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  • Publication
    Micropillar compression of Ti(C,N)-FeNi cermets: Microstructural, processing, and scale effects
    (Elsevier Ltd., 2023-07-01) Besharatloo, H.; Nicolás Morillas, María de; Chen, M.; Mateo, A.; Ferrari, B.; Gordo Odériz, Elena; Jiménez Piqué, Emilio; Wheeler, J. M.; Llanes, L.; Comunidad de Madrid
    The influence of microstructure and processing route on the small-scale mechanical response as well as on the deformation and failure mechanisms of Ti(C,N)-FeNi cermets were investigated by uniaxial compression of micropillars milled by focused ion beam with different sizes. Stress-strain curves were determined and associated deformation mechanisms were observed in-situ using scanning electron microscopy. The appropriate micropillars dimension was assessed, based on the microstructural characteristics of studied cermets, to overcome scale effect issues. A direct relationship was observed between yield strength and ceramic/metal ratio for colloidal samples. Meanwhile, deformation of metallic binder and glide between Ti(C,N)/Ti(C,N) particles were evidenced as dominant mechanisms during the compression for colloidal cermets with 70 and 80 vol% of ceramic phase, respectively. The obtained results illustrate that samples processed from powder attained by colloidal route provide superior mechanical behavior, as compared to that exhibited by specimens shaped following a conventional powder metallurgy one (wet ball-milling/drying).
  • Publication
    A novel and sustainable method to develop non-equiatomic CoCrFeNiMox high entropy alloys via spark plasma sintering using commercial commodity powders and evaluation of its mechanical behaviour
    (Elsevier B.V., 2023-06-30) Kumarán Venkatesh, S.; Garbiec, Dariusz; Torralba Castelló, José Manuel
    A novel approach to developing high entropy alloys (HEAs) using spark plasma sintering (SPS) was explored in this work where a mix of commercial commodity powders like Ni625, CoCrF75, and 316L was used instead of pre-alloyed powders avoiding the expensive pre-alloying steps like mechanical alloying or gas atomizing. Three non-equiatomic HEAs, based on Co, Cr, Fe, Ni, and Mo were designed and developed by blending the powders which were sintered via SPS and resulted in a single FCC phase after homogenization. The HEAs were microstructurally and mechanically characterized with tensile and hot compression tests up to a temperature of 750 degrees C showing excellent properties. The maximum room temperature tensile strength and ductility demonstrated was 712 MPa and 62% respectively, by the alloy Co23.28Cr28.57Fe25.03Ni21.01Mo2.1. Moreover, the same alloy exhibited a compression strength greater than 640 MPa with a ductility above 45% at a temperature of 750 degrees C. Also, this study paves the way for a novel fabrication route that offers more flexibility to develop new HEAs cost-effectively and efficiently which is crucial for the discovery of new materials over high-throughput techniques. Using such commodity alloys also opens the possibility of developing ingot casting from recycled scraps avoiding the direct use of critical metals.
  • Publication
    Assessment of Plasma Deposition Parameters for DED Additive Manufacturing of AA2319
    (MDPI, 2023-06-01) Rodriguez Gonzalez, Paula; Neubauer, Erich; Ariza, Enrique; Bolzoni, Leandro; Gordo Oderiz, Elena; Ruiz Navas, Elisa Maria; Comunidad de Madrid
    Arc-directed energy deposition using wire as feedstock is establishing itself as a 3D printing method capable of obtaining additively manufactured large structures. Contrasting results are reported in the literature about the effect of the deposition parameters on the quality of the deposited tracks, as it is highly dependent on the relationship and intercorrelations between the individual input parameters, which are generally deposition-technique-dependent. This study comprehensively analysed the effect of several deposition parameters and clarified their interactions in plasma metal deposition of Al alloys. It was found that, although no straightforward correlation between the individual input parameters investigated and the measured output deposition track's quality aspects existed, the input current had the greatest effect, followed by the wire feed speed and its interaction with the input current. Moreover, the greatest effect of changing the shielding gas atmosphere, including the gas mixture, flow rate and plasma flow, was on the penetration depth, and fine-tuning the frequency/balance ratio and the preheating of the deposition substrates reduced the amount of porosity. This study demonstrates that well-deposited multi-layer walls made out of Al alloys can successfully be achieved via plasma metal deposition.
