Publications (35)70.77 Total impact
-
Article: Study of Heating Efficiency as a Function of Concentration, Size, and Applied Field in γ‑Fe2O3 Nanoparticles
[show abstract] [hide abstract]
ABSTRACT: The specific absorption rate (SAR) of γ-Fe 2 O 3 nanoparticles (NPs) under an alternating magnetic field has been investigated as a function of size, concentration, coating, liquid carrier, and frequency and amplitude of the applied magnetic field. The NPs have been synthesized by coprecipitation method with sizes ranging from 6 to 14 nm with low polydispersity (0.2) and high crystallinity degrees. The small NPs size (6−14 nm) and the value of the maximum applied field (<7.5 kA/m) allow the use of the linear response theory for the analysis of the experimental SARs values. Under this condition, Neel−Brown relaxation times of about 10 −7 s are obtained from SAR field frequency dependence. The NPs have been immobilized in agar to investigate the heating mechanisms, i.e., inversion of the magnetic moments inside the monodomain volume or particle rotation. The results suggest that there is a critical size of around 12 nm for obtaining the most effective heating in viscous media. Furthermore, the surface modification by aminopropylsilane coating does not affect the heating efficiency, making these NPs good candidates for hyperthermia treatment as well as model samples for standardization of hyperthermia apparatus.The Journal of Physical Chemistry C 11/2012; 116:25602. · 4.80 Impact Factor -
Article: In vivo measurements of electrical conductivity of porcine organs at low frequency: New method of measurement.
[show abstract] [hide abstract]
ABSTRACT: Calculations of the induced currents created in the human body by external electromagnetic fields would be more accurate provided that more realistic experimental values of the electrical properties of the body were available. The purpose of this work is to experimentally obtain values for the conductivity of living organs in conditions close to the real situation. Two-electrode in vivo measurements of the bioimpedance of some porcine organs have been performed. From these measurements and taking into account geometrical considerations, the electrical conductivity for the kidney, liver, heart, and spinal cord has been obtained and were found to be higher than the values reported in the literature. Furthermore, a new experimental procedure is proposed where the conductivity is determined from the values of the electrical potential and currents that are induced by an external electromagnetic field created by a coil placed close to the organ under study. Bioelectromagnetics 33:612-619, 2012. © 2012 Wiley Periodicals, Inc.Bioelectromagnetics 03/2012; 33(7):612-9. · 1.84 Impact Factor -
Article: Grit blasting of medical stainless steel: implications on its corrosion behavior, ion release and biocompatibility.
[show abstract] [hide abstract]
ABSTRACT: This study reports on the biocompatibility of 316 LVM steel blasted with small and rounded ZrO(2) particles or larger and angular shaped Al(2)O(3) particles. The effect of blasting on the in vitro corrosion behavior and the associated ion release is also considered. Surface of Al(2)O(3) blasted samples was rougher than that of ZrO(2) blasted samples, which was also manifested by a higher surface area. Compared to the polished alloy, blasted steels exhibited a lower corrosion resistance at the earlier stages of immersion, particularly when using Al(2)O(3) particles. With increasing immersion time, blasted samples experienced an improvement of the corrosion resistance, achieving impedance values typical of passive alloys. Blasting of the alloy led to an increase in Fe release and the leaching of Ni, Mn, Cr and Mo. On all surfaces, ion release is higher during the first 24 h exposure and tends to decrease during the subsequent exposure time. Despite the lower corrosion resistance and higher amount of ions released, blasted alloys exhibit a good biocompatibility, as demonstrated by culturing osteoblastic cells that attached and grew on the surfaces.Journal of Materials Science Materials in Medicine 01/2012; 23(3):657-66. · 2.32 Impact Factor -
Article: Novel PLLA/magnesium composite for orthopedic applications: a proof of concept
Materials Letters 01/2012; 74(1):239-242. · 2.31 Impact Factor -
Article: On the role of RhoA/ROCK signaling in contact guidance of bone-forming cells on anisotropic Ti6Al4V surfaces
