Effects of zirconium and strontium on the biocorrosion of Mg-Zr-Sr alloys for biodegradable implant applications

Synergistic Improvement of Antibacterial and Osteogenic Differentiation of Thermomechanically Processed Mg-Zr-Sr-Ce Alloy: Insights into the Role of Precipitate Evolution Supported by AIMD Simulation Study

In the present study, we have discussed the influence of forging temperature (623 K (FT623), 723 K (FT723) and 823 K (FT823)) on microstructure and texture evolution and its implication on mechanical behavior, in vitro-in vivo biocorrosion, antibacterial response, and cytocompatibility of microalloyed Mg-Zr-Sr-Ce alloy. Phase analysis, SEM, and TEM characterization confirm the presence of Mg12Ce precipitate, and its stability was further validated by performing ab initio molecular dynamic simulation study. FT723 exhibits strengthened basal texture, higher fraction of second phases, and particle-stimulated nucleation-assisted DRX grains compared to other two specimens, resulting in superior strength with comparable ductility. FT723 also exhibits superior corrosion resistance mainly due to the strengthened basal texture and lower dislocation density. All the specimens exhibit excellent antibacterial behavior with Gram-negative E. coli, Gram-positive Staphylococcus aureus, and Pseudomonas aeruginosa bacteria. 100% reduction of bacterial growth is observed within 24 h of culture of the specimens. Cytocompatibility was determined by challenging specimen extracts with the MC3T3-E1 cell lines. FT723 specimen exhibits the highest cell proliferation and alkaline phosphatase activity (ALP) because of its superior corrosion resistance. The ability of the specimens to be used in orthopedic implant application was evaluated by in vivo study in rabbit femur. Neither tissue-related infection nor the detrimental effect surrounding the implant was confirmed from histological analysis. Significant higher bone regeneration surrounding the FT723 specimen was observed in SEM analysis and fluorochrome labeling. After 60 days, the FT723 specimen exhibits the highest bone formation, suggesting it is a suitable candidate for orthopedic implant application.

Synergistic Effects of Cerium and Hot Forging on Biodegradation, Antibacterial Properties, and In Vivo Biocompatibility of Microalloyed Mg-Zr-Sr Alloys

Biodegradable magnesium (Mg)-based alloys are potential candidates for orthopedic applications. In the present study, we have discussed the effect of cerium (Ce) addition and hot forging on mechanical properties, in vitro-in vivo corrosion, antibacterial activity, and cytocompatibility of microalloyed Mg-0.2Zr-0.1Sr-xCe (x = 0 [MZS], 0.5 wt % [MZS-Ce]) alloys. Addition of 0.5 wt % Ce to forged MZS alloys leads to strengthening of the basal texture as well as formation of a higher fraction of dynamic recrystallized (DRX) grains. Hot forging and addition of cerium to the MZS alloy improve both the yield strength and ultimate tensile strength of the forged MZS-Ce alloy by 1.39 and 1.21 times, respectively, compared to those of the forged MZS alloy. The potentiodynamic polarization test in Hank's solution indicates that the corrosion resistance of the forged MZS alloy improves with addition of 0.5 wt % Ce. Uniform distribution of Mg₁₂Ce precipitates, a higher DRX fraction, strengthened texture, and formation of a compact CeO₂ passive layer result in 1.68 times reduction in the immersion corrosion rate of the forged MZS-Ce alloy compared to that of the forged MZS alloy. Addition of Ce to the MZS alloy shows excellent antibacterial activity. The forged MZS-Ce alloy exhibited the highest antibacterial efficacy (76.73%). All the alloys show favorable cytocompatibility and alkaline phosphatase (ALP) activity with MC3T3-E1 cells. The improved corrosion resistance of the forged MZS-Ce alloy (95%) leads to higher cell viability compared to that of the forged MZS alloy (85%). In vivo biodegradation and the ability to generate new bones were analyzed by implanting cylindrical samples in the rabbit femur. Histological analysis showed no adverse effects around the implants. Gradual degradation of the implants and higher new bone formation around the forged MZS-Ce sample were confirmed by micro-CT analysis. Bone regeneration around the implants (58.21%) was validated by flurochrome labeling. After 60 days, the forged MZS-Ce alloy showed controlled corrosion and better bone-implant integration, presenting it as a potential candidate for internal fracture fixation materials.

