The metallurgical engineering of bioresorbable zinc (Zn)-based medical alloys would greatly benefit from clarification of the relationships between material properties and biological responses. Here we investigate the biocompatibility of three Zn-based silver (Ag)-containing alloys, ranging from binary to quinary alloy systems. Selected binary and quinary Zn-Ag-based alloys underwent solution treatment (ST) to increase the solubility of Ag-rich phases within the Zn bulk matrix, yielding two different microstructures (one without ST and a different one with ST) with the same elemental composition. This experimental design was intended to clarify the relationship between elemental profile/microstructure and biocompatibility for the Zn-Ag system. We found that the quinary alloy system (Zn-4Ag-0.8Cu-0.6Mn-0.15Zr) performed significantly better, in terms of histomorphometry, than any alloy system we have evaluated to date. Furthermore, when solution treated to increase strength and ductility and reduce the fraction of Ag-rich phases, the quinary alloy's biocompatibility further improved. In vitro corrosion testing and metallographic analysis of in vivo implants demonstrated a more uniform mode of corrosion for the solution treated alloy. We conclude that Zn-Ag alloys can be engineered through alloying to substantially reduce neointimal growth. The positive effect on neointimal growth can be further enhanced by dissolving the AgZn3 precipitates in the Zn matrix to improve the corrosion uniformity. These findings demonstrate that neointimal-forming cells can be regulated by elemental additions and microstructural changes in degradable Zn-based implant materials. STATEMENT OF SIGNIFICANCE: The metallurgical engineering of bioresorbable zinc (Zn)-based medical alloys would greatly benefit from clarification of the relationships between material properties and biological responses. Here, selected binary and quinary Zn-Ag-based alloys underwent solution treatment (ST) to increase the solubility of Ag-rich phases within the Zn bulk matrix, yielding two different microstructures (one without ST and a different one with ST) with the same elemental composition. We found that applying a thermal treatment restores mechanical strength and mitigates the strain rate sensitivity of Zn-Ag alloys by dissolving AgZn3 precipitates. Ag-rich nano-precipitates in Zn decrease biocompatibility, a phenomenon that can be counteracted by dissolving the AgZn3 precipitates in the bulk Zn matrix.

Texture evolution of an extruded dilute Mg-1Sn-1Zn-1Al alloy was thoroughly investigated based on the twinning and dynamic recrystallization (DRX) behavior via hot compression at a strain rate of 10 s−1 and temperature of 225°C. It was found that the types and intensities of the texture are strongly dependent on the fraction of twins and DRX modes as well as regions where sub-grain boundaries (sub-GBs) are intensively accumulated. At the initial stage of deformation, the formation of compression direction (CD)-tilted basal texture was mainly determined by the occurrence of {101¯2} extension twins. As the strain increases, the variation in the texture intensity was greatly dominated by the DRX modes but the type of main texture remained unchanged. These findings are of great importance for texture modification of wrought Mg-Sn-based alloys during post-deformation.

A novel Mg-2.0Zn-0.5Ca-0.4Mn alloy has been formulated and processed through melt spinning and hot extrusion to enhance its mechanical and degradation properties. Microstructural characterization of rapidly solidified alloy ribbons consolidated by extrusion revealed a fine and fully recrystallized microstructure with average size of 4 µ m. The conventionally extruded alloy consisted of several course second-phase strips as coarse as 100 µ m, while the extrusion-consolidated ribbons were devoid of any second phases larger than 100 nm. Rapid solidification followed by extrusion processing resulted in significantly randomized texture where the majority of the basal planes were tilted toward transverse and extrusion directions. Such a weak texture resulted in higher activity of basal planes and thereby considerably improved the fracture elongation from 4% to 19%, while retaining relatively high tensile strength of 294 MPa. In addition to high strength and ductility due to the reduced activity of deformation twining during compression, the extrusion-consolidated alloy ribbons showed lower yielding asymmetric ratio than that measured for the conventionally extruded alloy (1.25 versus 1.61). Electrochemical measurements and immersion tests indicated that application of rapid solidification followed by extrusion remarkably reduced the corrosion rate from 2.49 mm/year to 0.37 mm/year due to recrystallization completion and suppression of coarse second-phase formation.

Zinc (Zn) has emerged as a promising bioresorbable stent material because of its satisfactory corrosion behavior and excellent biocompatibility. However, for load-bearing implant applications, alloying is required to boost its mechanical properties as pure Zn exhibits poor strength. Unfortunately, an increase in inflammation relative to pure Zn is a commonly observed side effect of Zn alloys. Consequently, the development of a Znbased alloy that can simultaneously feature improved mechanical properties and suppress inflammatory responses is a big challenge. Here, a bioresorbable, biocompatible Zn-Ag-based quinary alloy was comprehensively evaluated in vivo, in comparison to reference materials. The inflammatory and smooth muscle cellular response was characterized and correlated to metrics of neointimal (NI) growth. We found that implantation of the quinary alloy was associated with significantly improved inflammatory activities relative to the reference materials. Additionally, we found that inflammation, but not smooth muscle cell hyperplasia, significantly correlates to NI growth for Zn alloys. The results suggest that inflammation is the main driver of NI growth for Zn-based alloys and that the quinary Zn-Ag-Mn-Zr-Cu alloy may impart inflammation-resistance properties to arterial implants.

