Synthesizing of Nanostructured Fe-Mn Alloys by Mechanical Alloying Process

Surface Modification of an Absorbable Bimodal Fe-Mn-Ag Alloy by Nitrogen Plasma Immersion Ion Implantation

Recently, Fe-Mn-based alloys have been increasingly catching the attention of the scientific community, because of their tunable and outstanding mechanical properties, and suitable degradation behavior for biomedical applications. In spite of these assets, their corrosion rate (CR) is, in general, too low to satisfy the requirements that need to be met for cardiovascular device applications, such as stents. In fact, the CR is not always the same for all of the degradation stages of the material, and in addition, a finely tuned release rate, especially during the first steps of the corrosion pattern, is often demanded. In this work, a resorbable bimodal multi-phase alloy Fe-3Mn-1Ag was designed by mechanical alloying and spark plasma sintering (SPS) to accelerate the corrosion rate. The presence of several phases, for example α-Fe, α-Mn, γ-FeMn and Ag, provided the material with excellent mechanical properties (tensile strength UTS = 722 MPa, tensile strain A = 38%) and a higher corrosion rate (CR = 3.2 ± 0.2 mm/year). However, higher corrosion rates, associated with an increased release of degradation elements, could also raise toxicity concerns, especially at the beginning of the corrosion pattern. In this study, The focus of the present work was the control of the CR by surface modification, with nitrogen plasma immersion ion implantation (N-PIII) treatment that was applied to mechanically polished (MP) samples. This plasma treatment (PT) improved the corrosion resistance of the material, assessed by static degradation immersion tests (SDITs), especially during the first degradation stages. Twenty-eight days later, the degradation rate reached the same value of the MP condition. Nitrogen compounds on the surface of the substrate played an important role in the corrosion mechanism and corrosion product formation. The degradation analysis was carried out also by potentiodynamic tests in modified Hanks' balanced salt solution (MHBSS), and Dulbecco's phosphate buffered saline solution (DPBSS). The corrosion rate was higher in MHBSS for both conditions. However, there was no significant difference between the corrosion rate of the PT in DPBSS (CR = 1.9 ± 0.6 mm/year) and in MHBSS (CR = 2 ± 1.4 mm/year). The cell viability was assessed with human vein endothelial cells (HUVECs) via an indirect metabolic activity test (MTT assay). Due to the lower ion release of the PT condition, the cell viability increased significantly. Thus, nitrogen implantation can control the in vitro corrosion rate starting from the very first stage of the implantation, improving cell viability.

Biodegradable Iron-Based Materials-What Was Done and What More Can Be Done?

Iron, while attracting less attention than magnesium and zinc, is still one of the best candidates for biodegradable metal stents thanks its biocompatibility, great elastic moduli and high strength. Due to the low corrosion rate, and thus slow biodegradation, iron stents have still not been put into use. While these problems have still not been fully resolved, many studies have been published that propose different approaches to the issues. This brief overview report summarises the latest developments in the field of biodegradable iron-based stents and presents some techniques that can accelerate their biocorrosion rate. Basic data related to iron metabolism and its biocompatibility, the mechanism of the corrosion process, as well as a critical look at the rate of degradation of iron-based systems obtained by several different methods are included. All this illustrates as the title says, what was done within the topic of biodegradable iron-based materials and what more can be done.

Investigation of the Microstructure and Compressibility of Biodegradable Fe-Mn-Cu/W/Co Nanostructured Alloy Powders Synthesized by Mechanical Alloying

In this research work, the nanostructured Fe-Mn (BM0), Fe-Mn-Cu (BM1), Fe-Mn-W (BM2), and Fe-Mn-Co (BM3) biodegradable alloys were successfully synthesized using mechanical alloying. The microstructure of the synthesized alloys was examined using XRD, SEM equipped with EDS, and HRTEM techniques. The results obtained based on these techniques confirmed the development of nanostructured BM0, BM1, BM2, and BM3 alloys and homogenous solid solutions with an even elemental dispersion. The compressibility of the synthesized alloys was investigated experimentally and empirically in the as-milled conditions and after applying a stress relief treatment (150 °C for 1 h). The load applied for compaction experiments ranged from 25–1100 MPa with a rate of 1 mm/min. According to the experimentation performed in the current study, the relative density of the as-milled BM0, BM1, BM2, and BM3 alloys was 72.90% and 71.64%, 72.32%, and 72.03%, respectively. After applying the stress relief treatment, the density was observed to increase to 75.23%, 77.10%, 72.65%, and 72.86% for BM0-S, BM1-S, BM2-S and BM3-S samples, respectively. A number of compaction models were tested to identify the optimum models for predicting the compressibility behavior of nanostructured Fe-Mn, Fe-Mn-Cu, Fe-Mn-W, and Fe-Mn-Co alloys in the as-milled and stress-relieved conditions.

Bimetallic MOF-templated synthesis of alloy nanoparticle-embedded porous carbons for oxygen evolution and reduction reactions

Pyrolysis of metal–organic frameworks (MOFs) to produce metal nanoparticles embedded inside a porous carbon matrix (M@PC) has drawn a lot of attention in recent years.