In vitro corrosion resistance of a Ta2O5 nanofilm on MAO coated magnesium alloy AZ31 by atomic layer deposition

An oxidized dextran-composite self-healing coated magnesium scaffold reduces apoptosis to induce bone regeneration

Self-healing coatings have shown promise in controlling the degradation of scaffolds and addressing coating detachment issues. However, developing a self-healing coating for magnesium (Mg) possessing multiple biological functions in infectious environments remains a significant challenge. In this study, a self-healing coating was developed for magnesium scaffolds using oxidized dextran (OD), 3-aminopropyltriethoxysilane (APTES), and nano-hydroxyapatite (nHA) doped micro-arc oxidation (MHA), named OD-MHA/Mg. The results demonstrated that the OD-MHA coating effectively addresses coating detachment issues and controls the degradation of Mg in an infectious environment through self-healing mechanisms. Furthermore, the OD-MHA/Mg scaffold exhibits antibacterial, antioxidant, and anti-apoptotic properties, it also promotes bone repair by upregulating the expression of osteogenesis genes and proteins. The findings of this study indicate that the OD-MHA coated Mg scaffold possessing multiple biological functions presents a promising approach for addressing infectious bone defects. Additionally, the study showcases the potential of polysaccharides with multiple biological functions in facilitating tissue healing even in challenging environments.

Atomic Layer Deposition of Tantalum Oxide Films on 3D-Printed Ti6Al4V Scaffolds with Enhanced Osteogenic Property for Orthopedic Implants

There is an evident advantage in personalized customization of orthopedic implants by 3D-printed titanium (Ti) and its alloys. However, 3D-printed Ti alloys have a rough surface structure caused by adhesion powders and a relatively bioinert surface. Therefore, surface modification techniques are needed to improve the biocompatibility of 3D-printed Ti alloy implants. In the present study, porous Ti6Al4V scaffolds were manufactured by a selective laser melting 3D printer, followed by sandblasting and acid-etching treatment and atomic layer deposition (ALD) of tantalum oxide films. SEM morphology and surface roughness tests confirmed that the unmelted powders adhered on the scaffolds were removed by sandblasting and acid-etching. Accordingly, the porosity of the scaffold increased by about 7%. Benefiting from the self-limitation and three-dimensional conformance of ALD, uniform tantalum oxide films were formed on the inner and outer surfaces of the scaffolds. Zeta potential decreased by 19.5 mV after depositing tantalum oxide films. The in vitro results showed that the adhesion, proliferation, and osteogenic differentiation of rat bone marrow mesenchymal stem cells on modified Ti6Al4V scaffolds were significantly enhanced, which may be ascribed to surface structure optimization and the compatibility of tantalum oxide. This study provides a strategy to improve the cytocompatibility and osteogenic differentiation of porous Ti6Al4V scaffolds for orthopedic implants.

Novel coatings for the continuous repair of human bone defects

Bone defects are the second most common tissue grafts after blood. However, bone grafts face several problems, such as bone scaffolds, which have low bioactivity and are prone to corrosion. Much of the current research on bone scaffolds is focused on the mechanical aspects such as structure and strength. Surface modification of the bone scaffold is carried out in terms of the mechanical structure or structural design of the bone scaffold with reference to a bionic structure. However, with the development of mechanical designs, materials science, and medicine, many studies have reported that promoting bone growth by modifying the structure of the scaffold or coating is not possible. Therefore, the application of a bioactive coating to the surface of the bone scaffold is particularly important to generate a synergistic effect between the structure and active coating. In this article, we present several perspectives to improve the bioactivity of bone scaffolds, including corrosion resistance, loading of bioactive coatings or drugs on bone scaffolds, improved adhesion to the surface of the bone scaffolds, immune response modulation, and drawing on bionic structures during manufacturing.

