Disinfection of Ocular Cells and Tissues by Atmospheric-Pressure Cold Plasma

Background: Low temperature plasmas have been proposed in medicine as agents for tissue disinfection and have received increasing attention due to the frequency of bacterial resistance to antibiotics. This study explored whether atmospheric-pressure cold plasma (APCP) generated by a new portable device that ionizes a flow of helium gas can inactivate ocular pathogens without causing significant tissue damage. Methodology and Principal Findings: We tested the APCP effects on cultured Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, Candida albicans, Aspergillus fumigatus and Herpes simplex virus-1, ocular cells (conjunctival fibroblasts and keratocytes) and ex-vivo corneas. Exposure to APCP for 0.5 to 5 minutes significantly reduced microbial viability (colony-forming units) but not human cell viability (MTT assay, FACS and Tunel analysis) or the number of HSV-1 plaque-forming units. Increased levels of intracellular reactive oxygen species (ROS) in exposed microorganisms and cells were found using a FACS-activated 2',7'-dichlorofluorescein diacetate probe. Immunoassays demonstrated no induction of thymine dimers in cell cultures and corneal tissues. A transient increased expression of 8-OHdG, genes and proteins related to oxidative stress (OGG1, GPX, NFE2L2) was determined in ocular cells and corneas by HPLC, qRT-PCR and Western blot analysis. Conclusions: A short application of APCP appears to be an efficient and rapid ocular disinfectant for bacteria and fungi without significant damage on ocular cells and tissues, although the treatment of conjunctival fibroblasts and keratocytes caused a time-restricted generation of intracellular ROS and oxidative stress-related responses

Bacterial Inactivation of Wound Infection in a Human Skin Model by Liquid-Phase Discharge Plasma

Background: We investigate disinfection of a reconstructed human skin model contaminated with biofilm-formative Staphylococcus aureus employing plasma discharge in liquid. Principal Findings: We observed statistically significant 3.83-log10 (p,0.001) and 1.59-log10 (p,0.05) decreases in colony forming units of adherent S. aureus bacteria and 24 h S. aureus biofilm culture with plasma treatment. Plasma treatment was associated with minimal changes in histological morphology and tissue viability determined by means of MTT assay. Spectral analysis of the plasma discharge indicated the presence of highly reactive atomic oxygen radicals (777 nm and 844 nm) and OH bands in the UV region. The contribution of these and other plasma-generated agents and physical conditions to the reduction in bacterial load are discussed. Conclusions: These findings demonstrate the potential of liquid plasma treatment as a potential adjunct therapy for chronic wounds

Autoignition quality of gasoline fuels in partially premixed combustion in diesel engines

A single-cylinder diesel engine has been run on gasolines of different octane numbers and on model fuels, mixtures of iso-octane, n-heptane and toluene, at different operating conditions. The autoignition quality of the fuel is best described by an Octane Index, OI = (1 - K) . RON + K . MON for fuels in the gasoline autoignition range where RON and MON are, respectively, the Research and Motor Octane numbers and K is an empirical constant which is measured to be negative. Hence for a given RON, a non-paraffinic fuel, of lower MON, will have higher OI and more resistance to autoignition. For a given operating condition, ignition delay increases non-linearly with OI and changes little over the autoignition range of practical diesel fuels. Heat release following the autoignition is influenced by the stratification which will increase as the time between the end of injection and start of combustion decreases and combustion phasing parameters such as Combustion Delay, the difference between the 50% burn time and the start of injection, become less correlated with fuel autoignition quality. Higher ignition delays facilitate premixed combustion in the diesel engine. If two fuels have similar combustion phasing at the same injection timing, their emissions performance is also similar. Hence a good surrogate for gasoline in partially premixed compression ignition engines is a mixture of toluene, iso-octane and n-heptane with the same RON and MON. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved

Surrogate fuels for premixed combustion in compression ignition engines

Simple surrogate fuels are needed to model practical fuels, which are complex mixtures of hydrocarbons. The surrogate fuel should match the combustion and emissions behaviour of the target fuel as much as possible. This paper presents experimental results using a wide range of fuels in both the gasoline and diesel auto-ignition range, but of different volatilities and compositions, in a single cylinder diesel engine. Premixed combustion in a compression ignition engine is defined, in this paper, to occur when the injection event is clearly separated from the combustion and the engine-out smoke is very low - below 0.05 FSN (filter smoke number). Under such circumstances, if the combustion phasing is matched for two fuels at a given operating condition and injection timing, the emissions are also comparable regardless of the differences in composition and volatility. For the experimental conditions considered, combustion phasing at a given operating condition and injection timing depends only on the octane index (OI), OI = (1-K)RON + KMON, where RON and MON are research and motor octane numbers and K is an empirical constant that depends on operating conditions. A mixture of iso-octane, n-heptane and toluene can be found to match the RON and MON of any practical gasoline and will be a very good surrogate for the gasoline since it will have the same OI. If the compression ratio is greater than 14, practical diesel fuels, with DCN (derived cetane number) between 40 and 60, will have comparable ignition delays to n-heptane, which is an adequate surrogate for such fuels. However, premixed combustion can be attained only at much lower loads at a given speed with diesel fuels compared to gasolines