Bioabsorbable Magnesium Alloy Research Articles

Influence of Noble Metals on Morphology and Topology of Structural Elements in Magnesium Alloy.

The main motivation for this study was to improve implant materials. The influence of silver and gold on the structure and mechanical properties of Mg-Nd-Zr alloy was studied. In the work, quantitative and qualitative evaluation of the structural components of magnesium alloy with noble metal additives was performed. The research methods used were investigation of the mechanical properties and observation of micro- and macrostructures. The results showed that modification of magnesium alloy with Ag and Au contributes to the formation of spherical intermetallics of smaller size groups, which become additional centers of crystallization and grind the cast structure. The best composition from additional alloying with silver and gold was determined. Their positive effect on the strength and ductility properties of the metal was established. Preclinical and clinical testing was performed and the prospects for noble metal modification of bioabsorbable magnesium alloy for implant production usage were shown.

Biodegradable PTMC-MAO composite coatings on AZ31 Mg-alloys for enhanced corrosion-resistance

Bio-absorbable magnesium (Mg) alloys exhibit significant promise for implantable medical devices, particularly in orthopedic applications. However, their limited corrosion resistance and rapid degradation rates have hindered their clinical translation. To address this long-standing challenge, here we developed a composite coating system (PTMC-MAO) for Mg-alloys, seamlessly integrating Microarc oxidation (MAO) and Poly-(Trimethylene Carbonate) (PTMC) layers. Leveraging the synergistic effects between MAO coatings, generated through micro-arc oxidation, and PTMC coatings, synthesized via gradual dropwise addition, our approach effectively controls corrosion and degradation rates of a widely applied Mg-alloy (AZ31) both in terms of kinetics and thermodynamics. Compared with the uncoated AZ31, the PTMC-MAO coatings exhibited greater positive Ecorr of −1290 mV and lower icorr of 5.3 nA· cm-2 with a significant 851-fold reduction. The coatings reached up to a distinguished protection efficiency (η) of 99.9 %, accompanying with the higher impedance |Z| of 4×105 Ω·cm2. The ΔpH change and the released Mg2+ concentration were 0.25 and 42 μg/ml, respectively, after 21 days of immersion. Both values were superior to those observed for the AZ31 substrate. These results highlight the transformational potential of PTMC-MAO composite coatings, indicating their feasibility as a new class of materials for engineering the surfaces of Mg-based degradable implants.

Metal Oxide Coating On Biodegradable Magnesium Alloys

Magnesium is a biodegradable metal that has potential in orthopaedics. It has several advantages over other metallic materials because it is biocompatible and degradable now being used for biomedical applications, including elimination of stress shielding effects, enhancing degradation properties and enhancing biocompatibility concern in vivo, eliminating the second surgery for implant removal. Bioabsorbable magnesium (Mg) and related alloys have been limited in their usage because of its lower corrosion resistance. Surface alteration and functionality, in addition to basic alloying, is an important technique to deal with Mg and its alloys' reduced corrosion resistance. Magnesium's rapid depreciation however is a double-edged sword because it's critical to match bone renewal to material corrosion. As a result, calcium phosphate coatings have been proposed as a way to slow down corrosion. There are various possible calcium phosphate phases and their coating methods and can give a few distinct properties to various applications. Despite magnesium's lower melting point and greater reactivity, calcium phosphate coatings require precise settings to be effective. Because of their toxicity, non-biodegradability, and much higher cost, the recently used inorganic conversion coatings are less appealing and their application is limited. Conversion coatings are a viable alternative technology that is based on a cost- effective, environmentally friendly, and biodegradable organic component. Surface chelating functional groups in these compounds allow them to link with the magnesium/surface hydroxide layer while also providing anchoring groups for the polymer topcoat. Nanoreservoirs with multilayer inhibitors for active self-healing corrosion resistance thrive in this environment. This study examines the organic conversion coatings for Mg and its alloys in depth.

