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Local drug delivery systems used in dental implants need to have uniform pore size distribution, adequate wettability, chemical composition, and biocompatibility. In the present work, titanium was treated by pulsed plasma electrolytic oxidation (PPEO), using 0.025 M sodium dihydrogen phosphate and 0.25 M calcium acetate as electrolytes, aiming at use in drug delivery systems. Pulse with Ton/Toff (width pulse/repetition time) of 50 μs/100 μs or 100 μs/50 μs, duty cycle 0,33, and 0.67, respectively, were used. After treatment, Ca/P ratio, wettability, crystalline phase, pore size and distribution were determined. The average pore size ranged from 1.5 μm to 2.3 μm according to the increase of energy supplied to the system. Pore distributions with lower dispersion were verified for the Ton/Toff condition of 50 μs /100 μs, using a current density of 30 mA/dm2. On the other hand, the 100 μs/50 μs conditions produce larger pores, but with greater dispersion. In general, conditions with lower currents (30 mA/dm2 and 38 mA/dm2) and Ton/Toff ratio = 50/100 were the most appropriate for use in drug delivery systems, due to their size and distribution of uniform pores, greater hydrophilicity, and Ca/P ratio close to desirable (1.67) was obtained.

In the plasma electrolytic oxidation (PEO) process, microdischarges are produced at the titanium surface immersed in an appropriate electrolyte by applying a voltage higher than dielectric breakdown of the oxide film. During this discharging stage, lasting between 30 and 300 μs, many species are transferred from electrolytic to surface producing the coatings. In the present work, pulses of electric current with duration of 50 μs and 100 μs were used in order to interrupt the microdischarges and, thus, control the PEO process. The effect of pulse duration, using different current densities and duty cycles, was investigated by the changes in energy consumption, in addition to the topographical, microstructural and chemical properties of the surface, in order to meet the requirements of a hypothetical surface for drug delivery from titanium implants. It was shown that surfaces treated with pulse duration of 50 μs had uniform pores and smaller mean diameters, better anatase/rutile and calcium/phosphorus ratios than those treated with pulses of 100 μs. Our results reveal that using a 50 μs current pulse, the process has lower energy consumption and more suitable properties for use in titanium implants with controlled drug delivery.

Plasma electrolytic oxidation (PEO) is an environmentally friendly anodizing technique that produces ceramic coatings using high voltage discharges. To the present work this technique was applied to treat aluminum surfaces using a pulsed current supply and sodium silicate electrolyte. The effect of the duty cycle and treatment time on the morphology, phase composition and tribo-mechanical properties of the formed layer was investigated. The current density was maintained at 12 A/dm2, with two different duty cycles, 30% and 50%, for total period of 100 μs. For each duty cycle two different treatment times (2 min and 12 min) was used. During each treatment, the voltage was monitored to determine the start of the rupture of the passive oxide layer. It was demonstrated that the increase in the duty cycle from 30% to 50% influenced the thickness and porosity of the film, verified by scanning electron microscopy (SEM) images. Phase γ-Al2O3 was predominant on the surface of the samples treated by PEO, although occurrence of mullite and α-Al2O3 were also observed. There was an inversion in the intensities of the diffraction peaks Al (200) and Al (111) after the formation of the oxide phase, suggesting a preferential oxidation in the Al (111) direction. The PEO process allows tuning of the hardness, yield strength and wear resistance by controlling film thickness, porosity and phases present. Keywords: PEO, Plasma, Duty cycle, Aluminum oxide, Nanohardness, Wear rate

Abstract Up to now, plasma electrolytic oxidation (PEO) has been either produced direct current or ultra-low frequency (< 1 kHz) pulsed discharge using high concentration alkaline-silicate electrolytic (Na2SiO3 > 8 g.L-1 with presence of KOH). In order to contribute to these studies, the effect of current pulse width and time duration was investigated using diluted silicate electrolytic (Na2SiO3 2 g.L-1) and high pulse frequencies (> 1 kHz). The PEO process was performed on pure aluminum to try to explain how the phases composing the coatings are formed and distributed over the treatment time. For this, was made in situ monitoring using optical emission spectroscopy (OES) coupled with CCD camera. The crystalline phases evolution in the sample surface was investigated using grazing incidence X-ray diffraction (GIXRD). Regarding the evolution of ceramic phases, it is possible to verify that, internally, the predominant phase is rhombohedral α-Al2O3 but, superficially, the predominant phase is cubic γ-Al2O3. It was verified the presence of Si on the borders of the pores or in proximity to cracks, especially in the treatments with higher pulse width. SEM analysis shows a reduction of the superficial porosity and an increase in coating thickness with pulse width and treatment time.

