Dispositivo de microdescargas em gases na pressão atmosférica

Neste trabalho foi desenvolvido um dispositivo de microdescargas em gases à pressão atmosférica para geração de plasma a fim de ser utilizado no tratamento de superfícies. O trabalho foi baseado em um estudo de iniciação científica que aconteceu em duas etapas. Na introdução apresentam-se as motivações do estudo, o dispositivo desenvolvido na primeira etapa do trabalho bem como os primeiros resultados e propostas de melhorias. Definem-se os objetivos da segunda etapa, que contemplam modificações no dispositivo de descarga e na fonte de alimentação. Em seguida são explanados os métodos utilizados para confecção do dispositivo, construção da fonte de alimentação e circuito de fotodetecção para observar as descargas. Apresenta-se o modelo e configurações dos experimentos, os resultados obtidos são expostos e debatidos brevemente. Colocam-se as conclusões do trabalho e novas propostas de investigação e melhoramentos para o estudo das microdescargas. Seguem-se os agradecimentos aos envolvidos no projeto e, por fim, a bibliografia utilizada

Designing atmospheric-pressure plasma sources for surface engineering of nanomaterials

Atmospheric-pressure plasma processing techniques emerge as efficient and convenient tools to engineer a variety of nanomaterials for advanced applications in nanoscience and nanotechnology. This work presents different methods, including using a quasi-sinusoidal high-voltage generator, a radio-frequency power supply, and a uni-polar pulse generator, to generate atmospheric-pressure plasmas in the jet or dielectric barrier discharge configurations. The applicability of the atmospheric-pressure plasma is exemplified by the surface modification of nanoparticles for polymeric nanocomposites. Dielectric measurements reveal that representative nanocomposites with plasma modified nanoparticles exhibit notably higher dielectric breakdown strength and a significantly extended lifetime.

Nanoscale surface and interface engineering : why plasma-aided?

This contribution provides arguments why and in which cases low-temperature plasmas should be used for nanoscale surface and interface engineering and discusses several advantages offered by plasma-based processes and tools compared to neutral gas fabrication routes. Relevant processes involve nanotexturing (etching, sputtering, nanostructuring, pre-patterning, etc.) and composition/structure control at nanoscales (phases, layering, elemental presence, doping, functionalization, etc.) and complex combinations thereof. A case study in p-Si/n-Si solar cell junction exemplifies a successful use of inductively coupled plasma-assisted RF magnetron sputtering for nanoscale fabrication of a bi-layered stack of unconventionally doped highly-crystalline silicon nanofilms with engineered high-quality interfaces.

Plasma polymer and biomolecule modification of 3-D scaffolds for tissue engineering

Plasma polymerization was used to coat a melt electrospun polycaprolactone scaffold to improve cell attachment and organization. Plasma polymerization was performed using an amine containing monomer, allylamine, which then allowed for the subsequent immobilization of biomolecules i.e. heparin and fibroblast growth factor-2. The stability of the plasma polymerized amine-coating was demonstrated by X-ray photoelectron spectroscopy analysis and imaging time-of-flight secondary ion mass spectrometry revealed that a uniform plasma amine-coating was deposited throughout the scaffold. Based upon comparison with controls it was evident that the combination scaffold aided cell ingress and the formation of distinct fibroblast and keratinocyte layers.

Homogenous demineralized dentin matrix and platelet-rich plasma for bone tissue engineering in cranioplasty of diabetic rabbits: biochemical, radiographic, and histological analysis

This study evaluated the effects of homogenous demineralized dentin matrix (HDDM) slices and platelet-rich plasma (PRP) in surgical defects created in the parietal bones of alloxan-induced diabetic rabbits, treated with a guided bone regeneration technique. Biochemical, radiographic, and histological analyses were performed. Sixty adult New Zealand rabbits were divided into five groups of 12: normoglycaemic (control, C), diabetic (D), diabetic with a PTFE membrane (DM), diabetic with a PTFE membrane and HDDM slices (DM-HDDM), and diabetic with PTFE membrane and PRP (DM-PRP). The quantity and quality of bone mass was greatest in the DM-HDDM group (respective radiographic and histological analyses: at 15 days, 71.70±16.50 and 50.80±1.52; 30 days, 62.73±16.51 and 54.20±1.23; 60 days, 63.03±11.04 and 59.91±3.32; 90 days, 103.60±24.86 and 78.99±1.34), followed by the DM-PRP group (respective radiographic and histological analyses: at 15 days 23.00±2.74 and 20.66±7.45; 30 days 31.92±6.06 and 25.31±5.59; 60 days 25.29±16.30 and 46.73±2.07; 90 days 38.10±14.04 and 53.38±9.20). PRP greatly enhanced vascularization during the bone repair process. Abnormal calcium metabolism was statistically significant in the DM-PRP group (P<0.001) for all four time intervals studied, especially when compared to the DM-HDDM group. Alkaline phosphatase activity was significantly higher in the DM-HDDM group (P<0.001) in comparison to the C, D, and DM-PRP groups, confirming the findings of intense osteoblastic activity and increased bone mineralization. Thus, HDDM promoted superior bone architectural microstructure in bone defects in diabetic rabbits due to its effective osteoinductive and osteoconductive activity, whereas PRP stimulated angiogenesis and red bone marrow formation.

Covalent immobilisation of VEGF on plasma-coated electrospun scaffolds for tissue engineering applications.

