Examinando por Autor "Torres, Belén"

Mostrando 1 - 20 de 23

Anticorrosion and Cytocompatibility Assessment of Graphene-Doped Hybrid Silica and Plasma Electrolytic Oxidation Coatings for Biomedical Applications
(ACS, 2021) Fernández-Hernán, Juan P.; López, Antonio J.; Torres, Belén; Martínez-Campos, Enrique; Matykina, Endzhe; Rams, Joaquín
Magnesium AZ31 alloy substrates were coated with different coatings, including sol−gel silica-reinforced with graphene nanoplatelets, sol−gel silica, plasma electrolytic oxidation (PEO), and combinations of them, to improve cytocompatibility and control the corrosion rate. Electrochemical corrosion tests, as well as hydrogen evolution tests, were carried out using Hanks’ solution as the electrolyte to assess the anticorrosion behavior of the different coating systems in a simulated body fluid. Preliminary cytocompatibility assessment of the different coating systems was carried out by measuring the metabolic activity, deoxyribonucleic acid quantification, and the cell growth of premyoblastic C2C12-GFP cell cultures on the surface of the different coating systems. Anticorrosion behavior and cytocompatibility were improved with the application of the different coating systems. The use of combined PEO + SG and PEO + SG/GNP coatings significantly decreased the degradation of the specimens. The monolayer sol−gel coatings, with and without GNPs, presented the best cytocompatibility improvement.
Application of DOE and ANOVA in Optimization of HVOF Spraying Parameters in the Development of New Ti Coatings
(Springer, 2020-02-03) Pulido-González, Nuria; García-Rodríguez, Sonia; Campo, Mónica; Rams, Joaquín; Torres, Belén
High velocity oxygen fuel (HVOF) thermal spray technique has been used to develop new Ti coatings on 1045 steel and 316L stainless steel for different applications. Optimization of the HVOF parameters requires numerous experiments to perform that can be reduced using the Taguchi Design of Experiment (DOE) methodology. By using DOE, it has been possible to identify the effects of the HVOF spraying parameters (spraying distance, number of layers, gun speed, powder feed rate, type of substrate and type of combustion) on the main characteristics of the coatings (porosity, thickness, hardness and adhesion). According to Taguchi method, the resulting orthogonal matrix corresponded to a L16 (44 × 22) matrix. Using this matrix, the number of experiments was reduced from 1024 to 16 and a first approximation of the best conditions for a real application was obtained. To evaluate the significant spraying variables, a statistical analysis of variance (ANOVA) was used. It has been determined that there is a relationship between coating characteristics and HVOF parameters. Also, the influence of the parameters on the characteristics and properties of the coatings (from high to low) is as follows: spraying distance, number of layers, gun speed, powder feed rate, type of substrate and mixture of gases used in the process.
Comparison of Different Additive Manufacturing Methods for 316L Stainless Steel
(MDPI, 2021-10-29) Bedmar, Javier; Riquelme, Ainhoa; Rodrigo, Pilar; Torres, Belén; Rams, Joaquín
In additive manufacturing (AM), the technology and processing parameters are key elements that determine the characteristics of samples for a given material. To distinguish the effects of these variables, we used the same AISI 316L stainless steel powder with different AM techniques. The techniques used are the most relevant ones in the AM of metals, i.e., direct laser deposition (DLD) with a high-power diode laser and selective laser melting (SLM) using a fiber laser and a novel CO2 laser, a novel technique that has not yet been reported with this material. The microstructure of all samples showed austenitic and ferritic phases, which were coarser with the DLD technique than for the two SLM ones. The hardness of the fiber laser SLM samples was the greatest, but its bending strength was lower. In SLM with CO2 laser pieces, the porosity and lack of melting reduced the fracture strain, but the strength was greater than in the fiber laser SLM samples under certain build-up strategies. Specimens manufactured using DLD showed a higher fracture strain than the rest, while maintaining high strength values. In all the cases, crack surfaces were observed and the fracture mechanisms were determined. The processing conditions were compared using a normalized parameters methodology, which has also been used to explain the observed microstructures.
