G. Barucca

Modified TiO2 particles differentially affect human skin fibroblasts exposed to UVA light

Numerous sunscreens contain titanium dioxide (TiO(2)) because of its ability to reflect, scatter, and absorb UV radiation, thus preventing sunlight-related skin disorders. Since TiO(2) is well known to generate reactive oxygen species (ROS) under photoexcitation, it is chemically modified when used in sunscreens. In the present study, five modified TiO(2) particles, specifically developed and marketed for sunscreens, were tested using different in vitro models, including cultured human skin fibroblasts (HuDe), to investigate their possible photocatalytic effects following UVA exposure. The results obtained show that the type of modification and crystal form determine their ability to (a) induce photobleaching of the DPPH radical, (b) photodegrade deoxyribose, (c) reduce cell viability, (d) increase/decrease DNA damage, and (e) increase/decrease intracellular ROS. This research concludes that some modified TiO(2) particles still retain photocatalytic activity under the experimental conditions employed, especially those in which the anatase crystal form of TiO(2) is present. The penetration of TiO(2) nanosized particles into the viable epidermis of skin is still under debate; thus, the results presented here contribute to gaining further knowledge on the potential effects of TiO(2) particles at the cellular level, in the worst possible case that they do penetrate.

Comparative toxicity of CuO nanoparticles and CuSO4 in rainbow trout.

This study compared the toxicity and accumulation of two different Cu compounds, CuO nanoparticles (NPs) and soluble CuSO4, in erythrocytes and different tissues in rainbow trout (Oncorhynchus mykiss). The crystal structure of CuO NP analysed by XRD indicates that the NP are Tenorite, a monoclinic CuO. The in vitro toxicity results indicate that both Cu compounds increase the haemolysis rate in a dose-dependent way, but the effect was reduced treating cells with CuO NP. Moreover, both Cu compounds induce DNA damage and the entity of the damage, similarly to haemolysis, was more marked in cells treated with CuSO4. In vivo results, obtained after intraperitoneal injection, showed that Cu concentrations were significantly higher in gills (p<0.0001), kidney (p=0.007) and liver (p<0.05) of exposed fish with a significant increase in plasma Cu concentration 15h after CuSO4 treatment. Cu concentrations were significantly higher in fish exposed to CuSO4 than CuO in kidney (p<0.05) and gills (p<0.0001). Significant DNA damage with respect to controls was detected only when Cu was injected as CuSO4. The present data could serve to evaluate environmental Cu toxicity in fish depending on Cu speciation.

Structural characterization of biomedical Co-Cr-Mo components produced by direct metal laser sintering.

Direct metal laser sintering (DMLS) is a technique to manufacture complex functional mechanical parts from a computer-aided design (CAD) model. Usually, the mechanical components produced by this procedure show higher residual porosity and poorer mechanical properties than those obtained by conventional manufacturing techniques. In this work, a Co-Cr-Mo alloy produced by DMLS with a composition suitable for biomedical applications was submitted to hardness measurements and structural characterization. The alloy showed a hardness value remarkably higher than those commonly obtained for the same cast or wrought alloys. In order to clarify the origin of this unexpected result, the sample microstructure was investigated by X-ray diffraction (XRD), electron microscopy (SEM and TEM) and energy dispersive microanalysis (EDX). For the first time, a homogeneous microstructure comprised of an intricate network of thin ε (hcp)-lamellae distributed inside a γ (fcc) phase was observed. The ε-lamellae grown on the {111}γ planes limit the dislocation slip inside the γ (fcc) phase, causing the measured hardness increase. The results suggest possible innovative applications of the DMLS technique to the production of mechanical parts in the medical and dental fields.

Hardening nanostructures in an AlZnMg alloy

The formation of nanoscale and sub-nanoscale solute aggregates (clusters, Guinier–Preston zones and precipitates) in an AlZnMg alloy (Al–2.1 at.% Zn–1.5 at.% Mg) has been followed by a combination of experimental techniques with the aim of correlating the properties of the aggregates with their thermal history. The choice of thermal treatments was guided by the results of mechanical and calorimetric characterizations, supported by transmission electron microscopy for the identification of the morphology of the aggregates. Positron annihilation spectroscopy (using two variants of this technique, coincidence Doppler broadening and lifetime spectroscopy) was adopted for determining the local chemistry in the proximity of open volume defects. The geometrical parameters of the distribution (size, volume fraction, numerical density of the solute aggregates) were obtained by small-angle X-ray scattering. The results of the investigation provide new information regarding: two families of vacancy-rich clusters formed during or immediately after quenching; Guinier–Preston zones formed at 95°C after room-temperature pre-ageing; growth of η′ and η phases at 150°C; solute clusters formed at room-temperature in conditions of secondary ageing after preliminary heating at 150°C.

DNA damage and repair following In vitro exposure to two different forms of titanium dioxide nanoparticles on trout erythrocyte.