[show abstract] [hide abstract]
ABSTRACT: Patterned surfaces direct cell spatial dynamics, yielding cells oriented along the surface geometry, in a process known as contact guidance. The Rho family of GTPases controls the assembly of focal adhesions and cytoskeleton dynamics, but its role in modulating bone-cell alignment on patterned surfaces remains unknown. This article describes the interactions of two human cell types involved in osseointegration, specifically mesenchymal stem cells and osteoblasts, with submicron- or nano-scale Ti6Al4V grooved surfaces generated by mechanical abrasion. The surface chemistry of the alloy was not affected by grinding, ensuring that the differences found in cellular responses were exclusively due to changes in topography. Patterned surfaces supported cell growth and stimulated mesenchymal stem cell viability. Anisotropic surfaces promoted cell orientation and elongation along the grates. Both cell types oriented on nanometric surfaces with grooves of 150 nm depth and 2 μm width. The number of aligned cells increased by approximately 30% on submicrometric grooves with sizes of about 1 μm depth and 10 μm width. Cells were treated with drugs that attenuate the activities of the GTPase RhoA and one of its downstream effectors, Rho-associated kinase (ROCK), and contact guidance of treated cells on the grooved surfaces was investigated. The data indicate that the RhoA/ROCK pathway is a key modulator of both mesenchymal stem cell and osteoblast orientation on nanometric surface features. RhoA and its effector participate in the alignment of mesenchymal stem cells on submicrometric grooves, but not of osteoblasts. These findings show that RhoA/ROCK signaling is involved in contact guidance of bone-related cells on metallic substrates, although to a varying extent depending on the specific cell type and the dimensions of the pattern.Acta Biomaterialia 01/2011; 7(4):1890-1901. · 4.86 Impact Factor -
Article: Roughening of metallic biomaterials by abrasiveless waterjet peening: Characterization and viability
Wear 01/2011; 270:634- 639. · 1.87 Impact Factor -
Article: Bacterial adhesion reduction on a biocompatible Si+ ion implanted austenitic stainless steel
Materials Science and Engineering C 01/2011; 31(7):1567-1576. · 2.69 Impact Factor -
Article: Novel approaches to determining residual stresses by ultramicroindentation techniques: Application to sandblasted austenitic stainless steel
[show abstract] [hide abstract]
ABSTRACT: This research addresses the determination of residual stresses in sandblasted austenitic steel by ultramicroindentation techniques using a sharp indenter, of which the sensitivity to residual stress effects is said to be inferior to that of spherical ones. The introduction of an angular correction in the model of Wang et al. which relates variations in the maximum load to the presence of residual stresses is proposed. Similarly, the contribution to the hardness of grain size refinement and work hardening, developed as a consequence of the severe plastic deformation during blasting, is determined in order to avoid overestimation of the residual stresses. Measurements were performed on polished cross sections along a length of several microns, thus obtaining a profile of the residual stresses. Results show good agreement with those obtained by synchrotron radiation on the same specimens, which validates the method and demonstrates that microindentation using sharp indenters may be sensitive to the residual stress effect.Acta Materialia. 01/2010; -
Article: Superficial severe plastic deformation of 316 LVM stainless steel through grit blasting: Effects on its microstructure and subsurface mechanical properties
Surface and Coatings Technology 01/2010; 205:1830-1837. · 1.87 Impact Factor -
Article: Novel approaches to determine residual stresses by ultramicroindentation techniques: application to sand blasted austenitic stainless steel
Acta Materialia 01/2010; 58:4191-4198. · 3.76 Impact Factor -
Article: Interplay between the magnetic anisotropy contributions of cobalt nanowires
[show abstract] [hide abstract]