Corrosion behavior of 316L stainless steel coatings on ZE41 magnesium alloy in chloride environments
(Elsevier, 2019-11-25) García-Rodríguez, Sonia; Torres, Belén; Pulido-González, Nuria; Otero, Enrique; Rams, Joaquín
The corrosion behavior of the ZE41 magnesium alloy with a HVOF 316L stainless steel coating was electrochemically evaluated in 3.5 wt% NaCl solution and by salt spray testing. Electrochemical Impedance Spectroscopy (EIS) allowed determining the resistance of the coatings deposited, the growth of compact corrosion products on the ZE41 Mg alloy and the failure of the non-optimized coatings. The best coating resisted the chloride attack for long times in immersion and in salt spray environments, and it drastically reduced galvanic couple formation. Its behavior is associated with its reduced porosity and its higher compactness and mechanical stability.
Effect of Heat Treatment on the Dry Sliding Wear Behavior of the Mg-3Zn-0.4Ca Alloy for Biodegradable Implants
(Multidisciplinary Digital Publishing Institute, 2023-01-10) Pulido-González, Nuria; García-Rodríguez, Sonia; Torres, Belén; Rams, Joaquín
The wear behavior of the Mg-3wt.% Zn-0.4wt.% Ca (ZX30) alloy was tested using a pin-on-disc configuration with AZ31 alloy discs as counterparts under dry sliding conditions. The ZX30 alloy was tested in different states: as-cast, solution-treated, peak-aged, and over-aged. Wear rates and friction coefficients were measured at different loads and sliding speeds. Abrasion and oxidation were the main wear mechanisms found in all the conditions tested. Moreover, aluminum oxides were detected on the worn surfaces, which indicates the presence of an adhesive wear mechanism. The wear behavior of the studied ZX30 alloy showed a greater tendency towards oxidative wear than other Mg alloys, and the microstructure observed strongly affected the wear behavior.
Effects of the heat treatment on the microstructure and corrosion behavior of 316 L stainless steel manufactured by Laser Powder Bed Fusion
(Elsevier, 2022) Bedmar, Javier; García-Rodríguez, Sonia; Roldán, M.; Torres, Belén; Rams, Joaquín
Additively manufactured AISI 316 L stainless steel samples were heat treated at temperatures from 400 ◦C to 1100 ◦C, and the corrosion behavior in chloride environments was electrochemically studied. Heat treatments at 400 ◦C and 650 ◦C increased the grain size and the treatment at 1100 ◦C formed MnCr2O4 inclusions. Also, these postprocessing techniques reduce the hardness and increased the porosity. Heat treatment at 400 ◦C increased the polarization resistance and maintained the pitting corrosion mechanisms of the additively manufactured samples. Heat treatments at higher temperatures reduced the polarization resistance but changed the corrosion resistance mechanisms.
High Power Diode Laser (HPDL) surface treatments to improve the mechanical properties and the corrosion behaviour of Mg-Zn-Ca alloys for biodegradable implants
(Elsevier, 2020-11-25) Pulido-González, Nuria; Torres, Belén; Zheludkevick, Mikhail L.; Rams, Joaquín
Biodegradability, low density and mechanical properties close to those of the bone are some of the intrinsic properties of the Mg-Zn-Ca alloys that have attracted significant attention for developing biodegradable implants. However, rapid degradation constitutes the main disadvantage of these alloys. In this work, two different alloys, Mg-1Zn-1Ca and Mg-3Zn-0.4Ca, were laser surface treated using a HPDL to increase hardness and to improve the corrosion performance. Depending on the laser parameters, a complete laser surface melting (LSM) or a selective laser surface melting (SLSM) were reached. The microstructure, mechanical properties and corrosion behaviour were established and compared. Higher laser input energies led to larger treated zones and in these cases two different regions could be distinguished: the outer zone, where the LSM took place, presented a more refined microstructure with a greater dispersion of secondary phases; the following zone suffered SLSM, in it only the secondary phases were modified by the HPDL. Hardness was 24%–27% higher than that of the untreated samples. The HPDL also reduced the corrosion rate by 21% and 37% for the Mg-1Zn-1Ca alloy and the Mg-3Zn-0.4Ca alloy, respectively, after 336 h of immersion in Hanks' solution at 37 °C.
