Pure Zn Research Articles

Biodegradable Zn-0.5Li alloy rib plate: Processing procedure development and in vitro performance evaluation

• Whole fabricating process of biodegradable Zn-Li alloy rib plates is developed. • Zn-0.5Li alloy rib plates have mechanical properties comparable to pure Ti. • Uniform corrosion dominates during immersion tests in SBF up to 30 days. • The Zn alloy rib plates have better biocompatibility than pure Zn rib plates. Trauma kills more than four million people worldwide each year, with chest trauma accounting for 25% of these deaths. Rib fractures are the main manifestation of chest trauma. Biodegradable Zn alloys offer a new option to overcome clinical problems caused by permanent rib fracture internal fixation materials, e.g., long-term stress masking and secondary surgery. In this study, the fabrication procedure of biodegradable Zn-0.5Li alloy rib plates is successfully developed, which consists of casting, hot-warm rolling, cutting, and pressing sequentially. Biomechanical three-point bending performance of the Zn alloy rib plates is comparable to that of commercial pure Ti rib plates, much higher than that of pure Zn rib plates. In addition, the Zn alloy exhibits the best antibacterial ability against E. coli and S. aureus among the three materials. Although the Zn alloy exhibits a weaker MC3T3 cytocompatibility than pure Ti, it is better than pure Zn. This study provides a foundation for the future development of various biodegradable Zn alloy rib plates.

Synthesis and in vitro evaluation of Ca-P coating on biodegradable Zn alloys

• Ca-P coating was fabricated on Zn-Mg alloy. • Ca-P coating inhibits the explosive release of Zn 2+ of Zn-Mg alloy. • Ca-P coating exhibits superior antibacterial activity and biocompatibility. The burst release of Zn 2+ from the naked pure Zn and Zn-based alloys could induce local and systemic toxicity, which limits their clinical applications as biodegradable implants. In order to inhibit the explosive release of zinc ions, a protective Ca-P coating was synthesized on biodegradable Zn alloy. The microstructure, corrosion resistance, antibacterial activity, and biosafety of the Ca-P coating are systematically investigated. Electrochemical tests revealed that Ca-P protective layer has enhanced the anti-corrosion behavior of Zn alloy. Furthermore, Ca-P protective layer showed good biocompatibility, as demonstrated by significantly increased cell viability, good attachment, and spreading at a higher cell density. Besides, the Ca-P coating could also retain the antibacterial ability and inhibit the bacterial adhesion. The Ca-P protective layer synthesized on biodegradable Zn alloy can be considered and applied in future biomedical applications.

Air and Vacuum Annealing Effect on the Highly Conducting and Transparent Properties of the Undoped Zinc Oxide Thin Films Prepared by DC Magnetron Sputtering

In this study, we aim to investigate the effect of zinc interstitials (Zni) and oxygen vacancies (VO) on the ZnO electrical conductivity. ZnO films were synthesized via DC magnetron sputtering process using pure Zn target in gases mixture of Ar/O2 = 80/17.5 (sccm). In order to improve the optical and electrical prosperities, the obtained films were subjected to air and vacuum annealing treatment. Several techniques such as field emission scanning electron microscopy (FESEM), Grazing Incidence X-ray Diffraction (GIXRD), Raman spectroscopy, photoluminescence spectroscopy (PL) and UV-visible were used to study the influence of heat treatment on structural and physical properties of ZnO films. Electrical conductivity of ZnO thin films was determined by measuring the sheet resistance and thickness of the films. XRD results confirm the synthesis of annealed ZnO films of the hexagonal structure with a preferential orientation along the (002) plane. The average crystallite size is altered between 22.6 to 28.4 nm dependent on the plan orientation of the ZnO film. Morphology and crystallinity of the ZnO structure could efficiently control the transmittance, electrical resistivity and optical band gap. As deposited ZnO film showed a lower electrical resistivity of 2.72×10-3 Ωcm due to the Zn-rich conditions. Under vacuum annealing, a combination of low resistivity (1.17×10-2 Ωcm) and better optical transmittance (87 %) are obtained. ZnO films developed in this study with high transmittance and low resistivity and good electro-optical quality supports their use in transparent and conductive electrode applications. The plan presentation was visualized using Vesta, with the lattice parameter set as follows: a = b = 3.249 Å; c = 5.207 Å; α = β = 90°; γ = 120°. Based on the construction and optimization of primitive cells, the supercells were constructed and then optimized. Finally, (002) and (103) planes were cut and the planar supercell structure was constructed. In order to make a plane representation for the solid bulk with 10 Å of thickness.