Method to Eliminate Fluoride Interference in the Spectrophotometric Estimation of Zirconium: Application to U-Zr Alloys

In the estimation of Zr using the ultraviolet-visible (UV-Vis) spectrophotometric technique, fluoride interference is a decade-old unsolved problem. The process of repeated fuming with strong acids is often used to remove fluoride from the solution in order to estimate Zr using spectrophotometry analysis. For the first time, in this work, a simple use of AlCl₃ is reported as a suppressing reagent to eliminate the interference of fluoride in the estimation of Zr. Xylenol orange in HCl medium is used as a complexing reagent. Linearity in the datum acquired from absorbance at 551 nm (λ_max) is achieved over the concentration range 0.25-4.5 µg mL^-1 of Zr with a molar absorptivity of 35<thinsp>030 L·mol^-1·cm^-1 and Sandell's sensitivity of 0.003 µg·cm^-2. Zr is quantified in the variety of U-Zr alloys and various water samples using spectrophotometric detection with a classical univariate calibration with suppressing of fluoride interference through AlCl₃. Results from this novel analytical method herein developed for the first time are compared with those achieved from gravimetric analysis.

Corrosion Behavior in Magnesium-Based Alloys for Biomedical Applications

Magnesium alloys exhibit superior biocompatibility and biodegradability, which makes them an excellent candidate for artificial implants. However, these materials also suffer from lower corrosion resistance, which limits their clinical applicability. The corrosion mechanism of Mg alloys is complicated since the spontaneous occurrence is determined by means of loss of aspects, e.g., the basic feature of materials and various corrosive environments. As such, this study provides a review of the general degradation/precipitation process multifactorial corrosion behavior and proposes a reasonable method for modeling and preventing corrosion in metals. In addition, the composition design, the structural treatment, and the surface processing technique are involved as potential methods to control the degradation rate and improve the biological properties of Mg alloys. This systematic representation of corrosive mechanisms and the comprehensive discussion of various technologies for applications could lead to improved designs for Mg-based biomedical devices in the future.

Stable and Antibacterial Magnesium-Graphene Nanocomposite-Based Implants for Bone Repair

Magnesium (Mg)-based alloys are promising biodegradable materials for bone repair applications. However, due to their rapid degradation and high corrosion rate, Mg-based alloys are typically associated with in vivo infections and implant failure. This study evaluated the synergistic stability and anti-inflammatory properties that could potentially be achieved by the modification of the Mg alloy with graphene nanoparticles (Gr). Incorporation of low dosages of Gr (0.18 and 0.50 wt %) in a Mg alloy with aluminum (Al, 1 wt %) and copper (Cu, 0.25 wt %) was successfully achieved by a spark plasma sintering (SPS) method. Notably, the degradation rate of the Mg-based alloys was reduced approximately 4-fold and the bactericidal activity was enhanced up to 5-fold with incorporation of only 0.18 wt % Gr to the Mg-1Al-Cu matrix. Moreover, the modified Mg-based nanocomposites with 0.18 wt % Gr demonstrated compressive properties within the range of native cancellous bone (modulus of approximately 6 GPa), whereas in vitro studies with human mesenchymal stromal cells (hMSCs) showed high cytocompatibility and superior osteogenic properties compared to non-Gr-modified Mg-1Al-Cu implants. Overall, this study provides foundations for the fabrication of stable, yet fully resorbable, Mg-based bone implants that could reduce implant-associated infections.

