R. P. del Real

A new method to produce macropores in calcium phosphate cements

A new way to create macropores in calcium phosphate cements has been developed. The method consists in adding NaHCO3 to the starting cement powder (Biocement D) and using two different liquids: first a basic liquid to form the paste and later an acid liquid to obtain CO2 bubbles. Mercury intrusion measurements showed a dramatic increase both in macropores with an average size of 100 m and in the total porosity (even higher than 50% with respect to the Biocement D). This method does not change in any significant way the final reaction products of the starting material after being soaked 3 days in Ringer solution. Only, due to the increase of the porosity. the compressive strength of the porous cement decreases significantly.

A novel bioactive and magnetic biphasic material.

A novel biphasic material has been synthetised from a sol-gel-derived glass (Si-Ca-P) and a glass-ceramic obtained from a melt-derived glass (Si-Ca-Fe). Both components of such a biphasic mixture are bioactive, but with different kinetics for the growth of an apatite-like layer on the surface of these materials, needing only one day for the sol-gel-derived glass and one month for the glass-ceramic. The glass-ceramic shows magnetic properties. The biphasic material, obtained from a mixture 1:1 of these components, is bioactive, and its surface is coated after 15 days of soaking in SBF. The biphasic material also exhibited magnetic behaviour, useful for hyperthermia.

Gentamicin release from hydroxyapatite/poly(ethyl methacrylate)/poly(methyl methacrylate)composites

In this work the release kinetics of gentamicin sulfate (GEN) in samples composed by hydroxyapatite, poly(methyl methacrylate), and poly(ethyl methacrylate) has been studied. The release study was performed by soaking three samples in simulated body fluid at 37 degrees C; the medium was periodically replaced during 70 days. The concentration of GEN was determined by the o-phtaldialdehyde method. The release profile shows three stages: the first stage, occurring during the first 10 h, corresponds to a fast release (nearly 30% of the drug is released in this period). The second stage is slower and includes from the first 10 h to 16 days, releasing 60% of the total amount of GEN. The final stage is the slowest and it takes from 16 to 70 days (10% of GEN is released). The fraction of released GEN versus square root of time can be fitted to a third order polynomial, corresponding with the model proposed by Cobby et al. (J Pharm Sci 1974;63:725-732). The characterization of the samples after the release study shows that a carbonate hydroxyapatite layer has grown on the whole surface of the composites.

In vitro release of gentamicin from OHAp/PEMA/PMMA samples.

The influence of hydroxyapatite (OHAp) and gentamicin sulphate (GEN) contents on the release kinetics of GEN, in samples composed of OHAp, poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA) has been studied. For this purpose, samples with 30 and 40% of OHAp and 5 and 9% of GEN were prepared. The in vitro release study was carried out soaking the samples in simulated body fluid (SBF) at 37 degrees C for 70 days. The release profiles showed a faster release during the first 10 h, diminishing progressively until the end of the study. It was noticed that the percentage of released GEN increased with the OHAp content. For samples with 40% of OHAp, GEN release is nearly independent of the initial amount of such drug (in the range 5-9%), whereas for samples with 30% of OHAp, the release process is favoured by higher contents of GEN, which would favour a higher SBF uptake. GEN release is related to SBF uptake, which is in turn related, on the one hand, to the OHAp content (increase of the porosity and the hydrophilic character of the samples) and on the other hand, to content of GEN.

Tuning the magnetization reversal process of FeCoCu nanowire arrays by thermal annealing

Arrays of hexagonally ordered Fe28Co67Cu5 nanowires with tailored diameter from 18 to 27 nm were prepared by electroplating into anodic alumina templates and annealed in the temperature range of 300–600 °C, preserving but refining their bcc crystal structure. Despite the partial reduction of saturation magnetization and corresponding shape anisotropy after annealing at 500 °C, larger coercivity, 0.36 T, and squareness ratio, Mr/Ms = 0.98, were obtained. This unexpected behavior is interpreted through micromagnetic simulations where the magnetic hardening is associated with the transition from vortex to transverse domain-wall reversal modes connected with the reduction of saturation magnetization. Simulations also predict a significant coercivity increase with decreasing nanowires diameter which agrees with experimental data in the overlapping diameter range.