Cationic Copper Species Stabilized by Zinc during the Electrocatalytic Reduction of CO2 Revealed by In Situ X‐Ray Spectroscopy

AbstractAdvanced in situ X‐ray absorption spectroscopy characterization of electrochemically co‐electrodeposited bi‐element copper alloy electrodes shows that zinc yields the formation of a stable cationic Cu species during the electroreduction of CO2 at high cathodic polarization. In contrast, the formation/stabilization of cationic Cu species in copper oxides, or doping Cu with another element, like Ni, is not possible. It is found that the pure and mixed Cu:Zn electrodes behave similarly in term of electrocatalytic selectivity to multi‐carbon products. At higher Zn concentrations the electrode behaves like the pure Zn catalyst, which indicates that the Cu cationic species do not have a significant influence on the selectivity to multi‐carbon products. It is found that in the non‐monotonically distribution of products is dominated in term of surface energy in which copper prefers the surface. Otherwise, this work highlights the importance of in situ characterization to uncover the mechanisms mediating the catalytic reactions in contrast to ex situ or post mortem analysis, which can be a source of misinterpretation.

Lithium-Induced Optimization Mechanism for an Ultrathin-Strut Biodegradable Zn-Based Vascular Scaffold.

To reduce incidences of in-stent restenosis and thrombosis, the use of a thinner-strut stent has been clinically proven to be effective. Therefore, the contemporary trend is toward the use of ultrathin-strut (≤70µm) designs for durable stents. However, stents made from biodegradable platforms have failed to achieve intergenerational breakthroughs due to their excessively thick struts. Here, microalloying is used to create an ultrathin-strut (65µm) zinc (Zn) scaffold with modified biodegradation behavior and improved biofunction, by adding lithium (Li). The scaffold backbone consists of an ultrafine-grained Zn matrix (average grain diameter 2.28µm) with uniformly distributed nanoscale Li-containing phases. Grain refinement and precipitation strengthening enable it to achieve twice the radial strength with only 40% of the strut thickness of the pure Zn scaffold. Adding Li alters the thermodynamic formation pathways of products during scaffold biodegradation, creating an alkaline microenvironment. Li2 CO3 may actively stabilize this microenvironment due to its higher solubility and better buffering capability than Zn products. The co-release of ionic zinc and lithium enhances the beneficial differential effects on activities of endothelial cells and smooth muscle cells, resulting in good endothelialization and limited intimal hyperplasia in porcine coronary arteries. The findings here may break the predicament of the next-generation biodegradable scaffolds.

Microstructure and mechanical performance of AZ31/6061 lap joints welded by laser-TIG hybrid welding with Zn-Al alloy filler metal

A series of Zn-xAl (x = 0‒35 wt.%) alloy filler metals were designed to join AZ31 Mg alloy to 6061 Al alloy by laser-TIG hybrid welding. The effect of Al content on the wettability of filler metals, microstructure evolution and strength of joint was investigated. The results indicated that the strength of joints was improved with the increase of Al content in filler metals. When Zn-15Al filler was used, the ultimate fracture load reached the maximum of 1475.3 N/cm, which was increased by 28% than that with pure Zn filler. The reason is that the Al element acts as a "reaction depressant" in filler metal, which contributes to inhibiting the dissolution of Mg base metal and the Mg-Zn reaction. The addition of appropriate quantity of Al element promoted the precipitation of Al-rich solid solution instead of Zn solid solution. The MgZn2 IMCs have lower lattice mismatch with Al solid solution than Zn solid solution, thus the strength of joints is improved. However, the excessive addition of Al caused the formation of brittle Mg32(Al,Zn)49 ternary compounds, leading to the deterioration of joint performance.