  • Publication
    Liquid phases tailored for introducing oxidation-sensitive elements through the master alloy route
    (Japan Society of Powder and Powder Metallurgy, 2016-04-01) Oro Calderón, Raquel de; Bernardo Quejido, Elena; Campos Gómez, Mónica; Gierl-Mayer, Christian; Danninger, Herbert; Torralba Castelló, José Manuel; European Commission
    Introducing alloying elements through Master Alloy (MA) additions provides the unique opportunity of designing their composition to enhance sintering by forming a liquid phase. However, working with liquid phases poses important challenges like maintaining a proper dimensional control and minimizing the effect of secondary porosity on the final performance of the steel. The critical parameters for designing low melting point compositions are analyzed in this work by combining the use of thermodynamic software tools, wetting angle/infiltration experiments, and advanced thermal analysis techniques. Due to their low ability to dissolve iron, Cu-based liquids present remarkable infiltration properties that provide homogeneous distribution of the alloying elements. Dissolutive liquids, on the other hand, tend to render more heterogeneous microstructures, rapidly solidifying in contact with the matrix. As a consequence of their lower infiltration capacity, dimensional changes upon liquid formation are significantly lowered. When using master alloys with high content in oxidation-sensitive alloying elements, the differences in oxygen affinity cause an oxygen transfer from the surface of the iron base particles to the surface of the master alloys. The change in the surface chemistry modifies the wetting capability of the liquid, and the dimensional stability becomes increasingly sensitive to the processing atmosphere.
  • Publication
    The Antimicrobial Activity of Micron-Thin Sol-Gel Films Loaded with Linezolid and Cefoxitin for Local Prevention of Orthopedic Prosthesis-Related Infections
    (MDPI, 2023-03-01) Toirac Chavez, Beatriz Dunia; Aguilera-Correa, John Jairo; Mediero, Aranzazu; Esteban, Jaime; Jiménez Morales, Antonia; Comunidad de Madrid; Ministerio de Educación, Cultura y Deporte (España)
    Orthopedic prosthesis-related infections (OPRI) are an essential health concern. OPRI prevention is a priority and a preferred option over dealing with poor prognosis and high-cost treatments. Micron-thin sol–gel films have been noted for a continuous and effective local delivery system. This study aimed to perform a comprehensive in vitro evaluation of a novel hybrid organic–inorganic sol–gel coating developed from a mixture of organopolysiloxanes and organophosphite and loaded with different concentrations of linezolid and/or cefoxitin. The kinetics of degradation and antibiotics release from the coatings were measured. The inhibition of biofilm formation of the coatings against Staphylococcus aureus, S. epidermidis, and Escherichia coli strains was studied, as well as the cell viability and proliferation of MC3T3-E1 osteoblasts. The microbiological assays demonstrated that sol–gel coatings inhibited the biofilm formation of the evaluated Staphylococcus species; however, no inhibition of the E. coli strain was achieved. A synergistic effect of the coating loaded with both antibiotics was observed against S. aureus. The cell studies showed that the sol–gels did not compromise cell viability and proliferation. In conclusion, these coatings represent an innovative therapeutic strategy with potential clinical use to prevent staphylococcal OPRI.
  • Publication
    New nanomaterials for applications in conservation and restoration of stony materials: A review
    (CSIC, 2017-01-01) Sierra Fernández, A.; Gómez Villalba, Luz Stella; Rabanal Jiménez, María Eugenia; Fort, R.; Comunidad de Madrid; Ministerio de Innovación y Educación (España)
    In recent times, nanomaterials have been applied in the construction and maintenance of the world's cultural heritage with the aim of improving the consolidation and protection treatments of damaged stone. These nanomaterials include important advantages that could solve many problems found in the traditional interventions. The present paper aims to carry out a review of the state of art on the application of nanotechnology to the conservation and restoration of the stony cultural heritage. We highlight the different types of nanoparticles currently used to produce conservation treatments with enhanced material properties and novel functionalities.