Progress in bioactive surface coatings on biodegradable Mg alloys: A critical review towards clinical translation

Mg and its alloys evince strong candidature for biodegradable bone implants, cardiovascular stents, and wound closing devices. However, their rapid degradation rate causes premature implant failure, constraining clinical applications. Bio-functional surface coatings have emerged as the most competent strategy to fulfill the diverse clinical requirements, besides yielding effective corrosion resistance. This article reviews the progress of biodegradable and advanced surface coatings on Mg alloys investigated in recent years, aiming to build up a comprehensive knowledge framework of coating techniques, processing parameters, performance measures in terms of corrosion resistance, adhesion strength, and biocompatibility. Recently developed conversion and deposition type surface coatings are thoroughly discussed by reporting their essential therapeutic responses like osteogenesis, angiogenesis, cytocompatibility, hemocompatibility, anti-bacterial, and controlled drug release towards in-vitro and in-vivo study models. The challenges associated with metallic, ceramic and polymeric coatings along with merits and demerits of various coatings have been illustrated. The use of multilayered hybrid coating comprising a unique combination of organic and inorganic components has been emphasized with future perspectives to obtain diverse bio-functionalities in a facile single coating system for orthopedic implant applications.

Surface Modification of WE43 Magnesium Alloys with Dopamine Hydrochloride Modified GelMA Coatings

As biodegradable medical implants, magnesium alloys have attracted great concerns due to their desirable biological and mechanical performances. Nevertheless, the overfast degradation rate of magnesium alloys makes it difficult to make full use of their potential in medical sciences. Therefore, it is a hot issue to control the degradation rate and functionalize the magnesium alloys via surface modifications. Herein, methacrylate gelatin (GelMA) hydrogel was adopted as coatings on the surface of WE43 magnesium alloys to control the degradation behaviors of magnesium alloys. Inspired by mussels, dopamine (DOPA) hydrochloride was adopted to modify GelMA to further functionalize the coatings. The compositions, swelling properties, degradation behaviors, and morphologies of samples were characterized by UV-Vis spectrophotometer, nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), and immersion test. It was shown that GelMA-DOPA composites could be obtained and the swelling and degradation behaviors of magnesium alloys could be controlled by adjusting the compositions of GelMA and DOPA. Furthermore, the GelMA-DOPA hydrogel coatings can be tightly bonded to the Mg alloys.

3D Printed Integrated Bionic Oxygenated Scaffold for Bone Regeneration

The repair of large bone defects remains a challenging problem in bone tissue engineering. Ischemia and hypoxia in the bone defect area make it difficult for seed cells to survive and differentiate, which fail to perform effective tissue regeneration. Current oxygen-producing materials frequently encounter problems such as a rapid degradation rate, insufficient mechanical properties, difficult molding, and cumbersome fabrication. Here, a novel three-dimensional (3D) printed integrated bionic oxygenated scaffold was fabricated with gelatin-CaO₂ microspheres, polycaprolactone (PCL), and nanohydroxyapatite (nHA) using low-temperature molding 3D printing technology. The scaffold had outstanding mechanical properties with bionic hierarchical porous structures. In vitro reports showed that the scaffold exhibited excellent cytocompatibility and could release O₂ sustainably for more than 2 weeks, which significantly enhanced the survival, growth, and osteogenic differentiation of bone marrow mesenchymal stem cells under hypoxia. In vivo experiments revealed that the scaffold facilitated efficient bone repair after it was transplanted into a rabbit calvarial defect model. This result may be due to the scaffolds reducing hypoxia-inducible factor-1α accumulation, improving the expression of osteogenic regulatory transcription factors, and accelerating osteogenesis. In summary, the integrated bionic PCL/nHA/CaO₂ scaffold had excellent capabilities in sustainable O₂ release and bone regeneration, which provided a promising clinical strategy for bone defect repair.

A Decade of Progress on MAO-Treated Tantalum Surfaces: Advances and Contributions for Biomedical Applications

Micro-structured coatings with functional properties have been investigated due to a wide range of applications. It is known that micro-structures can play an important role in surface interactions determining the materials’ performance. Amongst the other materials, there has been an increasing interest in tantalum oxide (Ta₂O₅). This attention is mainly due to its variety of properties: biocompatibility and bioactivity; high dielectric constant; good thermal and chemical stability; excellent corrosion and mechanical resistance. Moreover, there is a wide range of applications in which the properties can be fitted. Furthermore, according to the final application, these properties can be enhanced or tailored through surface micro-structures manipulation. Due to this purpose, over the past decade, Ta surface modification by micro-arc oxidation (MAO) has been investigated mostly for biomedical applications. Therefore, this review focuses on Ta surface functionalization using the MAO technique. A clear understanding of the micro-discharge phenomena and the formation mechanism of a Ta₂O₅ anodic coating by MAO is supplied. The Ta₂O₅ coating morphology, topography, chemistry, and structure are explored, establishing their correlation with the MAO parameters. Additionally, an understanding of Ta₂O₅’s biological, mechanical, and electrochemical properties is provided and reviewed.