Recent Developments in Magnesium Metal-Matrix Composites for Biomedical Applications: A Review

Recently, there is a growing interest in developing magnesium (Mg) based degradable biomaterial. Although corrosion is a concern for Mg, other physical properties, such as low density and Young's modulus, combined with good biocompatibility, lead to significant research and development in this area. To address the issues of corrosion and low yield strength of pure Mg, several approaches have been adopted, such as, composite preparation with suitable bioactive reinforcements, alloying, or surface modifications. This review specifically focuses on recent developments in Mg-based metal matrix composites (MMCs) for biomedical applications. Much effort has gone into finding suitable bioactive, bioresorbable reinforcements and processing techniques that can improve upon existing materials. In summary, this review provides a comprehensive overview of existing Mg-based composite preparation and their mechanical and corrosion properties and biological responses and future perspectives on the development of Mg-based composite biomaterials.

The Application of the Rare Earths to Magnesium and Titanium Metallurgy in Australia

Rare earth elements (REEs) have found application in metallurgical processes for nearly a century due to their unique chemical and physical properties but have gained increased attention in recent decades. Notably, the use of these elements may assist in the development of advanced magnesium and titanium products for applications spanning biomedicine, aerospace, and the automotive industry. To this end, current progress in this area, highlighting work done in Australian research organizations with particular academic expertise, is reviewed. Two areas that require further research are identified: the application of Sc and the heavy lanthanides to the development of novel magnesium alloys and the use of REEs as additives in the development of additive manufacturing of titanium parts.

Zehetbauer M, Orlov D. Surface Analysis of Biodegradable Mg-Alloys after Immersion in Simulated Body Fluid

Two binary biodegradable Mg-alloys and one ternary biodegradable Mg-alloy (Mg-0.3Ca, Mg-5Zn and Mg-5Zn-0.3Ca, all in wt%) were investigated. Surface-sensitive X-ray photoelectron spectroscopy analyses (XPS) of the alloy surfaces before and after immersion in simulated body fluid (SBF) were performed. The XPS analysis of the samples before the immersion in SBF revealed that the top layer of the alloy might have a non-homogeneous composition relative to the bulk. Degradation during the SBF immersion testing was monitored by measuring the evolution of H2. It was possible to evaluate the thickness of the sample degradation layers after the SBF immersion based on scanning electron microscopy (SEM) of the tilted sample. The thickness was in the order of 10-100 µm. The typical bio-corrosion products of all of the investigated alloys consisted of Mg, Ca, P and O, which suggests the formation of apatite (calcium phosphate hydroxide), magnesium hydrogen phosphate hydrate and magnesium hydroxide. The bioapplicability of the analyzed alloys with regard to surface composition and degradation kinetics is discussed.

Mechanical, corrosion, and biocompatibility properties of Mg-Zr-Sr-Sc alloys for biodegradable implant applications

Magnesium (Mg) and its alloys are considered promising biodegradable implant materials because of their strength and natural degradation in the human body. However, the high corrosion rate of pure Mg in the physiological environment leads to rapid degradation before adequate bone healing. This mismatch between bone healing and the degradation of Mg implants supports the development of new Mg alloys with the addition of other suitable alloying elements in order to achieve simultaneously high corrosion resistance and desirable mechanical properties. This study systematically investigates the microstructure, mechanical properties, corrosion behavior, and biocompatibility of Mg-based alloys with the addition of different concentrations of scandium (Sc), i.e., Mg-0.6Zr-0.5Sr-xSc (x = 0.5, 1, 2, 3 wt.%). Results indicated that high concentration of Sc in strontium (Sr)-containing Mg alloys can alter their microstructures by suppressing the intermetallic phases along the grain boundaries and improve the corrosion resistance by forming chemically stable Sc oxide layers on the surfaces of the Mg alloys. Cytotoxicity assessment revealed that the Sc containing Mg alloys did not significantly alter the viability of human osteoblast-like SaOS2 cells. This study highlights the advantages of using Sc as an alloying element to simultaneously tune Mg alloys with higher strength and slower degradation. STATEMENT OF SIGNIFICANCE: Rare earth elements such as scandium (Sc) with both a high solid-solubility and strong affinity towards oxygen can improve the mechanical and corrosion properties of magnesium (Mg) alloys. However, the feasibility of Sc-containing Mg alloys as biodegradable implant materials is scarcely reported. This study investigates the effects of different Sc concentrations on the mechanical, corrosion, and biocompatibility properties of Mg-Zr-Sr-Sc alloys. Our findings indicated that the addition of Sc significantly improves the mechanical and corrosion properties of Mg-Zr-Sr alloys. Moreover, in vitro cytotoxicity assessment of the Mg-Zr-Sr-Sc alloys did not show any adverse effects on the viability of osteoblast-like cells.

