Zn Sr Alloys Research Articles

Effect of strontium on microstructure, mechanical, and biological responses of Mg–Al–Zn–Sr alloys

In the present study, Mg alloys were prepared with different strontium contents and investigated for applications as resorbable implants (screws, plates, stents etc.). Microstructural characterisation and phase analysis were performed by optical microscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. Alloy with 0.5 wt-% strontium results in a microstructure with fine grains (179 ± 22 µm) and the highest second phase precipitates (area-fraction ∼1.55%). The immersion and electrochemical measurements were performed at different times in Hanks’ solution. The corrosion rate decreased with increasing strontium amount owing to precipitate barrier and protective corrosion products. In vitro biocompatibility test was carried out by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. The cell viability decreases with an increase in strontium content owing to presumably higher fraction of the Mg17Sr2 phase.

Biodegradable Zn–Sr alloys with enhanced mechanical and biocompatibility for biomedical applications

Zinc (Zn) is a new generation of biodegradable metal as temporary biomedical implants with a promising degradation rate. However, its clinical applications have been limited because of the insufficient mechanical properties. Considering the degradation property and biocompatibility, we proposed Zn–Sr alloys after extrusion treatments to simultaneously improve the mechanical strength and ductility. The in vitro and in vivo degradation and biocompatibility were also evaluated using electrochemical and immersion corrosion tests, various cell and bacterial models, together with subcutaneous and femoral implantations in rats. Results showed that the extruded Zn-0.7Sr alloys exhibited two times higher mechanical strengths (∼120 ​MPa) and better ductility (∼10%) than the pure Zn counterparts. The Zn–Sr alloys provided enhanced in vitro and in vivo biocompatibility along with promising antibacterial properties.

In vivo degradability and biocompatibility of a rheo-formed Mg–Zn–Sr alloy for ureteral implantation

• Refined and non-dendritic microstructure due to rheo-solidification. • Pronounced increases in tensile strength and elongation. • Homogeneous in vivo degradation process. • No obvious adverse effects on physiological indicators. • Evident antibacterial activity. The introduction of biodegradable implant materials has significantly improved the postoperative subjective feelings of patients within the past few decades, among which magnesium alloy is widely considered a favorable choice as its appropriate biodegradability and evident antibacterial activity. Here, we reveal a semisolid rheo-formed Mg–Zn–Sr alloy ureteral implant that displayed suitable degradability and biocompatibility in a pig model. Refined non-dendritic microstructure was observed in the rheo-formed alloy, which led to ca. 47% increase in ultimate tensile strength (from 195.0 MPa to 288.1 MPa) and more homogeneous degradation process compared with the untreated alloy. No post-interventional inflammation or pathological changes of the test animals were observed during the implantation period, and the corrosion rate (0.22 ± 0.04 mm·y −1 ) perfectly fitted the clinical ureteral stent indwelling time. The urine bacteria numbers decreased from 88 ± 13 CFU·mL −1 at 7 weeks post operation to 59 ± 8 CFU·mL −1 at 14 weeks post operation, which confirmed the evident antibacterial activity of the alloy. Our study demonstrates that the Mg–Zn–Sr alloy is clinically safe for urinary system, enabling its efficacious use as ureteral implant materials.

Biodegradable Zn–Sr alloy for bone regeneration in rat femoral condyle defect model: In vitro and in vivo studies

Bone defects are commonly caused by severe trauma, malignant tumors, or congenital diseases and remain among the toughest clinical problems faced by orthopedic surgeons, especially when of critical size. Biodegradable zinc-based metals have recently gained popularity for their desirable biocompatibility, suitable degradation rate, and favorable osteogenesis-promoting properties. The biphasic activity of Sr promotes osteogenesis and inhibits osteoclastogenesis, which imparts Zn–Sr alloys with the ideal theoretical osteogenic properties. Herein, a biodegradable Zn–Sr binary alloy system was fabricated. The cytocompatibility and osteogenesis of the Zn–Sr alloys were significantly better than those of pure Zn in MC3T3-E1 cells. RNA-sequencing illustrated that the Zn-0.8Sr alloy promoted osteogenesis by activating the wnt/β-catenin, PI3K/Akt, and MAPK/Erk signaling pathways. Furthermore, rat femoral condyle defects were repaired using Zn-0.8Sr alloy scaffolds, with pure Ti as a control. The scaffold-bone integration and bone ingrowth confirmed the favorable in vivo repair properties of the Zn–Sr alloy, which was verified to offer satisfactory biosafety based on the hematoxylin-eosin (H&E) staining and ion concentration testing of important organs. The Zn-0.8Sr alloy was identified as an ideal bone repair material candidate, especially for application in critical-sized defects on load-bearing sites due to its favorable biocompatibility and osteogenic properties in vitro and in vivo.