Recent findings in the field of biomaterials and tissue engineering provide evidence that surface immobilised growth factors display enhanced stability and induce prolonged function. Cell response can be regulated by material properties and at the site of interest. To this end, we developed scaffolds with covalently bound vascular endothelial growth factor (VEGF) and evaluated their mitogenic effect on endothelial cells in vitro. Nano- (254±133 nm) or micro-fibrous (4.0±0.4 μm) poly(ɛ-caprolactone) (PCL) non-wovens were produced by electrospinning and coated in a radio frequency (RF) plasma process to induce an oxygen functional hydrocarbon layer. Implemented carboxylic acid groups were converted into amine-reactive esters and covalently coupled to VEGF by forming stable amide bonds (standard EDC/NHS chemistry). Substrates were analysed by X-ray photoelectron spectroscopy (XPS), enzyme-linked immuno-assays (ELISA) and immunohistochemistry (anti-VEGF antibody and VEGF-R2 binding). Depending on the reaction conditions, immobilised VEGF was present at 127±47 ng to 941±199 ng per substrate (6mm diameter; concentrations of 4.5 ng mm(-2) or 33.3 ng mm(-2), respectively). Immunohistochemistry provided evidence for biological integrity of immobilised VEGF. Endothelial cell number of primary endothelial cells or immortalised endothelial cells were significantly enhanced on VEGF-functionalised scaffolds compared to native PCL scaffolds. This indicates a sustained activity of immobilised VEGF over a culture period of nine days. We present a versatile method for the fabrication of growth factor-loaded scaffolds at specific concentrations.

Atmospheric plasma treatment of porous polymer constructs for tissue engineering applications

Porous 3D polymer scaffolds prepared by TIPS from PLGA (53:47) and PS are intrinsically hydrophobic which prohibits the wetting of such porous media by water. This limits the application of these materials for the fabrication of scaffolds as supports for cell adhesion/spreading. Here we demonstrate that the interior surfaces of polymer scaffolds can be effectively modified using atmospheric air plasma (AP). Polymer films (2D) were also modified as control. The surface properties of wet 2D and 3D scaffolds were characterised using zeta-potential and wettability measurements. These techniques were used as the primary screening methods to assess surface chemistry and the wettability of wet polymer constructs prior and after the surface treatment. The surfaces of the original polymers are rather hydrophobic as highlighted but contain acidic functional groups. Increased exposure to AP improved the water wetting of the treated surfaces because of the formation of a variety of oxygen and nitrogen containing functions. The morphology and pore structure was assessed using SEM and a liquid displacement test. The PLGA and PS foam samples have central regions which are open porous interconnected networks with maximum pore diameters of 49 μm for PLGA and 73 μm for PS foams. (Figure Presented) © 2007 Wiley-VCH Verlag GmbH & Co. KGaA.

Electrostatically confined plasma in segmented hollow cathode geometries for surface engineering

A segmented hollow cathode (SHC) geometry was used for electrostatic confinement of plasma, and surface engineering treatments were conducted in this arrangement. The assessed processes included plasma nitriding, reactive deposition of sputtered material, and deposition of carbonaceous films by plasma-enhanced chemical vapor deposition with a bipolar pulsed-dc power supply on steel substrates. The treated specimens exhibited uniform surface morphology and deposition layers. Characterization techniques included optical microscopy, scanning electron microscopy with energy dispersive X-ray capability, and X-ray diffraction. The advantages and potential applications of the SHC arrangement are discussed in view of these results.

Corrosion studies on the plasma-sprayed nanostructured titanium dioxide coating

Purpose: The purpose of this paper is to report the resistance of plasma-sprayed titanium dioxide (TiO2) nanostructured coatings in a corrosive environment.----- Design/methodology/approach: Weight loss studies are performed according to ASTM G31 specifications in 3.5?wt% NaCl. Electrochemical polarization resistance measurements are made according to ASTM G59-91 specifications. Corrosion resistance in a humid and corrosive environment is determined by exposing the samples in a salt spray chamber for 100?h. Microstructural studies are carried out using an atomic force microscope and scanning electron microscope.----- Findings: The nanostructured TiO2 coatings offer good resistance to corrosion, as shown by the results of immersion, electrochemical and salt spray studies. The corrosion resistance of the coating is dictated primarily by the geometry of splat lamellae, density of unmelted nanoparticles, magnitude of porosity and surface homogeneity.----- Practical implications: The TiO2 nanostructured coatings show promising potential for use as abrasion, wear-resistant and thermal barrier coatings for service in harsh environments.----- Originality/value: The paper relates the corrosion resistance of nanostructured TiO2 coatings to their structure and surface morphology.

Using a current source to improve efficiency of a plasma system

This paper presents the possibility of utilizing a current source topology instead of a voltage source as an efficient, flexible and reliable power supply for plasma applications. A buck-boost converter with a current controller has been used to transfer energy from an inductor to a plasma system. A control strategy has also been designed to satisfy all the desired purposes. The main concept behind this topology is to provide high dv/dt regardless of the switching speed of a power switch and to control the current level to properly transfer adequate energy to various plasma applications.

Near infrared optical materials from polymeric amorphous carbon synthesized by collisional plasma process

The synthesis of polymerlike amorphous carbon(a-C:H) thin-films by microwave excited collisional hydrocarbon plasma process is reported. Stable and highly aromatic a-C:H were obtained containing significant inclusions of poly(p-phenylene vinylene) (PPV). PPV confers universal optoelectronic properties to the synthesized material. That is a-C:H with tailor-made refractive index are capable of becoming absorption-free in visible (red)-near infrared wavelength range. Production of large aromatic hydrocarbon including phenyl clusters and/or particles is attributed to enhanced coagulation of elemental plasma species under collisional plasma conditions. Detailed structural and morphological changes that occur in a-C:H during the plasma synthesis are also described.