In vitro degradation and multi-antibacterial mechanisms of β-cyclodextrin@curcumin embodied Mg(OH)2/MAO coating on AZ31 magnesium alloy

It is a challenging task to prepare a coating on Mg alloys for desirable corrosion resistance, good antibacterial ability and biocompatibility. In this research work, an in-situ Mg(OH)2 coating incorporated with sodium alginate (SA) and β-cyclodextrin (β-CD)@curcumin (Cur) was formed on the surface of micro arc oxidation (MAO) coated AZ31 alloy via a low temperature hydrothermal method. Characterization techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometer (FT-IR) and scanning electron microscope (SEM) were employed to characterize the chemical composition and surface morphology of the coatings. The corrosion protection ability of the coatings was monitored via electrochemical polarization, hydrogen evolution and immersion tests. Photothermal antibacterial ability and cytocompatibility of the coatings were evaluated by plate counting method under the irradiation of 808 nm-near infrared light, in vitro cytotoxicity tests (MTT) and live/dead cell staining. The results indicate that a chelation of the organic molecules led to the formation of a MAO/(β[email protected])-SA-Mg(OH)2 coating with excellent corrosion protection, multi- antibacterial ability and almost no toxicity to the cells. Especially, the coating provided photothermal performance through the light absorption of Cur, which was encapsulated by β-CD to improve its bioavailability. SA enhanced the binding force between the drug and the substrate. This novel coating designated the potential application on bioabsorbable magnesium alloys.

Evaluation of drug-eluting nanoparticle coating on magnesium alloy for development of next generation bioabsorbable cardiovascular stents.

Since the introduction of bioabsorbable magnesium alloys into cardiovascular stent technology, many researches have been conducted to improve these metallic scaffolds. Various coatings and different coating techniques, super plastic deformation techniques and synthesizing different Mg-based alloy are examples of such efforts. In this study, a magnesium based alloy (WE43) was coated with dexamethasone loaded polymeric nanoparticles via electrospraying method. Drug release behavior, drug inhibitory effects, surface properties and cell responses to the surface were evaluated. Drug release profile was investigated and compared to drug-loaded nanoparticle on stainless steel as a control. The inhibitory effects of the drug-loaded nanoparticle coatings on smooth muscle cells was evaluated via MTT assay. Endothelial cells response to the surface was investigated by SEM. The results showed that contact angle and roughness of the surface were 131° and 600-800nm, respectively. Drug release studies showed a burst release less than 30% after 24h which followed by nearly zero order release kinetic. MTT assay showed that SMCs viability decreased to 60% and 25% after 24 and 72h, respectively. SEM images indicated proper adhesion and proliferation of endothelial cells on the surface. The findings suggest that nanoparticle-coated surfaces could effectively inhibit SMC proliferation meanwhile provide desirable surface features for adhesion and proliferation of endothelial cell on magnesium alloy based stents.

A novel Mg(OH)2/MgFx(OH)1−x composite coating on biodegradable magnesium alloy for coronary stent application

To enhance the corrosion resistance of bioabsorbable magnesium alloys, a Mg(OH)2/MgFx(OH)1−x inorganic coating was prepared on a AZ31B magnesium alloy by a simple two-step immersion approach. The surface analysis, processing optimization, adhesion properties, in vitro corrosion behavior and biocompatibility were investigated. The composite coating significantly improved the adhesion of poly(trimethylene carbonate) coating on the surface (level 1). The corrosion resistance of the optimized sample was significantly improved (Icorr=7.1 × 10−8 A·cm–2) due to the blocking of defects by the Mg(OH)2 nanosheet. In addition, the optimized sample exhibited better in vitro cytocompatibility and hemocompatibility.