Biocompatibility and corrosion evaluation of niobium oxide coated AZ31B alloy for biodegradable implants

Biodegradable magnesium (Mg) based implants have considerable interest in the biomedical field as their use nullifies the necessity for implant removal surgery and avoids the long-standing adverse reaction of permanent bioimplants. The degradation resistance and biocompatibility of the Mg alloys can be improved by coating them with a suitable thin film. Here, thin films of niobium and niobium oxide were developed on the AZ31B Mg alloy by sputtering technique and their biocompatibility and corrosion resistance was examined. X-ray diffraction (XRD) and Transmission electron microscope (TEM) techniques confirmed the crystallinity of the thin films. Subsequently, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) techniques were employed to evaluate the morphology and chemical composition of the thin film surfaces, respectively. Thin-film coated Mg alloys revealed good corrosion resistance compared to their uncoated bare counterparts in simulated body fluid (SBF). The contact angle study was performed on the coated specimens to investigate their wettability which revealed their hydrophobic character. The cell viability studies on thin-film coated specimens exhibited significant cell proliferation, and cell morphological studies showed good cell attachment and growth. The in vitro MTT assay on mouse osteoblast precursor cells (MC3T3-E1) indicated that the Nb-based coatings are cytocompatible and promote cell proliferation.

Effect of Graphite Content on the Conductivity, Wear Behavior, and Corrosion Resistance of the Organic Layer on Magnesium Alloy MAO Coatings

To impart electrical conductivity on magnesium alloy micro-arc oxidation coatings, a graphite/epoxy conductive layer was prepared on the surface of a ceramic layer in this work, focusing on wear behavior and corrosion resistance of the coating. At a graphite weight of 80 wt%, the square resistance of the coating decreased to 217.6 kΩ/□, and it exhibited good resistance. Combined with the distribution of graphite particles in the coating and the change in surface resistance, we determined that the conductive mechanism of the coating occurred through quantum tunneling when the graphite content was 60 wt%. When the graphite content increased from 60 to 80 and 100 wt%, the formation of conductive paths on the surface of the coating further improved the conductivity. The hardness of the organic coatings was positively related to the graphite content. Analysis of the wear scars and wear debris after dry friction and wear testing showed that the wear forms of the coating consisted of abrasive wear when the graphite content was in the range of 20–40 wt%. When the graphite content was in the range of 60–100 wt%, the wear forms of the coating consisted of abrasive wear and peeling wear.

Synthesis of Star 6-Arm Polyethylene Glycol-Heparin Copolymer to Construct Anticorrosive and Biocompatible Coating on Magnesium Alloy Surface

Magnesium alloy has become a research hotspot of the degradable vascular stent materials due to its biodegradability and excellent mechanical properties. However, its rapid degradation rate after implantation and the limited biocompatibility restrict its application in clinic. Constructing a multifunctional bioactive polymer coating on the magnesium alloys represents one of the popular and effective approaches to simultaneously improve the corrosion resistance and biocompatibility. In the present study, the copolymer of 6-arm polyethylene glycol and heparin (PEG-Hep) was successfully synthesized and then immobilized on the surface of chitosan (Chi)-modified magnesium alloy surface through electrostatic interaction to improve the corrosion resistance and biocompatibility. The results of attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy showed that a dense and compact coating was created on the magnesium alloy surface. The coating displayed excellent hydrophilicity. At the same time, the as-prepared coating can significantly not only improve the corrosion potential, reduce the corrosion current and the pH changes of the immersion solution, but also keep a relatively intact surface morphology after immersing in simulated body fluid solution for 14 days, demonstrating that the coating can significantly improve the corrosion resistance of the magnesium alloy. Moreover, the magnesium alloy with PEG-Hep coating exhibited excellent hemocompatibility according to the results of the hemolysis rate and platelet adhesion and activation. In addition, the modified magnesium alloy had a good ability to promote the endothelial cell adhesion and proliferation. Therefore, the PEG-Hep multifunctional coating can be applied in the surface modification of the biodegradable magnesium alloy stent to simultaneously improve the corrosion resistance and biocompatibility.