Manipulating Horizontal Zn Deposition with Graphene Interpenetrated Zn Hybrid Foils for Dendrite‐Free Aqueous Zinc Ion Batteries

Aqueous zinc ion batteries (ZIBs) with intrinsic safety have great potentials in portable devices, but suffer from limited cycling life mainly caused by serious dendrite growth and unavoidable side reactions of Zn anodes. Herein, graphene interpenetrated Zn (GiZn) hybrid foils are developed for dendrite‐free and long‐term Zn anodes for high‐performance ZIBs. The GiZn anode is prepared by interfacial assembly of reduced graphene oxide (rGO) on the skeletons of zinc foams, followed by mechanical compression into hybrid foils and drying process. The presence of the rGO nanosheets in the GiZn hybrid foils provides abundant zincophilic sites to induce horizontal Zn deposition for Zn metal anodes without the growth of dendrites. Meanwhile, the uniform distribution of rGO nanosheets endows the hybrid foils with superior conductivity and wetting ability with electrolytes for reduced interfacial resistances. As a result, GiZn‐based symmetric cells exhibit a small voltage hysteresis of 30.4 mV and remarkable areal capacity of 30 mAh cm−2 at 0.5 mA cm−2. Further, GiZn anodes also enable the corresponding aqueous Zn||MnO2 batteries with high capacity of 168.5 mAh g−1 at 8 C, superior to the counterpart with pure Zn foil anodes (72.7 mAh g−1). Therefore, GiZn hybrid foil anodes will shed light on the rational construction of 2D material‐interpenetrated Zn hybrid foil anodes for high‐performance ZIBs.

Melamine Foam-Derived Carbon Scaffold for Dendrite-Free and Stable Zinc Metal Anode

Aqueous Zn-ion batteries (AZIBs) are one of the most promising large-scale energy storage devices due to the excellent characteristics of zinc metal anode, including high theoretical capacity, high safety and low cost. Nevertheless, the large-scale applications of AZIBs are mainly limited by uncontrollable Zn deposition and notorious Zn dendritic growth, resulting in low plating/stripping coulombic efficiency and unsatisfactory cyclic stability. To address these issues, herein, a carbon foam (CF) was fabricated via melamine-foam carbonization as a scaffold for a dendrite-free and stable Zn anode. Results showed that the abundant zincophilicity functional groups and conductive three-dimensional network of this carbon foam could effectively regulate Zn deposition and alleviate the Zn anode's volume expansion during cycling. Consequently, the symmetric cell with CF@Zn electrode exhibited lower voltage hysteresis (32.4 mV) and longer cycling performance (750 h) than the pure Zn symmetric cell at 1 mA cm-2 and 1 mAh cm-2. Furthermore, the full battery coupling CF@Zn anode with MnO2 cathode can exhibit a higher initial capacity and better cyclic performance than the one with the bare Zn anode. This work brings a new idea for the design of three-dimensional (3D) current collectors for stable zinc metal anode toward high-performance AZIBs.

Microstructural evaluation in dissimilar liquid phase bonding of cast Al–Si alloy and stainless steel using pure zinc filler metal

The metallurgical joining between cast A359 aluminium alloy and AISI321 stainless steel using pure Zn as the interlayer was performed slightly above Al–Zn eutectic temperature. The liquid phase was formed by a eutectic reaction between Al and Zn and subsequently isothermally solidified by diffusion of Zn into the A359 base metal (i.e. reactive transient liquid phase bonding). The formation of a Zn-rich diffusion affected zone in A359, incorporation of Si particles into the bond zone, formation of a thin Al–Fe–Si intermetallic at the steel interface, and isothermal solidification of the liquid phase and subsequent Al–Zn eutectoid transformation govern the microstructure of the joint. The resultant bond microstructure does not deleteriously affect the heat sink function of Al base metal.

