Corrosion reactions at liquid-solid interfaces critically impact infrastructure degradation and sustainability, and in medicine for biodegradable body implants. For the latter, Mg, is a promising candidate thanks to its biocompatibility and biodegradability, making it an excellent replacement for temporary implants made of Ti or steel. However Mg alloys corrode rapidly and uncontrollably, through mechanisms not fully understood, i.e. there remain open questions regarding the influence of different alloying elements, their distribution, as well as different electrolytes, on the corrosion processes. Understanding the corrosion processes at the reactive liquid-solid interface requires analytical methods with high local and chemical analysis capability and ideally to measure these reactions in-situ, on an atomic length scale, which is currently lacking. Atom probe tomography (APT) provides analytical imaging in 3D with equal chemical sensitivity across the periodic table even for light elements such as hydrogen and with comparable spatial resolution and can therefore close the gap. We demonstrate an quasi-"in-situ" approach to analyze the reactive solid-liquid interface by cryo-APT and investigate the early-stage corrosion mechanisms of a Mg0.1Ca alloy. A metastable defect phases at the reactive interface could be observed during the corrosion process, these early reaction products are highly reactive and must play a critical role in accelerating the corrosion. However, a better understanding of these early stages of corrosion and their products is necessary to advance the understanding of corrosion processes and their modeling, and consequently for higher level of control over the biodegradation rate of future implant material.

This study examines how corrosion affects the mechanical properties of two novel 300-micron magnesium alloy wires, WE43MEO and ZX10, with potential applications in temporary implants. Microstructure analysis revealed differences between the alloys, with WE43MEO showing smaller elongated grains and ZX10 exhibiting larger equiaxed grains. Bio-immersion testing demonstrated higher corrosion rate and mass loss for WE43MEO compared to ZX10. Micro-CT analysis confirmed these findings, with WE43MEO exhibiting larger pits. Furthermore, WE43MEO's mechanical properties, initially superior, dropped below ZX10's after exposure to the corrosive environment. These results suggest that microstructure directly impacts the suitability of these alloys for implants. WE43MEO's faster degradation makes it less ideal for long-term applications, but its initial strength advantage suggests potential for short-term implants requiring higher load bearing. Conversely, ZX10's more corrosion-resistant microstructure translates to slower mechanical decline, making it a promising candidate for longer-term implants. Future work should focus on refining microstructures for improved performance, potentially by achieving a more uniform distribution of smaller precipitates.

Additive manufacturing (AM) offers unique opportunities to meet the complex design requirements of implants such as stents. On the other hand, research on Fe-based biodegradable alloys for stent applications has significantly increased in the last decade due to their suitable mechanical properties such as ductility and high ultimate strength. In this work, the effect of laser powder bed fusion (LPBF) parameters on the corrosion of Fe20Mn0.5C was studied using potentiodynamic polarization and electrochemical impedance spectroscopy. An optimization of LPBF parameters was carried out by varying laser power and scanning speed considering volumetric energy density and sample porosity. Three conditions were selected for electrochemical tests: P160V640, P200V440, and P240V340. The results showed that corrosion resistance is strongly related to porosity, which in turn depends on the volumetric energy density of the LPBF system during the manufacturing process.

A multimaterial device, composed of Nickel-Titanium (NiTi) and Mg1.2Zn0.5Ca0.5Mn, is developed as a stiffness-matched approach for skeletal reconstruction application. Due to the rapid biodegradation of Mg in the body and the galvanic corrosion occurring due to the interaction of both metals in physiological fluid, we present preliminary results for delaying the degradation of Mg. First a Zn interlayer is introduced between the metals. Second, Mg surface treatment is conducted by via Micro-Arc Oxidation (MAO) and followed by CaP coating. Results shows a characteristic porous surface in the Mg component as result of the MAO treatment. The obtained surface will next work as a perfect surface to receive the CaP coating.

This study aims to develop bioresorbable Mg-Zn-Ca-Mn and Mg-Zn-Ga alloys for bone implants, with the objective of enhancing the bone tissue growth process. To enhance the mechanical properties and corrosion resistance, MgZn2Ca0.7Mn1 and MgZn2Ga2 alloys were manufactured through hot extrusion. The microstructure and mechanical properties were examined, and the corrosion rate was determined in Hank's solution. The assessment of alloy resorption parameters was also conducted at one, three-, and six-months post-surgery. Assessment of alloy resorption parameters was performed postoperatively. The biodegradation process was characterized by the systematic development of newly formed bone tissue. The results indicated that magnesium alloys are suitable for clinical use and showed complete resorption within six months.

Five alloys with different Zn and Ga contents were prepared by hot extrusion. For all alloys, the microstructure was studied and the mechanical properties were determined. In addition, the corrosion rate was determined for all alloys from the hydrogen evolution in Hank's solution. Increasing the alloying element content resulted in higher strength of the alloys. For example, when the Zn and Ga contents in the alloy extruded at 200 °C increased from 2 to 4 wt%, the TYS and UTS increased by 115 and 71 MPa, respectively, but El decreased from 13.9 to 7.6 %. It was found that the corrosion rate in Hank's solution depends on the chemical composition of the alloys.

The Mg-1Ca-0.5Zn-0.1Y-0.03Mn (at.%) alloy, known for its high mechanical properties due to long-period stacking ordered phases, shows promise as a biomedical material. This study assessed its biocompatibility and corrosion resistance under physiological conditions. Rapidly solidified and extruded disc samples were tested in vitro and in vivo, revealing good cytocompatibility with L929 and MG63 cells, a stable pH and osmolality, and a corrosion rate of 0.38 mm/year. In vivo implantation is performed on male Wistar rats with a calvaria bone defect.

