Bulk Ti nitride prepared from rutile TiO2 for its application as stimulation electrode in neuroscience.

Bulk titanium nitride (TiN) was synthesized by nitridation of TiO2 rutile substrates. TiN pellets were successfully achieved at 1100 °C in ammonia stream; these materials were characterized by the evaluation of their microstructure, surface, chemical composition and electrical and electrochemical properties, concluding that the synthesis promotes the creation of a TiNxOy surface, which shows high metallic conductivity (close to 102 S/cm) and a microstructure with micro- and nano-features. Electrochemical studies reveal high storage capacities which are delivered through an injection mechanism that involves the double charge layer and EIS show a high capacitive contribution to the mechanism. Neuron cell cultures assessed the biocompatibility of the sample prepared and put forward this material as a promising candidate for implantable stimulation electrode in neuroscience.

Scavenging activity of Magnéli phases as a function of Ti4+/Ti3+ ratios.

TiO2 is able to scavenge reactive oxygen and nitrogen species (ROS and RNS) in the absence of light. The scavenging mechanism has been related to the chemistry of defects (oxygen vacancy reduced oxidation states of Ti) but it is still unknown. This study describes the ROS scavenging activity of different titanium oxide phases and relates their scavenging activities with the Ti4+/Ti3+ molar ratio as well as the band gap value. The Ti5O9 phase, with a mixture of both oxidation states, presented a substantially higher percentage of 2,2-diphenyl-1-picrylhydracyl radicals (DPPH˙) eliminated per m2 of specific surface area in comparison to phases with predominant oxidation states Ti4+ or Ti3+ such as TiO2 and Ti2O3, respectively. The obtained results indicate that the DPPH˙ scavenging mechanism corresponds to a catalytic process on the Ti5O9 surface which is facilitated by the presence of charges that can easily move through the material. The mobility of charges and electrons in the semiconductor surface, related to the presence of oxidation states Ti4+ and Ti3+ and a small band gap, could create an attractive surface for radical species such as DPPH˙. This puts forward Ti5O9 as a promising candidate coating for implantable biomedical devices, as an electrode, since it can cushion inflammatory processes which could lead to device encapsulation and, consequently, failure.

An in vivo study on bone formation behavior of microporous granular calcium phosphate.

This study was developed based on in vivo investigation of microporous granular biomaterials based on calcium phosphates, involving matrices of ß-tricalcium phosphate (ß-TCP), hydroxyapatite (HA), biphasic compositions of both phases and a control group. The physicochemical characterization of materials was carried out by X-Ray diffraction (DRX) and mercury porosimetry. Biodegradability, bioactivity and neoformation processes were investigated by Raman spectroscopy, scanning electron microscopy (SEM) and polarized light conducted on biopsies obtained from in vivo tests for periods of 90 and 180 days. These were performed to evaluate the behavior of granular microporous compositions in relation to bone neoformation. Through the performance obtained from in vivo assays, excellent osseointegration and bone tissue neoformation were observed. The results are encouraging and show that the microporous granular biomaterials of HA, ß-TCP and biphasic compositions show similar results with perfect osseointegration. Architectures simulating a bone structure can make the difference between biomaterials for bone tissue replacement and repair.

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.

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.