High performance solar collectors are those with high selectivity surfaces, high solar radiation absorption and that do not thermally reemit to the external environment. Strategies to enhance this performance might involve surface porosity modification. In this work, a plasma treatment technique called plasma electrolytic oxidation (PEO) has been tested to produce porosity on aluminium surfaces in a controlled manner. The porosity control was made by varying the intensity, frequency and duty cycle of the applied voltage pulses. The aluminium sample was placed in a solution of 1 g/L Na2SiO3. Voltage of 500 V and current density of 0.17 A cm2 was applied between electrodes. Three duty cycles were used: 33.33%, 50.00% and 67.77%. After treatment, the size, number and distribution of pores were evaluated. These parameters were correlated with both surface reflectance and optical absorbance. It was possible to control the porosity by controlling the electrical parameters of the process. While the mean pore size was directly related to the duty cycle, the inverse occurred for the number of pores. Surface treated with duty cycle of 33.33% presented higher values of absorption for all wavelength range.

Titanium oxides such as rutile and anatase, are materials that stand out for exhibiting properties that act in biomedical and photocatalytic applications, among others. It is extreme importance to idealize new techniques that produce such compounds, being indispensable the improvement of characterizations for these materials. For this purpose, titanium comercially pure (CP) grade II cylindrical samples were oxidized ionically using titanium cage electric shields, oxidized at 350 ° C in 3 and 8 hours. Through Grazing Incidence X-ray Diffraction (GIXRD) analysis, was observed on the surface of the treated samples the formation of a TiO2 film with the anatase, rutile and brookite phases, the latter phase cited being difficult to produce in conventional thermochemical treatments. All samples treated showed a significant increase in wettability using distilled water. The higer value was for the sample with a 8 hours treatment time, in which this condition presented phases with greater intensity in the analysis of GIXRD

Electrical discharges in liquids are currently used to synthesize nanoparticles. The plasma-liquid interaction is complex, where parameters such as electric field, ion charges and other species present are important. In order to understand the mechanism of crystallization, mother liquor (saturated solution of NaCl, MgCl2 and KCl) was used to study the effectiveness and selectivity of the crystallization caused by the application of plasma. Discharge was applied with the solution at room temperature or during cooling. X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and chemical analysis was used to evaluate the structure and composition effects on crystal structure and composition. It was observed that the discharge induces selectively crystallization, and when compared to crystals obtained conventionally by cooling, were smaller and more uniform. We therefore confirm that plasma in liquid can also be used to selectively crystallize materials in atmospheric pressure, where the sizes of the crystals must be dependent on the parameters used.

AbstractPolyester fabric samples – PET (poly (ethylene terephtalate)), were treated with oxygen plasma, in order to alter the hydrophilicity of such material. The process parameters: working pressure, current, tension and temperature were kept constant, varying only the treatment time. In order to evaluate the change caused on samples hydrophilicity, as well as the influence of the treatment time, the vertical wicking test was used. The samples were stored at standard temperature and pressure conditions, and their wettability were measured one day after the treatment and repeated after 30, 60 and 360 days, in order to check the stability of the effects produced. Scanning electron microscopy (SEM), Raman and ATR (Attenuated total reflection) spectroscopies were used to evaluate physical and chemical alterations on the samples surface. The results have shown a substantial improvement on the hydrophilicity of the treated samples compared to the non-treated sample.

