The search for biocompatible and bioabsorbable metallic materials for temporary medical implants dates back to the late nineteenth century. Interest in these materials arises from their potential social and medical benefits. However, extensive research did not start until the early twentieth century, primarily focusing on magnesium (Mg), iron (Fe), and zinc (Zn) as biocompatible and biodegradable base metals. In this work, we explore the combination of two of these metals, Fe and Mg, and the opportunity to investigate Fe-Mg alloys as potential candidates for biomedical applications through a review of their development from their initial production to the present, as well as their future prospects. A distinctive characteristic of Fe-Mg systems is their mutual immiscibility in thermodynamic equilibrium, which poses significant processing challenges and explains why Fe-Mg alloys have been relatively unexplored. However, it is precisely this immiscibility that offers the opportunity to achieve a metastable state that potentiates degradation. As evidenced by the review of recent research on bioabsorbable Fe-Mg alloys developed specifically for biomedical applications, given their promising properties and potential applications, a more comprehensive exploration of this alloy system appears warranted.

Bioabsorbable metals offer great promise for temporary medical implants. Among them, iron (Fe) and magnesium (Mg) alloys are of particular interest due to their biocompatibility, mechanical properties, and degradation behavior. However, Fe degrades too slowly, while Mg degrades too quickly. Combining both elements has been proposed to overcome these drawbacks, though their immiscibility presents a processing challenge. In this study, Fe-5 wt% Mg powder was produced via high-energy ball milling (Fe5Mg-BM), and its degradation was compared with pure Fe (Fe99) and milled Fe (Fe-BM). In vitro degradation was evaluated in three simulated body fluids: phosphate-buffered saline (PBS), modified Hanks' balanced salt solution (HBSS), and Dulbecco's Modified Eagle Medium (DMEM). Ion release, pH changes, and degradation products were characterized, along with cytotoxicity and antibacterial activity. The results showed that Fe5Mg-BM exhibited accelerated degradation compared to Fe99 and Fe-BM. Among the media, modified HBSS induced the greatest diversity and quantity of degraded compounds. Ion analysis revealed negligible iron release in PBS and HBSS, with the highest levels in DMEM for Fe5Mg-BM. Magnesium release followed the trend: PBS < DMEM < HBSS. Fe5Mg-BM showed limited cytotoxicity at 3 days and enhanced antibacterial activity in PBS and HBSS compared to Fe-BM. These results indicate that the biological effects arise from complex interactions at the material interface and the solubility of degradation products, suggesting that Mg is a promising alloying element for enhancing the performance of Fe-based materials in biomedical applications.

Cardiovascular diseases are the leading cause of mortality globally, underscoring the importance of reliable treatments such as cardiovascular stents, which prevent arterial collapse and improve blood flow. Despite their widespread use, stents face challenges in mechanical performance and biological compatibility. This study focuses on the mechanical characterization of biodegradable metallic stents, addressing limitations in current testing methods and simulations. Novel specimen geometries, designed for tensile strength testing, were developed using additive manufacturing (AM) to minimize damage from gripping clamps during testing. Finite element modeling simulations and experimental tests were conducted to evaluate the mechanical behavior of stents under ideal and real-world conditions. The results revealed that the values provided by the most common mechanical tests and simulations do not correspond to the actual values of the meshed structure. The proposed geometries demonstrated consistent mechanical behavior, effectively mitigating stress concentrations and enabling reliable data acquisition. These findings highlight the potential of AM in stent testing and validate the integration of experimental and simulation approaches for optimizing stent design and performance. This study establishes a framework for future research aimed at improving stent safety and reliability.

Iron and its alloys are attractive as biodegradable materials because of their low toxicity and suitable mechanical properties; however, they generally have a slow degradation rate. Given that corrosion is an electrochemical phenomenon where an exchange of electrons takes place, the application of magnetic fields from outside the body may accelerate the degradation of a ferrous temporary implant. In the present study, we have investigated the effect of alternating and direct low magnetic field (H = 6.5 kA/m) on the corrosion process of pure iron (Fe) and an iron-manganese alloy (FeMnC) in modified Hanks' solution. A 14-day static immersion test was performed on the materials. The corrosion rate was assessed by mass and cross-sectional loss measurements, scanning electron microscopy, X-ray diffractometry, Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy before and after degradation. The results show that the presence of magnetic fields significantly accelerates the degradation rate of both materials, with the corrosion rate being twice as high in the case of Fe and almost three times as high for FeMnC. In addition, a homogenous degradation layer is formed over the entire surface and the chemical composition of the degradation products is the same regardless of the presence of a magnetic field.