In vitro degradation and biocompatibility of vitamin C loaded Ca-P coating on a magnesium alloy for bioimplant applications

Molecular recognition was utilized to fabricate bioinspired calcium phosphate (Ca-P) coating on bioabsorbable magnesium alloys through small biomolecules such as Vitamin C (VC). Ca-P and VC hybrid coating (Ca-PVC) was successfully fabricated on AZ31 Mg alloy. The surface morphology and chemical composition of the coatings were investigated using SEM, XRD, and FTIR together with XPS. The results showed that the Ca-PVC coating was composed of bamboo leaf-like Ca-P particles with a thickness of about three times that of the Ca-P coating. The surface roughness of the Ca-PVC coating (1.12 ± 0.12 μm) was lower than that (3.14 ± 1.93 μm) of Ca-P coating, suggesting the formation of refined Ca-P particles resulting from the VC addition. The corrosion resistance of the coated samples was characterized via electrochemical polarization, impedance spectroscopy, and immersion hydrogen evolution tests. The cell toxicity of the coated samples was evaluated utilizing mouse MC3T3-E1 pre-osteoblasts. The charge transfer resistance (Rct) of the Ca-PVC coated alloy increased as compared to the bare and Ca-P coated alloy samples. The Ca-PVC coated alloy exhibited minimal corrosion current density (1.36 × 10−6 A cm−2), which is one order of magnitude lower in comparison to that of the Ca-P coated alloy. These results confirm that VC addition greatly enhanced the coating resistance on AZ31 Mg alloy. It was also noticed that the Ca-PVC coated samples rapidly induced the formation of apatite after immersion in Hank's solution. VC was mainly transformed to L-Threonic acid, which facilitated the nucleation process of the Ca-PVC coating and significantly increased the thickness, density, and bonding strength of the coating. With enhanced corrosion resistance property and excellent biocompatibility, Ca-PVC coating has great potential for application in biodegradable Mg-based alloys.

Review – Investigation of bio-absorbable magnesium AZ91 alloy using powder metallurgy technique

Metal composites are used for a couple of cautious additions. Biomaterials are by and large used to supersede the declined bones and tissues. The non-biodegradable products are challaneging one for disposing without affect the global environment. Same problem also raised in medical non-biodegradable materials like bone transplant products. Magnesium combinations are preferred as biodegradable material that is imperative for human processing and regularly identified in bone. This research Bio-absorbable magnesium alloy (AZ91) selected as base material along with 1%-Zn, 9%-Al, 1–4%-Mn, made by powder metallurgy strategy and the properties are analysed. The hardness range and Microstrurcre nature investigated for load-bearing applications.

The use of bioabsorbable compression screws & polyethylene tension band for fixation of displaced olecranon fractures

IntroductionTransverse fractures of the olecranon are commonly fixed using tension-band wiring techniques. However the superficial nature of this area leads to high complication rates requiring removal of metalwork. The purpose of this retrospective study is to report and evaluate functional outcomes of polyethylene tension-band and bioabsorbable Magnesium alloy screw fixation of olecranon fractures. MethodsA retrospective case-control study was undertaken. Demographics, injury type and post-operative details were collected. All patients were treated in the same institution by a single surgeon. Primary outcomes included radiographic healing and post-operative range of motion. Secondary outcome was post-operative complications. ResultsA total of five cases were identified. Mean age was 52.4. The control group was made up of six patients treated with a traditional tension band wire fixation. One patient in study group was lost to follow up. 80% of fractures in study group demonstrated anatomic post-operative radiographic union, compared with 83% of control group. All patients had range of motion above 100°, with full protonation and supination. One patient did have an extension lag of 15°. ConclusionSurgical repair of olecranon fractures is often complicated by the need for re-operation. This method provides both intramedullary fixation and conversion of distraction forces to compression forces with bioabsorbable materials, and aims to reduce the high re-operation rates commonly seen by avoiding the use of permanent indwelling metal hardware.