Zn-based alloys are recognized as promising bioabsorbable materials for cardiovascular stents, due to their biocompatibility and favorable degradability as compared to Mg. However, both low strength and intrinsic mechanical instability arisen from strong strain rate sensitivity and strain softening behavior make development of Zn alloys challenging for stent applications. In this study, we developed binary Zn-4.0Ag and ternary Zn-4.0Ag-xMn (where x= 0.2-0.6wt%) alloys. An experimental methodology was designed by cold working followed by a thermal treatment on extruded alloys, through which the effects of the grain size and precipitates could be thoroughly investigated. Microstructural observations revealed a significant grain refinement during wire drawing, leading to an ultrafine-grained (UFG) structure with a size of 670nm and 240nm for the Zn-4.0Ag and Zn-4.0Ag-0.6Mn, respectively. Mn showed a powerful grain refining effect as it promoted the dynamic recrystallization. Furthermore, cold working resulted in dynamic precipitation of AgZn3 particles, distributing throughout the Zn matrix. Such precipitates triggered mechanical degradation through an activation of Zn/AgZn3 boundary sliding, reducing the tensile strength by 74% and 57% for Zn-4.0Ag and Zn-4.0Ag-0.6Mn, respectively. The observed precipitation softening caused strong strain rate sensitivity in cold drawn alloys. Short-time annealing significantly mitigated the mechanical instability by reducing the AgZn3 fraction. The ternary alloy wire showed superior microstructural stability to its Mn-free counterpart due to the pinning effect of Mn particles on the grain boundaries. Eventually, a shift of the corrosion regime from localized to more uniform was observed after the heat treatment, mainly due to the dissolution of AgZn3 precipitates.

Understanding the surface interactions and reactivity of zinc (Zn)-based biomaterials with constituents of physiological fluids such as proteins and ions is essential for an accurate evaluation of biomaterial corrosion initiation and progression. In this paper, the effect of the albumin addition on the corrosion behavior of pure Zn and Zn–4Ag alloy is discussed. The corrosion behavior of Zn-based materials was studied using potentiodynamic polarization, electrochemical impedance spectroscopy, immersion tests and X-ray photoelectron spectroscopy. It was found that the addition of albumins largely affects the chemical composition, morphology and compactness of the protective films formed on biomaterials. A shift of the corrosion regime from localized to more general was observed in the protein-containing electrolytes. The proteins acted as corrosion inhibitors, reducing the corrosion current density and promoting passivation of the metallic surfaces. The increase in the corrosion resistance of the Zn–4Ag alloy is attributed to a selective Zn ion leaching that leaves the metal surface enriched with electrochemically more stable alloying element.

Controlling the microstructure and texture of Mg-based alloys is of paramount importance aimed at improving their mechanical performances to an acceptable level required for automotive and aerospace applications. The effects of twinning and dynamic precipitation on texture evolution in the Mg-8Sn-1Zn-1Al alloy were investigated during the hot compression test at 473 K up to a logarithmic strain of 0.7 with strain rates ranging from 0.1 to 10 s(-1). The results indicate that the types and intensities of the texture strongly depend on the strain rates during hot compression. Texture evolution was thoroughly investigated in terms of type/fraction of twins, and twinning-induced dynamic recrystallized grains. Moreover, the hindering effect of dynamically precipitated Mg2Sn phases on the matrix lattice rotation was studied in detail. The findings provide a new insight into controlling the texture during the fabrication of wrought Mg alloys, which is critical for producing alloys suitable for high-performance applications.

The detrimental effect of natural aging on mechanical properties of zinc alloys restricts their application as bioresorbable medical implants. In this study, aging of Zn-0.05Mg alloy and the effect of 0.5 Cu and 0.1 Mn (in weight percent) addition on the microstructure and tensile properties were studied. The alloys were cold rolled, aged and annealed; aiming to investigate the effects of precipitates and grain size on the mechanical properties and their stability. TEM analysis revealed that in ultrafine-grained binary Zn-0.05Mg alloy, the natural aging occurred due to the formation of nano-sized Mg2Zn11 precipitates. After 90 days of natural aging, the yield strength and ultimate tensile strength of Zn-0.05Mg alloy increased from 197±4 MPa and 227±5 MPa to 233±8 MPa and 305±7 MPa, respectively, while the elongation was drastically reduced from 34±3% to 3±1%. This natural aging was retarded by adding the third element at either 0.1Mn or 0.5Cu quantities, which interacted with Mg in Zn solid solution and impeded the formation of Mg2Zn11 precipitates. The addition of Cu and Mn elements increased alloy's strength, ductility, and its mechanical stability at a room temperature. The measured tensile strength and elongation were 274±5 MPa and 41±1% for Zn-0.1Mn-0.05Mg and 312±2 MPa and 44±2% for Zn-0.5Cu-0.05Mg, respectively. Annealing the alloys at elevated temperatures caused increase in both grain size and dissolution of secondary phases, and both affected alloy deformation mechanisms.

