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Coatings, Volume 3, Issue 4 (December 2013) – 6 articles , Pages 177-300

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2096 KiB

Open AccessArticle

Gas Permeation, Mechanical Behavior and Cytocompatibility of Ultrathin Pure and Doped Diamond-Like Carbon and Silicon Oxide Films

by Juergen M. Lackner, Claudia Meindl, Christian Wolf, Alexander Fian, Clemens Kittinger, Marcin Kot, Lukasz Major, Caterina Czibula, Christian Teichert, Wolfgang Waldhauser, Annelie-Martina Weinberg and Eleonore Fröhlich

Coatings 2013, 3(4), 268-300; https://doi.org/10.3390/coatings3040268 - 16 Dec 2013

Cited by 6 | Viewed by 10528

Abstract

Protective ultra-thin barrier films gather increasing economic interest for controlling permeation and diffusion from the biological surrounding in implanted sensor and electronic devices in future medicine. Thus, the aim of this work was a benchmarking of the mechanical oxygen permeation barrier, cytocompatibility, and microbiological properties of inorganic ~25 nm thin films, deposited by vacuum deposition techniques on 50 µm thin polyetheretherketone (PEEK) foils. Plasma-activated chemical vapor deposition (direct deposition from an ion source) was applied to deposit pure and nitrogen doped diamond-like carbon films, while physical vapor deposition (magnetron sputtering in pulsed DC mode) was used for the formation of silicon as well as titanium doped diamond-like carbon films. Silicon oxide films were deposited by radio frequency magnetron sputtering. The results indicate a strong influence of nanoporosity on the oxygen transmission rate for all coating types, while the low content of microporosity (particulates, etc.) is shown to be of lesser importance. Due to the low thickness of the foil substrates, being easily bent, the toughness as a measure of tendency to film fracture together with the elasticity index of the thin films influence the oxygen barrier. All investigated coatings are non-pyrogenic, cause no cytotoxic effects and do not influence bacterial growth. Full article

(This article belongs to the Special Issue Advances in Medical Device Coatings)

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764 KiB

Open AccessArticle

Development and in Vitro Characterization of Photochemically Crosslinked Polyvinylpyrrolidone Coatings for Drug-Coated Balloons

by Svea Petersen, Ingo Minrath, Sebastian Kaule, Jürgen Köcher, Klaus-Peter Schmitz and Katrin Sternberg

Coatings 2013, 3(4), 253-267; https://doi.org/10.3390/coatings3040253 - 5 Dec 2013

Cited by 7 | Viewed by 11803

Abstract

Polyvinylpyrrolidone (PVP) is a conventionally applied hydrophilic lubricious coating on catheter-based cardiovascular devices, used in order to ease movement through the vasculature. Its use as drug reservoir and transfer agent on drug-coated balloons (DCB) is therefore extremely promising with regard to the simplification of its approval as a medical device. Here, we developed a PVP-based coating for DCB, containing paclitaxel (PTX) as a model drug, and studied the impact of crosslinking via UV radiation on drug stability, wash off, and transfer during simulated use in an in vitro vessel model. We showed that crosslinking was essential for coating stability and needed to be performed prior to PTX incorporation due to decreased drug bioavailability as a result of photodecomposition and/or involvement in vinylic polymerization with PVP under UV radiation. Moreover, the crosslinking time needed to be carefully controlled. While short radiation times did not provide enough coating stability, associated with high wash off rates during DCB insertion, long radiation times lowered drug transfer efficiency upon balloon expansion. A ten minutes radiation of PVP, however, combined a minimized drug wash off rate of 34% with an efficient drug transfer of 49%, underlining the high potential of photochemically crosslinked PVP as a coating matrix for DCB. Full article

(This article belongs to the Special Issue Advances in Medical Device Coatings)

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493 KiB

Open AccessArticle

Fabrication of Nanodiamond Coating on Steel

by Rafael Velázquez, Victor F. Neto, Kishore Uppireddi, Brad R. Weiner and Gerardo Morell

Coatings 2013, 3(4), 243-252; https://doi.org/10.3390/coatings3040243 - 2 Dec 2013