Biocorrosion resistance and biocompatibility of Mg–Al layered double hydroxide/poly-L-glutamic acid hybrid coating on magnesium alloy AZ31

It is of necessity to seal porous layered double hydroxide (LDH) coating on bioabsorbable magnesium alloys to further enlarge its long-term protection using an organic top layer with good biocompatibility. An Mg-Al LDH coating sealed by poly-l-glutamic acid (PGA) is prepared on the AZ31 magnesium alloy. The LDH coating and PGA coating are synthesized by hydrothermal treatment and vacuum freeze-drying method. The structure and morphology of the coatings are characterized by means of X-ray photoelectron spectrometer (XPS), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, field-emission scanning electronic microscope (FE-SEM) and energy dispersive X-ray spectrometer (EDS). The corrosion protection afforded by the coatings is measured using electrochemical polarization and impedance spectroscopy and hydrogen evolution tests. The results indicate that the appropriate addition of PGA can postpone the time that pH values reach the minimum. The hybrid coatings effectively provide a corrosion protection for the AZ31 alloy. An acceptable cytocompatibility for mouse embryonic fibroblasts (NIH 3T3) of the hybrid coating is shown by methyl thiazolyl tetrazolium (MTT) assay and live/dead staining. Finally, a biodegradation mechanism of the coating is proposed and discussed.

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.

Formation and Phase Transition of Crystalline Calcium Phosphate on Bioabsorbable Magnesium Alloy under Alkali Condition

In order to improve the corrosion resistance, bioabsorbable magnesium (Mg) alloy was immersed in an aqueous solution with three times of Ca2+ and HPO42- in comparison with those of conventional SBF at the moderate temperature. After immersion in the solution, the whole surface of Mg alloy was coated with plate-like crystals consisting of octacalcium phosphate (OCP). Then the OCP-coated Mg alloy was immersed in the alkali solution. Although significant change of morphology was not observed, the OCP formed on the Mg alloy was transformed to hydroxyapatite (HAp) under alkali condition.

Mechanical and morphological investigation of bio-degradable magnesium AZ31 alloy for an orthopedic application

Abstract Metallic materials are used for several surgical implants. Biomaterials are widely used to replace the degenerated organs. The non-biodegradable material must be removed by a secondary surgical procedure which causes additional risk to the patients. The magnesium alloys are used as a potential biodegradable material which is essential to human metabolism and found naturally in bone. In this study, Bio-absorbable magnesium alloy AZ31 is used as base material with 1%Zn-3%Al-1-6%Mn which is prepared by stir casting technique and evaluated under mechanical and morphological aspects. Finally the alloy can be preferred as an orthopedic implant for load bearing application.

In Vitro and in Vivo Studies on Two-Step Alkali-Fluoride-Treated Mg-Zn-Y-Nd Alloy for Vascular Stent Application: Enhancement in Corrosion Resistance and Biocompatibility.

Bioabsorbable magnesium alloys are becoming prominent materials for cardiovascular stents, as their desirable mechanical properties and favorable biosafety. However, the rapid corrosion of magnesium alloys under physiological conditions hinders their wider application as medical implant materials. Fluoride chemical conversion treatment is an effective and simple technique to improve the corrosion resistance for magnesium alloys. Despite previous literature reporting on fluoride chemical conversion treatment with hydrofluoric acid (HF) in different conditions, some defects are still present on the surface of the coating. In this study, we report on a two-step alkali-fluoride treatment of magnesium alloy by effectively removing the second phase in the substrate surface and form a dense and flawless magnesium fluoride (MgF2) coating to endow the magnesium alloy greater corrosion resistance. The results showed that the serious pitting corrosion caused by galvanic corrosion could be effectively prevented after removing of the second phase of the surface. In vivo tests in a rat subcutaneous implantation model showed that two-step alkali-fluoride-treated MgZnYNd alloy (MgZnYNd-A-F) uniformly corroded with a low corrosion rate. No subcutaneous gas cavities or significant inflammatory cell infiltration were observed for MgZnYNd-A-F in in vivo tests. The two-step alkali-fluoride treatment can significantly improve the corrosion resistance and biocompatibility of magnesium alloy, which has great potential in the application of vascular stents because of its simplicity and effectiveness.