  • Publication
    Evaluation of synthesis time in the growth of vertical-aligned MWCNTs by spray pyrolysis
    (Elsevier, 2023-09-01) Garzon Roman, A.; Ferreiro Fernández, Adalyz; Zuñiga Islas, C.; Rabanal Jiménez, María Eugenia; Comunidad de Madrid; Ministerio de Economía, Industria y Competitividad (España)
    Multi-Wall Carbon Nanotubes (MWCNTs) were analyzed on crystalline silicon substrates (type P) under optimal temperature conditions, using different synthesis times (2, 3, 4, 5, 10, 20, 30, 60, 120, and 180 min) in order to examine the effect on the structural quality and length of the CNTs produced by ultrasonic spray pyrolysis, using pure toluene and ferrocene as precursor solutions under argon flow. Structural, optical, and morphological differences of the MWCNTs grown were analyzed. Raman spectroscopy evidenced the MWCNTs' high quality, noted by the ID/IG (from 0.41 to 0.68) and I2D/IG intensity ratios around 0.75. Morphological differences of the MWCNTs grow evaluated by Field Emission Scanning Electron Microscopy (FE-SEM); the micrographs examined the thickness of CNTs' layers. High-Resolution Transmission Electron Microscopy (HRTEM) technique was used to determine the diameters of CNTs, which were found from 15 to 140 nm. X-Ray Diffraction (XRD) showed two characteristic peaks around 26° and 44°, which corroborated that the MWCNTs were well-graphitized. The influence of the time in these CNTs demonstrated that the final length of these nanotubes could easily reach micrometers. The alienation was better as time increased, and the graphitization extent is good in most cases compared to other more expensive synthesis methods.
  • Publication
    Wear Behavior of Copper-Graphite Composites Processed by Field-Assisted Hot Pressing
    (MDPI, 2019-03-25) Liu, Quian; Castillo-Rodriguez, Miguel; López Galisteo, Antonio Julio; Guzmán de Villoria Lebiedziejewski, Roberto; Torralba Castelló, José Manuel; Comunidad de Madrid
    Copper-graphite composites with 0-4 wt % graphite were fabricated by field-assisted hot pressing with the aim of studying the effect of graphite content on microhardness and tribological properties. Experimental results reveal that hardness decreases with the graphite content. Wear testing was carried out using a ball-on-disc tribometer with a normal load of 8 N at a constant sliding velocity of 0.16 m/s. The friction coefficient of composites decreases significantly from 0.92 to 0.29 with the increase in graphite content, resulting in a friction coefficient for the 4 wt % graphite composite that is 68.5% lower than pure copper. The wear rate first increases when the graphite content is 1 wt %; it then decreases as the graphite content is further increased until a certain critical threshold concentration of graphite, which seems to be around 3 wt %. Plastic deformation in conjunction with some oxidative wear is the wear mechanism observed in pure copper, while abrasive wear is the main wear mechanism in copper-graphite composites.
  • Publication
    Thermomechanical processing of cost-affordable powder metallurgy Ti-5Fe alloys from the blended elemental approach: Microstructure, tensile deformation behavior, and failure
    (MDPI, 2020-11) Romero, Carlos; Yang, Fei; Wei, Shanghai; Bolzoni, Leandro
    The development of cost-affordable Ti alloys is key for the application of Ti in other industries like the automobile sector. Therefore, a combination of powder metallurgy (PM) and low-cost compositions is an interesting approach. In this article, a cost-affordable PM Ti-5Fe alloy is processed following the blended elemental route and extruded at high temperature to remove porosity. Different extrusion temperatures and heat treatments (i.e., solution treatment and aging, STA) are performed to obtain ultrafine microstructures, and their effect on the mechanical behavior is studied. For extrusions in the β phase, microstructures consist of coarse lamellar colonies, resulting in alloys with improved properties compared to the as-sintered alloy but still lacking toughness due to the failure happening just after necking onset. Extruding in the α + β phase results in a bimodal microstructure of fine elongated primary α and coarse lamellar colonies, and the alloy becomes tougher. STA with aging below the eutectoid temperature of 590 °C leads to a hard but brittle alloy, whereas STA with aging above it results in alloys with strength comparable to the as-extruded conditions and enhanced ductility.