ABSTRACT: We report on the magnetic properties and the crystallographic structure of the cobalt nanowire arrays as a function of their nanoscale dimensions. X-ray diffraction measurements show the appearance of an in-plane hcp-Co phase for nanowires with 50 nm diameter, suggesting a partial reorientation of the magnetocrystalline anisotropy axis along the membrane plane with increasing pore diameter. No significant changes in the mag-netic behavior of the nanowire system are observed with decreasing temperature, indicating that the effective magnetoelastic anisotropy does not play a dominant role in the remagnetization processes of individual nano-wires. An enhancement of the total magnetic anisotropy is found at room temperature with a decreasing nanowire diameter-to-length ratio d / L, a result that is quantitatively analyzed on the basis of a simplified shape anisotropy model.Physical Review B 11/2009; 80:184424. · 3.69 Impact Factor -
Article: Influence of slight microstructural gradients on the surface properties of Ti6Al4V irradiated by UV
[show abstract] [hide abstract]
ABSTRACT: Ti6Al4V alloy is one of the most widely used materials for biomedical implants. Among its properties, it is remarkable the photoactivity displayed by its passive layer, which is mainly composed by titanium dioxide. However, variations in the processing conditions may yield to differences in the microstructure which can be reflected on the surface properties of the machined product. From contact angle measurements taken on different zones of samples removed from a commercial bar of Ti6Al4V, it has been shown that the modifications of the surface Gibbs energy suffered by the alloy under UV irradiation have a radial dependence. This behaviour is related to slight microstructural changes of the alloy, particularly with an increase in the volume fraction of the β-phase when moving to the interior of the sample, which alters the composition and/or microstructure of the passive layer along its radius. This study shows that gradients in the microstructure and physical properties are sample size dependent and are likely related to thermal gradients during processing.Applied Surface Science 01/2009; 255(22):9105-9111. · 2.10 Impact Factor -
Article: Influence of the sandblasting of 316 LVM steel on the subsurface microstructure: implications on the magnetic and mechanical properties
Materials Science and Engineering C 01/2009; 29:1357-1360. · 2.69 Impact Factor -
Article: Interrogations on the sub-surface strain hardening of grit blasted Ti-6Al-4V alloy
Surface and Coatings Technology 01/2009; 203:2036-2040. · 1.87 Impact Factor -
Article: Influencia del arenado de la aleación Ti6Al4V en la dureza subsuperficial y estado de tensiones residuales
[show abstract] [hide abstract]
ABSTRACT: Sandblasting of Ti6Al4V alloy is used to enhance mechanical fixation of the implants. Under the mechanical point of view, such treatment yields a decrease of the fatigue resistance. In this work we evaluate by means of synchrotron radiation the residual stress state in sandblasted specimens and the further relaxation process after a thermal oxidation treatment at 500 °C. It has been found a significant compressive stress gradient with a maximum of about 700 MPa near the surface. Despite the severe deformation experienced by the surface during sandblasting microhardness measurements failed to show any sufsurface hardening. A thermal oxidation treatment (500 °C/ 1h) of the sandblasted specimen yield the stress relief and a significant subsurface hardening.El arenado de la aleación Ti6Al4V es un tratamiento orientado a la mejora de la fijación mecánica de los implantes. Sin embargo, dicho tratamiento contribuye a una disminución de la resistencia a la fatiga del material. En este trabajo se ha determinado, mediante radiación sincrotrón, el estado de tensiones residuales en muestras arenadas de esta aleación y su posterior proceso de relajación tras un recocido a 500 °C. Se observa que el arenado ocasiona un gradiente de tensiones residuales de compresión con valores de hasta unos 700 MPa en las proximidades de la superficie. A pesar de la deformación severa que experimenta el material en esta zona, las medidas de microdureza arrojan valores similares a los obtenidos en el interior del material. Tras el tratamiento térmico se observa una relajación de las tensiones residuales y un importante aumento de la dureza superficial.Revista de Metalurgia 01/2009; 45:52-57. · 0.20 Impact Factor -
Article: Time dependence of electrical bioimpedance on porcine liver and kidney under a 50 Hz ac current.