Influence of design and postprocessing parameters on the degradation behavior and mechanical properties of additively manufactured magnesium scaffolds

Magnesium shows promising properties concerning its use in absorbable implant applications such as biodegradability, improved mechanical strength and plastic deformability. Following extensive research, the first fixation and compression screws composed of magnesium rare earth alloys were commercialised, notably in the field of orthopaedic surgery. Preclinical and clinical follow-up studies showed that the rapid degradation of unprotected metallic Magnesium surfaces and concomitant hydrogen gas bursts still raise concern regarding certain surgical indications and need to be further improved. In order to enlarge the scope of further applications, the development of future magnesium implants must aim at freedom of design and reduction of volume, hereby enabling higher functionalised implants, as e.g. plate systems or scaffold grafts for bone replacement therapy. In order to overcome the boundaries of conventional manufacturing methods such as turning or milling, the process of Laser Powder Bed Fusion (LPBF) for magnesium alloys was recently introduced. It enables the production of lattice structures, therefore allowing for reduction of implant material volume. Nevertheless, the concomitant increase of free surface of such magnesium scaffolds further stresses the aforementioned disadvantages of vast degradation and early loss of mechanical stability if not prevented by suitable postprocessing methods. Magnesium scaffold structures with different pore sizes were therefore manufactured by LPBF and consequently further modified either by thermal heat treatment or Plasma Electrolytic Oxidation (PEO). Implant performance was assessed by conducting degradation studies and mechanical testing. PEO modified scaffolds with small pore sizes exhibited improved long-term stability, while heat treated specimens showed impaired performance regarding degradation and mechanical stability. Statement of SignificanceMagnesium based scaffold structures offer wide possibilities for advanced functionalized bioabsorbable implants. By implementing lattice structures, big implant sizes and mechanically optimized implant geometries can be achieved enabling full bone replacement or large-scale plate systems, e.g. for orthopedic applications. As shape optimization and lattice structuring of such scaffolds consequently lead to enlarged surface, suitable design and postprocessing routines come into focus. The presented study addresses these new and relevant topics for the first time by evaluating geometry as well as heat and surface treatment options as input parameters for improved chemical and mechanical stability. The outcome of these variations is measured by degradation tests and mechanical analysis. Evaluating these methods, a significant contribution to the development of absorbable magnesium scaffolds is made. The findings can help to better understand the interdependence of high surface to volume ratio Magnesium implants and to deliver methods to incorporate such lattice structures into future large-scale implant applications manufactured from bioabsorbable Magnesium alloys.

Laser Shock Processing as an Advanced Technique for the Surface and Mechanical Resistance Properties Modification of Bioabsorbable Magnesium Alloys

Laser shock processing (LSP) is increasingly applied as an effective technology for the improvement of metallic materials’ mechanical and surface properties in different types of components, mostly as a means of enhancement of their fatigue life behavior. As reported in previous contributions by the authors, a main effect resulting from the application of the LSP technique consists in the generation of relatively deep compression residual stresses fields into metallic components allowing an improved mechanical behaviour. On the other hand, Mg and its alloys have gained increasing relevance as natural biomaterials as their mechanical properties are in the same range as those corresponding to natural bone as well as due to their inherent bioabsorbable properties. In the present paper, the application of the LSP technology to biocompatible bioabsorbable Mg alloys suitable for chirurgical implementation is envisaged, the experimental verification of the residual stresses fields induced and the experimental characterization of the surface properties introduced by means of the treatment being specifically considered.