This review explores the advancements in additive manufacturing (AM) of biodegradable iron (Fe) and zinc (Zn) alloys, focusing on their potential for medical implants, particularly in vascular and bone applications. Fe alloys are noted for their superior mechanical properties and biocompatibility but exhibit a slow corrosion rate, limiting their biodegradability. Strategies such as alloying with manganese (Mn) and optimizing microstructure via laser powder bed fusion (LPBF) have been employed to increase Fe’s corrosion rate and mechanical performance. Zn alloys, characterized by moderate biodegradation rates and biocompatible corrosion products, address the limitations of Fe, though their mechanical properties require improvement through alloying and microstructural refinement. LPBF has enabled the fabrication of dense and porous structures for both materials, with energy density optimization playing a critical role in achieving defect-free parts. Fe alloys exhibit higher strength and hardness, while Zn alloys offer better corrosion control and biocompatibility. In vitro and in vivo studies demonstrate promising outcomes for both materials, with Fe alloys excelling in load-bearing applications and Zn alloys in controlled degradation and vascular applications. Despite these advancements, challenges such as localized corrosion, cytotoxicity, and long-term performance require further investigation to fully harness the potential of AM-fabricated Fe and Zn biodegradable implants.

Poly(l-lactic) acid (PLLA) is commonly used in bioabsorbable medical implants, but it suffers from slow degradation rate and rapid decline in mechanical properties for orthopedic applications. To address this drawback, recent research has explored the use of Mg as a filler for PLLA, resulting in composites with improved degradation rate and cytocompatibility compared to neat PLLA. In this study, FeMg powder particles were proposed as fillers for PLLA to investigate the potential of PLLA/FeMg composites for bioabsorbable implants. Cylinder specimens of PLLA, PLLA/Fe, PLLA/Mg and PLLA/FeMg were prepared using solvent casting followed by thermo-molding. The microstructure, thermal behavior, in vitro degradation behavior in simulated body fluid, mechanical properties and cytocompatibility of these composites were examined. The results indicate that the presence of FeMg particles prevents the deterioration of the composite mechanical properties, at least up to 14 days. Once a certain amount of degradation of the composite is reached, the degradation is faster than that of PLLA. Direct cytotoxicity assays revealed that pre-osteoblast MC3T3-E1 cells successfully adhered to and proliferated on the PLLA/FeMg surface. The inclusion of a low percentage of Mg into the Fe lattice not only accelerated the degradation rate of Fe but also improved its cytocompatibility. The enhanced degradation rate, mechanical properties, and osteoconductive properties of this composite make it a promising option for temporary orthopedic biomedical devices.

UV-curable coatings possess numerous advantages, including high production rate, low environmental impact, and customizability, making them highly appealing for a wide range of applications. However, one of the greatest challenges in UV-curable coating is achieving an optimal low-gloss surface by adding matting agents to the coating formulation. Therefore, it is essential to find a suitable matting agent type and an efficient roughness creation method to tailor the surface gloss and generate a controlled low-gloss surface. In this study, modified magnetic particles were added to the coating formulation as matting agents, and the UV curing process was conducted under a magnetic field of 10 to 100 mT. The combined effect of adding magnetic particles and magnetic field during UV curing on the coatings’ surface gloss was investigated. The impact of modification, dispersion, and concentration of magnetic particles and the effect of magnetic field force on the final surface gloss and roughness were assessed. Moreover, the effect of the dispersion and concentration of magnetic particles on the photopolymerization of the coating was evaluated. The result indicated that both the magnetic field force and modification of the magnetic particles impact the surface roughness. A CI-APTES 5% wt. sample cured under a 60 mT magnetic field led to the highest decrease in 20° gloss.

Magnesium and its alloys are an outstanding option for designing temporary medical devices because of their mechanical properties and biocompatibility. However, to achieve the accurate requirements for different medical treatment, it is necessary to control their degradation process. This can be accomplished by controlling the composition, their microstructure and their surface. This work reviews the role of Mg as bioabsorbable material by remarking different strategies intended to control its degradation process: purification of magnesium, research of alloys firstly developed for industrial applications other than medical, specific design of alloys for biodegradable implants and the incorporation of magnesium as reinforcing phase of biodegradable polymeric matrix composites