Polydopamine (PDA) coatings with endothelial vascular growth factor (VEGF) immobilization inhibiting neointimal formation post zinc (zn) wire implantation in rat aortas

BackgroundBioresorbable stents are designed to provide temporary mechanical support to the coronary arteries and then slowly degrade in vivo to avoid chronic inflammation. Zinc (Zn) is a promising material for bioresorbable stents; However, it can cause inflammation and neointimal formation after being implanted into blood vessels.MethodsTo improve biocompatibility of Zn, we first coated it with polydopamine (PDA), followed by immobilization of endothelial vascular growth factor (VEGF) onto the PDA coatings. Adhesion, proliferation, and phenotype maintenance of endothelial cells (ECs) on the coated Zn were evaluated in vitro. Then, a wire aortic implantation model in rats mimicking endovascular stent implantation in humans was used to assess vascular responses to the coated Zn wires in vivo. Thrombosis in aortas post Zn wire implantation, degradation of Zn wires in vivo, neointimal formation surrounding Zn wires, and macrophage infiltration and extracellular matrix (ECM) remodeling in the neointimas were examined.ResultsIn vitro data showed that the PDA-coated Zn encouraged EC adhesion, spreading, proliferation, and phenotype maintenance on its surfaces. VEGF functionalization on PDA coatings further enhanced the biocompatibility of Zn to ECs. Implantation of PDA-coated Zn wires into rat aortas didn’t cause thrombosis and showed a faster blood flow than pure Zn or the Zn wires coated with VEGF alone. In addition, the PDA coating didn’t affect the degradation of Zn wires in vivo. Besides, the PDA-coated Zn wires reduced neointimal formation, increased EC coverage, decreased macrophage infiltration, and declined aggrecan accumulation in ECM. VEGF immobilization onto PDA coatings didn’t cause thrombosis and affect Zn degradation in vivo as well, and further increased the endothelization percentage as compared to PDA coating alone, thus resulting in thinner neointimas.ConclusionThese results indicate that PDA coatings with VEGF immobilization would be a promising approach to functionalize Zn surfaces to increase biocompatibility, reduce inflammation, and inhibit neointimal formation after Zn implantation in vivo.Graphical

Towards a dependable TEM characterization of hot-dip galvanized steels with low and high Si content

Designing Advanced High-Strength Steels assumes fine-tuning of alloying elements to enhance performance properties. This affects the kinetics of Fe-Zn interaction during further galvannealing. A key role here belongs to the inhibition layer at the steel/coating interface. Applying mutually-reinforcing TEM techniques, we traced the evolution of Zn-Fe phases in low- and high-Si steels during galvannealing. It has been shown that conventional room temperature Ga FIB for TEM sample preparation is applicable only to annealed low-Si steel, a coating of which comprises equilibrium Zn-Fe compounds. The phases were validated via electron microscopy and diffraction methods. In contrast, even relatively long annealing of the high-Si steel was not sufficient to form stable Zn-Fe phases pointing to a hampering of the interphase reactions. As-galvanized and annealed high-Si specimens contain almost pure Zn and are affected by Ga via a eutectic reaction during FIB preparation. Thus, low-temperature FIB has been applied for reliable Zn-coated steel preparation. We refined with HRTEM the inhibition layer structures specific for low- and high-Si steel grades. While the typical Fe2Al5-xZnx interface layer has been found in the low-Si samples, for high-Si ones the formation of a quite stable Si-Mn mixed oxide membrane, which drastically hinders Fe-Al reaction, has been disclosed.

Effects of thermomechanical processing on microstructures, mechanical properties, and biodegradation behaviour of dilute Zn–Mg alloys