A numerical study on the application of the functionally graded bioabsorbable materials in the stent design

BackgroundAngioplasty with stenting is one of the primary treatment for coronary artery disease, hence, performance of the stent is deemed important. Bioabsorbable stents are the new generation of stents. Bioabsorbable magnesium alloys are a promising solution for adverse effects of long-term usage of stents. While their corrosion mechanics and biocompatibility have extensively been studied, there are no studies on application of functionally graded materials (FGM) on reduction of dogboning in bioabsorbable stents. MethodsThe objective of this study was at reducing the dogboning via the application of the FGM. A combination of the finite element (FE) method and optimization algorithm were employed to analyse/optimize the mechanical behaviour of bioabsorbable stents. Proposed FGM, in this study, was a combination of AZ80 and WE43 magnesium alloys. Dogboning of the FGM stent was chosen as objective function to be minimized and heterogeneous index was chosen as control variable in the optimization algorithm. ResultsThe results revealed that the optimum FGM stent with heterogeneous index of 1.4625 has lower dogboning (63%) compared to that of the uniform stents made of AZ89 or WE43 magnesium alloy. ConclusionsFurthermore, the results suggested that the plastic material properties have higher impact on the mechanical behaviour of the stent in comparison to the elastic material properties.

Effect of Crystalline Calcium Phosphate Coatings Prepared in an Aqueous Solution on Corrosion Resistance of Bioabsorbable Magnesium Alloy

Bioabsorbable magnesium (Mg) alloy was anodized in 1.0 M NaOH solution. Then the anodized Mg alloy was immersed in an aqueous solution with three times concentration of Ca2+and HPO42-in comparison with those of biological environment to improve its corrosion resistance. The whole surface of Mg alloy was successfully coated with crystalline calcium phosphate (CaP) within 1 day. The CaP coated Mg alloys showed high corrosion resistance in SBF.

A feasibility study of using biodegradable magnesium alloy in glaucoma drainage device.

Technological advances in glaucoma have challenged the traditional treatment paradigm. Historically incisional surgery has been used in cases of advanced disease and/or uncontrolled intraocular pressures resistant to medical or laser interventions. More recently, perhaps due to advancements in imaging, surgery has been suggested to be beneficial earlier in the treatment paradigm. Despite these trends, surgical manipulation of the tissues and unpredictability of wound healing continue to result in surgical failure. Magnesium is an essential element for human body and plays a critically important role in maintaining the functional and structural integrity of several tissues, including the eye. Due to several of its advantageous properties such as non-toxicity, biodegradability, and high biological compatibility, magnesium alloy has attracted great attention as a novel biomaterial. Biodegradable cardiovascular stents made of magnesium alloy have already been introduced into clinical practice. The purpose of this review is to determine if bioabsorbable magnesium alloys can be utilized as a promising candidate for the development of a new generation of glaucoma surgical assistive devices.

Design and development of an ultrasonic vibration assisted turning system for machining bioabsorbable magnesium alloys

Magnesium alloys are emerging as potential candidates for degradable temporary implants thanks to their mechanical properties that are closer to those of the natural bone compared to other metals, their good biocompatibility, non-toxicity and biodegradability. However, once placed in the human body, they tend to corrode too quickly, loosening their structural stability before the end of the period of complete healing. Different techniques have been applied to magnesium alloys in order to improve their surface integrity, which is directly correlated with the corrosion resistance. In this study, an Ultrasonic Vibration Turning (UVT) system was applied to machine a biodegradable magnesium alloy. The vibrating tool was preliminary designed with Finite Element (FE) software aid, in order to identify a first model of sonotrode shape, to match the resonance frequency of a commercial transducer. Consequently, a procedure for the system fine tuning was carried out, involving the indirect measure of the system impedance. Finally, different process parameters, namely cutting speed and depth of cut, were used in order to machine the magnesium alloy, obtaining different surface textures. The obtained results suggest that the ultrasonic vibration turning can be efficiently applied to machine biodegradable magnesium-based materials for biomedical applications.