Ag-containing antibacterial self-healing micro-arc oxidation coatings on Mg–Zn–Sr alloys

ABSTRACTThe rapid degradation rate restricts the application of magnesium-based biomaterials. Therefore, we constructed Ag-containing micro-arc oxidation (MAO) coatings on Mg–3Zn–0.5Sr alloys to improve the properties of magnesium alloys. Different concentrations of CH3COOAg (0, 1, 2, 3 g L−1) were added into the electrolyte to investigate the effects of Ag+ content on properties of MAO coatings. The addition of CH3COOAg led to the formation of Ag2O and Ag2CO3 phases, which sealed the micro-pores and improved the corrosion resistance of the samples significantly. The samples with addition of 2 and 3 g L−1 CH3COOAg exhibited strong antibacterial ability against E.coli due to the gradual release of Ag+ in the degradation process. It was verified that the samples with addition of 2 g L−1 CH3COOAg obtained the most high bonding strength, dense construction, excellent corrosion resistance, cytocompatibility and antibacterial properties. The bacteria-killing methods of Ag-containing MAO coatings were discussed in the article.

Microstructure, Texture Characteristics, Mechanical and Bio-Corrosion Properties of High Strain Rate Rolled Mg–Zn–Sr Alloys

Microstructure, texture characteristics, mechanical and bio-corrosion properties of the Mg–5Zn–xSr alloys (x = 0, 0.2, 0.6, 1.0) prepared by high strain rate rolling are carefully studied. A low level of Sr addition enhances dynamic precipitation of nano-scale MgZn2 particles in the as-rolled Mg–5Zn alloy, with 0.6%Sr showing the maximum efficiency. These high-density MgZn2 particles can pin grain boundaries of dynamic recrystallization grains and inhibit their growth. A low level of Sr addition (≤ 0.6%) enhances the (0002) basal texture, but 1.0%Sr is just the reverse. The as-rolled Mg–5Zn–0.6Sr alloy exhibits the best combination of ultimate tensile strength (359 MPa) and elongation to rupture (20%). The high strength can be attributable to a reduced grain size, precipitation and basal texture strengthening. The Mg–5Zn–xSr alloys exhibit excellent bio-corrosion resistance, but a minor Sr addition cannot bring about further bio-corrosion resistance improvement due to the multiple actions of grain size, DRX degree, dynamic precipitates and texture characteristics. The 0.6%Sr addition can greatly improve the strength of the as-rolled alloy at no expense of bio-corrosion resistance.

Antimicrobial Bioresorbable Mg-Zn-Ca Alloy for Bone Repair in a Comparison Study with Mg-Zn-Sr Alloy and Pure Mg.

Magnesium-zinc-calcium (Mg-Zn-Ca) alloys have attracted increasing attention for biomedical implant applications, especially for bone repair, because of their biocompatibility, biodegradability, and similar mechanical properties to human bone. The objectives of this study were to characterize Mg-2 wt % Zn-0.5 wt % Ca (named ZC21) alloy pins microstructurally and mechanically, and determine their degradation and interactions with host cells and pathogenic bacteria in vitro and in vivo in comparison with the previously studied Mg-4 wt % Zn-1 wt % strontium (named ZSr41) alloy and Mg control. Specifically, the in vitro degradation and cytocompatibility of ZC21 pins with bone marrow derived mesenchymal stem cells (BMSCs) were investigated using both direct culture and direct exposure culture methods. The adhesion density of BMSCs on ZC21 pins (i.e., direct contact) was significantly higher than on pure Mg pins in both in vitro culture methods; the cell adhesion density around ZC21 pins (i.e., indirect contact) was similar to the cell-only positive control in both in vitro culture methods. Interestingly, ZC21 showed a higher daily degradation rate, crack width and crack area ratio in the direct exposure culture than in the direct culture, suggesting different culture methods did affect its in vitro degradation behaviors. When cultured with Gram-positive bacteria methicillin-resistant Staphylococcus aureus (MRSA), ZC21 reduced bacterial adhesion on the surface more significantly than that of ZSr41 and Mg. The in vivo degradation and biocompatibility of the ZC21 pins for bone regeneration were studied in a mouse femoral defect model. The in vivo degradation rate of ZC21 pins was much slower than that of ZSr41 alloy and Mg control pins. After 12 weeks of implantation in vivo, the ZC21 group showed the shortest gap at the femoral defect, indicating that ZC21 pins promoted osteogenesis and bone healing more than ZSr41 and Mg control pins. Overall, the ZC21 alloy is promising for bone repair, while providing antibacterial activities, and should be further studied toward clinical translation.