Magnesium (Mg) has attracted great interest as a biodegradable metallic implant due to the formation of bioresorbable corrosion products during its degradation in the body. Yet, a challenge in the reliable prediction of degradation mechanism is that currently performed in-vitro experiments typically induce the formation of corrosion products with different chemical structures and transport properties than those observed in animal studies (in-vivo). From a materials perspective, another complexity level is generated by the low solubility of alloying and impurity elements in magnesium, resulting in the formation of cathodic secondary phases. To investigate the influence of these cathodic secondary phases on the Mg corrosion behavior in a physiological mimicking environment, low-purity Mg containing a high amount of Fe-rich intermetallic phases and ultra-high purity Mg without any secondary phases were exposed to our new formulation of simulated interstitial body fluid (SIBF). The composition of SIBF is based on the measured values of inorganic ions and organic species in human body fluid. The pH of SIBF was regulated with dynamic bicarbonate buffering and flown over Mg. Electrochemical and surface characterizations showed the significantly reduced cathodic reactivity of the intermetallic phases on low-purity Mg, where the obtained values became comparable to those of ultra-high purity. Furthermore, corrosion products formed in solutions with different ions were studied on both purity degrees, revealing that the levels of free calcium, phosphate, and carbonate ions have opposite effects on the electrochemical reactivity of Mg depending on the presence of Fe-rich intermetallic phases. The results indicate that any deviation from physiological concentrations of these ions might be responsible for microstructure-dependent variations seen between in-vivo and in-vitro studies.

This work presents a new correlative microscopy workflow that combines quantitative 3D X-ray ptychography (PXCT) with high-resolution electron microscopy. The combination allowed us to successfully investigate corrosion in a medical Mg alloy (ZX00) with minimal damage to the sample while still closely approximating in situ conditions.

Atomic layer deposition (ALD) as a coating technique has several potential advantages for the development of magnesium (Mg) based bioresorbable cardiovascular stents and the control of Mg’s rapid corrosion rates: ALD eliminates issues related to line-of-sight coating methods and can produce conformal coatings with tuneable, nanoscale thicknesses1, that do not deleteriously impact on the overall stent geometry from an overall strut thickness perspective2. Hafnium dioxide (HfO2) is commonly produced by ALD and there is an emerging interest in its use as a suitable biomaterial. This study aims to investigate the potential of HfO2 coatings, deposited via ALD, in conjunction with poly lactic co glycolic acid (PDLGA) – a common drug eluting polymer employed for cardiovascular stents – to regulate the degradation rates of WE43 magnesium alloy for stent applications. HfO2 coatings were grown at 150°C by ALD on WE43 Mg coin components to produce HfO2 layers with a thickness of 5 nm, 50 nm and 100 nm. XPS was conducted to assess coating composition. SEM studies evaluated the structure and morphology of the coating. Degradation studies were conducted in simulated body fluid (SBF) to measure hydrogen (H2) evolution. Additionally, 0.3 mm dia. WE43 wires were coated with 50 nm HfO2 and subsequently dip coated with PDLGA. Wires were immersed in SBF to assess the corrosion resistance of the HfO2-PDLGA coatings and tensile testing was conducted before and after immersion for 40 hrs. SEM images revealed a uniform HfO2 coating on the Mg surface. XPS analysis revealed an atomic concentration of O and Hf at a ratio of 2:1, indicating an adequate coating process. H2 evolution studies revealed a thickness-based reduction in H2 evolution across HfO2 coated samples in a 21-day period. Tensile tests of the coated wires demonstrated improved retention of yield strength of HfO2 coated wire specimens after immersion in SBF. HfO2 coatings demonstrated improved corrosion resistance of Mg, which was tuneable with respect to the coating thickness. Tensile testing of the coated wires demonstrated improved strength retention of the HfO2 coated wires after immersion in SBF, although the addition of PDLGA-coating increased variability considerably. This study provides interesting preliminary insights into the potential role of HfO2 as a coating material for controlling Mg degradation.

To build a suitable corrosion environment for testing the degradation behavior of magnesium alloy in vitro, the medium and test environment are constantly optimized. However, the applicability of medium renewal mode is still vague. In this study, based on three representative test protocols, the influence of the specific ratio of media volume to surface area and the disposable medium real-time renewal mode (flow-through) on Mg corrosion were investigated. It is found that in flow-through medium renewal mode, the composition of the medium is maintained quasi-constant which is essential for corrosion tests. The selection suggestion on medium renewal mode was also proposed. This work is beneficial for ultimately establishing the representative in vitro testing protocols for Mg bioabsorbable materials.

Magnesium (Mg) alloys have been potentially classified as candidates for use as tissue implants due to their biocompatibility, biodegradability, and mechanical properties. These alloys have been extensively investigated in orthopedic implants, and additive manufacturing of scaffolds has been seen as one of the most attractive alternatives for bone repair. In this study three gyroid structures with different pore sizes and cell wall thickness were generated using Creo 7.0 software. Mg-5Gd feedstock comprised of the raw powder and polymer binder materials and fused granular fabrication technique was used to 3D print these scaffolds, as a final part of the production process green parts were sintered under argon at 648 °C for 32h. Characterization by micro-Tomography revealed the cell wall thickness of 650 µm, 790 µm, and 1000 µm, corresponding to 1250 µm, 1080 µm and 720 µm pore sizes, respectively in the produced structures. All samples were tested in vitro, a homogeneous layer on the surface containing nodular morphologies and some needle-like crystals were found. It was found that the smaller pore sized P1000 scaffold showed a lower degradation rate compared to others. Additionally, to maintain the mechanical stability of the scaffolds during degradation, a thicker strut i.e. smaller pore size can be beneficial. Hence, pore size is significantly influential in modulating degradation behavior.

