Self-Photopolymerizable Hydrogel-Ceramic Composites with Scavenger Properties

The photocatalytic behaviours of semiconductive ceramic nanoparticles such as TiO₂, ZnO, Fe₂O₃, and Fe₃O₄, have been extensively studied in photocatalysis and photopolymerization, due to their ability to produce radical species under ultraviolet-visible light, and even in dark conditions. In addition, in the form of microparticles, TiO₂ and its Magnéli phases are capable of neutralizing radical species, and a heterogeneous catalytic process has been suggested to explain this property, as it is well known as scavenging activity. Thus, in this study, we demonstrate that these ceramic powders, in the form of microparticles, could be used as photoinitiators in UV polymerization in order to synthesize a hydrogel matrix. Them, embedded ceramic powders could be able to neutralize radical species of physiological media once implanted. The hydrogel matrix would regulate the exchange of free radicals in any media, while the ceramic particles would neutralize the reactive species. Therefore, in this work, the scavenger activities of TiO₂, ZnO, Fe₂O₃, and Fe₃O₄ microparticles, along with their photoinitiation yield, were evaluated. After photopolymerization, the gel fraction and swelling behaviour were evaluated for each hydrogel produced with different ceramic initiators. Gel fractions were higher than 60%, exhibiting variation in their scavenging activity. Therefore, we demonstrate that ceramic photoinitiators of TiO₂, ZnO, Fe₂O₃, and Fe₃O₄ can be used to fabricate implantable devices with scavenger properties in order to neutralize radical species involved in inflammatory processes and degenerative diseases.

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 TiN_xO_y 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.

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.

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.