Absorbable metals have potential for making in-demand rigid temporary stents for the treatment of urinary tract obstruction, where polymers have reached their limits. In this work, in vitro degradation behavior of absorbable zinc alloys in artificial urine was studied using electrochemical methods and advanced surface characterization techniques with a comparison to a magnesium alloy. The results showed that pure zinc and its alloys (Zn–0.5Mg, Zn–1Mg, Zn–0.5Al) exhibited slower corrosion than pure magnesium and an Mg–2Zn–1Mn alloy. The corrosion layer was composed mostly of hydroxide, carbonate, and phosphate, without calcium content for the zinc group. Among all tested metals, the Zn–0.5Al alloy exhibited a uniform corrosion layer with low affinity with the ions in artificial urine.

In this study, the effect of grain size and precipitates on tensile properties of Zn-1.0Cu alloy were investigated. The alloy was cold rolled and annealed to manipulate the grain size and precipitation of CuZn4 particles at grain boundaries. Cold rolling resulted in an almost ultrafine-grained structure alongside precipitation of nano-sized CuZn4 particles. Strain induced precipitates triggered room temperature superplasticity through activation of Zn/CuZn4 boundary sliding, exhibiting maximum elongation of 470% at the strain rate of 1.0 x 10(-4) s(-1). Short-time annealing led to significantly reduced strain rate sensitivity due to the reduction of CuZn4 fraction, while the grain size remained nearly intact. This suggests that precipitates rather than grain size mainly influence the mechanical properties of Zn alloys. (C) 2019 Elsevier B.V. All rights reserved.

During the last two decades, increasing efforts have been made in the development of biocompatible and biodegradable metallic materials for load-bearing implant applications. So far, magnesium-, iron-, and zinc-based alloys have been proposed as biodegradable metals for medical applications. Over the last decade, extensive research works have been carried out on Mg and Fe. Fe-based alloys show appropriate mechanical properties, while their very low degradation rate is considered to result in reactions similar to those observed in permanent applications. On the other hand, alongside the insufficient mechanical performance, Mg degradation rate has proved to be too fast in physiological environment and rarely homogeneous. During the last few years, Zn has been introduced to the biomedical community as a potential material for bioabsorbable cardiovascular stents due to its prominent corrosion rate and controllable mechanical properties.

Microstructural changes of magnesium alloy AZ91 after fatigue loading in the EX-ECAP state were evaluated using EBSD. It was found that both the number fraction of low-angle boundaries and parameter KAM decreased after the testing at a stress amplitude of 160 MPa but started to increase with the increasing stress amplitude. This behaviour can be explained with a mutual influence of dislocation accumulation (which is stronger with a higher stress amplitude) and dynamic softening (which is weaker with a decreasing number of cycles/cycles to failure). The average grain size remained almost unchanged except at a stress amplitude of 180 MPa, which could have been caused by certain conditions allowing an ideal development of both mentioned phenomena.

The search for biodegradable metals with mechanical properties equal or higher to those of currently used permanent biomaterials, such as stainless steels, cobalt chromium and titanium alloys, desirable in vivo degradation rate and uniform corrosion is still an open challenge. Magnesium (Mg), iron (Fe) and zinc (Zn)-based alloys have been proposed as biodegradable metals for medical applications. Over the last two decades, extensive research has been done on Mg and Fe. Fe-based alloys show appropriate mechanical properties, but their degradation rate is an order of magnitude below the benchmark value. In comparison, alongside the insufficient mechanical performance of most of its alloys, Mg degradation rate has proven to be too high in a physiological environment and corrosion is rarely uniform. During the last few years, Zn alloys have been explored by the biomedical community as potential materials for bioabsorbable vascular stents due to their tolerable corrosion rates and tunable mechanical properties. This review summarizes recent progress made in developing Zn alloys for vascular stenting application. Novel Zn alloys are discussed regarding their microstructural characteristics, mechanical properties, corrosion behavior and in vivo performance. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The major drawback of Fe-based materials for biodegradable implant applications is their slow degradation rate. Addition of second phase particles into the Fe matrix can increase the degradation rate at the beginning of the corrosion process. However, so far, there is neither quantitative data on in vitro degradation nor direct experimental evidence for long-term dissolution of Fe-based biodegradable composites. Here, a series of immersion tests at different exposure intervals (20, 50 and 100 days) to modified Hanks' solution were performed to study the degradation behavior of Fe and Fe/Mg2Si composites prepared by different powder metallurgy techniques. The results revealed the role of Mg2Si in the composition and stability of the protective films formed during the static corrosion experiments. Fe/Mg2Si composites showed higher degradation rates than those of pure Fe at all stages of immersion. Degradation rates at distinct exposure intervals strongly depended on the composition and stability of formed oxide, hydroxide, carbonate and phosphate protective films on the degraded surfaces. The release of Fe ions into the solution at later stages of the experiment was limited due to the barrier effect of the insoluble deposit. This fundamental study provided a basis for the processes of protective film formation in modified Hanks' solution, which enables a detailed identification of its characteristic features.