  • Publication
    Influencia de diferentes tratamientos termoquímicos en aceros sinterizados base molibdeno
    (Consejo Superior De Investigaciones Científicas (CSIC), 2001-04) Candela Vázquez, Nuria; Plaza, R.; Ruiz Amador, Diego; Velasco López, Francisco Javier; Torralba Castelló, José Manuel
    Polvos prealeados de aceros con diferentes contenidos de Mo - Cu - Ni -C se compactaron a 700 MPa y se sinterizaron a 1.120 ºC en atmósfera de 95 % Nz,5 % H2. Después de la sinterización, los materiales se trataron termoquímicamente para su cementación (proceso endogas). Para la caracterización de todos los materiales se realizaron ensayos de compresión del tipo "radial crushing strength", se calculó la densidad y se hizo un completo estudio de las superficies de fracturas a través de microscopía electrónica de barrido. Los resultados de resistencia a compresión muestran, después de la cementación, valores superiores a los encontrados en el estado sinterizado. La superficie de fractura da idea de la fragilidad del material y de la profundidad del tratamiento. En estado sinterizado, se observa una superficie de fractura totalmente dúctil, donde aparecen las características cavidades. Las superficies de fractura, tras distintos tipos de cementación, reflejan un comportamiento frágil en el exterior, mientras que el interior aparece una mezcla de fractura dúctil con frágil.
  • Publication
    Effect of small variations in Zr content on the microstructure and properties of ferritic ODS steels consolidated by SPS
    (MDPI, 2020-03-06) Garcia Junceda Ameigenda, Andrea; Macía Rodríguez, Eric; Garbiec, Dariusz; Serrano, Marta; Torralba Castelló, José Manuel; Campos Gómez, Mónica; Ministerio de Economía y Competitividad (España)
    Two different zirconium contents (0.45 and 0.60 wt.%) have been incorporated into a Fe-14Cr-5Al-3W-0.4Ti-0.25Y2O3 oxide dispersion-strengthened (ODS) steel in order to evaluate their effect on the final microstructure and mechanical properties. The powders with the targeted compositions were obtained by mechanical alloying (MA), and subsequently processed by spark plasma sintering (SPS) at two different heating rates: 100 and 400 °C·min-1. Non-textured bimodal microstructures composed of micrometric and ultrafine grains were obtained. The increase in Zr content led to a higher percentage of Zr nano-oxides and larger regions of ultrafine grains. These ultrafine grains also seem to be promoted by higher heating rates. The effective pinning of the dislocations by the Zr dispersoids, and the refining of the microstructure, have significantly increased the strength exhibited by the ODS steels during the small punch tests, even at high temperatures (500 °C)
  • Publication
    Effects of powder reuse on the microstructure and mechanical behaviour of Al-Mg-Sc-Zr alloy processed by laser powder bed fusion (LPBF)
    (Elsevier, 2020-12) Córdova González, Laura; Bor, Ton; Smit, Marc De; Carmignato, Simone; Campos Gómez, Mónica; Tinga, Tiedo
    Laser powder-bed fusion (LPBF) technology is one of the additive manufacturing (AM) processes that uses metal powder to produce parts for various industry sectors such as medical, aerospace, automotive and oil & gas. As an ‘additive’ based process, the material is selectively melted by a focused laser. By this working principle material is added in a layer-by-layer approach only where is needed. Therefore, this technology enables a high reduction of waste by avoiding chips typically generated in ‘subtractive’ based processes such as milling and drilling. However, to ensure lower waste consumption the metal powder surrounding the solidified part must be reused in subsequent build jobs. Current knowledge on the effect of powder reuse on LPBF builds is mostly limited to titanium- and nickel- based alloys. The aim of this paper is to study the effect of powder reuse on Al–Mg–Sc–Zr, a high strength aluminium-based alloy, manufactured by LPBF. Here, powder properties such as morphology, composition, particle size distribution are studied of virgin (pristine) and reused Al–Mg–Sc–Zr powder. The mechanical properties of specimens made of virgin powder and after four build cycles are analysed and compared to assess the influence of a mixture of virgin and reused powder material on the consolidated material properties. In general, the powder does not present large differences in composition and morphology, only the reused powder presents coarser particle size distribution (PSD) as previously observed in other alloy compositions. The microstructure of the studied specimens is very similar unlike the porosity. The specimens built with reused powder show a few small micro-sized pores which do not show significant differences in the mechanical properties. In fact, the ultimate tensile strength (UTS) and elongation to break of specimens, respectively built with virgin and reused powder are 565 MPa, 13% and 537 MPa, 11%. Based on the obtained results, it is concluded that it is feasible to reuse Al–Mg–Sc–Zr powder in four subsequent build jobs with proper powder sieving and a rejuvenation step mixing 40% of virgin powder.