Currently, zinc has been considered as one new attractive biodegradable metal for medical implant applications due to its favoured properties such as biocompatibility and recyclability. However, the cast pure zinc usually possesses coarsening microstructures, which hinders it to obtain a suitable combination of mechanical strength and degradation rate. Here, the microstructural controlling of zinc was firstly realized via alloying dilute Mg contents and thermomechanical processing. Then, the in vitro biodegradation behaviour of dilute Zn–Mg alloys was investigated accordingly using the Hank's solution. Finally, the mechanisms of mechanical strengthening and in vitro biodegradation were explored. Specifically, the Mg-50wt%Zn master alloy was added into cast Zn melt to form the binary Zn–Mg alloys with different Mg addition contents (i.e. 0, 0.05wt%, 0.1wt%, and 0.4wt%). The initial reduction of grain sizes was achieved by over 90% owing to the grain refinement generated by master alloy. In the as-cast alloys, the average grain size was decreased from over 2 mm for pure Zn to 23.7 μm for Zn-0.4wt%Mg. Subsequently, the thermomechanical processing (i.e. hot rolling at room temperature, 100°C, 150°C, and 250°C) was applied onto the cast Zn–Mg alloys to achieve further microstructural manipulation. Further grain refinement occurred in the different as-rolled Zn–Mg alloys. The in vitro corrosion resistance of all samples was assessed through the potentiodynamic polarization (PDP) test in the Hanks' solution for 14 days at 37°C. The corrosion rates depended on alloying contents, grain sizes, twins and texture. The synergetic regulation of mechanical strength and degradation rate could be adjusted by appropriately using master alloys and thermomechanical processing. For practical medical applications, the present work provides some insights on solving the dilemma between mechanical properties and biodegradation process.

Effect of molybdenum partitioning on the evolution of microstructure, grain boundary constitution and corrosion behaviour of electrodeposited zinc-molybdenum coatings

Effect of compositional partitioning on microstructural evolution and corrosion behaviour of Zn-Mo coatings (Mo: 2.8 – 6.5 wt%) electrodeposited on mild steel substrate has been explored. Corrosion resistance of Zn coating increased with Mo addition until an optimum addition (Zn-4.2 wt% Mo) beyond which it decreased for higher Mo content (Zn-6.5 wt% Mo). The corrosion current density (icorr) values for pure Zn, Zn-2.8 wt% Mo, Zn-4.2 wt% Mo, Zn-6.5 wt% Mo coating was 17 μA/cm2, 12.25 μA/cm2, 7.5 μA/cm2, 14.2 μA/cm2 respectively. Incorporation of Mo resulted in the formation of Zn-Mo solid solution and Zn3Mo2 compound phases along with segregation of Mo at Zn grain boundaries. High corrosion resistance of Zn-4.2 wt% Mo coating was due segregation of Mo at Zn grain boundaries, higher fraction of low angle grain boundaries and coincidence site lattices when compared to the pristine Zn coating. Lower corrosion resistance of Zn-6.5 wt% Mo coating was primarily due to higher coating strain because of the solid solution of Mo in Zn and formation of Zn3Mo2 particles in the coating matrix.

Introducing novel bioabsorbable Zn–Ag–Mg alloys intended for cardiovascular applications

Zn is considered an excellent candidate material for endovascular applications due to its outstanding combination of biodegradability and biofunctionality. The present work introduces two novel Zn–Ag–Mg alloys with highly desirable mechanical, corrosion, and biological performance. Microstructural characterization revealed a significant grain refinement as a consequence of alloying (Ag) in conjunction with an adequate thermomechanical processing route for both alloy systems. Tensile test results indicated that the best mechanical properties in terms of yield strength (YS), ultimate tensile strength (UTS), and elongation to failure (% E) were achieved for the unidirectional rolled (UR) Zn–6Ag–0.5Mg alloy with values of ∼ 300 MPa, ∼ 370 MPa, and ∼ 40%, respectively. However, a superior UTS was exhibited for the Zn–10Ag–0.9Mg alloy with a value of ∼ 430 MPa. The observed corrosion rate (CR) trend measured by potentiodynamic polarization test was Zn–6Ag–0.5Mg = 2.232 (mm/year) > Zn–10Ag–0.9Mg = 1.405 (mm/year) > pure Zn = 0.935 (mm/year). When static immersion tests were performed, it was observed an unexpected static corrosion rate (SCR) with the following trend: pure Zn = 0.14 (mm/year) > Zn–6Ag–0.5Mg = 0.07 (mm/year) > Zn–10Ag–0.9Mg = 0.05 (mm/year). Moreover, the indirect cell test showed grade 0 of cytotoxicity at 10% and 1% of metal extracts for both ternary alloys. Finally, the proposed alloys possess excellent hemocompatibility characteristics indicating an ideal balance between mechanical integrity and biocompatibility required for the intended application.

