Slow Dynamics in a Quasi-Two-Dimensional Binary Complex Plasma.

Slow dynamics in an amorphous quasi-two-dimensional complex plasma, comprised of microparticles of two different sizes, was studied experimentally. The motion of individual particles was observed using video microscopy, and the self-part of the intermediate scattering function as well as the mean-squared particle displacement was calculated. The long-time structural relaxation reveals the characteristic behavior near the glass transition. Our results suggest that binary complex plasmas can be an excellent model system to study slow dynamics in classical supercooled fluids.

Interparticle Attraction in 2D Complex Plasmas.

Complex (dusty) plasmas allow experimental studies of various physical processes occurring in classical liquids and solids by directly observing individual microparticles. A major problem is that the interaction between microparticles is generally not molecularlike. In this Letter, we propose how to achieve a molecularlike interaction potential in laboratory 2D complex plasmas. We argue that this principal aim can be achieved by using relatively small microparticles and properly adjusting discharge parameters. If experimentally confirmed, this will make it possible to employ complex plasmas as a model system with an interaction potential resembling that of conventional liquids.

Collective effects in vortex movements in complex plasmas.

We study the onset and characteristics of vortices in complex (dusty) plasmas using two-dimensional simulations in a setup modeled after the PK-3 Plus laboratory. A small number of microparticles initially self-arranges in a monolayer around the void. As additional particles are introduced, an extended system of vortices develops due to a nonzero curl of the plasma forces. We demonstrate a shear-thinning effect in the vortices. Velocity structure functions and the energy and enstrophy spectra show that vortex flow turbulence is present that is in essence of the "classical" Kolmogorov type.

Cold atmospheric plasma, a new strategy to induce senescence in melanoma cells.

Over the past few years, the application of cold atmospheric plasma (CAP) in medicine has developed into an innovative field of research of rapidly growing importance. One promising new medical application of CAP is cancer treatment. Different studies revealed that CAP may potentially affect the cell cycle and cause cell apoptosis or necrosis in tumor cells dependent on the CAP device and doses. In this study, we used a novel hand-held and battery-operated CAP device utilizing the surface micro discharge (SMD) technology for plasma production in air and consequently analysed dose-dependent CAP treatment effects on melanoma cells. After 2 min of CAP treatment, we observed irreversible cell inactivation. Phospho-H2AX immunofluorescence staining and Flow cytometric analysis demonstrated that 2 min of CAP treatment induces DNA damage, promotes induction of Sub-G1 phase and strongly increases apoptosis. Further, protein array technology revealed induction of pro-apoptotic events like p53 and Rad17 phosphorylation of Cytochrome c release and activation of Caspase-3. Interestingly, using lower CAP doses with 1 min of treatment, almost no apoptosis was observed but long-term inhibition of proliferation. H3K9 immunofluorescence, SA-ß-Gal staining and p21 expression revealed that especially these low CAP doses induce senescence in melanoma cells. In summary, we observed differences in induction of apoptosis or senescence of tumor cells in respond to different CAP doses using a new CAP device. The mechanism of senescence with regard to plasma therapy was so far not described previously and is of great importance for therapeutic application of CAP.

Randomized placebo-controlled human pilot study of cold atmospheric argon plasma on skin graft donor sites.

Cold atmospheric plasma has already been shown to decrease the bacterial load in chronic wounds. However, until now it is not yet known if plasma treatment can also improve wound healing. We aimed to assess the impact of cold atmospheric argon plasma on the process of donor site healing. Forty patients with skin graft donor sites on the upper leg were enrolled in our study. The wound sites were divided into two equally sized areas that were randomly assigned to receive either plasma treatment or placebo (argon gas) for 2 minutes. Donor site healing was evaluated independently by two blinded dermatologists, who compared the wound areas with regard to reepithelialization, blood crusts, fibrin layers, and wound surroundings. From the second treatment day onwards, donor site wound areas treated with plasma (n = 34) showed significantly improved healing compared with placebo-treated areas (day 1, p = 0.25; day 2, p = 0.011; day 3, p < 0.001; day 4, p < 0.001; day 5, p = 0.004; day 6, p = 0.008; day 7, p = 0.031). Positive effects were observed in terms of improved reepithelialization and fewer fibrin layers and blood crusts, whereas wound surroundings were always normal, independent of the type of treatment. Wound infection did not occur in any of the patients, and no relevant side effects were observed. Both types of treatment were well tolerated. The mechanisms contributing to these clinically observed effects should be further investigated.