Advances in coatings on magnesium alloys for cardiovascular stents - A review

Magnesium (Mg) and its alloys, as potential biodegradable materials, have drawn wide attention in the cardiovascular stent field because of their appropriate mechanical properties and biocompatibility. Nevertheless, the occurrence of thrombosis, inflammation, and restenosis of implanted Mg alloy stents caused by their poor corrosion resistance and insufficient endothelialization restrains their anticipated clinical applications. Numerous surface treatment tactics have mainly striven to modify the Mg alloy for inhibiting its degradation rate and enduing it with biological functionality. This review focuses on highlighting and summarizing the latest research progress in functionalized coatings on Mg alloys for cardiovascular stents over the last decade, regarding preparation strategies for metal oxide, metal hydroxide, inorganic nonmetallic, polymer, and their composite coatings; and the performance of these strategies in regulating degradation behavior and biofunction. Potential research direction is also concisely discussed to help guide biological functionalized strategies and inspire further innovations. It is hoped that this review can give assistance to the surface modification of cardiovascular Mg-based stents and promote future advancements in this emerging research field.

Sequence Does Not Matter: The Biomedical Applications of DNA-Based Coatings and Cores

Biomedical applications of DNA are diverse but are usually associated with specific recognition of target nucleotide sequences or proteins and with gene delivery for therapeutic or biotechnological purposes. However, other aspects of DNA functionalities, like its nontoxicity, biodegradability, polyelectrolyte nature, stability, thermo-responsivity and charge transfer ability that are rather independent of its sequence, have recently become highly appreciated in material science and biomedicine. Whereas the latest achievements in structural DNA nanotechnology associated with DNA sequence recognition and Watson–Crick base pairing between complementary nucleotides are regularly reviewed, the recent uses of DNA as a raw material in biomedicine have not been summarized. This review paper describes the main biomedical applications of DNA that do not involve any synthesis or extraction of oligo- or polynucleotides with specified sequences. These sequence-independent applications currently include some types of drug delivery systems, biocompatible coatings, fire retardant and antimicrobial coatings and biosensors. The reinforcement of DNA properties by DNA complexation with nanoparticles is also described as a field of further research.

Accelerated biodegradation of iron-based implants via tantalum-implanted surface nanostructures

In recent years, pure iron (Fe) has attracted significant attention as a promising biodegradable orthopedic implant material due to its excellent mechanical and biological properties. However, in physiological conditions, Fe has an extremely slow degradation rate with localized and irregular degradation, which is problematic for practical applications. In this study, we developed a novel combination of a nanostructured surface topography and galvanic reaction to achieve uniform and accelerated degradation of an Fe implant. The target-ion induced plasma sputtering (TIPS) technique was applied on the Fe implant to introduce biologically compatible and electrochemically noble tantalum (Ta) onto its surface and develop surface nano-galvanic couples. Electrochemical tests revealed that the uniformly distributed nano-galvanic corrosion cells of the TIPS-treated sample (nano Ta–Fe) led to relatively uniform and accelerated surface degradation compared to that of bare Fe. Furthermore, the mechanical properties of nano Ta–Fe remained almost constant during a long-term in vitro immersion test (~40 weeks). Biocompatibility was also assessed on surfaces of bare Fe and nano Ta–Fe using in vitro osteoblast responses through direct and indirect contact assays and an in vivo rabbit femur medullary cavity implantation model. The results revealed that nano Ta–Fe not only enhanced cell adhesion and spreading on its surface, but also exhibited no signs of cellular or tissue toxicity. These results demonstrate the immense potential of Ta-implanted surface nanostructures as an effective solution for the practical application of Fe-based orthopedic implants, ensuring long-term biosafety and clinical efficacy.

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The degradation rate of nanostructured Fe implants was accelerated by TIPS technique.

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Ta ions were accelerated strongly toward the Fe surface by TIPS process.

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Nano Ta–Fe showed long-term mechanical stability and accelerated degradation rate.