TiO2 has been widely used to promote organic compounds degradation on waste aqueous solution, however, data on TiO2 nanotoxicity to aquatic life are still limited. In this in vitro study, we compare the toxicity of two different families of TiO2 nanoparticles on erythrocytes from Oncorhynchus mykiss trout. The crystal structure of the two TiO2 nanoparticles was analyzed by XRD and the results indicated that one sample is composed of TiO2 in the anatase crystal phase, while the other sample contains a mixture of both the anatase and the rutile forms of TiO2 in a 2:8 ratio. Further characterization of the two families of TiO2 nanoparticles was determined by SEM high resolution images and BET technique. The toxicity results indicate that both TiO2 nanoparticles increase the hemolysis rate in a dose dependent way (1.6, 3.2, 4.8 μg mL−1) but they do not influence superoxide anion production due to NADH addition measured by chemiluminescence. Moreover, TiO2 nanoparticles (4.8 μg mL−1) induce DNA damage and the entity of the damage is independent from the type of TiO2 nanoparticles used. Modified comet assay (Endo III and Fpg) shows that TiO2 oxidizes not only purine but also pyrimidine bases. In our experimental conditions, the exposure to TiO2 nanoparticles does not affect the DNA repair system functionality. The data obtained contribute to better characterize the aqueous environmental risks linked to TiO2 nanoparticles exposure.

Characterization of C-N thin films deposited by reactive excimer laser ablation of graphite targets in nitrogen atmosphere

Abstract Carbon nitride films were deposited at room temperature on 〈111〉 Si substrates by XeCl laser ablation of graphite in low pressure (1–50 Pa) N2 atmosphere at a fluence of 12 J/cm2. N/C atomic ratios up to 0.5 were inferred from Rutherford backscattering measurements. Different diagnostic techniques (ARXPS, FTIR transmission spectroscopy, EDS, SEM and XRD) were used to characterize the deposited films. XRD spectra indicate a polycrystalline structure of the films.

Nb clusters formation in Nb-doped magnesium hydride

Extended x-ray absorption fine structure spectroscopy, x-ray diffraction and transmission electron microscopy were used to analyze the Nb coordination and clustering in Nb-doped (5 at. %) h-Mg film samples deposited by rf magnetron sputtering. Results show that the catalytic effect of the Nb doping in the H2 absorption and desorption kinetics is connected with the formation of Nb nanoclusters dispersed in the host matrix. The H2 desorption from β-MgH2 is favored by local elastic stresses produced by β-NbH0.89 clusters on the MgH2 matrix that reduces the stability of the hydride phase and by preferential paths in the nanocomposite hydride.

Phase separation as origin of the magnetic anomalies in La0.85Sr0.15CoO3

The dependence of the ac-magnetic susceptibility of La0.85Sr0.15CoO3 on the annealing temperature used during synthesis is addressed. Such dependence has been previously attributed to compositional inhomogeneities. Nevertheless, the presence of distinct phases with different chemical compositions is excluded after explorations by several techniques. Instead it is proposed that an electronic phase separation takes place in the material, whose state is changed after charge-carrier redistributions due to the thermal history of the samples, analogously to parent manganese-based perovskites.

Effects of thermal treatments on microstructure and mechanical properties of a Co-Cr-Mo-W biomedical alloy produced by laser sintering.

Direct Metal Laser Sintering (DMLS) technology based on a layer by layer production process was used to produce a Co-Cr-Mo-W alloy specifically developed for biomedical applications. The alloy mechanical response and microstructure were investigated in the as-sintered state and after post-production thermal treatments. Roughness and hardness measurements, and tensile and flexural tests were performed to study the mechanical response of the alloy while X-ray diffraction (XRD), electron microscopy (SEM, TEM, STEM) techniques and microanalysis (EDX) were used to investigate the microstructure in different conditions. Results showed an intricate network of ε-Co (hcp) lamellae in the γ-Co (fcc) matrix responsible of the high UTS and hardness values in the as-sintered state. Thermal treatments increase volume fraction of the ε-Co (hcp) martensite but slightly modify the average size of the lamellar structure. Nevertheless, thermal treatments are capable of producing a sensible increase in UTS and hardness and a strong reduction in ductility. These latter effects were mainly attributed to the massive precipitation of an hcp Co3(Mo,W)2Si phase and the contemporary formation of Si-rich inclusions.

Growth and characterization of SiC layers obtained by microwave-CVD

Abstract Silicon carbide is a wide band gap semiconductor of interest for its application in many electronic devices. In recent years, a large research activity has been devoted to growth techniques for amorphous, polycrystalline or even epitaxial structures. In this paper, we have reported results on microcrystalline and polycrystalline SiC layers grown by high temperature ECR-CVD over 4″ (100) silicon wafer in SiH4+CH4 gas mixtures. The structure of the films has been investigated by X-ray diffractometry, micro-Raman spectroscopy and transmission electron microscopy (TEM). Stoichiometric SiC films containing a complete chemical order, 3C–SiC crystals with orientation close to that of Si substrate and lateral dimensions larger than 100 nm have been obtained.