Papers by Author: Dora A. Cortés-Hernández

Abstract: The aim of this work was the synthesis of bioactive magnetic particles (BMP) which are expected to form a thin apatite layer on its surface that may bond to bone with the osseous carcinogen tissue. Magnetite and Mg_0.6Ca_0.4Fe₂O₄ nanoparticles were obtained by a reverse co-precipitation and sol-gel methods, respectively. Magnetite particles were coated with chitosan in order to obtain a stable ferrofluid. Then both ferrites were biomimetically treated using two different simulated body fluids (SBF and 1.5 SBF). An apatite layer was formed on both types of BMP after the biomimetic treatment. Both ferrites showed superparamagnetic behavior before and after the apatite formation. Their time-dependent temperature profiles were measured under the effect of an AC magnetic field (AMF). After less than 20 min of applying the AMF an appropriate temperature for hyperthermia treatment was obtained. No citotoxicity was observed after osteosarcoma cell culture testing of BMP. Furthermore, after applying an AMF to the cells in contact with the BMP, the cells viability decreased considerably.

Abstract: In this work, the synthesis of CoFe2O4 via sol-gel auto-combustion method, using iron nitrate, cobalt nitrate and citric acid, with subsequent heat treatment in air was studied. The effects of the molar ratio of the metal nitrates to citric acid and the heat treatment temperatures on the magnetic properties have been investigated. The X-ray diffraction patterns showed peaks consistent with cubic spinel-type structure. The average crystallite sizes were determined from the (311) peak of the diffraction pattern using Scherrer equation. Particle sizes in the range of 18-44 nm were obtained. The crystallite size increases with annealing temperature. Magnetic properties, such as saturation magnetization (Ms), remanent magnetization (Mr) and coercivity field (Hc) were measured at room temperature using a vibrating sample magnetometer. Saturation magnetization was found to increase with particle size, whereas coercivity was found to reduce exponentially as the particle size was increased, apart from the Hc of the sample treated at 300 °C. The present work shows that magnetic properties vary over a wide range by changing the synthesis conditions.

Abstract: Gentamicin sulphate was mixed with two different sol-gel derived calcium silicates (akermanite or wollastonite). Each of the mixtures was isostatically pressed. Samples were immersed in simulated body fluid for 21 days. The presence of the antibiotic showed no effect on the in vitro bioactivity of the ceramics. For evaluating the gentamicin sulphate release, samples were immersed in a phosphate buffered saline solution for different periods of time. Most of the gentamicin sulphate was released during the first 7 days. However, akermanite showed a lower antibiotic release rate than that observed for wollastonite.

Abstract: Two different techniques were used to promote a bioactive surface on a cobalt base alloy: i) the cobalt alloy melt was cast into wollastonite-coated cavities of an investment mold, or ii) wollasonite-encapsulated as-cast samples were heat treated at 1220°C for 1 h, this is the typical treatment performed to this alloy for improving its mechanical behavior. In vitro bioactivity was assessed by immersing samples in a simulated body fluid for 21 days. Potentially bioactive layers were obtained in both of the cases. A thicker apatite layer was formed on the samples obtained by investment casting. However, since the heat treatment needs to be performed, the heat treatment method is also a promising technique for promoting the bone-bonding ability of this Co alloy.

Abstract: The effect of the chemical treatment of zirconia/alumina composites followed by a biomimetic treatment has been studied. The composites are prepared from a powder mixture of Mg- PSZ and Al2O3. The powders are ball-milled in acetone and uniaxially pressed after drying. The specimens are sintered at 1550 °C in air. After sintering, chemical treatment is performed by immersing the samples in a 5M aqueous solution of phosphoric acid at 95 °C for 4 days. The biomimetic method consists of immersing the chemically-treated samples in simulated body fluid at 36.5 °C. In some cases a wollastonite bed is used as a supplier of calcium ions, resulting in the formation of a bonelike apatite layer. The presence of this bioactive system during the biomimetic process has a positive significant effect on the bioactivation of the composites for either short or long times of immersion of the composites in simulated body fluids. The chemical treatment increases also the rate of apatite formation at short immersion periods.