Manipulating the degradation behavior and biocompatibility of Mg alloy through a two-step treatment combining sliding friction treatment and micro-arc oxidation

Manipulating the degradation rate of biomedical Mg alloys has always been a challenge. In this study, a two-step treatment including sliding friction treatment (SFT) and micro-arc oxidation (MAO) was adopted to acquire a unique Mg-based architecture containing three typical layers comprising a MAO coating/nanocrystalline (NC) layer/coarse-grained (CG) matrix. It was found that the modified topmost MAO coating possessed enhanced corrosion resistance, cytocompatibility and hemocompatibility. The intermediate NC layer sandwiched between the coating and CG matrix was an ideal transition layer capable of avoiding degradation rate upsurge caused by coating breakdown; meanwhile, it provided an effective reinforcing effect on the overall mechanical strength. More importantly, the corrosion resistance of these layers was ranked in the order: MAO coating > NC layer > CG matrix. This kind of gradually increasing corrosion rate of the three layers with depth renders the two-step treatment a promising approach to design Mg-based implants possessing controllable degradation rates.

Effect of the second-step voltages on the structural and corrosion properties of silicon-calcium-phosphate (Si-CaP) coatings on Mg-Zn-Ca alloy

The applications of magnesium (Mg) alloys as biodegradable orthopedic implants are mainly restricted due to their rapid degradation rate in the physiological environment. In this study, Si-CaP micro-arc oxidation (MAO) coatings were prepared on a Mg-Zn-Ca alloy by a second-step MAO process at different voltages in order to decrease the degradation rate and increase the bioactivity of the alloy. The microstructure and morphology of the samples were characterized using XRD, FT-IR SEM and EDS. The degradation behaviours of samples were evaluated using electrochemical techniques, and immersion tests in simulated body fluid (SBF). The results indicate that the morphology of the Si-CaP coatings changed significantly with the increase in Ca/P ratio as the second-step voltage increased. The Si-CaP containing coating produced at 450 V could significantly decrease the degradation rate of Mg and caused a slow increase in pH of the SBF solution. The haemolysis test concluded that the coating C3 did not cause a haemolytic reaction. The corrosion resistance of Mg alloy was greatly improved with the Si-CaP coatings, and the Mg alloy with Si-CaP coating prepared at 450 V had the best corrosion resistance, which indicates that the Si-CaP coatings are promising for improving the biodegradation properties of Mg-based orthopedic implants. Haemolysis tests indicated that the Si-CaP coating prepared at 450 V conforms to the given standard (YY/T0127.1-93).

In Vitro Degradation Behaviors of Manganese-Calcium Phosphate Coatings on an Mg-Ca-Zn Alloy

In order to decrease the degradation rate of magnesium (Mg) alloys for the potential orthopedic applications, manganese-calcium phosphate coatings were prepared on an Mg-Ca-Zn alloy in calcium phosphating solutions with different addition of Mn2+. Influence of Mn content on degradation behaviors of phosphate coatings in the simulated body fluid was investigated to obtain the optimum coating. With the increasing Mn addition, the corrosion resistance of the manganese-calcium phosphate coatings was gradually improved. The optimum coating prepared in solution containing 0.05 mol/L Mn2+ had a uniform and compact microstructure and was composed of MnHPO4·3H2O, CaHPO4·2H2O, and Ca3(PO4)2. The electrochemical corrosion test in simulated body fluid revealed that polarization resistance of the optimum coating is 36273 Ωcm2, which is about 11 times higher than that of phosphate coating without Mn addition. The optimum coating also showed the most stable surface structure and lowest hydrogen release in the immersion test in simulated body fluid.