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Nanostructured Ta–Fe surface showed enhanced in vitro and in vivo cellular responses.

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Ta-implanted Fe is a promising material for biodegradable orthopedic implants.

Solution-Processed Two-Dimensional Metal Oxide Anticorrosion Nanocoating

Molecularly thin two-dimensional (2D) nanomaterials are attractive building blocks for constructing anticorrosion nanocoatings as an ultimate pursuit in the metal-related industry. However, the nanocoating of prefocused graphene is far from industrial demands due to its high cost, low scalability, and insufficient quality. We propose all requirements to realize rational anticorrosion nanocoating of metal oxide nanosheets. The proof-of-concept study with Ti_0.87O₂ and Ca₂Nb₃O₁₀ nanosheets demonstrates that the 10 and 20 nm thick coatings fabricated by a facile layer-by-layer (LbL) self-assembly on stainless steel (SUS) give perfect inhibition efficiency (IE) values of 99.92% and 99.89%, respectively. A driving test with a nanosheet-coated car-baffle demonstrated suitable corrosion resistance and mechanical and thermal robustness for industrial applications. The revealed and controlled thermal oxidation mechanisms are critical toward high-temperature application of the 2D oxide anticorrosion nanocoating. The advantages of nanosheet coating and extensible materials design will open a solid but exciting route to anticorrosion nanotechnology.

Preliminary study on modelling, fabrication by photo-chemical etching and in vivo testing of biodegradable magnesium AZ31 stents

Magnesium metal (Mg) is a promising material for stent applications due to its biocompatibility and ability to be resorbed by the body. Manufacturing of stents by laser cutting has become an industry standard. Our alternative approach uses photo-chemical etching to transfer a pattern of the stent onto a Mg sheet. In this study, we present three stages of creating and validating a stent prototype, which includes design and simulation using finite element analysis (FEA), followed by fabrication based on AZ31 alloy and, finally, in vivo testing in peripheral arteries of domestic pigs. Due to the preliminary character of this study, only six stents were implanted in two domestic farm pigs weighing 25-28 kg and they were evaluated after 28 days, with an interim follow-up on day 14. The left and right superficial femoral, the left iliac, and the right renal artery were selected for this study. The diameters of the stented artery segments were evaluated at the time of implantation, on day 14 and then, finally, on day 28, by quantitative vessel analysis (QVA) using fluoroscopic imaging. Optical Coherence Tomography (OCT) imaging displayed some malposition, breaks, stacking, and protrusion into the lumen at the proximal, distal, and mid-sections of the stented arteries. The stents degraded with time, but simultaneously became embedded in the intima. After 28 days, the animals were euthanized, and explanted vessels were fixed for micro-CT imaging and histology studies. Micro-CT imaging revealed stent morphological and volumetric changes due to the in-body degradation. An in vivo corrosion rate of 0.75 mm/year was obtained by the CT evaluation. The histology suggested no-life threatening effects, although moderate injury, inflammation, and endothelialization scores were observed.

Construction of tantalum/poly(ether imide) coatings on magnesium implants with both corrosion protection and osseointegration properties

Poly(ether imide) (PEI) has shown satisfactory corrosion protection capability with good adhesion strength as a coating for magnesium (Mg), a potential candidate of biodegradable orthopedic implant material. However, its innate hydrophobic property causes insufficient osteoblast affinity and a lack of osseointegration. Herein, we modify the physical and chemical properties of a PEI-coated Mg implant. A plasma immersion ion implantation technique is combined with direct current (DC) magnetron sputtering to introduce biologically compatible tantalum (Ta) onto the surface of the PEI coating. The PEI-coating layer is not damaged during this process owing to the extremely short processing time (30 s), retaining its high corrosion protection property and adhesion stability. The Ta-implanted layer (roughly 10-nm-thick) on the topmost PEI surface generates long-term surface hydrophilicity and favorable surface conditions for pre-osteoblasts to adhere, proliferate, and differentiate. Furthermore, in a rabbit femur study, the Ta/PEI-coated Mg implant demonstrates significantly enhanced bone tissue affinity and osseointegration capability. These results indicate that Ta/PEI-coated Mg is promising for achieving early mechanical fixation and long-term success in biodegradable orthopedic implant applications.