INTRODUCTION: The growing need for alternatives to autologous bone grafts when treating bone defects leads to the development of bioresorbable materials like zinc-magnesium. This work investigates the biocompatibility, cytotoxicity, and osteoblast cell growth of additively manufactured (AM) zinc-magnesium specimens to assess this alloy for clinical application (e.g. patient specific, load-bearing implants). METHODS: Zn1Mg alloy cylinders from Nanoval GmbH & Co. KG were fabricated using a modified laser powder bed fusion machine from Aconity 3D with a diameter of 6 mm and a thickness of 1 mm. The specimens are “as-manufactured” (i.e. no further post-processing) for all tests. Osteoblasts were cultured in DMEM (Pan Biotech, Aidenbach, Germany, catalog number: P04-05550, 37°C, 5% CO2) with the cylinders for up to 14 days to determine first aspects of biocompatibility and growth properties of the alloy. Cell viability, cytotoxicity, and proliferation were assessed using Live/Dead staining with calcein, DAPI staining, with subsequent fluorescence microscopy, and flow cytometry (FACS). Additionally, cellular morphology was examined using Phalloidin/DAPI staining and scanning electron microscopy (SEM). RESULTS: Live/Dead staining shows high osteoblasts viability and proliferation on Zn1Mg after 7 days. FACS analysis confirms a 99.1% survival rate out of 40k cells (fig. 1, top). Fluorescence microscopy of DAPI-stained cells indicates an increase in nuclei over 3, 7, and 14 days. Furthermore, the phalloidin/DAPI staining (fig. 1 (center)) reveals a pronounced development of the cytoskeleton after 14 days. SEM images of the Zn1Mg cylinder surface after contact with the cells for 14 days (fig. 1 (bottom)) display the typical texture of additively manufactured parts, characterized by unmelted particles sintered to the surface. Embedded in this texture, osteoblasts can be seen. DISCUSSION & CONCLUSIONS: The 99.1% survival rate significantly exceeds the 70% minimum requirement of DIN EN ISO 10993-5, classifying Zn1Mg alloy as non-toxic. Cell viability and proliferation show positive responses to the alloy and its degradation products. Surface roughness does not hinder cell attachment, as indicated by observed filopodia suggesting cell migration. These findings support future use of AM Zn1Mg for patient-specific implants and scaffolds enhancing cell ingrowth.

Magnesium (Mg) materials are interesting for use in guided bone and tissue regeneration. However, Mg-based material carry the risk of inhomogeneous degradation in aqueous environment. Electropolishing is an attractive surface treatment to improve the corrosion behaviour of Mg, but it is not well known how the modified surface affects the biocompatibility of this resorbable metal. The aim of this study was to investigate the degradation and biocompatible behaviour of electropolished Mg to assess the effects of corrosion and surface treatment on tissue regeneration under physiological conditions. Extruded pure Mg discs with a diameter of 10 mm and a height of 2 mm were electropolished in a mixture of phosphoric acid and ethanol for 5 min at a current density of 0.08 A/cm². The degradation behaviour was observed in Dulbecco´s Modified Eagle´s Medium (DMEM) + 10% fetale bovine serum (FBS) and the wetting behaviour was determined by measuring the contact angle. The investigation of the biocompatibility of the Mg samples included a live dead staining of human mesenchymal stem cells incubated at the material surface for 5 days. The degradation rate of electropolished Mg samples was, compared to mechanically polished surfaces, more than 15 times lower with values of about 0.08 mm/year. With a contact angle of approx. 30° in DMEM + 10% FBS, electropolished Mg surfaces exhibit optimized wettability. After electropolishing, cells could adhere to the Mg surface, but to a smaller extent. The electrochemical treatment can give an important contribution to the corrosion control of Mg materials, without having a cytotoxic effect on cells. However, the extremely smooth surface after the post-treatment restricts their adhesion. Moreover, it can be assumed that a wettable surface leads to a more even distribution of body fluids on the Mg component, so that the corrosive attack can also occur more uniform. The fact that Mg implants are designed to degrade means that the material surface and therefore its surface properties are constantly changing during the lifetime of an implant. This requires further in vitro investigation methods to be optimized and evaluated.

INTRODUCTION: Flow diverters (FDs) are braided stents used to treat intracranial aneurysms. Bioresorbable flow diverters (BRFDs) aim to serve their temporary function of occluding the aneurysm before safely absorbing into the body. This may mitigate complications associated with the permanent presence of conventional FDs such as device induced thromboembolism, stenosis, and side branch occlusion. In this work, we evaluate an iron-based BRFD in the rabbit elastase induced aneurysm model. METHODS: BRFDs and control FDs were constructed to the same geometry. BRFDs contained 36 FeMnN alloy (35% Mn, 0.15% N, balance Fe, by wt%) wires and 12 polyimide coated Ta wires to impart radiopacity. The control FDs were composed entirely of permanent 35NLT/Pt-DFT wires. Wire components were manufactured by Fort Wayne Metals. BRFDs were deployed for 3 months (n=7 rabbits) to treat aneurysms induced in the rabbit elastase model. Digital subtraction angiography and gross dissection microscopy were used to assess aneurysm occlusion. BRFDs and control FDs were deployed in the abdominal aorta for 3 (n=7 rabbits) or 6 (n=3 rabbits) months. MicroCT and H&E staining were used to assess the resorption rate and biological response, respectively, of the aortic implants. RESULTS: The BRFDs failed to completely occlude the aneurysm in 6 rabbits. MicroCT analysis determined that the volume of FeMnN alloy wires in BRFDs deployed within the aorta lost 61±14% and 83±13% (mean ± standard error) of their initial volume after 3 and 6 months, respectively. H&E staining demonstrated there was minimal stenosis in the control FDs and BRFDs at 3 and 6 months. No adverse tissue reactions were observed in any of the BRFDs in response to notable corrosion. CONCLUSIONS: We believe rapid and localized corrosion resulted in BRFD wires fragmenting away from the aneurysm neck before becoming covered with neointima and occluding the aneurysm. The FeMnN wires corroded faster than anticipated, but their corrosion did not appear to elicit any adverse tissue responses. In conclusion, the FeMnN alloy appears to be safe in terms of localized toxicity in the arterial environment, but future work should focus on bioresorbable materials with slower, more uniform corrosion for the BRFD application.