Solidification Analysis of Mg–4Zn–xSr System to Study Phase Transformations in Mg-Rich Corner

Mg–Zn–Sr alloys are suitable for biodegradable orthopaedic implants due to excellent biocompatibility and bone regeneration effect of Sr. For Sr additions exceeding 0.2 wt%, ternary phases are observed in the microstructure contrary to binary MgxZny and Mg17Sr2 intermetallics predicted by the existing phase diagrams and corrosion and mechanical properties reduce drastically. Thermal analysis employed for Mg–4Zn–xSr alloys (0 ≤ x≤2) recorded two peaks, hitherto unreported, at temperatures of ~ 514 and 409 °C with 2 wt%, and ~ 549 and 428 °C with 1 wt% of Sr added to Mg–4Zn alloy. In conjunction with SEM–EDAX and XRD analysis, one of these phases is identified as Mg11Zn4Sr3, with second one an unknown intermetallic (IM2). Formation of Mg17Sr2 phase is suppressed in the presence of Zn, and the ternary phase is favoured beyond the solid solubility of Sr in Mg. Solidification pathway of L → α-Mg + Mg11Zn4Sr3 + unknown intermetallic (IM2) has been proposed for the ternary compositions with Sr > 0.2 wt% investigated in the current study.

Microstructures, mechanical and cytocompatibility of degradable Mg–Zn based orthopedic biomaterials

The Mg–1Zn–xSr (x=0.2, 0.5, 0.8 and 1wt.%) alloys have been prepared by zone purifying solidification followed by backward extrusion (BE). The grain size was reduced and the hardness was improved with the increased concentration of strontium (Sr) after backward extrusion. The BE–Mg–1Zn–0.8Sr alloy was mostly composed of fine precipitates (MgZn and Mg17Sr2) and Mg matrix. At the same time, the mechanical properties of BE–Mg–Zn–Sr alloys were increased with the increment of strontium, which were strongly associated with fine average grain size and homogeneous secondary precipitates. The degradation rate is significantly increased when Sr content is over 0.8wt.%. The homogenous degradation rate is achieved. The degradation products show good biocompatibility evaluated by MTT method using L929 cell line. It is demonstrated that the micro-alloying element of Sr is a potential approach to develop novel Mg–Zn based biomaterials.

The effect of strontium in plasticity of magnesium alloys

The objective of this article is to quantify relationships between microstructural changes and the room temperature mechanical behavior of novel extruded Mg–Al–Zn–Sr alloys. To this aim, targeted mechanical testing coupled with full-field strain measurements and simultaneous acoustic emission recordings is further combined with grain-scale observations. To date, the precise effect of alloying elements on the plasticity of Mg alloys is still largely unknown. Strontium in wrought Mg alloys has already been shown to reduce grain size and texture anisotropy, as well as improve their creep resistance, replicating the effects of rare earth elements. To further investigate the effects of Sr on the mechanical properties and plasticity of Mg alloys compression tests were performed and were coupled with nondestructive measurements provided by digital image correlation and acoustic emission monitoring. The results presented herein demonstrate the effect of the extrusion temperature and provide direct correlations between Sr content and bulk mechanical properties, overall plasticity and texture evolution in these novel alloys. Furthermore, the addition of Sr was found to be related to distinct strain localizations near yielding, which were linked to twinning activity, providing in this way a route for quantitative control of their microstructural design.

The Microstructure and the Degradation Behaviour of a Novel Biomaterial Mg–Zn–Sr Alloy Sheet in Simulated Body Fluid (SBF)

The Microstructure and the Degradation Behaviour of a Novel Biomaterial Mg–Zn–Sr Alloy Sheet in Simulated Body Fluid (SBF)

Investigation of the mechanical and degradation properties of Mg–Sr and Mg–Zn–Sr alloys for use as potential biodegradable implant materials

Magnesium (Mg) has garnered significant interest for its potential use as a biodegradable implant material. Of specific interest in this study is the effect of zinc (Zn) and strontium (Sr) additions on both the mechanical and degradation behaviors in Mg due to their established beneficial effect on strength and microstructural grain refinement while being biocompatible. Three binary Mg–x wt% Sr (x=0.5,1.0,1.5) alloys and three ternary Mg–x wt%Zn–0.5wt% Sr (x=2.0,4.0,6.0) were studied to evaluate their mechanical and degradation behavior. Mechanical testing was performed at room temperature on solution-treated and peak aged alloys using microhardness and tensile tests. Degradation was studied using immersion tests in Hanks’ solution. Results indicate a decrease in grain size and an increase in strength with increasing Sr and Zn content. When considering degradation behavior Mg–0.5wt%Sr demonstrated the lowest degradation rate among binary alloys. At constant Sr content at 0.5wt%, the addition of Zn increased the corrosion rate, with the highest rate for the Mg–6.0wt%Zn–0.5wt%Sr. The alloys which best optimized both mechanical and degradation behaviors were Mg–2.0wt%Zn–0.5wt%Sr and Mg–4.0wt%Zn–0.5wt%Sr. Finally, microstructure and property relationships were evaluated and discussed in reference to each alloy’s potential use as a biodegradable implant material.

Microstructural investigation and thermodynamic calculations on the precipitation of Mg–Al–Zn–Sr alloys

Abstract