E. Chinarro

Bulk and grain boundary conductivity of Ca0.97Ti1−xFexO3−δ materials

Abstract Polycrystalline Ca 0.97 Ti 1− x Fe x O 3− δ samples with x =0, 0.01, 0.035, 0.07 and 0.15 were prepared by a conventional ceramic route and characterised by impedance spectroscopy at different temperatures in air. Spectra obtained for samples with low iron contents ( x

Titanium oxide as substrate for neural cell growth

Titanium oxide has antiinflammatory activity and tunable electrochemical behavior that make it an attractive material for the fabrication of implantable devices. The most stable composition is TiO2 and occurs mainly in three polymorphs, namely, anatase, rutile, and brookite, which differ in its crystallochemical properties. Here, we report the preparation of rutile surfaces that permit good adherence and axonal growth of cultured rat cerebral cortex neurons. Rutile disks were obtained by sinterization of TiO2 powders of commercial origin or precipitated from hydrolysis of Ti(IV)-isopropoxide. Commercial powders sintered at 1300-1600 degrees C produced rutile surfaces with abnormal grain growth, probably because of impurities of the powders. Neurons cultured on those surfaces survived in variable numbers and showed fewer neurites than on control materials. On the other hand, rutile sintered from precipitated powders had less contaminants and more homogenous grain growth. By adjusting the thermal treatment it was possible to obtain surfaces performing well as substrate for neuron survival for at least 10 days. Some surfaces permitted normal axonal elongation, whereas dendrite growth was generally impaired. These findings support the potential use of titanium oxide in neuroprostheses and other devices demanding materials with enhanced properties in terms of biocompatibility and axon growth promotion.

Electrical characterisation of ceramic conductors for fuel cell applications

Abstract In electrochemical devices, such as direct methanol fuel cells (DMFCs) or proton exchange membrane fuel cells (PEMFCs), it is necessary to reduce Pt loading to 0.3 mg/cm 2 at the electrodes. Furthermore, partial Pt replacement by other electrocatalysts is desirable. Use of ceramic compounds as electrodes might be an important technology innovation. The transition metal perovskite oxides LaNiO 3− δ , SmCoO 3 , which have been selected as candidate materials for this application, are metallic conductors and some undergo metallic–semiconductor transitions. The combustion synthesis method is used to prepare the corresponding powders. Specific surface areas as high as 10 m 2 /g and average particle size of the order of 10 nm were achieved, depending on precursors/fuel rate used. The as-prepared powders were XRD amorphous. The electrical characterisation of these materials was carried out by Complex Impedance Spectroscopy on four-probe arrangement samples.

Targeting Neural Stem Cells with Titanium Dioxide Nanoparticles Coupled to Specific Monoclonal antibodies

Aiming to characterize the use of biomaterials in cancer therapy, we took advantage of the n-type semiconductor properties, which upon irradiation excite their electrons into the conduction band to induce photoelectrochemical reactions generating oxygen reactive species (ROS). Indeed, photoactivated TiO2 nanoparticles have been shown to kill in vitro either bacteria or tumor cells in culture following UV irradiation, as a consequence of the ROS levels generated; the killing was highly effective although devoid of specificity. In this report, we have directed the TiO2 nanoparticles to particular targets by coupling them to the monoclonal antibody (mAb) Nilo1, recognizing a surface antigen in neural stem cells within a cell culture, to explore the possibility of making this process specific. TiO2 nanoparticles generated with particular rutile/anatase ratios were coupled to Nilo1 antibody and the complexes formed were highly stable. The coupled antibody retained the ability to identify neural stem cells and upon UV irradiation, the TiO2 nanoparticles were activated, inducing the selective photokilling of the antibody-targeted cells. Thus, these data indicate that antibody-TiO2 complexes could be used to specifically remove target cell subpopulations, as demonstrated with neural stem cells. The possible applications in cancer therapy are discussed.

Physico-chemical properties of the Ti5O9 Magneli phase with potential application as a neural stimulation electrode

This work offers a description of the physico-chemical and electrochemical properties of one of the titanium-based Magneli phases, known as TinO2n-1, for its possible application as an electrode for neural tissue stimulation in neural disorders and Central Nervous System (CNS) injuries. Ti5O9 is one of the less-known Magneli phases that exhibits high electronic conductivity and high chemical and thermal inertness. The material, prepared in a reducing atmosphere by ceramic methods, is composed of a porous surface responsible for most of its properties. Chemical and physical features of the surface were studied with the aim of establishing a relationship between them and the surface electrochemistry. The chemical composition of the surface was studied by XRD and XPS. The topography was studied by AFM and the morphology of the outer side of a fracture was observed by SEM. The conductivity was measured by the four point method in DC finding extremely high values, 9500 S cm-1 at 37 °C. The study of the surface electrochemistry in contact with media, which simulate physiological conditions, was carried out by cyclic voltammetry and EIS. With these measurements the charge injection mechanism has been elucidated, and the charge storage capacity of the material has been determined, finding higher values than those reported for other ceramic electrodes. Finally, cell cultures realised with neural cells were obtained from the cerebral cortex of E18 Wistar rat embryos. They were observed after 4 and 10 DIV and helped in the determination of the biocompatibility of the material.