Cited by 10 | Viewed by 7760

Abstract

The hardness, heat conductivity and low friction coefficient of microcrystalline diamond make it a suitable candidate for tribological applications. However, its roughness and high deposition temperature pose significant obstacles to these applications. We have successfully grown nanocrystalline diamond on steel at 400 °C by hot-filament chemical vapor deposition by employing a CrN interfacial layer. Nanocrystalline diamond combines hardness and surface smoothness required in tribological applications. Microcrystalline diamond and carbon nanotubes can also be grown by controlling the deposition parameters. The fabricated films were characterized with Raman spectroscopy, X-ray diffraction (XRD), Transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Full article

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1018 KiB

Open AccessArticle

A Study of a Powder Coating Gun near Field: A Case of Staggered Concentric Jet Flow

by Graham Payne, Darko Matovic and Edward Grandmaison

Coatings 2013, 3(4), 208-242; https://doi.org/10.3390/coatings3040208 - 1 Nov 2013

Cited by 3 | Viewed by 7749

Abstract

This paper examines, experimentally and numerically, an isothermal coaxial air jet, created by an innovative nozzle design for an air propane torch, used for the thermal deposition of polymers. This design includes staggering the origins of the central and annular jets and creating an annular air jet with an inward radial velocity component. The experimental work used a Pitot tube to measure axial velocity on the jet centerline and in the fully developed flow. The static gauge pressure in the near field was also measured and found to be positive, an unexpected result. The numerical work used Gambit and Fluent. An extensive grid sensitivity study was conducted and it was found that results from a relatively coarse mesh were substantially the same as results from a mesh with almost 11 times the number of control volumes. A thorough evaluation of all of the RANS models in Fluent 6.3.26 found that the flow fields they calculated showed at most partial agreement with the experimental results. The greatest difference between numerical and experimental results was the incorrect prediction by all RANS models of a recirculation zone in the near field on the jet axis. Experimental work showed it did not exist. Full article

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1150 KiB

Open AccessArticle

Optimization Studies of Photocatalytic Tungsten-Doped Titania Coatings Deposited by Reactive Magnetron Co-Sputtering

by Marina Ratova, Glen T. West and Peter J. Kelly

Coatings 2013, 3(4), 194-207; https://doi.org/10.3390/coatings3040194 - 25 Oct 2013

Cited by 24 | Viewed by 6454

Abstract

In this article we investigate the structural and photocatalytic properties of W-doped titanium dioxide coatings. TiO₂-W thin films were deposited onto glass slides by reactive magnetron co-sputtering. The properties of the films were analyzed using such techniques as XRD, Raman spectroscopy, EDX, TEM, and surface profilometry. The photocatalytic properties of the coatings were assessed using the methylene blue (MB) degradation test under UV and fluorescent light sources. The methylene blue decomposition experiments showed that, at the optimum dopant concentration of tungsten, the photocatalytic activity can be improved by a factor of 6, compared to undoped titania. For the coatings discussed within this work, the optimum dopant concentration was determined to be 5.89 at.% of W. The results indicated that tungsten doping at this level extends the lifetime of the photogenerated charge carriers and significantly increases the photocatalyst surface area. Full article

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1282 KiB

Open AccessArticle

Photocatalytic Activity of Reactively Sputtered Titania Coatings Deposited Using a Full Face Erosion Magnetron

by Nick Farahani, Peter J. Kelly, Glen West, Claire Hill and Vladimir Vishnyakov

Coatings 2013, 3(4), 177-193; https://doi.org/10.3390/coatings3040177 - 25 Oct 2013

Cited by 7 | Viewed by 6467

Abstract

Titanium dioxide (titania) is widely used as a photocatalyst for its moderate band gap, high photoactivity, recyclability, nontoxicity, low cost and its significant chemical stability. The anatase phase of titania is known to show the highest photocatalytic activity, however, the presence of this phase alone is not sufficient for sustained activity. In this study TiO₂ coatings were deposited onto glass substrates by mid-frequency pulsed magnetron sputtering from metallic targets in reactive mode using a Full Face Erosion (FFE) magnetron, which allows the magnetic field to be modulated during the deposition process. The as-deposited coatings were analysed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and micro-Raman spectroscopy. Selected coatings were then annealed at temperatures in the range of 400–700 °C and re-analysed. The photocatalytic activity of the coatings was investigated through measurements of the degradation of organic dyes, such as methyl orange, under the influence of UV and fluorescent light sources. It has been demonstrated that, after annealing, the pulsed magnetron sputtering process produced photo-active surfaces and that the activity of the coatings under exposure to fluorescent lamps was some 35%–45% of that observed under exposure to UV lamps. Full article

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