Lean magnesium–calcium based biodegradable metallic alloys (BMAs) have been studied in various pre-clinical settings and present a promising alternative to permanent metallic implant materials for potential clinical use in traumatology. To further explore the efficiency of osteotomy stabilization using BMA-based screw-plate implants, a large-animal study with a cranio-maxillofacial defect model is being conducted over an extended time duration of 42 months. The study covers four different timepoints of sacrifice, ranging from two, six, and 24 months until complete material biodegra¬dation. Initial results for the two- and six-months groups demonstrated promising outcomes for the Mg-based implants. Here, complementary and extending data are presented up to its currently latest observation timepoint of 30 months. Each animal received osteotomies with fully mobilized bone fragments located at the calvarial (CD) and zygomatic arc (ZAD) regions, representing mechanically non- and moderately loaded cranio-maxillofacial areas. The fragments were refixated by screw-plate implants of plasma electrolytic oxidation (PEO)-coated ultra-high-purity Mg–Ca (UHP-X0) alloy implants, and (ii) titanium-based implants as a reference. Radiographic data on implant-volume loss, gas-cavity formation, and bone response was evaluated up to the latest time point. Implant volume loss was found to be nearly linear and similar for both anatomical regions. The gas evolution fluctuations of the Mg samples within the first two months coincided with higher implant-volume losses. In contrast, the later gas-cavity volume increase was not reflected by respective degradation-rate variations. Around the Mg implants, signs of osteostimulative effects were seen, but bone resorption was also observed to some extent. Signs of bone-tissue resorption were observed in week two, when increased gas-volume formation was also measured, and were also found in later degradation stages up to 30 months. On the other hand, new bone deposition was found to start equally for both material groups from week four on and was consistently higher for the Mg group. The bone-implant contact was higher for the Mg group than for the Ti reference for the moderately loaded osteotomies, possibly due to an induced mechanical stimulus. There are also various indications that the Mg-based material positively affects the local bone metabolism upon continuous implant degradation.

Magnesium based alloys have been extensively researched as biodegradable materials, however, the commercialisation of Mg based implants is still at the infant stage. The present research explores the impact of microstructural engineering on the development of biodegradable Mg alloys. The bio corrosion performance of various thermo-mechanically processed Mg alloy samples are investigated. The research pioneers in understanding the role of microstructural engineering and the corresponding underlying mechanisms on the bio-corrosion behaviour of different sample conditions. The combined effect of grain size (GS), secondary phase and crystallographic orientation on bio-corrosion mechanism of these Mg alloy sample conditions are proposed for the first time. The microstructural engineering increased the bio-corrosion resistance significantly and proved to be a promising technology to develop biodegradable Mg implants.

INTRODUCTION: The process of manufacturing biodegradable magnesium implants is complex, combining the requirements of materials engineering, surface engineering, corrosion engineering and medical engineering [1, 2]. For this study, only the protective coatings will be considered. Conversion coatings have multiple functions: they slow down the dissolution rate of magnesium in physiological environments, reduce the amount of hydrogen released from the raw material and increase the adhesion of biological coatings to magnesium surfaces by increasing the surface roughness. This study describes anodic oxidation conversion coatings on biodegradable MgZn1Ca0.2Li1 and MgZn1Ca1Li1 alloys after hydrostatic extrusion. METHODS: To characterize the protective coatings synthesized on biodegradable magnesium alloys a comprehensive analysis was conducted using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Additionally, a hydrogen release station was used to determine the corrosion rate. The study meticulously examined the influence of various parameters in the coating manufacturing process (such as: process time and current density) in KOH+KF solution. RESULTS: The chemical composition of biodegradable magnesium alloys plays an important role. Higher calcium content in magnesium alloys increases hydrogen release, indicating a higher corrosion rate. Simultaneously, the hydrostatic extrusion reduces the grain size from above 300 to 1.8-4 microns, depending on the material and sample. Grain reduction affects the strength and corrosion properties of biodegradable magnesium alloys. Hydrostatic extrusion significantly enhances the strength properties of biodegradable magnesium alloys, it also increases hydrogen release. Conversion coatings produced in a KOH+KF solution consist of potassium, fluorine, oxygen, and magnesium, with dominant phases being MgF and KMgF and significantly reduce the dissolution kinetics of the magnesium alloy. Results from immersion corrosion tests revealed a significant positive impact of the investigated coatings on reducing hydrogen evolution, underscoring their potential to enhance the performance and biocompatibility of magnesium alloys in biomedical applications. DISCUSSION & CONCLUSIONS: In conclusion, magnesium alloys with alloying additives such as calcium, zinc and lithium are promising materials for medical applications due to their similar properties to bone tissue, biodegradability and potential biocompatibility. Anodizing is a promising method of producing a protective coating due torelatively low cost of producing coatings, high adhesion of coatings to substrates and reasonable control over their properties obtained by optimizing process parameters, such as electrolyte used, current density, or duration of surface treatment.

Bioresorbable metal stents are designed to maintain a vascular lumen for up to 2 years. Complete dissolution of the device results in the elution of beneficial byproducts and allows reintervention at the site of implant. Development of these devices requires a material that is both biodegradable and hemocompatible. Preliminary investigation of magnesium demonstrated reduced activation of the coagulation cascade when compared to other biodegradable metals.1 The exact mechanism by which magnesium reduces thrombogenicity, particularly as it relates to surface interactions, is unknown. To assess the mechanism, this work tested the role of alloyed materials, pH and Mg2+ ion concentration against a clinical control on the in vitro activation of the coagulation cascade. All alloys had longer fibrin generation times (Fig 1) and lower FXIIa detected compared to CoCr. Specifically, plasma alone generated significantly less FXIIa compared to CoCr, but produced an equivalent amount of FXIIa to any of the alloys. All Mg alloy wires trended towards longer fibrin generation times than CoCr, with AZ31, RLM, and ZX10 having significantly longer times. An increased pH in the PPP abolished detectable FXIIa at a different rate than the magnesium wire. Finally, the Mg ion solution showed a significant difference in clotting time between ions and the wire, indicating that there is a difference between material and eluted corrosion byproducts. Mg alloys performed similarly to pure magnesium in the in vitro assays. Mg alloys had a reduced level of FXIIa and fibrin generation compared to a CoCr clinical control indicating their value as materials for a bioresorbable stent. pH and ion concentration did not recapitulate the effect of the wire itself, suggesting that the mechanism is tied to the material. Ongoing work with surface modified magnesium alloys seeks to understand the effect of different surface modifications on the anti-thrombogenicity of magnesium alloys. Future work will incorporate platelets and endothelial cell testing to gain a deeper understanding of hemocompatibility and vascular healing.