Cylindrical samples of AISI 1020 steel were nitrided, using the techniques of conventional plasma nitriding and cathodic cage. In the latter, the samples are kept at floating potential, inside of a cage that works as a cathode and to shield the samples from the cathodic potential. A systematic study was conducted in order to evaluate the efficiency of this technique in the elimination of edge effect, in comparison with conventional plasma nitriding. In addition, another comparative study of the phases obtained using the conventional plasma nitriding and nitriding with cathodic cage was performed. Two metallic cages were used, one made of austenitic stainless AISI 316 and other one made of AISI 1020 steel, to prove the effect of deposition in nitriding with cathodic cage. The samples which were nitrided by this new technique had shown nitriding rates, crystalline phases, and microhardness, similar to those samples which were nitrided conventionally. However, it was possible to confirm the elimination of edge effect through the characterization by optical microscopy and by microhardness test along the samples surfaces. The samples were characterized by optical microscopy, microhardness tests and X-ray diffraction.

Cathodic cage discharge was developed recently in order to eliminate phenomena as edge effect and overheating, which occurs during conventional processes. In this study, the effect of cage configuration in active species during the deposition process and optical properties of TiN film were studied. TiN compound was chosen because its optical properties are very sensitive to slight variations in microstructure and film thickness, becoming a good monitoring tool in fabrication process control. Cages were made of titanium and have different holes numbers and holes diameter. Electrical efficiency of the system and optical properties of TiN films were strongly influenced by experimental conditions. It was found that with more holes at the top of cage, deposition rate and crystallinity were higher, if compared to cages with a small number of holes at the top. On the other hand, the opposite behavior was observed when more holes were located at the sidewall of cage.

AISI 409 ferritic stainless steel samples were nitrided using the cathodic cage plasma nitriding technique (CCPN), with the addition of methane to reduce chromium precipitation, increase hardness and wear resistance and reduce the presence of nitrides when compared to plasma carbonitriding. Microhardness profiles and X-Ray analysis confirm the formation of a very hard layer containing mainly ε-Fe3N and expanded ferrite phases.

La hidroxiapatita es catalogada como un material bioactivo cuya capacidad de interacción con el hueso ha permitido su uso de forma satisfactoria para aplicaciones ortopédicas y dentales. En el presente trabajo la hidroxiapatita producida por el Centro Nacional de Investigaciones Científicas fue proyectada mediante una antorcha de plasma atmosférico sobre un sustrato de acero inoxidable austenítico. El tamaño de partículas fue determinado por dispersión láser y la distancia de proyección fue variada entre 20 y 60 mm. La microestructura y composición de fase del polvo, así como la del recubrimiento obtenido fueron examinados por microscopia óptica, microscopia electrónica de barrido y difracción de rayos X (DRX). La composición química puntual del recubrimiento fue analizada por espectrometría de dispersión de energía (EDS), también fueron medidos la dureza, el espesor de capa y la cristalinidad. Los resultados indican que la cristalinidad disminuye con el incremento de la distancia de proyección, no así su dureza y espesor de capa.Hydroxyapatite is classified as a bioactive material whose ability of interaction with bone allowed its use in a satisfactory way for orthopedic and dental application. In present paper the hydroxyapatite produced by the National Center of Scientific Researches, was projected by means of an atmospheric plasma torch on an austenitic stainless steel substrate. The particles' size was determined by laser dispersion and the projection distance fluctuates between 20 and 60 mm. The microstructure and the powder phase composition, as well as the coating achieved were examined by optical microscopy, scanning electron microscopy and X-rays diffraction (XRD). The coating's point chemical composition was analyzed by energy-dispersion spectrometry (EDS) and the hardness, layer thickness and crystallization were measured. Results showed that crystallization decreases according to the increase of projection distance, but not its hardness and layer thickness.

Mechanical and tribological properties os AISI 304 and AISI 316 stainless steels submited to glow discharge ion nitriding are reported.The atmosphere was 20:80 - N2:H2 with substrate temperatures ranging from 300 to 500 °C. Treatment at 300 °C produced expanded austenite (γN) in both steels. Increasing the temperature, the phases γ´-Fe4N and - Fe2+xN were present and the latter is the major phase for AISI 304. At 500 °C, the CrN phase was also identified in both steels. Hardnesses of about 13-14 GPa at near surface regions were obtained in both steels. Moreover, AISI 316 nitrided at 500 °C has the deepest hard layer. Tribological tests showed that wear can be reduced by up to a factor of six after the nitriding processes, even for a working temperature of 300 °C. The profiles during and after nanoscratch tests did not reveal significant differences after nitriding processes in both steels.