Supersaturated solid solution enhanced biodegradable Zn-Mn alloys prepared by mechanical alloying and selective laser melting

Zn-Mn alloys have been recognized as promising biodegradable metals due to moderate degradation and good osteogenesis. However, the alloying content of Mn has been severely limited by the low solid solubility (0.8 wt%) in conventional preparation process to avoid the excessive formation of brittle intermetallics. In this work, supersaturated solid solution was achieved in Zn-Mn alloys via mechanical alloying (MA) and selective laser melting (SLM). During MA process, the mixed Zn and Mn powders experienced repeated welding and fracturing, which resulted in refined grains and abundant crystal defects that stored extra energy. This could reduce the energy barrier of interatomic diffusion and induce the rapid diffusion of Mn atoms, leading to supersaturated solid solution with ∼3.6 wt% Mn homogeneously dissolved in Zn lattices. Moreover, the rapid solidification process of SLM effectively maintained the metastable supersaturated structure. In addition, the Zn-15Mn alloys prepared by MA and SLM were composed of fine equiaxed grains (∼4.34 µm) and high content of high-angle grain boundaries (54.8%). Owing to solution strengthening and grain refinement, the Zn-15Mn alloy prepared by MA and SLM exhibited a compressive yield strength of 178 MPa which was 2.8 times and 1.6 times those of pure Zn and Zn-15Mn alloy without MA process, respectively, as well as a more ductile fracture. Meanwhile, the Zn-Mn alloys exhibited accelerated degradation and comparable cytocompatibility to pure Zn. These findings indicated that the combined process of MA and SLM may be an efficient strategy for the preparation of alloys characterized by supersaturated solid solution and refined grain structure.

Endowing biodegradable Zinc implants with dual-function of antibacterial ability and osteogenic activity by micro-addition of Mg and Ag (≤ 0.1 wt.%)

Infection remains the devastating complications associated with surgical fixation of bones fractured during trauma. In this study, we report a low-alloyed Zn-Mg-Ag that simultaneously has optimized strength degeneration profiles during degradation, outstanding antibacterial efficacy and osteogenic activity. Our results showed that Zn-0.05Mg-0.1Ag alloy had favorable mechanical properties (UTS: 247.8 ± 1.6 MPa, Elong.: 35 ± 2.2 %) and presented a better hold of mechanical integrity than pure Zn during 28 days corrosion, 2.6 % vs. 18.7 % reduction. After one-year of natural aging, the alloy still preserved an elongation of 24.07 ± 3.84 %. As verified by microbial cultures, Zn-0.05Mg-0.1Ag alloy demonstrated high antibacterial performance against Gram-positive and Gram-negative strains, as well as antibiotic-resistant strains (MRSA) in vitro and in vivo due to the synergistic antibacterial actions of Zn2+ and Ag+. Meanwhile, Zn-Mg-Ag alloy also exhibited enhanced viability, osteogenic differentiation, and gene expressions of osteoblasts in vitro, as well as promoted osteogenic activity than pure Zn in the femoral condyle defect repair model. The co-releasing of Zn, Mg and Ag ions did not induce toxic side effects. Collectively, low alloyed Zn-0.05Mg-0.1Ag indicated long-lasting mechanical integrity during degradation, and presented the ability to synergistically inhibit bacteria and promote osteogenesis, possessing tremendous potential in treating implant-associated infections. STATEMENT OF SIGNIFICANCE: Infection after fracture fixation (IAFF) remains the most common and serious side effects of orthopedic surgery. Additionally, widespread antibiotic use contributes to the development of multi-drug resistant bacteria such as methicillin-resistant staphylococcus aureus (MRSA), which exacerbates IAFF treatment and prevention. IAFF treatment and prevention remain clinically challenging, so implants with dual antibacterial and osteogenic functions are in high demand. The antibacterial efficacy and osteogenic activity of low-alloyed Zn-Mg-Ag (≤0.1 wt.% Mg, Ag) alloys were investigated in vitro and in vivo. The results showed that micro addition of Mg and Ag could significantly improve osseointegration function, mechanical properties, and antibacterial performance. These quantification findings shed new light on the development and understanding of dual functional Zn-based orthopedic implants.