This study investigates the relationship between microstructure and mechanical properties of pure zinc and zinc-magnesium alloys (with 0.6 and 1.2 wt% Mg) prepared by casting and a two-step plastic deformation process (hot extrusion and hydrostatic extrusion in four passes). XRD analysis revealed that pure zinc consists of α-Zn, while the alloys contain α-Zn and Mg2Zn11 intermetallic phases. SEM/EBSD characterization showed that hydrostatic extrusion results in a composite-like microstructure with Mg2Zn11 bands located along the extrusion direction. The dominant orientations <2-1-10> for pure Zn, <0001> for ZnMg1.2, and both <2-1-10> and <10-10> for ZnMg0.6 were observed. Heating at 50°C improved mechanical properties without significant changes in the microstructure. Long-term heating indicated that dominant orientations remain stable, with magnesium diffusion observed in the alloys. The study concludes that hydrostatic extrusion affects dynamic recrystallization and dislocation density differently in pure zinc and zinc-magnesium alloys, with magnesium addition inhibiting static recrystallization.

For revealing the impact of Zn in extruded Mg-Zn-Ca alloys, the Zn content and the extrusion speed were varied. The microstructure devel-opment and the influence on the mechanical properties were analysed to reveal the impact of developing microstructure to a potential proper-ty profile for specific applications. Ultra-pure Mg is often used for medical applications, but the present study shows that this is not neces-sary. Enormous potential savings could be achieved by using conventional pure Mg.

This study introduces a novel low-temperature method for producing metal-ceramic composites, traditionally made at high temperatures. A metallic scaffold is created via additive manufacturing and then infiltrated with alpha tricalcium phosphate (α-TCP) paste, which is converted into hydroxyapatite through hydrothermal treatment. The formation of hydroxyapatite near room temperature was confirmed by X-ray diffraction and scanning electron microscopy, revealing an entangled network of hydroxyapatite crystals and a corrosion layer on the Mg surface. Infiltrating the scaffolds with hydroxyapatite reduced porosity and increased compressive strength, surpassing the strength of individual components, including the Ti scaffold. These new interpenetrating phase composites show promising potential to reduce the metal fraction in bone repair implants without compromising mechanical strength.

INTRODUCTION: The degradation rate of Fe based biomaterials can be accelerated through the incorporation of Mg in the Fe lattice or as nanoparticles [1,2]. Being Fe ferromagnetic, it is expected that Fe-Mg also reacted under magnetic fields. On the other hand, given that Fe and Mg are immiscible, the processed Fe-Mg based alloy is in a metastable state, and thus, it may be especially sensible to thermal treatments. In this work, we present preliminary results on magnetic and thermal behaviour of two Fe-Mg and two Fe-Zn-Mg alloy powders. Fe-Mg based alloys might be used in a variety of applications, such as graft powder, reinforcing particles of biodegradable polymers [3], after consolidation, and as feedstock for the additive manufacture of implants. METHODS: Powders of Fe-5Mg, Fe-10Mg, Fe20Zn, (Fe-20Zn)-5Mg and (Fe-20Zn)-10Mg (wt%) were obtained from elemental powders (Fe: 99.7%, dia. ≤74 µm; Mg: 99.8%, dia. ≤100 µm, Zn: >99.9%, dia. ≤45 µm) by attrition milling at 1400 rpm under nitrogen atmosphere. Fe powder was also milled for comparison purposes. Hysteresis loops at 5 K and 300 K and magnetization versus temperature at 5000 Oe were performed by a Quantum Design SQUID magnetometer. Differential scanning calorimetry (DSC) studies were conducted using a TA DSC 25 calorimeter. Samples, weighing about 5 mg, were heated from 50 ºC to 700 ºC at a rate of 10 ºC/min. Transmission electron microscopy (TEM), JEOL JEM 3000F, was employed to measure the lattice parameters of the powders in order to compare them with those of Fe. RESULTS: Hysteresis loops (Figure 1) show that the addition of Mg or Zn produces an increase of the coercive field and slight changes in the saturation magnetization when compared with pure milled Fe. Magnetic properties of the ternary powder suggest the presence of two magnetic phases. Preliminary results inferred from DCS curves (not shown) seem to corroborate the presence of metastable states that transform into stable ones with increasing temperature. Fig. 1: Hysteresis loops of milled Fe (left) and Fe5Mg alloy (right) at 5 K and 300 K. Inset: low magnetic field magnification. Lattice parameters obtained from TEM images show a slight increase with respect to Fe for the Fe-Mg alloy powders, Fe-20Zn shows a larger increase, whereas in (Fe-20Zn)-Mg powders the lattice parameters resulted similar to that of Fe, Figure 2. Fig. 2: TEM images: Fe5Mg, FeZn & FeZn10Mg. DISCUSSION & CONCLUSIONS: Metastable Fe(-Zn)-Mg powders present unique behaviours in terms of magnetic properties and thermal evolution probably because of the change in Fe interplanar distances due to inclusion of Mg and Zn atoms in the Fe lattice. These changes of properties might be used for tailoring degradation rate of Fe-based implants. REFERENCES: 1 Y. Guangyin, N. Jialin (2012) Patent CN103028148A. 2 R.G. Estrada, M. Multigner, M. Lieblich, et al (2022) Metals, 12(1). 3 R. G. Estrada, M. Multigner, N. Fagali, et al (2023) Heliyon, 9(12) e22552. ACKNOWLEDGEMENTS: Grants PID2022-139323NB-I00, PID2021-123891OB-I00, PID2021-123112OB-C21 and PRE2020-092118 (R.G.E.) funded by MCIN/AEI/ 10.13039/501100011033. ICTS-CNME. CAI-Técnicas Geológicas.