  • Publication
    Effect of Y2O3 addition on the microstructure and mechanical properties of an Al1.8CoCrCu0.5FeNi BCC HEA
    (Elsevier, 2023-10-15) Reverte Palomino, Eduardo; Keller, Clement; Calvo-Dahlborg, Monique; Alcala, German; Campos Gómez, Mónica; Cornide Arce, Juan; Comunidad de Madrid; Ministerio de Ciencia e Innovación (España); Agencia Estatal de Investigación (España)
    The present study investigated the influence of Y2O3 addition by mechanical alloying (MA) on the microstructure evolution of a BCC High Entropy Alloy (HEA). The characterisation and mechanical properties of the alloy were explored using X-ray diffraction, SEM, EBSD, and nano-indentation. The sintered Al1.8CoCrCu0.5FeNi HEA shows a microstructure formed by an ordered BCC phase (Al-rich) and a second disordered BCC (Cr-rich), while a minor FCC (Cu-rich) appears. These BCC phases show a wide morphology evolution from cuboidal and wave-like structures to irregular shapes. The minor FCC phase also adopts several morphologies as the MA is performed. The introduction of oxide reinforcements and microstructure refinement through mechanical alloying yields a change in phase quantification and grain structure. In accordance with the hardness and elastic modulus values from ordered/disordered BCC phases, the disordered BCC shows higher values than the ordered one. The grain size reduction as well as the solid solution strengthening from the microstructure evolution consequence of the MA are shown to be the main contributors to the increase in hardness and elastic modulus in the consolidated samples.
  • Publication
    Wire Arc Additive Manufacturing (WAAM) for Aluminum-Lithium Alloys: A Review
    (MDPI, 2023-02-01) Rodriguez Gonzalez, Paula; Ruiz Navas, Elisa María; Gordo Odériz, Elena; Comunidad de Madrid
    Out of all the metal additive manufacturing (AM) techniques, the directed energy deposition (DED) technique, and particularly the wire-based one, are of great interest due to their rapid production. In addition, they are recognized as being the fastest technique capable of producing fully functional structural parts, near-net-shape products with complex geometry and almost unlimited size. There are several wire-based systems, such as plasma arc welding and laser melting deposition, depending on the heat source. The main drawback is the lack of commercially available wire; for instance, the absence of high-strength aluminum alloy wires. Therefore, this review covers conventional and innovative processes of wire production and includes a summary of the Al-Cu-Li alloys with the most industrial interest in order to foment and promote the selection of the most suitable wire compositions. The role of each alloying element is key for specific wire design in WAAM; this review describes the role of each element (typically strengthening by age hardening, solid solution and grain size reduction) with special attention to lithium. At the same time, the defects in the WAAM part limit its applicability. For this reason, all the defects related to the WAAM process, together with those related to the chemical composition of the alloy, are mentioned. Finally, future developments are summarized, encompassing the most suitable techniques for Al-Cu-Li alloys, such as PMC (pulse multicontrol) and CMT (cold metal transfer).