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PEI coating with subsequent Ta ion implantation was prepared on WE43 Mg alloy implant.

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The corrosion resistance of Mg alloy implant was improved by Ta embedded PEI coating.

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The wettability of PEI coating layer was enhanced by embedded Ta on its top-surface.

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Ta embedded PEI coating significantly improved in vitro and in vivo responses.

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Ta embedded PEI-coated Mg is highly suitable as a biodegradable orthopedic implant material.

In vivo assessment of biodegradable magnesium alloy ureteral stents in a pig model

Today, ureteral stent technology is making progress towards the reduction of complications and patient discomfort. Therefore, magnesium alloys have become excellent candidate materials for manufacturing ureteral stents due to their biodegradability and antibacterial activity. Built on our previous work on biodegradable magnesium alloys, this article reports a semisolid rheo-formed magnesium implant that displays degradability and biocompatibility in vivo, and feasibility as ureteral stents in a pig model. Refined non-dendritic microstructure was observed in the rheo-formed alloy, whose grain size and shape factor were ca. 25.2 μm and ca. 1.56 respectively. Neither post-interventional inflammation nor pathological changes were observed in the urinary system during the implantation period of 14 weeks, and the degradation profile (14 weeks) meets the common requirement for the indwelling time of ureteral stents (8 to 16 weeks). Furthermore, histopathological observation and urinalysis results confirmed that the alloy had significantly higher antibacterial activity than the medical-grade stainless steel control. To our knowledge, this is the first in vivo study of biodegradable magnesium alloy as urinary implants in large animal models. Our results demonstrate that magnesium alloys may be a reasonable option for manufacturing biodegradable ureteral stents.

Effect of GelMA Hydrogel Coatings on Corrosion Resistance and Biocompatibility of MAO-Coated Mg Alloys

Micro-arc oxidation (MAO) treatment is a simple and effective technique to improve the corrosion resistance for magnesium alloys. However, the presence of micro-pores and cracks on the coatings provides paths for corrosive ions to penetrate into and react with the substrate, limiting the long-term corrosion resistance. In this paper, we designed a composite coating with which GelMA hydrogel coatings with varying thicknesses were prepared on the surface of MAO-coated magnesium alloys via a dip-coating method, aiming to improve the biocorrosion resistance and biocompatibility. The surface morphology, the chemical composition of GelMA hydrogels, and the crystallographic structure of magnesium alloys were characterized by scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD), respectively. The corrosion resistance and biocompatibility of all samples were evaluated through electrochemical and biological experiments. The results demonstrated that the addition of GelMA hydrogel could effectively seal the pores and improve the corrosion resistance and biocompatibility of MAO-coated magnesium alloys, especially for the sample with one layer of GelMA hydrogel, showing high cell proliferation rate, and its current density (Icorr) was two orders of magnitude lower than that of the MAO coating. Besides, the balance mechanism between corrosion and protection was proposed. As a result, the GelMA hydrogel coatings are beneficial to the application of MAO-coated magnesium alloys in bone tissue engineering and other fields.

Insights into self-healing behavior and mechanism of dicalcium phosphate dihydrate coating on biomedical Mg

Self-healing coatings have been developed as smart surface coatings for Mg and its alloys to retain local corrosion from the coating damages. In this study, we prepared dicalcium phosphate dihydrate (DCPD) coating on biomedical Mg, and found that the artificial scratches in DCPD coating can be efficiently sealed by anti-corrosive products in both Hank's and normal saline (NS) solutions. Besides, the in-depth study revealed that DCPD was served as not only a physical barrier but also a self-healing agent, demonstrating an autonomous self-healing coating without embedded extra corrosion inhibitors. Moreover, Hank's solution provided foreign-aid film-forming ions to promote self-healing behavior. The findings might offer new opportunities for further studies and applications of efficient self-healing coatings on biodegradable Mg implants.

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DCPD coating on Mg exhibited self-healing behavior in Hank's and NS solutions.

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DCPD was acted as not only a physical barrier but also a self-healing agent.

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DCPD was sensitive to pH, and offered Ca²⁺ and PO₄³⁻ ions for self-healing.

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Hank's solution provided extra film-forming ions to promote self-healing behavior.