Label-free live-cell imaging with confocal Raman microscopy.

Confocal Raman spectroscopy is a noninvasive alternative to established cell imaging methods because it does not require chemical fixation, the use of fluorescent markers, or genetic engineering. In particular, single live-cell, high-resolution imaging by confocal Raman microscopy is desirable because it allows further experiments concerning the individually investigated cells. However, to derive meaningful images from the spectroscopic data, one must identify cell components within the dataset. Using immunofluorescence images as a reference, we derive Raman spectral signatures by means of information measures to identify cell components such as the nucleus, the endoplasmic reticulum, the Golgi apparatus, and mitochondria. The extracted signatures allow us to generate representations equivalent to conventional (immuno)fluorescence images with more than three cell components at a time, exploiting the Raman spectral information alone.

Cold atmospheric air plasma sterilization against spores and other microorganisms of clinical interest.

Physical cold atmospheric surface microdischarge (SMD) plasma operating in ambient air has promising properties for the sterilization of sensitive medical devices where conventional methods are not applicable. Furthermore, SMD plasma could revolutionize the field of disinfection at health care facilities. The antimicrobial effects on Gram-negative and Gram-positive bacteria of clinical relevance, as well as the fungus Candida albicans, were tested. Thirty seconds of plasma treatment led to a 4 to 6 log(10) CFU reduction on agar plates. C. albicans was the hardest to inactivate. The sterilizing effect on standard bioindicators (bacterial endospores) was evaluated on dry test specimens that were wrapped in Tyvek coupons. The experimental D(23)(°)(C) values for Bacillus subtilis, Bacillus pumilus, Bacillus atrophaeus, and Geobacillus stearothermophilus were determined as 0.3 min, 0.5 min, 0.6 min, and 0.9 min, respectively. These decimal reduction times (D values) are distinctly lower than D values obtained with other reference methods. Importantly, the high inactivation rate was independent of the material of the test specimen. Possible inactivation mechanisms for relevant microorganisms are briefly discussed, emphasizing the important role of neutral reactive plasma species and pointing to recent diagnostic methods that will contribute to a better understanding of the strong biocidal effect of SMD air plasma.

Contact-free inactivation of Candida albicans biofilms by cold atmospheric air plasma.

Candida albicans is one of the main species able to form a biofilm on almost any surface, causing both skin and superficial mucosal infections. The worldwide increase in antifungal resistance has led to a decrease in the efficacy of standard therapies, prolonging treatment time and increasing health care costs. Therefore, the aim of this work was to demonstrate the applicability of atmospheric plasma at room temperature for inactivating C. albicans growing in biofilms without thermally damaging heat-sensitive materials. This so-called cold atmospheric plasma is produced by applying high voltage to accelerate electrons, which ionize the surrounding air, leading to the production of charged particles, reactive species, and photons. A newly developed plasma device was used, which exhibits a large plasma-generating surface area of 9 by 13 cm (117 cm(2)). Different time points were selected to achieve an optimum inactivation efficacy range of ≥3 log(10) to 5 log(10) reduction in CFU per milliliter, and the results were compared with those of 70% ethanol. The results obtained show that contact-free antifungal inactivation of Candida biofilms by cold atmospheric plasma is a promising tool for disinfection of surfaces (and items) in both health care settings and the food industry, where ethanol disinfection should be avoided.

Contact-free cold atmospheric plasma treatment of Deinococcus radiodurans.