Investigation on Composition, Mechanical Properties, and Corrosion Resistance of Mg-0.5Ca-X(Sr, Zr, Sn) Biological Alloy

Four nontoxic biological alloys, Mg-0.5Ca-1Sr-4Zr (Alloy 1), Mg-0.5Ca-1Sr-1.5Zr (Alloy 2), Mg-0.5Ca-3Sr-1.5Zr (Alloy 3), and Mg-0.5Ca-1Sr-0.5Sn (Alloy 4), were prepared by vacuum smelting, gravity casting, and hot rolling. The composition and microstructure of the alloys were investigated by optical microscope, X-ray fluorescence spectrometer (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersion spectroscopy (EDS). The mechanical properties and corrosion behaviors of the alloys in Hank's solution were studied. Results showed that a large amount of fine and uniformly distributed second-phase particles (Zr, Mg₁₇Sr₂, and CaMgSn) was observed in four alloys obtained after rolling and alloying. The segregation of Zr in alloys was observed in EDS image, and chemical analysis showed that there was macrosegregation of the elements in the alloys. Furthermore, Mg₁₇Sr₂ phases in the Mg-0.5Ca-1Sr-0.5Sn alloy homogenized the distribution of CaMgZn phases. The comprehensive mechanical properties of four newly designed rolled alloys were much higher than those of pure Mg, and the compressive strength of the alloys was more than twice as high as that of pure magnesium. The Mg-0.5Ca-1Sr-0.5Sn alloy released the least hydrogen in Hank's solution, which was lower than that of pure magnesium. Electrochemical test results in Hank's solution further showed that the Mg-0.5Ca-1Sr-0.5Sn alloy had delayed corrosion and lowest I_corr which was 25% of that of pure magnesium. Biological experiments results showed that the Mg-0.5Ca-1Sr-0.5Sn alloy had better biocompatibility and optimal potential for bone substitute material.

Preparation and characterization of laser-melted Mg-Sn-Zn alloys for biomedical application

The rapid degradation rate of Magnesium (Mg) alloy limits its biomedical application even though it possesses outstanding biological performance and biomechanical compatibility. In this study, a combined method of laser rapid melting and alloying Zinc (Zn) was proposed to decrease the degradation rate of Mg-Sn alloy. The microstructure, degradation behaviors and mechanical properties of the laser-melted Mg-5Sn-xZn (x = 0, 2, 4, 6 and 8 wt.%) alloys were investigated. The results indicated that the grain size of the alloys decreased with increasing Zn content, due to the increased number of nucleation particles formed in the process of solidification. Moreover, the laser-melted Mg-Sn alloys possessed finer grains compared with traditional as-cast and as-rolled Mg-Sn alloys. The degradation rate of the alloys decreased with increasing Zn content (0-4 wt.%), which was ascribed to the grain refinement and the formation of Zn(OH)₂ protective layer. However, the degradation rate increased as the Zn content further increased (4-8 wt.%), which was caused by the galvanic corrosion between the Mg matrix and the generated Mg₇Zn₃ phase. Besides, Zn also increased the hardness of the alloys owing to the grain refinement strengthening and solid solution strengthening.

Enhancing the performance of Mg-based implant materials by introducing basal plane stacking faults

One of the keys to allowing Mg alloys to serve as biodegradable materials is how to balance their degradation behaviours and mechanical properties in physiological environment. In this study, a novel Mg-6Ho-0.5Zn alloy (wt%) containing profuse basal plane stacking faults (SFs) is prepared. This newly-developed alloy with SFs exhibiting uniform corrosion behaviour, low corrosion rate and high mechanical properties, as compared to the classic Mg-Ho based alloys (Mg-6Ho and Mg-6Ho-1.5Zn). Furthermore, the Mg-6Ho-0.5Zn alloy shows no significant toxicity to Saos-2 cells. An original uniform corrosion mechanism is proposed by combining the special defect structure, orientation of SFs and promptly effective corrosion film. The development of the new microstructure for Mg-Ho based alloys with desirable corrosion performance has important implications in developing novel degradable Mg-based implant materials.