Ceramic conductors for electrochemical cell applications: new perspectives in materials and synthesis

Abstract A great number of compounds with electronic and ionic conductivity and new synthesis routes are being explored for electrochemical applications. In this work, selected examples are described. (a) CaO–TiO 2 –Fe 2 O 3 materials prepared by combustion synthesis are low cost products with interesting mixed conduction, the electrical behavior of which indicates the existence of a transition, where the grain interior electrical contribution is the dominant effect from 7% mol iron content. (b) Mixed electronic–ionic conducting SmCoO 3 perovskites with dispersed Pt particles were prepared by combustion synthesis. The as-prepared powders showed very small metallic Pt particles and exhibited acceptable catalytic performance in methanol oxidation. (c) Materials belonging to the Ti 1− x Ru x O 2 system, 0≤ x ≤1 (mol), were synthesized by a polymeric sol-gel route. Two types of electrical behavior were detected in sintered materials of this system: semiconductor and metallic. A wide semiconductor/metal transition was observed. The metal/electrical percolation could be located at a composition of x =0.26. (d) On the other hand, amorphous nanopore materials with protonic conduction obtained by appropriate synthesis can be used as electrolytes in PEMFCs. SiO 2 nanopore ceramic membranes were prepared using a colloidal sol-gel technique. The chips were mesoporous with an average pore size of 3.5 nm.

TiO2 surfaces support neuron growth during electric field stimulation

TiO2 is proposed here for the first time as a substrate for neural prostheses that involve electrical stimulation. Several characteristics make TiO2 an attractive material: Its electrochemical behaviour as an insulator prevents surface changes during stimulation. Hydration creates -OH groups at the surface, which aid cell adhesion by interaction with inorganic ions and macromolecules in cell membranes. Its ability to neutralize reactive oxygen and nitrogen species that trigger inflammatory processes confers biocompatibility properties in dark conditions. Here, physicochemical characterization of TiO2 samples and their surfaces was carried out by X-ray diffraction, X-ray photoelectronic emission spectroscopy, scanning electron microscopy, atomic force microscopy and by contact angle measurements. Its properties were related to the growth parameters and morphology of amphibian spinal neurons cultured on TiO2 samples. Neurons adhered to and extended neurites directly on TiO2 surfaces without pre-coating with adhesive molecules, indicating that the material permits intimate neuron-surface interactions. On TiO2 surfaces the distal tips of each extending neurite and the neurite shafts themselves showed more complex filopodial morphology compared with control cultures on glass. Importantly, the ability of TiO2 to support neuron growth during electric field exposure was also tested. The extent of growth and the degree of neurite orientation relative to the electric field on TiO2 approximated that on glass control substrates. Collectively, the data suggest that TiO2 materials support neuron growth and that they have potential utility for neural prosthetic applications incorporating electric field stimulation, especially where intimate contact of neurons with the material is beneficial.

Ti4O7 Used as Electrode in Biomedicine and for Electrochemical Study of Scavenging Mechanism

The biocompatibility of TiO2 is due to the activity that it shown in front of oxygen and nitrogen reactive species. Some authors suggest that the mechanism go through oxidation reduction reactions where changes of oxidation state in the Titanium and phases are involve. For this reason, Anderson-Magnelli phases could present scavenging activity. Moreover, these materials are use as electrodes and in that way are proposed as electrodes for study their scavenging mechanism by electrochemical methods.

Synthesis of Cermet Sr(Ti,Fe)O3-δ-PtRu by Combustion

High specific surface area metallic, ceramic and cermet powders may be active electrocatalyst materials, particularly for hydrocarbon oxidation in the anode compartment of a PEMFC, DMFC or SOFC. Several synthesis techniques are available for electrocatalyst preparation. Sol-gel and coprecipitation are considered dependable methods but are time-consuming and complex. Combustion synthesis is a rapid and reliable route that allows powders of metals, ceramics and cermets free of impurities, with nanoparticle scale and high specific surface area to be obtained. In this work, cermet material in the system SrTiFeO3-δ/ Pt-Ru was prepared for electrochemical applications by combustion synthesis. The perovskite (SrTiFeO3-δsupport for the Pt/Ru particles may decrease the Pt poisoning by CO. The Pt-Ru alloy particle size was around 15 nm. The material has been tested as anode electrocatalyst in a protonic exchange membrane fuel cell; polarization curves have been obtained with power output of 25 mW/cm2.