Clodomiro Alves Júnior

Effect of titanium surface modified by plasma energy source on genotoxic response in vitro

Titanium (Ti) is currently the most widely used material for the manufacture of orthopedic and dental implants. Changes in the surface of commercial pure Ti (cp Ti) can determine the functional response of cells, and is therefore a critical factor for the success of the implant. However, the genotoxicity of titanium surfaces has been poorly studied. Thus, the purpose of this study was to evaluate the genotoxic potential of a new titanium surface developed by plasma treatment using argon-ion bombardment and compare it with an untreated titanium surface. Accordingly, comet assay, analysis of chromosomal aberrations (CAs), and Cytokinesis Block Micronucleus (CBMN) assay were carried out, using CHO-K1 (Chinese hamster ovary) cells grown on both titanium surfaces. Our results show that the untreated titanium surface caused a significant increase in % tail moment, in the number of cells with CAs, tetraploidy, micronucleus frequency, and other nuclear alterations when compared with the negative control and with the plasma-treated titanium surface. This difference may be attributed to increased surface roughness and changes in titanium oxide layer thickness.

Effects of Methane Cold Plasma in Sisal Fibers

One of the main problems in using vegetable fibers as reinforcement in aggressive cement matrix is the penetration of alkaline products in the porous structure of the filaments, making them very fragile with the time. In this sense a series of physical and chemical methods of surface modification has been used in order to improve its characteristics. The plasma surface modification technique is a physical method surface modification that utilizes ionized gas at low pressure to change the chemical nature and the substrate surface morphology of both organic and inorganic materials without changing their intrinsic properties. This is considered an environmentally friendly process without generation of contamination and has a low operating cost compared to some chemical (such as silane based) treatments. In the present study, the sisal fibers were treated with methane plasma generated by direct electric current during 10, 20 and 30 min with gas flow of 5 cm3/s and current of 0.10 A. The study presents some mechanical, physics and chemical characteristics of sisal fiber after being subjected to treatment with methane cold plasma. The results presented indicate that treatment with methane cold plasma induced changes in sisal fibers at all times of exposure to treatment (10, 20 and 30 min). However, the major changes in structural and mechanical components may be seen in fibers treated with 10 min of exposure to plasma.

A sinterização rápida: sua aplicação, análise e relação com as técnicas inovadoras de sinterização

Recently some innovative sintering techniques have been reported. They are able to densify structures in rather short times. Moreover it is known that samples heated up fastly present high sintering rates. This paper presents these innovative sintering techniques as well as reviews the rapid sintering process. The main topics are: results of rapid sintering, rapid sintering mechanisms in solid and liquid phases, and its applicability. It is concluded that the attractive results of the innovative sintering techniques are just consequence of the fast heating which is their characteristic. In other words, these techniques are only a way to obtain fast sintering.

Water uptake mechanism and germination of Erythrina velutina seeds treated with atmospheric plasma

The effect of plasma applied to mulungu (Erythrina velutina) seeds was studied to verify its influence on the germination, water absorption, wettability and structure of the seeds. The plasma jet used in this study was produced by dielectric barrier discharge (DBD) in a helium gas flow of 0.03 L/s at a distance of 13 mm for 60 s. The plasma treatment significantly affected the seed germination rate, which was approximately 5% higher than that of the untreated group. Micropyle and hilum contributed a greater proportion to uptake. When sealed in the hilar or micropyle regions the amount of water absorbed into the seed decreased approximately 75% compared to the unsealed seed. This difference suggests that these two regions together act cooperatively in the water absorption. However, when plasma treated seed was blocked in the micropyle region, water absorption was higher higher than in seeds blocked hilum. This difference suggests that the plasma treatment changed the wettability of the hilum more effectively than it changed the micropyle. These results indicate that plasma can significantly change the hydrophilicity, water absorption and percentage of seed germination in E. velutina.

Teoria de sinterização por fase sólida; uma análise crítica de sua aplicação

Solid phase sintering is a very complex phenomenon. Theories describing sintering are unsatisfactory. Furthermore, their practical use leads to a series misunderstandings with consequent misleading conclusions. This work presents the structure of the traditional theory of single phase solid state sintering, makes an analysis of its limits and criticizes its use, proposing a way of approaching the sintering process

OES during reforming of methane by microwave plasma at atmospheric pressure

Reform of methane was produced in a quartz tube by microwave plasma at atmospheric pressure. A flux of 10 l/min and 5 l/min of pure argon was inserted in the plasma and then a small amount of methane (from 0.5 to 5 sccm) was added to the argon. The species present in the plasma at discharge and post-discharge were monitored by optical emission spectroscopy (OES) diagnostic during the process. The efficiency of dissociation was evaluated by both the density of species H α (656.6 nm) and CH (431.4 nm).

Influence of Oxynitrided Surface in the Production of a Less Susceptible Titanium Surface to Skin‐Borne Bacterial Adhesion

There is a growing quest for an ideal biomaterial that shows appropriate cellular response and is not susceptible to microbial adhesion. In this study, commercial grade II titanium was submitted to RF/DC plasma surface modification at 2.2 mbar, using gas mixtures of argon, nitrogen, and oxygen at proportions 4:1:2 and 4:1:3. The surfaces were physically and chemically characterized. In order to evaluate bacterial response, the surfaces were exposed to Staphylococcus epidermidis. Oxynitrided samples, although having a higher roughness as compared with untreated samples, exhibited lower bacterial growth. This observation is probably due to the formation of different crystalline phases of nitrides and oxides caused by plasma treatment. The surface with highest contact angle and highest surface tension showed lower bacterial adhesion. These results were confirmed by scanning electron microscopy. The role of nitrogen in reducing bacterial adhesion is clear when this material is compared with untreated titanium, on which only an oxide film is present.

Effect of cage configuration in structural and optical properties of tin films grown by cathodic cage discharge

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.

Cathodic cage nitriding of AISI 409 ferritic stainless steel with the addition of CH4

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 e-Fe3N and expanded ferrite phases.

Nitriding of AISI 1020 steel: comparison between conventional nitriding and nitriding with cathodic cage

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.