Zn–0.8Mn alloy for degradable structural applications: Hot compression behaviors, four dynamic recrystallization mechanisms, and better elevated-temperature strength

• Hot deformation behavior of Zn-0.8Mn alloy are revealed. • Constitutive equation and processing map of the alloy are established. • Four DRX mechanisms, i.e., DDRX, CDRX, TDRX and PSN, are activated. • The alloy exhibits excellent elevated-temperature strengths. Environmentally degradable Zn-0.8Mn alloy is highly ductile, which lays the foundation for developing high-performance Zn-Mn-based alloys. However, not only constitutive equation of this alloy is unknown, but also its dynamic recrystallization (DRX) behavior is unclear, which makes optimization of hot processing parameters of this alloy almost dependent on trial-and-error. This work aims to tackle these problems. The constitutive equation was deduced to be ε ˙ = 1.38 × 10 12 × [sin h (0.009 σ )] 8 exp(–135150/ RT ). A processing map of the alloy was obtained for the first time, which shows that it has excellent hot formability with narrow instability zones. At a final true strain of 0.8, the volume fraction of DRX grains increased from 37% to 79% with temperature increasing from 150 °C to 350 °C and strain rate decreasing from 10 s –1 to 10 –3 s –1 . Discontinuous DRX (DDRX), continuous DRX (CDRX), twinning-induced DRX (TDRX), and particle stimulated nucleation (PSN) were activated during hot compressions. DDRX was always the main mechanism. TDRX was completely suppressed at 300 °C and above. PSN arose from dispersed MnZn 13 particles. Furthermore, Zn-0.8Mn alloy exhibited elevated-temperature strengths better than pure Zn and Zn-Al-based alloys. At 300 °C and 0.1 s –1 , its peak stress was 1.8 times of pure Zn, owing to MnZn 13 particles of 277 ± 79 nm impeding the motion of grain boundaries and dislocations.

Microstructures, mechanical and corrosion properties of graphene nanoplatelet-reinforced zinc matrix composites for implant applications.

Zinc (Zn)-based alloys and composites are gaining increasing interest as promising biodegradable implant materials due to their appropriate biodegradation rates and biological functionalities. However, the inadequate mechanical strength and ductility of pure Zn have restricted its application. In this study, Zn matrix composites (ZMCs) reinforced with 0.1-0.4wt.% graphene nanoplatelets (GNP) fabricated via powder metallurgy were investigated as potential biodegradable implant materials. The microstructures, mechanical properties, and corrosion behaviors of the GNP-reinforced ZMCs were characterized using optical microscopy, scanning electron microscopy combined with energy-dispersive X-ray spectroscopy, Raman spectroscopy, compression testing, and electrochemical and immersion testing in Hanks' balanced salt solution (HBSS). The microstructural study revealed that the GNP was uniformly dispersed in the ZMCs after ball milling and sintering at 420°C for 6h. The microhardness, compressive yield strength, ultimate compressive strength, and compressive strain of the ZMC-0.2GNP were 69 HV, 123MPa, 247MPa, and 23 %, respectively, improvements of ∼ 18 %, 50%, ∼ 28%, and ∼ 15% compared to pure Zn. The corrosion rate of the ZMCs were lower than that of the pure Zn in HBSS, and the ZMC-0.2GNP composite exhibited the lowest corrosion rate of 0.09 mm/y as measured by electrochemical testing. Biocompatibility assessment indicated that the diluted extracts of pure Zn and GNP-reinforced ZMCs with concentrations of 12.5% and 6.25% exhibited no cytotoxicity after cell culturing for up to 5 days, and the diluted extracts of ZMC-0.2 GNP composite revealed more than 90% cell viability after cell culturing of 3 days, showing the satisfying cytocompatibility. STATEMENT OF SIGNIFICANCE: Biodegradable Zn is a promising candidate material for orthopedic implant applications. Nonetheless, the inadequate mechanical strength and ductility of pure Zn limited its clinical application. In this study, Zn matrix composites (ZMCs) reinforced with 0.1-0.4 wt.% graphene nanoplatelets (GNP) were developed via powder metallurgy, and the reinforcing efficacy of GNP on their mechanical properties was investigated. The addition of GNP significantly improved the compressive properties of ZMCs, with the Zn-0.2GNP composite exhibiting the best compressive properties, including 123 MPa compressive yield strength, 247 MPa ultimate compressive strength, and 22.9% compressive strain. Further, the 12.5% concentration extract of the ZMCs exhibited no cytotoxicity after cell culturing for 5 d toward SaOS2 cells.