Influence of roughness and grinding direction on the thickness and adhesion of sol-gel coatings deposited by dip-coating on AZ31 magnesium substrates. A Landau–Levich equation revision
(Elsevier, 2021-01-02) Fernández-Hernán, Juan Pablo; López, Antonio Julio; Torres, Belén; Rams, Joaquín
AZ31 magnesium alloys with four different roughness values and two different grinding directions were coated with sol-gel silica coatings to assess the influence of the initial surface conditions of the substrates on the final coating thickness. Sol-gels were prepared from two silicon alkoxide precursors and deposited on the surface of the magnesium substrates by the dip-coating method. Roughness tester and scanning electron microscopy (SEM) were used to assess the thickness of the silica coatings and the presence of defects in the coatings. Shear stress tests were developed to study the adhesion of the coatings. An analysis of variance was carried out to determine the implication of the substrate roughness and the direction of the grinding lines in the final sol-gel coating thickness and its adhesion on the substrate. The results show that the roughness has a significant influence both on the thickness and on the adhesion of the coatings. Thus, thicker coatings were obtained on substrates with higher roughness values, going from 2.18 μm to 1.42 μm for substrate roughness values of 1.47 μm and 0.27 μm respectively, in the case of horizontal grinding lines, and from 2.01 μm to 1.37 μm for substrate roughness values of 1.47 μm and 0.27 μm respectively, in the case of vertical grinding lines. However, the grinding direction has no significant influence on the thickness nor the adhesion, but it has a clear influence on the formation of defects in the coatings. Finally, the inclusion of the r parameter in the Landau-Levich equation is proposed to adjust it, taking into account the roughness of the substrates intended to be coated and the evaporation of solvent and water from the coating during the dip-coating.
Influence of the surface state on the corrosion behavior of the 316 L stainless steel manufactured by laser powder bed fusion
(Elsevier, 2022) Bedmar, Javier; Abu-Warda, Najib; García Rodríguez, Sonia; Torres, Belén; Rams, Joaquín
The effect of surface roughness on the corrosion behavior of 316 L stainless steel manufactured by LPBF has been evaluated. The behavior of the steel in the as-built state was compared to that ground up to 2500 grade. Three different aggressive environments were used: 3.5 wt% NaCl water solution, 3 wt% H2SO4 solution, and hightemperature oxidation at 800 ºC. The ground specimens showed higher corrosion resistance. The corrosion resistance was much smaller in the as-built samples for electrochemical tests, and the lowest mass gain after hightemperature oxidation was found in the ground specimens.
Magnesium Alloys: Fundamentals and Recent Advances
(Elsevier, 2022) Rams, Joaquín; Torres, Belén; Pulido-González, Nuria; García-Rodríguez, Sonia
Magnesium alloys are finding a relevant role in the materials sectors mainly due to its lightness but also to other properties such as high specific mechanical properties, high castability and an adequate compatibility to the human body. Due to this, Magnesium alloys can be used in different systems that include the transportation section, mainly in the automotive one, the electronics and household appliances, but also in prosthesis that can be absorbed by the human body. In this article, a revision on the general characteristics of Magnesium alloys, as well as to the applications that Magnesium is currently finding is made. Due to the combination of lightness, castability, recyclability and biocompatibility, Magnesium alloys are helping to the reduction of pollution, increase the electronics portability and even helping to solve serious health issues that would require the use of medical implants.
Manufacturing of Aluminum Matrix Composites Reinforced with Carbon Fiber Fabrics by High Pressure Die Casting
(MDPI, 2022-05-09) Bedmar, Javier; Torres, Belén; Rams, Joaquín
Aluminum matrix composites reinforced with carbon fiber have been manufactured for the first time by infiltrating an A413 aluminum alloy in carbon fiber woven using high-pressure die casting (HPDC). Composites were manufactured with unidirectional carbon fibers and with 2 2 twill carbon wovens. The HPDC allowed full wetting of the carbon fibers and the infiltration of the aluminum alloy in the fibers meshes using aluminum at 680 C. There was no discontinuity at the carbon fiber-matrix interface, and porosity was kept below 0.1%. There was no degradation of the carbon fibers by their reaction with molten aluminum, and a refinement of the microstructure in the vicinity of the carbon fibers was observed due to the heat dissipation effect of the carbon fiber during manufacturing. The mechanical properties of the composite materials showed a 10% increase in Young’s modulus, a 10% increase in yield strength, and a 25% increase in tensile strength, which are caused by the load transfer from the alloy to the carbon fibers. There was also a 70% increase in elongation for the unidirectionally reinforced samples because of the finer microstructure and the load transfer to the fibers, allowing the formation of larger voids in the matrix before breaking. The comparison with different mechanical models proves that there was an effective load transference from the matrix to the fibers.
Metastable FeMg particles for controlling degradation rate, mechanical properties, and biocompatibility of Poly(l-lactic) acid (PLLA) for orthopedic applications
(Elsevier, 2023) Estrada, Rafael Guillermo; Multigner, Marta; Fagali, Natalia; Lozano, Rosa María; Muñoz, Marta; Cifuentes, Sandra Carolina; Torres, Belén; Lieblich, Marcela
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 preosteoblast 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.