[show abstract] [hide abstract]
ABSTRACT: The purpose of this work is to study the changes of the bioimpedance from its 'in vivo' value to the values measured in a few hours after the excision from the body. The evolution of electrical impedance with time after surgical extraction has been studied on two porcine organs: the liver and the kidney. Both in vivo and ex vivo measurements of electrical impedance, measuring its real and imaginary components, have been performed. The in vivo measurements have been carried out with the animal anaesthetized. The ex vivo measurements have been made more than 2 h after the extraction of the organ. The latter experiment has been carried out at two different stabilized temperatures: at normal body temperature and at the standard preservation temperature for transplant surgery. The measurements show a correlation between the biological evolution and the electrical bioimpedance of the organs, which increases from its in vivo value immediately after excision, multiplying its value by 2 in a few hours.Physics in Medicine and Biology 04/2008; 53(6):1701-13. · 2.83 Impact Factor -
Article: Synthesis and characterization of FePt/Au core-shell nanoparticles
[show abstract] [hide abstract]
ABSTRACT: In this work, the structural and magnetic properties of the gold-coated FePt nanoparticles synthesized from high-temperature solution phase are presented. The amount of gold was optimized to obtain most of the FePt particles coated. The particle diameter increases from 4 to 10 nm as observed by TEM. The magnetic properties are largely affected by the coating. At low temperature, the coercive field Hc of the coated nanoparticles decreases about three times respect to the uncoated and the blocking temperature reduces to the half. The changes of the magnetic behavior are discussed in terms of the effect of the gold atoms at the FePt core surface. r 2007 Elsevier B.V. All rights reserved. PACS: 75.50.Bb; 75.50.Tt; 75.75.+aJournal of Magnetism and Magnetic Materials 03/2007; 316:753-755. · 1.78 Impact Factor -
Article: Structural and magnetic characterization of oleic acid and oleylamine-capped gold nanoparticles
[show abstract] [hide abstract]
ABSTRACT: In this work the study of oleic acid and oleylamine-capped gold nanoparticles is presented. The structural characterization of the sample shows 6.7 nm gold nanoparticles with a narrow size distribution. The experimental optical absorption spectrum has a maximum at 2.35 eV. The calculated optical absorption spectrum is shifted and narrower than the experimental one, indicating that the oleic acid and oleylamine do not merely passivate the metallic nanoparticles but modify its electronic structure. These gold nanoparticles show in addition a kind of magnetic order similar to other organic passivated gold nanoparticles as thiol-capped gold nanoparticles. Although the magnetic interactions seem to be weaker than in thiol-capped ones, the magnetic behavior looks similar to that, i.e., an invariant temperature dependence of the magnetization from 5 to 300 K and a noticeable coercive field. We analyze the influence of the organic layer bonding the nanoparticles on the magnetic behavior.Journal of Applied Physics 01/2007; · 2.17 Impact Factor -
Article: Fe impurities weaken the ferromagnetic behavior in Au nanoparticles.
[show abstract] [hide abstract]
ABSTRACT: In this Letter, we report on a crucial experiment showing that magnetic impurities reduce the ferromagnetic order temperature in thiol-capped Au glyconanoparticles (GNPs). The spontaneous magnetization of AuFe GNPs exhibits a fast decrease with temperature that contrasts with the almost constant value of the magnetization observed in Au NPs. Moreover, hysteresis disappears below 300 K. Both features indicate that Fe impurities reduce the high local anisotropy field responsible for the ferromagnetic behavior in Au GNPs. As a consequence, the amazing ferromagnetism in Au NPs should not be associated with the presence of magnetic impurities.Physical Review Letters 11/2006; 97(17):177203. · 7.37 Impact Factor -
Article: Permanent magnetism, magnetic anisotropy, and hysteresis of thiol-capped gold nanoparticles.
[show abstract] [hide abstract]
ABSTRACT: We report on the experimental observation of magnetic hysteresis up to room temperature in thiol-capped Au nanoparticles with 1.4 nm size. The coercive field ranges from 860 Oe at 5 K to 250 Oe at 300 K. It is estimated that the Au atoms exhibit a magnetic moment of mu=0.036mu(B). However, Au nanoparticles with similar size but stabilized by means of a surfactant, i.e., weak interaction between protective molecules and Au surface atoms, are diamagnetic, as bulk Au samples are. The apparent ferromagnetism is consequently associated with 5d localized holes generated through Au-S bonds. These holes give rise to localized magnetic moments that are frozen in due to the combination of the high spin-orbit coupling (1.5 eV) of gold and the symmetry reduction associated with two types of bonding: Au-Au and Au-S.Physical Review Letters 09/2004; 93(8):087204. · 7.37 Impact Factor
Top co-authors
Top Journals
Institutions
-
2009–2012
-
Centro Nacional de Investigaciones Metalúrgicas (CENIM)
Madrid, Madrid, Spain
-
-
2010
-
Instituto de Salud Carlos III
Madrid, Madrid, Spain
-
-
2008
-
Complutense University of Madrid
Madrid, Madrid, Spain
-