In this work, bioresorbable zinc-magnesium alloys are 3D-printed by PBF-LB/M. The goal is to manufacture load-bearing, implants (e.g. patient-specific scaffolds or cages) with suitable degradation properties without damage to the surrounding tissue.

Ideal Zn-based biodegradable metal bone implants necessitate customizable biodegradable behaviours and improved osteogenic ability, conforming to the individual requirements of specific patients. Although design of implant material composition is a prevalent strategy, its efficacy in modulating the implant’s performance is notably restricted. Structure design has shown efficacy in regulating the performance of bio-inert metal implants, like Ti alloy scaffolds. However, no study has been systematically conducted on the impact of structure design on the performance of biodegradable Zn-based metal scaffolds. The mechanism that how structure design controls the biodegradable performance and osteogenic ability of scaffolds remains unclear. Hence, in this study, Zn-2Mg alloy scaffolds with different porosities and different unit sizes were designed and fabricated to study the influence and the underlying influencing mechanism of structure design on the in vitro and in vivo behaviour of Zn alloy scaffolds.

Biodegradable metals, particularly zinc (Zn) and magnesium (Mg) alloys, offer significant potential for biomedical applications, especially in temporary implants that gradually degrade within the body. Recent studies demonstrate the feasibility of additive manufacturing (AM) of both materials to address patient-specific solutions with high geometric complexity. This study explores the innovative combination of Zn1Mg and WE43MEO alloys using multi-material AM techniques, aiming to synergize the unique properties of these materials for optimized performance in medical devices. However, to succesfully combine both alloy systems several challenges need to be tackled, e.g. the bonding parameters and the powder deposition accuracy. In the context of this study, the optimum built plate material as well as bonding parameter are identified by analysing the relative density of cuboid specimens. Additionally. the parameters of the recoating unit are optimized towards the layer wise combination of both materials representing the basis of the processing within one printing job.

Zn is a biodegradable metal with intermediate corrosion rates between Fe and Mg, but it is the least studied to date, and the in vivo effects in the medium/long term are not yet fully understood. Studies so far have shown that Zn has good corrosion resistance and acceptable biocompatibility. Still, significant concerns have been raised due to its poor mechanical strength, aging at room temperature, creep effects, and high sensitivity to strain rate. This study determined if the quantity of Mg of Zn-Mg-based alloys in hybrid samples processed through high-pressure torsion alters the effectiveness of PEO. Results support that aspects such as the techniques for obtaining the alloy, composition, and coatings could synergistically promote the degradation behavior and biocompatibility of materials used as biodegradable implants.

The use of biodegradable magnesium alloys in cardiovascular applications supports the "leave nothing behind" strategy, necessitating materials with high tensile strength, elongation, and fine grain sizes. This study investigated the mechanical properties, microstructure, and surface quality of three magnesium alloys (WE43, ZX00, AZ31) subjected to a custom low-profile extrusion process. The alloys were cast, extruded into 9.5 mm billets, and further extruded into wires with diameters of 1.5 - 2.5 mm. Process variables included temperature, speed, method (direct/indirect), and extrusion ratio. Results showed that press speed and temperature are interconnected, with higher speeds raising forming temperatures due to friction and adiabatic heating. Contrary to expectations, press speed alone did not significantly affect outcomes within the tested range. Lower temperatures required higher forming forces, notably in WE43 at 460°C. Surprisingly, higher tensile strengths were achieved with direct pressing despite the higher forming temperatures. For WE43, a tensile strength of 415 MPa was achieved at low temperature and high speed. Recrystallization during forming resulted in finer grain structures, with smaller grains seen in wires with higher deformation degrees. Both tensile strength and elongation varied, with no clear trend linking them; however, higher strengths were sometimes accompanied by higher elongations. The pressing method significantly impacted the mechanical properties, with direct pressing enhancing tensile strength across all alloys. In conclusion, WE43 and ZX00 alloys showed significant process parameter influences on tensile strength. The study suggests that process optimization, especially in press method and temperature control, can enhance the mechanical properties of biodegradable magnesium alloys for cardiovascular applications.

Fe-Mn-C alloys have significant applications in developing temporary implants like bioabsorbable stents. Laser powder bed fusion, a promising additive-manufacturing technique, allows tailoring the microstructure by adjusting laser process parameters, expected to improve the degradation rate and mechanical properties of Fe-Mn alloys. In this study, we produced Fe-16Mn-0.7C bulk samples by varying laser power (50÷70 W) and scanning speed (700÷1000 mm/s), while maintaining a constant volumetric energy density (VED) of 88 J/mm³, to understand the effect of printing parameters on the alloy's performances. Fully austenitic microstructure and mechanical properties (microhardness approximately of 300 HV) appear comparable among the different samples. However, the defect analysis via X-ray micro-computed tomography identified an operational window for producing fully dense Fe-16Mn-0.7C bulk samples using LPBF. This operational window resulted in laser parameters much lower than those reported in the literature. Ongoing corrosion tests are being conducted to validate the obtained results further.