In this study we investigated the sensitivity of Deinococcus radiodurans to contact-free cold atmospheric plasma treatment as part of a project to establish new efficient procedures for disinfection of inanimate surfaces. The Gram-positive D. radiodurans is one of the most resistant microorganisms worldwide. Stationary phases of D. radiodurans were exposed to cold atmospheric plasma for different time intervals or to ultraviolet C (UVC) radiation at dose rates of 0.001-0.0656 J cm⁻², respectively. A methicillin-resistant Staphylococcus aureus strain (MRSA) served as control for Gram-positive bacteria. The surface microdischarge plasma technology was used for generation of cold atmospheric plasma. A plasma discharge was ignited using ambient air. Surprisingly, D. radiodurans was sensitive to the cold atmospheric plasma treatment in the same range as the MRSA strain. Survival of both bacteria decreased with increasing plasma exposure times up to 6 log10 cycles (>99.999 %) within 20 s of plasma treatment. In contrast, UVC radiation of both bacteria demonstrated that D. radiodurans was more resistant to UVC treatment than MRSA. Cold atmospheric plasma seems to be a promising tool for industrial and clinical purposes where time-saving is a critical point to achieve efficient disinfection of inanimate surfaces and where protection from corrosive materials is needed.

Primary cold atmospheric plasma combined with low dose cisplatin as a possible adjuvant combination therapy for HNSCC cells-an in-vitro study.

BACKGROUND: The aim of the present study was to examine the cytostatic effects of cold atmospheric plasma (CAP) on different head and neck squamous carcinoma (HNSCC) cell lines either in isolation or in combination with low dose cisplatin. The effect of CAP treatment was investigated by using three different HNSCC cell lines (chemo-resistant Cal 27, chemo-sensitive FaDu and OSC 19). MATERIALS AND METHOD: Cell lines were exposed to CAP treatment for 30, 60, 90, 120 and 180 s (s). Cisplatin was added concurrently (cc) or 24 h after CAP application (cs). Cell viability, DNA damage and apoptosis was evaluated by dye exclusion, MTT, alkaline microgel electrophoresis assay and Annexin V-Fit-C/PI respectively. RESULTS: In all cell lines, 120 s of CAP exposure resulted in a significant reduction of cell viability. DNA damage significantly increased after 60 s. Combined treatment of cells with CAP and low dose cisplatin showed additive effects. A possible sensitivity to cisplatin could be restored in Cal 27 cells by CAP application. CONCLUSION: CAP shows strong cytostatic effects in HNSCC cell lines that can be increased by concurrent cisplatin treatment, suggesting that CAP may enhance the therapeutic efficacy of low dose cisplatin.

Freezing of Lennard-Jones-type fluids.

We put forward an approximate method to locate the fluid-solid (freezing) phase transition in systems of classical particles interacting via a wide range of Lennard-Jones-type potentials. This method is based on the constancy of the properly normalized second derivative of the interaction potential (freezing indicator) along the freezing curve. As demonstrated recently it yields remarkably good agreement with previous numerical simulation studies of the conventional 12-6 Lennard-Jones (LJ) fluid [S.A.Khrapak, M.Chaudhuri, G.E.Morfill, Phys. Rev. B 134, 052101 (2010)]. In this paper, we test this approach using a wide range of the LJ-type potentials, including LJ n-6 and exp-6 models, and find that it remains sufficiently accurate and reliable in reproducing the corresponding freezing curves, down to the triple-point temperatures. One of the possible application of the method--estimation of the freezing conditions in complex (dusty) plasmas with "tunable" interactions--is briefly discussed.

Communication: Universality of the melting curves for a wide range of interaction potentials.

We demonstrate that the melting curves of various model systems of interacting particles collapse to (or are located very close to) a universal master curve on a plane of appropriately chosen scaled variables. The physics behind this universality is discussed. An equation for the emerging "universal melting curve" is proposed. The obtained results can be used to approximately predict melting of various substances in a wide range of conditions.

