Angela M. Bowman

Cold atmospheric pressure air plasma jet for medical applications

By flowing atmospheric pressure air through a direct current powered microhollow cathode discharge, we were able to generate a 2cm long plasma jet. With increasing flow rate, the flow becomes turbulent and temperatures of the jet are reduced to values close to room temperature. Utilizing the jet, yeast grown on agar can be eradicated with a treatment of only a few seconds. Conversely, animal studies show no skin damage even with exposures ten times longer than needed for pathogen extermination. This cold plasma jet provides an effective mode of treatment for yeast infections of the skin.

Plasma Membrane Permeabilization by Trains of Ultrashort Electric Pulses

Ultrashort electric pulses (USEP) cause long-lasting increase of cell membrane electrical conductance, and that a single USEP increased cell membrane electrical conductance proportionally to the absorbed dose (AD) with a threshold of about 10 mJ/g. The present study extends quantification of the membrane permeabilization effect to multiple USEP and employed a more accurate protocol that identified USEP effect as the difference between post- and pre-exposure conductance values (Deltag) in individual cells. We showed that Deltag can be increased by either increasing the number of pulses at a constant E-field, or by increasing the E-field at a constant number of pulses. For 60-ns pulses, an E-field threshold of 6 kV/cm for a single pulse was lowered to less than 1.7 kV/cm by applying 100-pulse or longer trains. However, the reduction of the E-field threshold was only achieved at the expense of a higher AD compared to a single pulse exposure. Furthermore, the effect of multiple pulses was not fully determined by AD, suggesting that cells permeabilized by the first pulse(s) in the train become less vulnerable to subsequent pulses. This explanation was corroborated by a model that treated multiple-pulse exposures as a series of single-pulse exposures and assumed an exponential decline of cell susceptibility to USEP as Deltag increased after each pulse during the course of the train.

Gadolinium blocks membrane permeabilization induced by nanosecond electric pulses and reduces cell death

It has been widely accepted that nanosecond electric pulses (nsEP) are distinguished from micro- and millisecond duration pulses by their ability to cause intracellular effects and cell death with reduced effects on the cell plasma membrane. However, we found that nsEP-induced cell death is most likely mediated by the plasma membrane disruption. We showed that nsEP can cause long-lasting (minutes) increase in plasma membrane electrical conductance and disrupt electrolyte balance, followed by water uptake, cell swelling and blebbing. These effects of plasma membrane permeabilization could be blocked by Gd(3+) in a dose-dependent manner, with a threshold at sub-micromolar concentrations. Consequently, Gd(3+) protected cells from nsEP-induced cell death, thereby pointing to plasma membrane permeabilization as a likely primary mechanism of lethal cell damage.

Nanosecond-Duration Electric Pulses Open Nanometer-Size Pores in Cell Plasma Membrane

We found that ultra-short electric pulses (60 or 600 ns duration) applied to mammalian cells cause profound, dose-dependent increase of plasma membrane electrical conductance. This effect is detectable even minutes after the exposure and is explained by formation of long-lived, voltagesensitive, inward-rectifying pores of nanometer diameter (”nanopores”). The phenomenon of nanoelectroporation and the extended lifetime of nanopores can also be demonstrated by a surge of Tl + uptake in the presence of K + channel blockers, as well as in CHO cells that express no endogenous voltage-gated K + channels. Due to their long lifetime, nanopores can have significant impact on cell physiology.

Treatment of skin infections with DC operated afterglow air plasma jet

We have developed a non-thermal plasma jet, which is generated with a dc voltage from ambient air1. By flowing air through the channel of a microhollow cathode discharge geometry at rates of 7-15 Ltr/min, a 10-20-mm long afterglow plasma plume is observed. The temperature in this expelled afterglow plasma reaches values that are close to room temperature at a distance of 5 mm from the discharge origin. Emission spectra show that atomic oxygen, hydroxyl ions and various nitrogen compounds are generated in the discharge and are driven out with the gas flow. These radicals are considered highly effective in the decontamination and sterilization of surfaces. We have investigated the effectiveness of this microplasma jet against notoriously difficult to treat yeast infections. In an in vitro study, complete eradication of Candida kefyr (a model for Candida albicans - the most common yeast infection) could be achieved with an exposure of 90 seconds at distances of 10 mm and more. Other pathogens that were tested, also respond well. The safety of the treatment was studied by an in vivo skin model. The exposure of healthy skin to the plasma jet, when using the same treatment parameters as for the in vitro studies, and even a treatment with a ten times higher dose, did not result in any damage. Possible interaction mechanisms were investigated. Treatment parameters, such as the penetration depth of radicals into skin, were studied with skin substitutes.

DC operated atmospheric pressure air plasma jet for biomedical applications

We have previously presented a gas discharge assembly based on a microhollow cathode geometry which can be operated with a dc current at atmospheric pressure with ambient air1. By flowing air through the discharge channel at a rate of about 7 Ltr/min a 10-20-mm long plume is observed. The temperature in this expelled afterglow plasma reaches values that are close to room temperature at a distance of 5 mm from the discharge origin. Emission spectra show that atomic oxygen, hydroxyl ions and various nitrogen compounds are generated in the discharge and are driven out with the gas flow. The most prominent secondary discharge product, ozone, is detected in high concentrations. The low heavy-particle temperature allows us to use this exhaust stream on biological samples and tissues without thermal damage. The high levels of reactive species suggest an effective treatment for pathological skin conditions caused, in particular, by infectious agents. In the first experiments, we have successfully tested the efficacy of this afterglow plasma on Candida kefyr (a yeast), E.coli (bacteria), and a matching E.coli strain-specific virus, 0X174 (a bacteriophage). All pathogens investigated responded well to the treatment. In the yeast case, complete eradication of the organism in the treated area could be achieved with an exposure of 90 seconds at a distance of 5 mm. A 10-fold increase of exposure, to 900 seconds caused no observable damage to murine integument. The quantification of the response, and studies of possible mechanisms are underway.