  • Publication
    Polydopamine surface functionalized submicron ZnO for broadening the processing window of 3D printable PLA composites
    (Springer, 2023-05) Yang, Xiao-Mei; Yin, Guang-Zhong; Zafra Amorós, Olga; Arroyo Hernández, María; La Vega, Jimena de; Torralba Castelló, José Manuel
    The “catalytic degradation” of metal oxides limits the wide application of PLA when PLA needs to be modified by adding metal oxides to achieve desired properties. Zinc oxide (ZnO) is a common and widely used agent as it can be used for many properties, such as antioxidant, antibacterial, etc. However, detrimental effects often exist on the properties of polymers after introducing the ZnO, due to the catalytic degradation. In this study, we used polydopamine (PDA) to construct ZnO@PDA core-shell submicron particles via the self-polymerization of dopamine (DA) in alkaline solution, aimed to produce a surface functionalization that would be used to control the rate of degradation of PLA by ZnO during thermal processing, and promote the preservation of mechanical properties. PLA with different contents of ZnO and ZnO@PDA were prepared by a simple melt extrusion method. The degradation behavior, mechanical properties and antibacterial activity of ZnO/PLA and ZnO@PDA/PLA were investigated. It was found that the incorporation of ZnO@PDA in PLA at different contents exhibits a dramatic control over the degradation rate when compared to that of the ZnO/PLA with the same filler content. Notably, the T5% and T50% of 3%-ZnO@PDA/PLA increased by 36.4 oC and 31.9 oC. GPC results showed the molecular weight of 3%-ZnO@PDA/PLA was only reduced by 15.8% after thermal processing. In addition, 3%-ZnO@PDA/PLA can be 3D-printed smoothly. That is to say, the introduction of ZnO@PDA can increase the processing window of PLA/ZnO composites, providing the possibility for materials that need to be included in civil application. Accordingly, ZnO@PDA/PLA samples showed higher tensile strength and elongation at break than that of corresponding ZnO/PLA samples. Regarding the antibacterial behavior, the ZnO@PDA/PLA have more bacterial growth disability effect against Gram(+) bacteria than that of pure PLA.
  • Publication
    Thermophysical properties of porous Ti2AlC and Ti3SiC2 produced by powder metallurgy
    (Elsevier, 2021-03-15) Tsipas, Sophia Alexandra; Tabares Lorenzo, Eduardo; Weissgaerber, Thomas; Hutsch, Thomas; Sket, Federico; Velasco Núñez, Beatriz; Comunidad de Madrid; Ministerio de Economía y Competitividad (España)
    The physicochemical properties of porous Ti2AlC and Ti3SiC2 MAX phase compounds with controlled porosity and grain size obtained by powder metallurgy techniques was studied in depth in order to access their suitability of applications such as catalytic devices on vehicles, heat exchangers or impact resistant structures. The study was performed on isostatic consolidated samples with different amount (20-60 vol%) and size of space holder (250-1000 µm) and in samples without space holder. Oxidation tests were performed at different temperatures for each material depending on their maximum service temperature. In order to understand the oxidation mechanism, oxidation kinetics were analysed to determine the influence of size and amount of porosity in each case. In addition, the microstructure and composition of the oxide layers formed after the tests were analysed by scanning electron microscopy (SEM). Electrical and thermal conductivity where studied at room temperature and at temperature up to 1000 degrees C. The effect of pore size and cell wall thickness is discussed. Permeability of foams was also measured. The effect of micro porosity and macro porosity on permeability is discussed. The coefficient of thermal expiation was also measured for all foams produced. It is established that these porous MAX phases have suitable properties for their use as catalytic substrates, heat exchanges, high temperature filters or volumetric solar receivers.
  • Publication
    Sliding wear behavior of intermetallic Ti-45Al-2Nb-2Mn-(at%)-0.8vol%TiB2 processed by centrifugal casting and hot isostatic pressure: Influence of microstructure
    (MDPI, 2022-11-02) Shagñay Pucha, Segundo Manuel; Cornide Arce, Juan; Ruiz Navas, Elisa María
    Intermetallic alloys such as titanium aluminides (TiAl) are potential materials for aerospace applications at elevated temperatures. TiAl intermetallics have low weight and improved efficiency under aggressive environments. However, there is limited information about wear behavior of these alloys and their microstructure. The present work aims to study the influence of the microstructure in the tribological behavior of TiAl intermetallic alloy (45Al-2Mn-2Nb(at%)-0.8 vol%TiB2). Wear tests were performed on samples manufactured by centrifugal casting (CC) and hot isostatic pressure (HIP). Reciprocating sliding wear test was carried out for TiAl, it was combined with different loads and frequencies. Wear tracks were analyzed through opto-digital microscopy and electron microscopy (SEM). The results obtained reveal that CC intermetallics present the lowest volume wear lost, approximately 20% less than HIP intermetallics. This good behavior could be related to the high hardness material, associated with the main microstructure where CC intermetallic has nearly lamellar microstructure and HIP intermetallics present duplex microstructure.