Accurate freezing and melting equations for the Lennard-Jones system.

Analyzing three approximate methods to locate liquid-solid coexistence in simple systems, an observation is made that all of them predict the same functional dependence of the temperature on density at freezing and melting of the conventional Lennard-Jones (LJ) system. The emerging equations can be written as T=Aρ(4)+Bρ(2) in normalized units. We suggest to determine the values of the coefficients A at freezing and melting from the high-temperature limit, governed by the inverse 12th power repulsive potential. The coefficients B can be determined from the triple point parameters of the LJ fluid. This produces freezing and melting equations which are exact in the high-temperature limit and at the triple point and show remarkably good agreement with numerical simulation data in the intermediate region.

Plasma medicine: possible applications in dermatology.

As a result of both the better understanding of complex plasma phenomena and the development of new plasma sources in the past few years, plasma medicine has developed into an innovative field of research showing high potential. While thermal plasmas have long been used in various medical fields (for instance for cauterization and sterilization of medical instruments), current research mainly focuses on application of non-thermal plasmas. Experiments show that cold atmospheric plasmas (CAPs) allow efficient, contact-free and painless disinfection, even in microscopic openings, without damaging healthy tissue. Plasmas influence biochemical processes and offer new possibilities for the selective application of individually designable medically active substances. In dermatology, new horizons are being opened for wound healing, tissue regeneration, therapy of skin infections, and probably many more diseases. First clinical trials show the efficacy and tolerability of plasma in treating infected chronic wounds. A major task will be the introduction of plasma into clinical medicine and, simultaneously, the further investigation of the mechanisms of action of plasma at the cellular level.

Solid phases in electro- and magnetorheological systems.

Ensembles of particles with a spherically symmetric repulsive Yukawa interaction and additional dipole-dipole interaction induced by an external field exhibit numerous solid-solid phase transitions controlled by the magnitude of the field. Such interactions emerge most notably in electro- and magnetorheological fluids and plasmas. We propose a simple variational approach based on the Bogoliubov inequality for determining equilibrium solid phases. Phase diagrams for several regimes are calculated and compared with previously performed Monte Carlo and molecular dynamics simulations.

Effects of cold atmospheric plasma (CAP) on bacteria and mucosa of the upper aerodigestive tract.

OBJECTIVE: Ear, nose and throat infections are among the most common reasons for absence from work. They are usually caused by various bacteria like Haemophilus influenzae, Staphylococcus aureus, Streptococcus pneumoniae and Streptococcus pyogenes. Cold atmospheric plasma (CAP) can effectively eliminate even multi-resistant bacteria and has no cytotoxic or mutagenic effects on the mucosa when applied for less than 60s. Aim of the study was to evaluate the effects of CAP on common ENT bacteria and on the mucosa of the upper aerodigestive tract. METHODS: The bactericidal effects of CAP against the bacteria most commonly causing ENT infections were investigated using the colony-forming units assay (CFU) on a Müller-Hinton agar plate after applying CAP for 30, 60, 90 and 120s. To evaluate the interaction of CAP with mucosal cells, 3D mini organ cultures were treated for up to 180s, after which cell viability and necrosis induction were evaluated. RESULTS: Treatment with CAP for 60s or longer induced at least a 3-log10 reduction in the bacterial load (> 99.9%). Treatment times shorter than 60s had only slight cytotoxic effects on cell viability and necrosis whereas treatment times above 60s showed a fast increase of cytotoxic side effects. CONCLUSION: CAP exhibited strong bactericidal effects on the most common ENT pathogens. Treatment times of up to 60s showed only minimal adverse reactions in healthy mucosa. CAP could be a promising new therapeutic modality for ENT infections.

Wakes in complex plasmas: A self-consistent kinetic theory.

