Papers by Author: José C. Escobedo-Bocardo

Abstract: A method to promote a bioactive surface on the cobalt base alloy ASTM F75 was tested. A set of cylindrical samples was obtained using the investment casting technique and one of the flat surfaces of each sample was polished. The samples were packed in wollastonite powder and then heat treated for 1 h at 1220°C. To characterize the in vitro bioactivity, a set of heat treated metallic specimens was immersed in a simulated body fluid with an ionic concentration nearly equal to that of human blood plasma (SBF) for 7, 10 and 21 days. To evaluate the effect of increasing the concentration of the simulated body fluid on the bioactivity of the material, a second set of heat treated samples was immersed in a more concentrated solution (1.5 SBF). In both cases the solution was renewed every 7 days. After heat treatment, fine agglomerates homogeneously distributed, containing O, Ca, Si and Al were observed on the metallic surface. After immersion of the samples in simulated body fluids, a ceramic layer containing Ca and P was formed on all the samples. A thicker layer, identified as apatite by XRD, was formed on the samples immersed for 21 days in SBF and as early as 7 days in 1.5 SBF. This may indicate that the heat treated material is useful for bone replacement and tissue regeneration under highly loaded conditions.

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: 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: 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: A titanium base alloy and a cobalt base alloy have been subjected to a biomimetic process. Samples of titanium and cobalt alloys have been immersed in 10M and 5M NaOH solutions, respectively, then the samples have been heat treated and finally, immersed in either a simulated body fluid (SBF) with ionic concentration close to human blood plasma or in a simulated body fluid with an ionic concentration 1.5 times that of the SBF (1.5SBF) for a period of 21 days. An apatite layer has been observed after the immersion of the samples in SBF for both Ti and Co base alloys. The apatite layer observed on the Ti alloy samples is more homogeneous and thicker than that observed on the Co alloy samples. However, the apatite layer on both samples is not continuous and homogeneous along the surface. The layer of apatite formed is thicker on samples immersed in 1.5SBF. This is attributed to the higher ion concentrations, mainly of calcium and phosphorus. The Ca/P ratios measured in the apatite layers are close to that of bone.

Abstract: Wollastonite ceramics was used in a biomimetic method to promote apatite formation on a Co-Cr-Mo alloy (ASTM F-75). The metallic samples were initially chemically treated in a 5M NaOH aqueous solution. The treated samples were immersed for 7 days in SBF on a bed of wollastonite and then immersed 7 or 14 days in 1.5SBF. For comparative purposes no wollastonite was used during the first 7 days in some tests. A homogeneous bonelike apatite layer was formed on the samples immersed in SBF on the wollastonite bed. The morphology and the Ca/P ratio of the layer were closely similar to those observed on the existing bioactive systems. A thinner homogeneous bonelike apatite layer was formed on the samples immersed in SBF and 1.5SBF without using wollastonite. However, the morphology and the Ca/P ratio of this layer differs slightly to that observed on the existing bioactive systems. The immersion of the samples during the first days in SBF on a wollastonite bed improves significantly the quality and thickness of the bonelike apatite layer.