Objetivo: el objetivo principal de este trabajo es estudiar la posibilidad de que sean empleados como sistema de liberación controlada de fármacos, discos de Hidroxiapatita (HA) cubana, fabricados por prensado y sinterizado en hornos eléctrico, sin el empleo de agentes formadores de poros, con porosidades aparentes de 12, 20 y 40%, que fueron dopados por sobre presión con una solución acuosa de alginato de sodio al 5 % y 55 ppm de ceftazidima. Métodos: se estudió la relación entre la penetración del polímero y la porosidad aparente con la liberación del fármaco. Resultados: se demostró que estos discos infiltrados con el polímero que encapsula el fármaco pueden ser utilizados como sistema de liberación controlada. Se demuestra que la porosidad aparente y el tamaño de los poros son influyentes en la penetración del polímero y la masa de fármaco liberado. Conclusiones: En las curvas de liberación obtenidas se observa que los discos pueden ser un potencial material para soportar medicamentos porque se evidencia como el material es capaz de controlar la liberación del medicamento remanente ocluido por un método de dopaje a sobre presión.El perfil indica que en un periodo de siete días se libera controladamente el medicamento.

A 12.4 kDa laminarin (LM) composed of β(1→3)-glucan with β(1→6)-branches was extracted from brown seaweed Lobophora variegata and modified via carboxylation using dielectric barrier discharge (LMC), conjugation with gallic acid (LMG), and sulfation (LMS). Analyses of the chemical composition of LMC, LMG, and LMS yielded 11.7% carboxyl groups, 1.5% gallic acid, and 1.4% sulfate content, respectively. Antioxidant activities of native and modified laminarins were assessed using six different in vitro methods. Sulfation stopped the antioxidant activities of LM. On the other hand, carboxylation improved cooper chelation (1.2 times). LMG was found to be a more efficient antioxidant agent than LM in terms of copper chelation (1.3 times), reducing power (1.3 times), and total antioxidant capacity (80 times). Gallic acid conjugation was further confirmed using Fourier transform infrared spectroscopy (FT-IR) and one- and two-dimensional NMR spectroscopy analyses. LMG also did not induce cell death or affect the cell cycle of Madin–Darby canine kidney (MDCK) cells. On the contrary, LMG protected MDCK cells from H2O2-induced oxidative damage. Taken together, these results show that LMG has the potent antioxidant capacity, and, therefore, potential applications in pharmacological and functional food products.

Aim: To evaluate the adhesion of mouse bone marrow mesenchymal cells (MBMMC) on different titanium surfaces. Methods: Grade II titanium discs (ASTM F86) received two different surface treatments: polished (S1) and cathodic cage plasma nitriding (S2). MBMMC were cultured on titanium discs in 24-well cell culture plates, at a density of 1 x 104 cells per well. After 24 h, the adhesion was evaluated using a hemocytometer. Results: The mean adhesion was greater on S2, though without statistically significant difference from S2 (p>0.05). Conclusions: It was demonstrated that titanium surface treatment with ionic nitriding in a cathodic cage is biocompatible since it preserved the integrity of the cultivated MBMMC for a period of 24 h, allowing their adhesion.

Objetivo: el propósito central de este trabajo es evaluar la bioactividad in vitro de capas de alginato de sodio en discos de hidroxiapatita. Métodos: los discos de hidroxiapatita fueron elaborados mediante procesos sucesivos de prensado y de sinterizado en un horno eléctrico. Las capas de alginato de sodio se obtuvieron empleando el método de sobrepresión y una disolución acuosa de alginato de sodio al 5 %. En el ensayo de bioactividad las muestras a estudiar fueron sumergidas en fluido biológico simulado. La caracterización de las muestras se realizó empleando microscopia electrónica de barrido y energía dispersiva de rayos X. Resultados: en las muestras de hidroxiapatita sometidas al ensayo de bioactividad, con y sin capas de alginato de sodio, se observó la formación de precipitados ricos en calcio y fósforo. Además, se determinó que con el aumento del tiempo de inmersión en el fluido biológico simulado se incrementan las dimensiones de los aglomerados formados por partículas apatíticas. Conclusiones: los resultados experimentales corroboran que la hidroxiapatita es bioactiva y demuestran que las capas estudiadas de alginato de sodio en discos de hidroxiapatita poseen un comportamiento bioactivo.