Out of the three main families of biodegradable metals (Fe, Mg, and Zn), biomedical Zn-alloys have recently attracted significant attention as promising materials for biodegradable implants due to their intermediate biodegradation rate compared to Fe and Mg. Although Zn-alloys exhibit optimal biocompatibility, their poor mechanical aspects such as strength, ductility, and recrystallisation hinder their implementation for biodegradable implants. Due to the favourable mechanical properties induced by Mg alloying, Zn-Mg alloys have garnered increased interest in recent years. Based on experimental evaluations and thermodynamic calculations, a Mg alloying content of less than 1 wt.% has been identified as ideal for improving tensile strength while minimally compromising ductility. Furthermore, the complexity of natural bone makes Additive Manufacturing (AM) a promising method for bone replacement due to its superior design flexibility and its unique ability to tailor microstructure and mechanical properties. The purpose of this study was to evaluate the mechanical behaviour of three additively manufactured Zn-xMg (x = 0.06, 0.5, and 1 wt.%) alloys in relation to their microstructure, influenced by Mg content. Alloys prepared by mixing powders of pure Zn and pure Mg were printed using laser powder bed fusion (L-PBF). As a measure of print quality, bulk density of as-printed samples was primarily quantified using image analysis of light optical microscopy (LOM) images. Phase analysis was performed using a combination of X-ray diffraction and energy dispersive X-ray spectroscopy. The microstructure was characterised using scanning electron microscopy and LOM. Mechanical properties were preliminarily assessed through microhardness measurements. Relative densities greater than 99.5% were achieved for all three alloys under different processing conditions (laser power, scanning speed, and hatch distance). A hierarchical microstructure was observed featuring melt pool boundaries, columnar, dendritic, and combined structures. Solid solution strengthening and strengthening via Mg2Zn11 intermetallic precipitates were identified as the primary strengthening mechanisms. This was evidenced by a gradual increase in microhardness with increasing Mg content, attributed to the increased amount of intermetallic. In conclusion, Mg alloying is a promising approach to addressing the poor mechanical properties of Zn and future work aims to characterise the tensile properties and recrystallisation effects.

A homogenous microstructure in Mg materials facilitates not only a homogenous degradation but also improved cell adhesion characteristics. Additive manufacturing (AM) technologies like metal injection molding (MIM) and 3D printing use polymeric binders mixed with Mg alloy powders to improve flow and shape characteristics. Analysing the sintered microstructures for suface contaminations becomes important and therefore in this study Raman spectroscopy was utilized to reveal carbonaceous residuals in the MIM Mg-0.6Ca sintered microstructures. EDX analysis predominantly showed oxygen (O), calcium (Ca) and silicon (Si) intensities. Certain precipitates comprised only O intensities whereas Ca and Si intensities coexist at random precipitations in the microstructure. Raman modes observed at nearly 1370 cm-1 and 1560 cm-1 are generally ascribed to the presence of elemental C and the modes observed at 1865 cm-1 are probable C=C stretching. The hydrocarbon cracking during thermal debinding process (400-550 °C) releases C that might interact with Mg to form metastable carbides. The C=C stretching can therefore be related to MgC2 type carbides. Additionally, free C radicals are probable due to accelerated vacuum thermal decomposition of the hydrocarbons in the binder material, which is evident at wavenumbers 1370 cm-1 and 1560 cm-1. Grain interiors are mostly free of any precipitation giving rise to noisy signal in Raman due to the specimen’s metallic nature.The results indicate that Raman is a viable option to characterize carbon impurities on metallic biomaterial surfaces. The exact stoichiometry with respect to Ca and Si elements still needs evaluation, however, the presence of surface C impurities might be important for future cell culture.

This paper concisely reviews the development of a dental implant (DI) manufactured from the novel TiMg bioactive composite material named BIACOM©. BIACOM© enables reduction of the stress-shielding effect and it leads to better biocompatibility compared with that of the traditional Ti and Ti alloys used in dentistry. BIACOM© was fabricated by cold consolidation of atomised TiGr1 and Mg99.8% powder blend. BIACOM© comprises bioabsorbable Mg component in the form of interconnected filaments, elongated along the direction of extrusion, which are embedded within a permanent, bioinert ultrafine-grained Ti matrix. The Ti component provides the mechanical properties, required for a function of the implant during its service. As the Mg content increases, the discrete filaments become interconnected with each other and form a continuous spatial network. The Mg component with low Young`s modulus (E), homogeneously dispersed within the Ti matrix, reduces E of BIACOM©. Moreover, Mg gradually dilutes at a controlled rate from the implant`s surface in contact with a corrosive environment after implantation. As a result, the pores gradually form at prior Mg sites, composite`s E decreases further down, and the stress-shielding phenomenon is reduced. Also, Mg promotes the osseointegration process and a bonding strength increases at the interface between the bone and implant, eventually. In the current paper we report the development of DI, which was manufactured from the optimized BIACOM© composite by an efficient hydro-extrusion consolidation process. The implant was designed in a way to reflect the properties and peculiarities of this novel Ti17Mg composite material. Two different implants designs and two surface finishes were pursued. Static mechanical performance was assessed by the finite element analysis and experimentally verified in compliance with the standard for the fatigue testing of endosseous DI. The corrosion of Mg from the surface of DI was evaluated by H2 evolution volumetric method. In-vitro cytotoxicity biological response was assessed by the indirect contact MTT assay using DMEM extracts of DI and L929 cell line.