This paper shows the results of applying a combination of high energy processing and magnesium (Mg) as an alloying element in a strategy for enhancing the degradation rate of iron (Fe) for applications in the field of non-permanent medical implants. For this purpose, Fe powder was milled with 5 wt% of Mg (Fe5Mg) and its microstructure and characterized degradation behavior. As-received Fe powder was also milled in order to distinguish between the effects due to high energy processing from those due to the presence of Mg. The powders were prepared by high energy planetary ball milling for 16 h. The results show that the initial crystallite size diminishes from >150 nm to 16 nm for Fe and 46 nm for Fe5Mg. Static degradation tests of loose powder particles were performed in Hanks’ solution. Visual inspection of the immersed powders and the X-ray diffraction (XRD) phase quantification indicate that Fe5Mg exhibited the highest degradation rate followed by milled Fe and as received Fe, in this order. The analysis of degradation products of Fe5Mg showed that they consist on magnesium ferrite and pyroaurite, which are known to present good biocompatibility and low toxicity. Differences in structural features and degradation behaviors of milled Fe and milled Fe5Mg suggest the effective dissolution of Mg in the Fe lattice. Based on the obtained results, it can be said that Fe5Mg powder would be a suitable candidate for non-permanent medical implants with a higher degradation rate than Fe.

To modulate the properties of degradable implants from outside of the human body represents a major challenge in the field of biomaterials. Polylactic acid is one of the most used polymers in biomedical applications, but it tends to lose its mechanical properties too quickly during degradation. In the present study, a way to reinforce poly-L lactic acid (PLLA) with magnetic nanoparticles (MNPs) that have the capacity to heat under radiofrequency electromagnetic fields (EMF) is proposed. As mechanical and degradation properties are related to the crystallinity of PLLA, the aim of the work was to explore the possibility of modifying the structure of the polymer through the heating of the reinforcing MNPs by EMF within the biological limit range f·H < 5·× 109 Am−1·s−1. Composites were prepared by dispersing MNPs under sonication in a solution of PLLA. The heat released by the MNPs was monitored by an infrared camera and changes in the polymer were analyzed with differential scanning calorimetry and nanoindentation techniques. The crystallinity, hardness, and elastic modulus of nanocomposites increase with EMF treatment.

Zeolites are widely used in high-temperature oil refining processes such as fluid catalytic cracking (FCC), hydrocracking, and aromatization. Significant energy cost are associated with these processes due to the high temperatures required. The induction heating promoted by magnetic nanoparticles (MNPs) under radio frequency fields could contribute to solving this problem by providing a supplementary amount of heat in a nano-localized way, just at the active centre site where the catalytic process takes place. In this study, the potential of such a complementary route to reducing energetic requirements is evaluated. The catalytic cracking reaction under a hydrogen atmosphere (hydrocracking) applied to the conversion of plastics was taken as an application example. Thus, a commercial zeolite catalyst (H-USY) was impregnated with three different magnetic nanoparticles: nickel (Ni), cobalt (Co), maghemite (γ-Fe2O3), and their combinations and subjected to electromagnetic fields. Temperature increases of approximately 80 °C were measured for H-USY zeolite impregnated with γ-Fe2O3 and Ni-γ-Fe2O3 due to the heat released under the radio frequency fields. The potential of the resulting MNPs derived catalyst for HDPE (high-density polyethylene) conversion was also evaluated by thermogravimetric analysis (TGA) under hydrogen atmosphere. This study is a proof of concept to show that induction heating could be used in combination with traditional resistive heating as an additional energy supplier, thereby providing an interesting alternative in line with a greener technology.

The ultra-stable Y (H-USY) zeolite is used as catalyst for the conversion of plastic feedstocks into high added value products through catalytic cracking technologies. However, the energy requirements associated with these processes are still high. On the other hand, induction heating by magnetic nanoparticles has been exploited for different applications such as cancer treatment by magnetic hyperthermia, improving of water electrolysis and many other heterogeneous catalytic processes. In this work, the heating efficiency of γ-Fe2O3 nanoparticle impregnated zeolites is investigated in order to determine the potential application of this system in catalytic reactions promoted by acid catalyst centers under inductive heating. The γ-Fe2O3 nanoparticle impregnated zeolite has been investigated by X-ray diffraction, electron microscopy, ammonia temperature program desorption (NH3-TPD), H2 absorption, thermogravimetry and dc and ac-magnetometry. It is observed that the diffusion of the magnetic nanoparticles in the pores of the zeolite is possible due to a combined micro and mesoporous structure and, even when fixed in a solid matrix, they are capable of releasing heat as efficiently as in a colloidal suspension. This opens up the possibility of exploring the application at higher temperatures.