Drug release and in vitro assays of bioactive polymer/glass mixtures

The bioactive behaviour and drug release of samples composed by sol gel glass with composition 80SiO2-16CaO2-4P2O5% mol, polymethylmethacrylate (PMMA) and gentamicine or ibuprofen have been studied. The bioactive behaviour of the samples does not depend on the amount (5% and 10% in weight) or on the type of drug used in this study. In all the cases the SEM micrographs show the formation of a layer that covers the surface of the samples after 24 hours soaked in simulated body fluid (SBF). X ray diffraction patterns show two broad peaks after being soaked 3 days. These peaks could be identified with an apatite-like phase, characteristic in this kind of studies.On the contrary, the release kinetics is strongly dependent on the drug employed. In the case of gentamicine, the curve shows a high slope during the first day soaked in SBF and the complete release occurs before 150 hours. For the ibuprofen samples, the drug release is much slower; the samples containing 10% of ibuprofen do not reach the total release after 600 hours. This different behaviour could be related with the solubility of both drugs in aqueous media.

Amorphous wire magnetic field and DC current sensor based on the inverse Wiedemann effect

A magnetic field sensor is presented which is based on the inverse Wiedemann effect (IWE) on amorphous wires. The external magnetic DC field to be detected changes the time symmetry of the output voltage induced in a pick-up coil, creating even harmonics. Measurement results show important advantages in sensitivity and working frequencies mainly due to the cores geometry. The sensor has outstanding sensitivity for magnetic fields below 0.02 mT, as well as a low working frequency and current intensity. >

Magnetic behavior of NiCu nanowire arrays: Compositional, geometry and temperature dependence

Arrays of Ni100−xCux nanowires ranging in composition 0 ≤ x ≤ 75, diameter from 35 to 80 nm, and length from 150 nm to 28 μm have been fabricated by electrochemical co-deposition of Ni and Cu into self-ordered anodic aluminum oxide membranes. As determined by X-ray diffraction and Transmission Electron Microscopy, the crystalline structure shows fcc cubic symmetry with [111] preferred texture and preferential Ni or Cu lattice depending on the composition. Their magnetic properties such as coercivity and squareness have been determined as a function of composition and geometry in a Vibrating Sample Magnetometer in the temperature range from 10 to 290 K for applied magnetic fields parallel and perpendicular to the nanowires axis. Addition of Cu into the NiCu alloy up to 50% enhances both parallel coercivity and squareness. For the higher Cu content, these properties decrease and the magnetization easy axis becomes oriented perpendicular to the wires. In addition, coercivity and squareness increase by decrea...

Temperature dependent magnetization in Co-base nanowire arrays: Role of crystalline anisotropy

Co, Co(1−x)Pdx, and Co(1−y)Niy nanowire arrays have been prepared by electrochemical template-assisted growth. Hcp, fcc or both phases are detected in Co nanowires depending on their length (300 nm to 40 μm) and on the content of Pd (0 ≤ x ≤ 0.4) and Ni (0 ≤ y ≤ 0.8). Their magnetic behavior has been studied under longitudinal and perpendicular applied fields. The effective magnetic anisotropy is mostly determined by the balance between the shape and the crystalline terms, the latter depending on the fractional volume of hcp phase with strong perpendicular anisotropy and fcc phase with weaker longitudinal anisotropy. The temperature dependence of remanence and coercivity and the eventual observation of compensation temperature is interpreted as due to the different temperature dependence of shape and hcp crystalline anisotropy. Optimum longitudinal magnetic anisotropy is achieved in low Pd-content CoPd nanowires and in short Co nanowires.

Vortex magnetic structure in circularly magnetized microwires as deduced from magneto-optical Kerr measurements

The magneto-optic Kerr effect has been employed to determine the magnetization process and estimate the domain structure of microwires with circular magnetic anisotropy. The diameter of microwires was 8 μm, and pieces 2 cm long were selected for measurements. The analysis of the local surface longitudinal and transverse hysteresis loops has allowed us to deduce a vortex magnetic structure with axial core and circular external shell. Moreover, a bamboo-like surface domain structure is confirmed with wave length of around 10 to 15 μm and alternating chirality in adjacent circular domains. The width of the domain wall is estimated to be less than 3 μm. Finally, closure domain structures with significant helical magnetization component are observed extending up to around 1000 μm from the end of the microwire.