In ground-based experiments with complex (dusty) plasmas, charged microparticles are levitated against gravity by an electric field, which also drives ion flow in the parent gas. Existing analytical approaches to describe the electrostatic interaction between microparticles in such conditions generally ignore the field and ion-neutral collisions, assuming free ion flow with a certain approximation for the ion velocity distribution function (usually a shifted Maxwellian). We provide a comprehensive analysis of our previously proposed self-consistent kinetic theory including the field, ion-neutral collisions, and the corresponding ion velocity distribution. We focus on various limiting cases and demonstrate how the interplay of these factors results in different forms of the shielding potential.

Effects of cold atmospheric plasma (CAP) on ß-defensins, inflammatory cytokines, and apoptosis-related molecules in keratinocytes in vitro and in vivo.

Cold atmospheric plasma (CAP) has been gaining increasing interest as a new approach for the treatment of skin diseases or wounds. Although this approach has demonstrated promising antibacterial activity, its exact mechanism of action remains unclear. This study explored in vitro and in vivo whether CAP influences gene expression and molecular mechanisms in keratinocytes. Our results revealed that a 2 min CAP treatment using the MicroPlaSter ß in analogy to the performed clinical studies for wound treatment induces expression of IL-8, TGF-ß1, and TGF-ß2. In vitro and in vivo assays indicated that keratinocyte proliferation, migration, and apoptotic mechanisms were not affected by the CAP treatment under the applied conditions. Further, we observed that antimicrobial peptides of the ß-defensin family are upregulated after CAP treatment. In summary, our results suggest that a 2 min application of CAP induces gene expression of key regulators important for inflammation and wound healing without causing proliferation, migration or cell death in keratinocytes. The induction of ß-defensins in keratinocytes describes an absolutely new plasma strategy. Activation of antimicrobial peptides supports the well-known antibacterial effect of CAP treatment, whereas the mechanism of ß-defensin activation by CAP is not investigated so far.

Inactivation of a foodborne norovirus outbreak strain with nonthermal atmospheric pressure plasma.

UNLABELLED: Human norovirus (NoV) is the most frequent cause of epidemic nonbacterial acute gastroenteritis worldwide. We investigated the impact of nonthermal or cold atmospheric pressure plasma (CAPP) on the inactivation of a clinical human outbreak NoV, GII.4. Three different dilutions of a NoV-positive stool sample were prepared and subsequently treated with CAPP for various lengths of time, up to 15 min. NoV viral loads were quantified by quantitative real-time reverse transcription PCR (RT-qPCR). Increased CAPP treatment time led to increased NoV reduction; samples treated for the longest time had the lowest viral load. From the initial starting quantity of 2.36 × 10(4) genomic equivalents/ml, sample exposure to CAPP reduced this value by 1.23 log10 and 1.69 log10 genomic equivalents/ml after 10 and 15 min, respectively (P < 0.01). CAPP treatment of surfaces carrying a lower viral load reduced NoV by at least 1 log10 after CAPP exposure for 2 min (P < 0.05) and 1 min (P < 0.05), respectively. Our results suggest that NoV can be inactivated by CAPP treatment. The lack of cell culture assays prevents our ability to estimate infectivity. It is possible that some detectable, intact virus particles were rendered noninfectious. We conclude that CAPP treatment of surfaces may be a useful strategy to reduce the risk of NoV transmission in crowded environments. IMPORTANCE: Human gastroenteritis is most frequently caused by noroviruses, which are spread person to person and via surfaces, often in facilities with crowds of people. Disinfection of surfaces that come into contact with infected humans is critical for the prevention of cross-contamination and further transmission of the virus. However, effective disinfection cannot be done easily in mass catering environments or health care facilities. We evaluated the efficacy of cold atmospheric pressure plasma, an innovative airborne disinfection method, on surfaces inoculated with norovirus. We used a clinically relevant strain of norovirus from an outbreak in Germany. Cold plasma was able to inactivate the virus on the tested surfaces, suggesting that this method could be used for continuous disinfection of contaminated surfaces. The use of a clinical strain of norovirus strengthens the reliability of our results as it is a strain relevant to outbreaks in humans.