The oxygen reduction reaction (ORR) contributes to the total cathodic process during Mg corrosion, being secondary process, compared to hydrogen evolution reaction (HER). Previous finding suggested that the contribution of ORR decreases with time due to thickening of corrosion product layer, impeding O2 diffusion to Mg interface where ORR can take place. Recent findings indicate that high electronic conductivity of the layer, e.g. due to re-deposition of metallic Ag (example of Mg-4Ag alloy), can support ORR for extended periods of time (at least up to 72h), even when a thick layer of corrosion products (5-20 micron) is grown.

The choice of implant material at the fracture site has an influence on the fracture healing from biological as well as mechanical perspective. Biodegradable implants such as magnesium (Mg), zinc (Zn) have shown a faster secondary bone healing process as compared to bioinert implants such as titanium (Ti). In general, this benefit was seen mostly only from the biological perspectives. However, the advantage of biodegradable implants such as of Mg is also there from mechanical perspectives. We studied the effect of Ti and Mg as base implant materials from mechanical perspectives in the initial phase of bone healing. The focus was on the displacements at the fracture site of the tibia and their influence on the interfragmentary strain distribution (IFM) for bone healing. Tissue differentiation theory from Shefelbine was used to evaluate the conditions for secondary healing at the callus. In addition, the stress distribution in the implant and on bone was measured in order to quantify the change in the stress shielding conditions. In comparison, Mg implants have minimal stress shielding problem than that of Ti, which led to better mechanical stimulus at the fracture site. The conditions for secondary bone healing were better when Mg implants were used. The study illustrates the benefits of Mg for osteological implants from mechanical perspectives and the potential to replace Ti for fracture treatment in the future.

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) 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.

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.

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).