Abstract: Both solid-state reaction and glass-ceramic methods are used to obtain bioactive materials (CaSiO3) with different concentrations of MgO (6, 8, and 10 wt %) on the basis of the stoichiometric composition of CaO·SiO2. The in vitro bioactivity assessment is performed by immersing samples in SBF (simulated body fluids) for different periods of time. The analysis of the materials before immersion indicates the presence of different phases (akermanite, wollastonite and diopside) in the materials obtained by the solid state reaction method. It is possible to obtain wollastonite with incorporation of magnesium in its structure ((Ca, Mg)·SiO6) by the glass-ceramic method. The results obtained after immersing the samples in SBF indicate that a Ca, P-rich layer is formed on all the materials tested, even in those containing a high quantity of MgO. However, the layer formed in the MgO-free CaSiO3 ceramic is thicker than that formed in the MgO-containing materials.

Abstract: In order to decrease its degradation rate, pure magnesium was subjected to the following treatments: (1) heat treatment at 345oC for 15 min and (2) heat treatment at 380°C for 30 min followed by hot rolling at 350°C. The treated samples and non-treated controls were immersed in simulated body fluid (SBF) at 37oC for different periods of time. In all cases, the magnesium released into the SBF, the weight loss of the specimens and the pH of SBF increased with time of immersion. The hot-rolled samples showed a lower degradation rate and lower pH values. A lower increase of magnesium concentration in the SBF corresponding to the hot-rolled samples was also observed. The main and unexpected positive finding of this work was that in all cases, a layer of Ca, P-rich was formed on the substrates after only 3 days of immersion in SBF. This indicates that metallic magnesium is a potential bioactive material. In the aim to promote the formation of a thicker bioactive layer than the one observed on the samples immersed in single SBF, hot-rolled magnesium was biomimetically-treated using wollastonite ceramics, SBF and a more concentrated solution (1.5 SBF). A homogeneous and dense bone-like apatite layer was observed on the biomimetically-treated samples.

Abstract: Hydroxyapatite, porcelain and wollastonite coatings on stainless steel 316L were produced by electrophoretic deposition (EPD) in ethanol and acetone using a voltage between 200 and 1000 V during 0.5 to 60 s. The particle size distribution of the starting suspension was 0.3 to 4.9 microns with an average size of 1.5 microns. The coatings were analyzed using scanning electron microscopy. The amount of ceramic material on the surface of the metallic samples was evaluated by determining their difference in weight before and after the electrophoretic deposition process. The conductivity and zeta potential of the dispersing media were also evaluated. Dense, homogeneous and crack-free green coatings were obtained. The deposition rate was higher by using acetone as dispersing media. The higher zeta potential and the lower viscosity were attributed to be the cause of the better electrophoretic deposition of the acetone and methanol ceramic suspensions. Submicron particle coatings were then sintered between 800 and 1000 C during 2 h. The sintered coatings presented a very homogeneous polycrystalline structure free of cracks. The results show that the application of high voltage during short periods of time is an effective method to obtain ceramic coatings with good sinterability.

Abstract: Natural wollastonite was electrophoretically deposited on 316L stainless steel in order to promote a bioactive surface. The effect of the disperse media and the deposition time on the deposit weight and microstructure of the wollastonite coatings was evaluated. The disperse media were methanol, acetone, ethanol, propyl alcohol and the deposition time was in the range of 1 to 180 s. Suspensions were prepared by using wollastonite powder with a mean particle size of 2 μm at a concentration of 1 g/L. The deposition was performed under a DC field of 800 V. The coated substrates were sintered at temperatures ranging from 900 to 1050oC in air for 2 to 4 h. Dense, homogeneous and crack-free coatings were obtained by using methanol and acetone. No wollastonite coating was obtained by using ethanol at these processing conditions and few wollastonite particles were deposited on the metallic substrates by using propyl alcohol. The deposit weight increases as the deposition time is increased in all the cases.

Abstract: In the aim to decrease the degradation rate of magnesium in simulated body fluid, pure magnesium was treated by two different routes, i) by soaking specimens in an HF aqueous solution at 30oC for 30 min and ii) by heating specimens at 345oC for 15 min. The treated samples were immersed in simulated body fluid (SBF) at 37oC for different periods of time. Samples with no treatment were also immersed in SBF. The magnesium released into the SBF, the weight loss of the specimens and the pH of SBF increased with time of immersion in all the cases. The heat treated samples showed a lower degradation rate and lower pH values. A substantial decrease of magnesium concentration in the SBF corresponding to the heat treated samples was also observed. However, the degradation rate of the heat treated samples remains being extremely high. On the other hand, a bonelike apatite layer was observed after only 3 days of immersion in SBF in all the cases. The thickness of this layer increased with time of immersion. Further research needs to be performed to decrease the degradation rate. However, these results indicate that magnesium is a highly potential bioactive material for biomedical applications.