue engineering applications and describes recent progress in the design of novel structure design Mg alloys and potential approaches to improve their biodegradation performance.

Magnesium Implants: Prospects and Challenges.

Owing to their suitable mechanical property and biocompatibility as well as the technological possibility of controlling their high corrosion rates, magnesium and its alloys have attracted significant attention as temporary bio-implants. Though the ability of magnesium to harmlessly biodegrade and its inherent biocompatibility make magnesium alloys a suitable choice for a temporary implant, their high corrosion rates limit their practical application, as the implants can potentially corrode away even before the healing process has completed. Different approaches, such as alloying, surface modification, and conversion coatings, have been explored to improve the corrosion resistance of various magnesium alloys. However, the corrosion behavior of magnesium implants with and without a surface modification has been generally investigated under in-vitro conditions, and studies under in-vivo conditions are limited, which has contributed to the lack of translation of magnesium implants in practical applications. This paper comprehensively reviews the prospects of magnesium alloy implants and the current challenges due to their rapid degradation in a physiological environment. This paper also provides a comprehensive review of the corrosion mitigation measures for these temporary implants.

Predicting the Biodegradation of Magnesium Alloy Implants: Modeling, Parameter Identification, and Validation.

Magnesium (Mg) and its alloys can degrade gradually up to complete dissolution in the physiological environment. This property makes these biomaterials appealing for different biomedical applications, such as bone implants. In order to qualify Mg and its alloys for bone implant applications, there is a need to precisely model their degradation (corrosion) behavior in the physiological environment. Therefore, the primary objective develop a model that can be used to predict the corrosion behavior of Mg-based alloys in vitro, while capturing the effect of pitting corrosion. To this end, a customized FORTRAN user material subroutine (or VUMAT) that is compatible with the finite element (FE) solver Abaqus/Explicit (Dassault Systèmes, Waltham, MA, USA) was developed. Using the developed subroutine, a continuum damage mechanism (CDM) FE model was developed to phenomenologically estimate the corrosion rate of a biocompatible Mg–Zn–Ca alloy. In addition, the mass loss immersion test was conducted to measure mass loss over time by submerging Mg–Zn–Ca coupons in a glass reactor filled with simulated body fluid (SBF) solution at pH 7.4 and 37 °C. Then, response surface methodology (RSM) was applied to calibrate the corrosion FE model parameters (i.e., Gamma (γ), Psi (ψ), Beta (β), and kinetic parameter (Ku)). The optimum values for γ, ψ, β and Ku were found to be 2.74898, 2.60477, 5.1, and 0.1005, respectively. Finally, given the good fit between FE predictions and experimental data, it was concluded that the numerical framework precisely captures the effect of corrosion on the mass loss over time.

Enhanced corrosion and wear resistance of AZ31 magnesium alloy in simulated body fluid via electrodeposition of nanocrystalline zinc

In order to prolong the service life of magnesium-based implants in the human body, nanocrystalline zinc (30 nm) was electrodeposited on AZ31 magnesium alloy, its electrochemical and tribological properties in simulated body fluid (SBF) were investigated. It was demonstrated that electrodeposition of nanocrystalline zinc resulted not only in more than 4 times increase in corrosion resistance, but also in a significant enhancement in corrosive wear resistance of magnesium alloy. Detailed analyses were conducted to clarify the mechanism responsible for performance improvements. This is a biocompatible, economical and simple approach with the promise for large-scale application in surface modification of magnesium alloy implants.

Corrosion-resistant fluoridated Ca–Mg–P composite coating on magnesium alloys prepared via hydrothermal assisted sol–gel process

Abstract