INTRODUCTION: Physical vapor deposition (PVD), allowing the condensation of material from the vapor of a solid target, is a widely-used thin film deposition technique already employed in several industries, from microelectronics to biomedical engineering 1,2. PVD systems differ according to the way the vapor is produced: one of them is called magnetron sputtering. It involves bombarding a target material, ejecting its atoms and directing it toward the substrate through appropriate magnetic fields, that leads to the formation of thin films on the substrate3. Magnetron sputtering (MS) can be used to obtain coatings through a controlled deposition rate, offering a fine tuning of the properties of the condensed material. This is needed especially for those applications in which a strict property control is needed, like for biomedical ones 4,5. The technique allows the deposition of pure elements, alloys, ceramic and other compounds, with or without the use of reactive gases. In this work, MS was used for deposition of several biodegradable coatings containing Fe- and Mg- for different applications. The effects of working gases and deposition parameters such as power and substrate temperature on the properties of the coatings were analyzed. METHODS: The coatings were deposited using a MS system (Plasmionique MS300, QC, Canada). Coatings were deposited on a silicon substrate for preliminary process analysis, and then on functional substrates, for example Mg. The sputtering gas was Ar. The properties of the coatings were characterized using scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and other complementary techniques to assess physical, electrochemical and mechanical properties; in particular, the corrosion behavior was studied in Hanks’ solution. RESULTS: Fig. 1 presents the cross-section micrographs of two Fe-Mn-based coatings enriched with W. The chemical composition was related to the different power applied respectively to the Fe-Mn-C target, and to the W one: for example, the thickness for PW = 100 W was t = 0.8 μm, while for PW = 400 W to the thickness was t = 1.8 μm, with subsequent W increase, because of the increased sputtering rate of W. The corrosion rates associated with powers of 100 W and 400 W were 0.26 mm/y and 59.06 mm/y, respectively. In addition, it was found that increasing the substrate temperatures produced more homogeneous surfaces, decreased corrosion rates, and increased mechanical properties. Fig 1. Cross-sections of Fe-Mn-C-W films deposited with a) PW = 100 W and b) PW = 400 W for 1 h Mg-containing coatings showed a morphology, and corrosion properties related to the microstructure and to the presence of Mg. DISCUSSION & CONCLUSIONS: Investigating various parameters and working gases in this work provides a template for design and optimization of coatings for diverse applications. Overall, the results contributed to increase the knowledge about magnetron sputtering coatings as a valid technique for deposition of resorbable coatings with controlled properties. REFERENCES: 1 Deng Y, et al. (2020), Ceram Int 46:18373–18390; 2 Gupta G, et al. (2020). Mater Today Proc 38:259–264; 3 Heimann RB (2021), Surf Coat Tech 405:126521; 4 Li J, et al. (2022). JOM 74:3069–3081; 5 Nilawar S, et al. (2021). Mater Adv 2:7820–7841. ACKNOWLEDGEMENTS: This work was supported by NSERC-Canada-Alliance. DM holds a Canada Research Chair Tier I (2012-2026).

Despite breakthroughs and advances in research of novel magnesium (Mg) biodegradable implants, there is still a misalignment of in vitro and in vivo material performance. This is partially due to the limitations of current evaluation methods. Few in vitro strategies and experimental frameworks can mimic the complex dynamic process in the body. Mechanical properties, particularly during the degradation process, are a performance parameter that requires an improved assessment technique. Traditional Mg biodegradable materials (BMs) mechanical properties focused solely on performance before implantation/degradation. However, recent shifts in the field have begun to add mechanical integrity, strength during degradation, as an evaluation criterion. Currently pseudo in-situ mechanical testing is commonly employed as a standard practice. Nonetheless, there is a lack of standardization, and this method is constrained by multiple limitations, while other strategies, such as stress corrosion cracking (SCC) testing offer great promise. The evaluation of SCC has the potential to become a more reliable indicator of in vivo mechanical performance. As our field expands it is imperative to review and propose enhanced testing techniques for novel biodegradable metals.

This study investigates the influence of powder preparation on the microstructure, mechanical properties, and degradation behavior of Fe-Mn-C alloys for temporary biomedical implants. Fe-Mn-C alloys have recently raised interest for such applications due to their outstanding mechanical properties. However, controlling their degradation rate is crucial to broadening their applicability. Two types of Fe-Mn-C powders, mixed (MX) and mechanically milled (MM), were used to produce four groups of sintered samples including MX, 25MM, 50MM, and 75MM. The number in the condition name specifies the weight amount of MM powder. Results indicated that powder preparation methods significantly influenced alloy properties. The 75MM sample exhibited the highest mechanical properties but slower degradation, while the 25MM sample demonstrated a balanced degradation rate and mechanical strength, making it suitable for biodegradable implants such as suture anchors. This study highlights the importance of powder preparation in tailoring the characteristics of sintered Fe-Mn-C alloys for biodegradable implant applications, thus optimizing their performance.

Magnesium and its alloys exhibit attractive properties such as an excellent strength-to-weight ratio, good fatigue, or biocompatibility. As a result, Mg-based alloys are widely used in many industries such as aerospace, automotive, and biomedical applications. The last-mentioned use is possible due to biodegradability1 which is attractive for temporary implants or stents. The corrosion of Mg-based alloys is largely responsible for the formation of galvanic links between the existing phases of the alloy2. For this reason, knowledge of the phase equilibria, occurring between elements forming an alloy and thus between existing intermetallic compounds, phases, and invariant reactions, which describe thermodynamic transformations is an important aspect in designing new material. Such information can be read from the available phase diagrams or can be calculated if appropriate data exists. Therefore, among other considerations, a thorough examination of phase equilibrium systems, from binary to multi-component systems, is essential for developing alloys with potential biomedical applications. Despite being widely studied for various industrial applications, magnesium-based alloys are not always fully understood in terms of their thermodynamic properties. Even after many years of research, some phase diagrams are still either unknown or only exist as theoretical models. Such is the case with Ag-Mg-Ti and Cu-Mg-Ti systems. This work presents the results of the mixing enthalpy change (ΔmixH) of the liquid Ag-Mg-Ti and Cu-Mg-Ti solutions obtained from the high-temperature drop calorimetric technique. Based on the achieved results and the thermodynamic properties of binary systems, the liquid phase of both systems was described by symmetrical Muggianu3 and asymmetrical Toop4 models. To accomplish that, homemade software (TerGexHm) was used. The presented results of the calorimetric measurements are the first step in the investigation and future evaluation of the thermodynamics of phases and the calculation of the phase diagrams of the mentioned systems, which may prove useful in the design of new biodegradable alloys.