Mg as Bioabsorbable Material
(Elsevier, 2022) Multigner, Marta; Muñoz, Marta; Pulido-González, Nuria; Torres, Belén; Cifuentes, Sandra C.
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.
Mg–1Zn–1Ca alloy for biomedical applications. Influence of the secondary phases on the mechanical and corrosion behaviour
(Elsevier, 2020-08-05) Pulido-González, Nuria; Torres, Belén; García-Rodríguez, Sonia; Rodrigo, Pilar; Bonache, Victoria; Hidalgo-Manrique, Paloma; Mohedano, Marta; Rams, Joaquín
An as-cast Mg–1Zn–1Ca alloy has been soundly characterized to be used as a biodegradable material in biomedical applications. Ca and Zn additions have a great influence in the microstructure, mechanical properties and corrosion behaviour of Mg alloys. SEM examinations revealed that most of the Ca and Zn atoms form Mg2Ca and Ca2Mg6Zn3 precipitates, which distribute preferentially along the grain boundaries forming a continuous network of secondary phases. The results of nanoindentation tests show differences in hardness and elastic modulus between the α-Mg matrix and the secondary phases. The results of three-point bending tests shows that cracks propagate following the network formed by the intermetallic compounds at the grain boundaries (GBs). The evolved hydrogen after immersion in Hank’s solution of the alloy has been also estimated, showing a change in the corrosion mechanism after 160 h. The intermetallic compounds act as a barrier against corrosion, so that it progresses through the α-Mg matrix phase.
Microstructural, mechanical and corrosion characterization of an as-cast Mg–3Zn–0.4Ca alloy for biomedical applications
(Elsevier, 2020-06) Pulido-González, Nuria; Torres, Belén; Rodrigo, Pilar; Hort, Norbert; Rams, Joaquín
The as-cast Mg–3Zn–0.4Ca alloy shows a great potential to be used in biomedical applications due to its composition, mechanical properties and biodegradability. Zn and Ca appear naturally in the organism accomplishing vital functions. The alloy consists of an α-Mg matrix and a eutectic composed of α-Mg + Ca2Mg6Zn3. The eutectic product enhances the mechanical properties of the studied alloy, causing strengthening and providing superior hardness values. In this alloy, cracks initiate at the intermetallic compounds and progress through the matrix because of the open network formed by the eutectics. Attending to the corrosion results, the eutectic product presents a noble potential compared to the α-Mg phase. For this reason, the corrosion progresses preferentially through the matrix, avoiding the (α-Mg + Ca2Mg6Zn3) eutectic product, when the alloy is in direct contact to Hank's solution.
Microstructure and Wear Behavior of Heat-Treated Mg-1Zn-1Ca Alloy for Biomedical Applications
(Multidisciplinary Digital Publishing Institute, 2023-12-22) Pulido-González, Nuria; García-Rodríguez, Sonia; Torres, Belén; Rams, Joaquín
The microstructure and wear properties of a Mg-1wt.% Zn-1wt.% Ca (ZX11) alloy with different heat treatments have been investigated. The ZX11 alloy was tested in the as-cast state and after different heat treatment conditions: solution-treated (at 450 °C for 24 h), peak-aged (solution-treated + aged at 180 °C for 3 h), and over-aged (solution-treated + aged at 180 °C for 24 h). The microstructure of the as-cast sample showed a continuous intermetallic phase at the grain boundaries, while the heat-treated samples exhibited discrete precipitated particles within the grains. To evaluate the wear behavior, the samples were tested using a pin-on-disc configuration, where the wear rates and friction coefficients were measured at different loads and sliding speeds. An AZ31 magnesium alloy was used as the counterbody. The worn surfaces and the wear debris were studied to identify the main wear mechanisms corresponding to each test condition. The results indicated the presence of abrasion, oxidation, and adhesive wear mechanisms in all testing conditions. In the as-cast state, delamination and plastic deformation were the dominant wear mechanisms, while they were less relevant in the heat-treated conditions. The peak-aged samples exhibited the lowest wear rates, suggesting that modifying the distribution of intermetallic precipitates contributed to enhancing the wear resistance of the alloy.
Modulation of Crystallinity through Radiofrequency Electromagnetic Fields in PLLA/Magnetic Nanoparticles Composites: A Proof of Concept
(MDPI, 2021-07-31) Multigner, Marta; Morales, Irene; Muñoz, Marta; Bonache, Victoria; Giacomone, Fernando; de la Presa, Patricia; Benavente, Rosario; Torres, Belén; Mantovani, Diego; Rams, Joaquín
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 10^9 Am-1s-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.