Corrosion Resistance of Micro-Arc Oxidation/Graphene Oxide Composite Coatings on Magnesium Alloys

The micro-arc oxidation/graphene oxide (MAO/GO) composite coatings were successfully prepared on the surface of magnesium alloys by the MAO and electrodeposition technologies. The morphology and composition of the MAO/GO composite coatings were characterized by scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis spectroscopy, Raman spectroscopy, roughness test, and binding test. The electrochemical impedance spectroscopy, polarization curve, and immersion test were used to evaluate the protection performance of MAO/GO composite coatings provided to a substrate. The test results showed that GO covered the surface of the MAO film and had a multilayer structure in the composite coatings. The composite coatings performed the function of sealing the micropores of the MAO film. The elements in the surface of the composite coatings were evenly distributed and the C element content was high. We find that the composite coatings were smoother than the MAO film. The bonding force of the composite coating needs to be enhanced. The corrosion resistance of the MAO/GO composite coatings was obviously better than that of a single MAO film.

Biodegradation behavior of micro-arc oxidation coating on magnesium alloy-from a protein perspective

Protein exerts a critical influence on the degradation behavior of absorbable magnesium (Mg)-based implants. However, the interaction mechanism between protein and a micro-arc oxidation (MAO) coating on Mg alloys remains unclear. Hereby, a MAO coating was fabricated on AZ31 Mg alloy. And its degradation behavior in phosphate buffer saline (PBS) containing bovine serum albumin (BSA) was investigated and compared with that of the uncoated alloy. Surface morphologies and chemical compositions were studied using Field-emission scanning electron microscope (FE-SEM), Fourier transform infrared spectrophotometer (FT-IR) and X-ray diffraction (XRD). The degradation behavior of the bare Mg alloy and its MAO coating was studied through electrochemical and hydrogen evolution tests. Cytotoxicity assay was applied to evaluate the biocompatibility of Mg alloy substrate and MAO coating. Results indicated that the presence of BSA decreased the degradation rate of Mg alloy substrate because BSA (RCH(NH₂)COO‾) molecules combined with Mg²⁺ ions to form (RCH(NH₂)COO)₂Mg and thus inhibited the dissolution of Mg(OH)₂ by impeding the attack of Cl‾ ions. In the case of MAO coated Mg alloy, the adsorption of BSA on MAO coating and the formation of (RCH(NH₂)COO)₂Mg exhibited a synergistic effect and enhanced the corrosion resistance of the coated alloy significantly. Furthermore, cell bioactive assay suggested that the MAO coating had good viability for MG63 cells due to its high surface area.

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BSA reduces degradation of Mg substrate due to the formation of (RCH(NH₂)COO)₂Mg.

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BSA inhibits degradation of MAO coating by acting as a protective layer.

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MAO coating promotes cell proliferation due to higher surface area.

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Cells were rounded shaped on MAO coating owing to the rough surface.

In vitro degradation of pure magnesium-the synergetic influences of glucose and albumin

The biocorrosion of magnesium in the external physiological environment is still difficult to accurately evaluate the degradation behavior in vivo, particularly, in the microenvironment of the patients with hyperglycemia or diabetes. Thus, we explored the synergistic effects of glucose and protein on the biodegradation of pure magnesium, so as to have a deeper understanding the mechanism of the degradation in vivo. The surface morphology and corrosion product composition of pure magnesium were investigated using SEM, EDS, FTIR, XRD and XPS. The effect of glucose and albumin on the degradation rate of pure magnesium was investigated via electrochemical and immersion tests. The adsorption of glucose and albumin on the sample surface was observed using fluorescence microscopy. The results showed that the presence of 2 g/L glucose changed the micromorphology of corrosion products on the magnesium surface by reacting with metal cations, thus inhibiting the corrosion of pure magnesium. Protein formed a barrier layer to protect the magnesium at early stage of immersion. The chelation reaction between protein and magnesium surface might accelerate the degradation at later stage. There may be a critical glucose (albumin) content. Biodegradation of pure magnesium was inhibited at low concentrations and promoted at high concentrations. The synergistic effect of glucose and protein restrained the adsorption of aggressive chloride ions to a certain extent, and thus inhibited the degradation of pure magnesium considerably. Moreover, XPS results indicated that glucose promoted the adsorption of protein on the sample surface.