Microstructure, mechanical properties, in vitro degradation behavior and cytocompatibility of biodegradable Zn-3Fe-HAP composites prepared by vacuum heating-press sintering

Zinc (Zn) is a promising biodegradable material, and have attracted widespread attention due to its befitting degradation rate compared to magnesium (Mg) and iron (Fe). However, the inferior mechanical strength of pure Zn limits its application for bone repair. Therefore, there is an urgent need to improve its mechanical properties, regulate its degradation rate, and endow it with optimal biocompatibility. The alloying of metallic elements and preparation of Zn-based composites can be a promising approach for this purpose. In this study, the pure Zn and Zn-3 wt%Fe-xHAP (x = 0, 5, 10, 15, 20 wt%) samples were fabricated by vacuum heating-press sintering. The microstructure, compressive mechanical property, in vitro degradation behavior, antibacterial property and in vitro cytocompatibility of different samples were investigated. We confirmed that the secondary phase Zn13Fe significantly improved the mechanical property, and micro-galvanic between Zn and Fe accelerated degradation of the samples. Compressive yield strength of all samples ranges from 85.65 MPa to 301.99 MPa, compressive elastic modulus varies between 8.26 GPa and 15.03 GPa, and corrosion rates are significantly improved which are about 0.005–3.065 mm/y. Moreover, Zn-3Fe-xHAP samples exhibited better biocompatibility and antibacterial property than pure Zn, especially the sample of Zn-3Fe-5HAP. In summary, biodegradable Zn-based composites prepared by vacuum heating-press sintering could be promising material for bone repair.

Degradation behavior, biocompatibility and antibacterial activity of plasma electrolytic oxidation treated zinc substrates

A ZnO/Zn(OH)2 hybrid coating was fabricated in situ via plasma electrolytic oxidation (PEO) in Na2CO3 electrolyte on pure Zn surface for elucidating the influence of PEO treatment on the degradation behavior of Zn and Zn-based materials. Degradation effects, including surface morphology evolution, corrosion product generation and degradation rate, were systematically investigated through simulated body fluid (SBF) immersion and Hank's solution immersion tests. The results confirm that PEO treatment accelerates the degradation of Zn. With the rise in applied voltage, the initial degradation rate decreases from 0.60 to 0.20 mm/year, whereas the long-term degradation rate can reach 0.50–0.70 mm/year. Especially, the degradation rate acquired at 400 V could meet the general design criteria for degradation rate of biodegradable metallic devices. The corrosion products mainly consist of Zn(OH)2, ZnO, Zn3(PO4)2 and CaP matters. They aggregate to form a bi-layer on the as-formed PEO coating surface. Furthermore, the good in vitro biocompatibility and antibacterial properties of the PEO-treated Zn indicate that PEO is a promising method to treat Zn and Zn-based implants for orthopedic application. When the applied voltage is 400 V, the increased hydrophilicity (WCA <25°), good biocompatibility (cell viability >100 %) and the best enhanced antibacterial performance (53.3 % for S. aureus, 88.3 % for E. coli) compared to that of pure Zn are observed.