Plasma electrolytic oxidation of AZ31 magnesium stents for degradation rate control
(Elsevier, 2024-03-15) Muñoz, Marta; Fernández-Hernán, Juan Pablo; Torres, Belén; Pulido-González, Nuria; Zhang, Guangqi; Shanov, Vesselin; Moreno, Lara; Matykina, Endzhe; Rams, Joaquín
Cardiovascular disease caused by the accumulation of atheroma plaques in the coronary arteries and the subsequent decrease in the blood flow through the affected vessel, known as atherosclerosis, is responsible for a high percentage of deaths worldwide. Angioplasty is practiced to treat atherosclerosis which involves inserting a stent inside the occluded vessel to expand it and restore normal blood flow. In this work, temporary biodegradable stents made of AZ31 magnesium alloy have been fabricated using photo-chemical etching. The stents were coated via plasma electrolytic oxidation (PEO) technique. The radial strength of the stents was evaluated by cyclic compression, and the corrosion protection provided by the PEO coatings was studied by electrochemical and in vitro corrosion tests respectively. The stents showed an optimal maximum radial force of 0.147 N/mm and revealed elastic recuperation lower than 7 % of the total deformation after expansion. The applied PEO coating helped to control the corrosion of the magnesium alloy, delaying its initiation and, once it has started, decreased the degradation rate compared with the bare AZ31 samples. Thus, the stents treated with the PEO coatings developed in this research present promising results for their use as temporary medical devices used in angioplasty.
Silicon oxide multilayer coatings doped with carbon nanotubes and graphene nanoplatelets for corrosion protection of AZ31B magnesium alloy
(Elsevier, 2020-06-20) Fernández-Hernán, Juan Pablo; López, Antonio Julio; Torres, Belén; Rams, Joaquín
Magnesium (Mg) AZ31B alloy substrates were coated by the dip-coating method to obtain four different coating configurations. Three different sol-gels were synthesized to create different monolayer and multilayer coating configurations from two silicon alkoxides, tetraethyl orthosilicate (TEOS) and methyl-triethoxysilane (MTES). Two of these sol-gel solutions were doped with nanocharges. The final concentration of nanocharges in the coatings was 0.045 wt% and 0.046 wt% for multiwall carbon nanotubes (MWCNTs) and functionalized graphene nanoplatelets (COOH-GNPs), respectively. The anti-corrosion behaviour of these coatings was assessed by electrochemical and hydrogen evolution tests in 3.5 wt% NaCl solution. All of the coating configurations significantly improved the behaviour against corrosion compared with the bare substrate, especially the SG + SG/GNP (sol-gel + sol-gel doped with 0.046 wt% COOH-GNPs) multilayer coating system. The sol-gel synthesis combined with the dip-coating method was demonstrated to be an effective way to generate compact and homogeneous coatings for corrosion protection.
Sol-gel coatings doped with graphene nanoplatelets for improving the degradation rate and the cytocompatibility of AZ31 alloy for biomedical applications
(Elsevier, 2021-09-23) Fernández-Hernán, Juan Pablo; Torres, Belén; López, Antonio Julio; Rams, Joaquín; Martínez-Campos, Enrique
SiO2 coatings doped with four different functionalized graphene nanoplatelets (COOH-GNPs) concentrations (from 0.005 to 1 wt%) were deposited on AZ31 magnesium substrates to control the corrosion rate and to increase the cytocompatibility of this alloy for MC3T3 pre-osteoblastic cells, to develop biodegradable implants for bone fracture and orthopedic applications. The results show that the highest nanoplatelets concentration promoted the generation of nanoparticle aggregates acting as crack-nucleation points embedded in the coating, decreasing the protective behavior of these coatings. Nanoplatelets concentrations of 0.005 wt% and 0.05 wt% led to obtaining crack-free coatings that provided an improved barrier effect. Cytocompatibility tests show that all the conditions, even the bare AZ31, led to cell proliferation. However, low cell adhesion was found in the bare substrate, contrary to the coated substrates. The coatings with the highest nanoplates concentrations augmented the metabolic activity of cell cultures. The sol-gel coating doped with 0.05 wt% COOH-GNPs presented the best corrosion rate control behavior and improved cytocompatibility, with the generation of a confluent preosteoblastic monolayer on its surface after one week of cell culture.