  • Publication
    Strategies to Control in Vitro Degradation of Mg Scaffolds Processed by Powder Metallurgy
    (MDPI, 2022-04-01) Cifuentes Cuéllar, Sandra Carolina; Alvarez, Lucia; Arias Arias, Luis Andres; Fey, Tobias; Tsipas, Sophia Alexandra; Comunidad de Madrid; Ministerio de Ciencia, Innovación y Universidades (España)
    Magnesium scaffolds are biodegradable, biocompatible, bioactive porous scaffolds, which find applications within tissue engineering. The presence of porosity increases surface area and enhances cell proliferation and tissue ingrowth. These characteristics make Mg scaffolds key materials to enhance the healing processes of tissues such as cartilage and bone. However, along with the increment of porosity, the corrosion of magnesium within a physiological environment occurs faster. It is, therefore, necessary to control the degradation rate of Mg scaffolds in order to maintain their mechanical properties during the healing process. Several studies have been performed to increase Mg scaffolds' corrosion resistance. The different approaches include the modification of the Mg surface by conversion coatings or deposited coatings. The nature of the coatings varies from ceramics such as hydroxyapatite and calcium phosphates to polymers such as polycaprolactone or gelatin. In this work, we propose a novel approach to generating a protective bilayer coating on the Mg scaffold surface composed of a first layer of naturally occurring Mg corrosion products (hydroxide and phosphates) and a second layer of a homogeneous and biocompatible coating of polylactic acid. The Mg scaffolds were fabricated from Mg powder by means of powder metallurgy using ammonium bicarbonate as a space holder. The size and amount of porosity were controlled using different size distributions of space holders. We addressed the influence of scaffold pore size on the conversion and deposition processes and how the coating process influences the in vitro degradation of the scaffolds.
  • Publication
    Influence of Addition of Antibiotics on Chemical and Surface Properties of Sol-Gel Coatings
    (MDPI, 2022-07-02) Toirac Chávez, Beatriz Dunia; García Casas, Amaya; Monclús Palazón, Miguel Alberto; Aguilera Correa, John J.; Esteban, Jaime; Jiménez Morales, Antonia; Comunidad de Madrid; Ministerio de Educación, Cultura y Deporte (España)
    Infection is one of the most common causes that leads to joint prosthesis failure. In the present work, biodegradable sol-gel coatings were investigated as a promising controlled release of antibiotics for the local prevention of infection in joint prostheses. Accordingly, a sol-gel formulation was designed to be tested as a carrier for 8 different individually loaded antimicrobials. Sols were prepared from a mixture of MAPTMS and TMOS silanes, tris(tri-methylsilyl)phosphite, and the corresponding antimicrobial. In order to study the cross-linking and surface of the coatings, a battery of examinations (Fourier-transform infrared spectroscopy, solid-state 29Si-NMR spectroscopy, thermogravimetric analysis, SEM, EDS, AFM, and water contact angle, thickness, and roughness measurements) were conducted on the formulations loaded with Cefoxitin and Linezolid. A formulation loaded with both antibiotics was also explored. Results showed that the coatings had a microscale roughness attributed to the accumulation of antibiotics and organophosphites in the surface protrusions and that the existence of chemical bonds between antibiotics and the siloxane network was not evidenced.
  • Publication
    Study on the growth and properties of electrolessly deposited thin copper coatings on epoxy-based CFRP
    (MDPI, 2020-03) Juan, Sergio De; Gordo Odériz, Elena; Jiménez Morales, Antonia; Sirois, Frédéric
    In this study, copper coatings smaller than 3 µm were created by electroless deposition on epoxy-based carbon fiber-reinforced polymer (CFRP) laminates for enhancing their electrical properties. This well-known method of metallization was employed with a self-designed combination of reagents, and the coatings were studied to evaluate their physical and chemical properties. A five-stage plating strategy was applied to 40 mm × 40 mm samples, and three different coatings were produced during the work. The metal layers created were studied and characterized to evaluate their, electrical conductivity, thickness, and adhesion to substrates, among other properties. In addition, the growth mechanisms of the microstructure were analyzed in detail for a better understanding of the process. The results showed that the proposed metallization strategy presents good characteristics and is a strong candidate for enhancing the electrical performance of CFRP.