This work deals with the surface modification of 316LVM stainless steel by Si+ ion implantation and the in vitro study of its effect on the short-term corrosion behaviour and ion release. In order to achieve a high Si content close to the surface, the experimental set up was designed with different implantation doses, acceleration voltages and angles of incidence. Corrosion tests were carried out by Electrochemical Impedance Spectroscopy (EIS). A special feature of this paper is the evaluation of the EIS data obtained through a critical analysis of the existing equivalent electrical circuits, in order to establish adequate parameters and scientific criteria to propose a classification of the corrosion response of the investigated surfaces. It has been demonstrated that doses of Si+ ion implantation equal to 2.5 x 10(16) ion/cm(2) and an acceleration voltages of 50 keV enhanced the corrosion protection. In contrast, higher ion-implantation dose (1 x 10(17) ion/cm(2)) and acceleration voltage (80 keV) produced worse results, probably due to the development of strain induced alpha'-martensite. The quantity of relevant ions (Cr, Fe, Mn, Mo, Ni and Si) released to the medium was determined by an optimized Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) method. It has been shown that a better corrosion resistance is accompanied by a reduction in the amount of ions released. (C) 2016 Elsevier B.V. All rights reserved.

Roughening of Ti6Al4V by blasting with alumina or zirconia particles improves the mechanical fixation of implants by increasing the surface area available for bone/implant apposition. Additional thermal oxidation treatments of the blasted alloy have already shown to be a complementary low-cost solution to enhancing the in vitro biocompatibility and corrosion resistance of the alloy. In this work, the effects of oxidation treatment on a grit blasted Ti6Al4V biomedical alloy have been analysed in order to understand the net effect of the combined treatments on the alloy fatigue properties. Synchrotron radiation diffraction experiments have been performed to measure residual stresses before and after the treatments and microstructural and hardness changes have been determined. Although blasting of Ti6Al4V with small spherical zirconia particles increases the alloy fatigue resistance with respect to unblasted specimens, fatigue strength after oxidation decreases below the unblasted value, irrespective of the type of particle used for blasting. Moreover, at 700 °C the as-blasted compressive residual stresses (700 MPa) are not only fully relaxed but even moderate tensile residual stresses, of about 120 MPa, are found beneath the blasted surfaces. Contrary to expectations, a moderate increase in hardness occurs towards the blasted surface after oxidation treatments. This can be attributed to the fact that grit blasting modifies the crystallographic texture of the Ti6Al4V shifting it to a random texture, which affects the hardness values as shown by additional experiments on cold rolled samples. The results indicate that the oxidation treatment performed to improve biocompatibility and corrosion resistance of grit blasted Ti6Al4V should be carried out with caution since the alloy fatigue strength can be critically diminished below the value required for high load-bearing components.

In this paper, the physical properties of half-doped manganite La0.5Ca0.5MnO3 with crystallite sizes ranging from 15 to 40 nm are investigated. As expected, ferromagnetic order strengthens at expense of antiferromagnetic one as crystallite size is reduced to 15 nm. However, contrary to previously reported works, an enhancement of saturation magnetization is observed as crystallite size increases from 15 to 22 nm. This unexpected behavior is accompanied by an unusual cell volume variation that seems to induce ferromagnetic-like behavior at expense of antiferromagnetic one. Besides, field cooled hysteresis loops show exchange bias field and coercivity enhancement for increasing cooling fields, which suggest a kind of core-shell structure with AFM-FM coupling for crystallite sizes as small as 15 nm. It is expected that inner core orders antiferromagnetically, whereas uncompensated surface spins behave as spin glass with ferromagnetic-like ordering. (C) 2014 AIP Publishing LLC.

316LVM austenitic stainless steel is often the material of choice on temporal musculoskeletal implants and surgical tools as it combines good mechanical properties and acceptable corrosion resistance to the physiologic media, being additionally relatively inexpensive.This study has aimed at improving the resistance to bacterial colonization of this surgical stainless steel, without compromising its biocompatibility and resistance. To achieve this aim, the effect of Si ion implantation on 316LVM has been studied. First, the effect of the ion implantation parameters (50 keV; fluence: 2.5-5 x 10(16) ions/cm(2); angle of incidence: 45-90 degrees) has been assessed in terms of depth profiling of chemical composition by XPS and nano-topography evaluation by AFM. The in vitro biocompatibility of the alloy has been evaluated with human mesenchymal stem cells. Finally, bacterial adhesion of Staphylococcus epidermidis and Staphylococcus aureus on these surfaces has been assessed.Reduction of bacterial adhesion on Si implanted 316LVM is dependent on the implantation conditions as well as the features of the bacterial strains, offering a promising implantable biomaterial in terms of biocompatibility, mechanical properties and resistance to bacterial colonization. The effects of surface composition and nano-topography on bacterial adhesion, directly related to ion implantation conditions, are also discussed. (C) 2014 Elsevier B.V. All rights reserved.

Trabajo presentado en el 25th European Conference on Biomaterials (ESB 2013), celebrado en Madrid (Espana), del 8 al12 de Septiembre 2013