In the present work, both the surface chemical contamination and the mechanical alteration of Ti-6Al-4V (Ti64) and Ti-6Al-4V extra low interstitial (Ti64ELI) titanium alloys subjected to superplastic forming (SPF) for the manufacturing of highly customized biomedical prostheses have been investigated. As case study, a cranial implant was considered. The design of the manufacturing process was assisted by a numerical model calibrated on free inflation experimental tests. Glow discharge optical emission spectrometry (GDOES) analyses, nanoindentation tests, and metallographic analyses allowed to relate the mechanical alteration to the oxygen enrichment due to the environmental exposition during processing. While similar diffusion kinetics were found, different oxidation rates were measured in the two investigated alloys. The hardness variation was strictly related to the oxygen content. In order to verify the material biocompatibility, cytotoxicity tests were conducted on the most oxidized part. Results highlighted that the oxygen enrichment due to the manufacturing process did not significantly affect the cells viability.

Iron-based materials showed a high potential for degradable biomaterial applications. However, their slow corrosion rate limits their use as a biodegradable implant material. One approach to control and modify their mechanical properties is the use of reinforcement particles, to create metal matrix composites in which the second phase is aimed at tuning not only the mechanical properties but also the corrosion mode and rate in a physiological environment. Here, Fe/Mg2Si composites were produced via powder metallurgy from pure Fe and Mg2Si powders. The different conditions were fabricated by various combinations of milling or mixing processes followed by hot rolling consolidation. The effect of the Mg2Si addition on corrosion behavior of Fe/Mg2Si composites was studied by performing cyclic polarization and static corrosion tests for an immersion time of 24 and 240 h. The presence of the reinforcement particles played a crucial role in the susceptibility of Fe-based composites to localized corrosion attack. The corrosion initiation and its development were systematically monitored. Scanning electron microscopy, X-ray diffraction, and atomic emission spectroscopy were employed to investigate the corrosion mechanism. The importance of Mg2Si particles in the triggering of corrosion processes was explained. Electrochemical measurements and static immersion tests implied that the introduction of Mg2Si particles could accelerate the corrosion rate of Fe. It was confirmed that the size and distribution of the reinforcement influenced considerably the uniformity of the corrosion attack.

In order to improve the stretch formability of magnesium alloy sheets, {10–12} tension twins were introduced by pre-compression along the rolling (RD) and transverse directions (TD) with 1.6%, 3.3%, and 5.4% strain levels. Subsequent annealing at 473 K was conducted for 6 h to preserve twinning lamellae. In order to avoid bending–buckling, a special fixture for thin sheet compression has been developed. In addition, hemispherical tests were performed at room temperature. The mechanical properties were improved, while the Lankford value (r-value) decreased and the strain hardening exponent (n-value) increased as the pre-compression level increased compared with the as-received sheet. The stretch formability was also improved. The Erichsen value was dramatically improved the most, from 2.83 mm in the as-received to 5.36 mm and 6.78 mm in TD and RD pre-compressed 5.4% Mg specimens, respectively, which increases by 89% and 139%. The stretch formability was enhanced much more with the pre-compression along the RD as compared to the TD.

In this paper tensile properties at elevated temperature of extruded AZ91 magnesium alloy and the same alloy further processed by ECAP (exECAP) are compared. The tensile tests were performed at room temperature and for the temperature range of 100 to 300 °C. Loading speed 2 mm/min was used for the tests. At room temperature mechanical properties except elongation were slightly higher for extruded material yet still very similar to properties of exECAPed material. Overall trend of properties evolution with increasing temperature was also similar but the decrease of strength or the increase of elongation and reduction of area respectively is more intensive for exECAPed material. Elongation of exECAPed material exceeded elongation of extruded material more than twice at 300 °C and with value of ~260% this alloy exhibited pseudosuperplastic behavior.