Jennifer L. Zirnheld

Preferential induction of apoptotic cell death in melanoma cells as compared with normal keratinocytes using a non-thermal plasma torch

Selective induction of apoptosis in melanoma cells is optimal for therapeutic development. To achieve this goal, a non-thermal helium plasma torch was modified for use on cultured cells in a temperature-controlled environment. Melanoma cells were targeted with this torch (1) in parallel cultures with keratinocytes, (2) in co-culture with keratinocytes and (3) in a soft agar matrix. Melanoma cells displayed high sensitivity to reactive oxygen species generated by the torch and showed a 6-fold increase in cell death compared with keratinocytes. The extent of cell death was compared between melanoma cells and normal human keratinocytes in both short-term (5 min) co-culture experiments and longer assessments of apoptotic cell death (18–24 h). Following a 10 sec plasma exposure there was a 4.9-fold increase in the cell death of melanoma vs. keratinocytes as measured after 24 h at the target site of the plasma beam. When the treatment time was increased to 30 sec, a 98% cell death was reported for melanoma cells, which was 6-fold greater than the extent of cell death in keratinocytes. Our observations further indicate that this preferential cell death is largely due to apoptosis.. In addition, we report that this non-thermal plasma torch kills melanoma cells growing in soft agar, suggesting that the plasma torch is capable of inducing melanoma cell death in 3D settings. We demonstrate that the presence of gap junctions may increase the area of cell death, likely due to the “bystander effect” of passing apoptotic signals between cells. Our findings provide a basis for further development of this non-invasive plasma torch as a potential treatment for melanoma.

Nonthermal Plasma Needle: Development and Targeting of Melanoma Cells

A nonthermal plasma torch has been developed to study the targeted killing of melanoma cells. In this paper, 1205Lu melanoma cells and keratinocytes were exposed to the plasma. These cells were transfected with green fluorescent protein in order to establish a system for coculture with primary keratinocytes. Results show that a 10 s treatment with plasma causes a morphological change in the melanoma cells, as observed after 18 h. However, after only 15 min following plasma treatment, a significant killing of melanoma cells was observed, with a much reduced killing of keratinocytes. Nonthermal plasma may serve as an effective tool for future therapeutic cancer treatment.

Partial discharge analysis of prestretched and unstretched acrylic elastomers for Dielectric Elastomer Actuators (DEA)

Partial discharges (PD) occur in solid insulating materials when the insulating material is partially bridged by an electrical discharge in response to an applied voltage stress. PDs typically occur at localized points of high field stresses or at voids and other inhomogeneities within the insulator. The applied fields effect on the frequency of occurrence and intensity of PDs can be used to assess the electrical breakdown strength and aging characteristics of insulating materials. PD testing is therefore a promising characterization method to understand the insulating properties of the elastomers and geometries commonly used in DEAs. Prestretched (~100% and ~230% biaxial) and unstretched acrylic elastomers (3M VHB tapes) with solid metal electrodes have been tested. We have found the number and intensity of PDs increase with applied field, and that a significant number of PDs are detected before any actuation was visibly observed, implying that the fields required for actuation will cause material aging and degradation over time. Most interestingly, the number of PDs steadily increase as the applied voltage increases up to a sufficiently high voltage, where the PDs suddenly cease. Since internal voids can cause PDs, this may indicate that the Maxwell stress minimized the thickness of or eliminated these voids, which could explain how prestretching improves performance.

Electric Explosion of Aluminum Metallized Film

Two types of capacitor-grade aluminum metallized polypropylene film were studied to investigate the factors that affect specific action integral and energy dissipation in the electrical explosion of a film, a phenomenon that occurs when a film is exposed to a high-density current pulse on the order of 107 - 108 A/cm2. The factors studied include film cross-sectional area, film length, film sheet resistance, and discharge circuit inductance. All film samples were subjected to a 2.5-kV capacitive discharge. The basic principles of the exploding-film phenomenon and the detailed effects of the stated factors are discussed.

Temporal Analysis of Exploding Film Burst Phenomenon

A technique to determine the time of burst for exploding aluminum metallized films has been studied. An experimental approach has been taken to determine the burst time relative to the discharge current, voltage, resistance, and power waveforms. A microphone transducer was employed to detect the time of burst from the sound produced by the bursting of the film and was compared to the calculated burst times. A theoretical discussion on the energy needed to melt and vaporize the film is also presented and compared to the experimental results.

Anticipating electrical breakdown in dielectric elastomer actuators

The output strain of a dielectric elastomer actuator is directly proportional to the square of its applied electric field. However, since the likelihood of electric breakdown is elevated with an increased applied field, the maximum operating electric field of the dielectric elastomer is significantly derated in systems employing these actuators so that failure due to breakdown remains unlikely even as the material ages. In an effort to ascertain the dielectric strength so that stronger electric fields can be applied, partial discharge testing is used to assess the health of the actuator by detecting the charge that is released when localized instances of breakdown partially bridge the insulator. Pre-stretched and unstretched samples of VHB4910 tape were submerged in dielectric oil to remove external sources of partial discharges during testing, and the partial discharge patterns were recorded just before failure of the dielectric sample.

Effect of Substrate Thickness on Exploding Films

The exploding wire phenomenon is well researched due to its vast and practical applications which include, but are not limited to, shock wave generation, pulsed power, Z pinch physics, plasma ignition, fuses, and fusing applications. However, the focus of this research is on a surrogate for exploding wires. In this research, metallized capacitor grade-polypropylene film was used as an alternative for the traditional wire of a uniform diameter. The films that were studied have a broad variety of thicknesses ranging from 7 micron to 5 mil, lengths ranging from 5.08 cm to 19.05 cm, and sheet resistances of 1 ohm/square and 7 ohms/square. These films were used to study the effect of film properties on the transient plasma generation mechanism when exposed to a rapid high voltage discharge. The effect of these properties can be seen in the current waveform, similar to that of a uniform diameter exploding wire. By precisely understanding how the film properties affect the transient plasma formation, one can fine tune these variables to control the resulting characteristic pulse wave shape to fit a desired application.

Partial discharge monitoring in dielectric elastomer actuators

Dielectric elastomer actuators represent an interesting use of dielectric materials for two reasons. First, being a soft material that is designed to exert mechanical strains, the aging and dielectric breakdown mechanisms are often the result of mechanical phenomena less common in other high voltage insulating systems that use rigid dielectrics selected solely for their electrical properties. Secondly, these systems are rather unique in that realtime insulation health monitoring can provide meaningful insights to extend the working life of the system. Like most high voltage systems, dielectric breakdown results in the irreversible and catastrophic failure of the system. However, since the system can be used at lower operating voltages, albeit at a lower effectiveness, if the operating voltage can be lowered as the dielectric shows signs of aging, the useful life of the system can be extended. Partial discharge testing has been used to assess the health of the polymer films used in these systems, and the procedures for real-time monitoring of partial discharges are explored in this paper.

Examination of Initial Strike and Restrike Modes in Exploding Metallized Films

The discharge modes of a capacitive exploding metallized film setup are discerned. Long exposure still images of the plasma formation during the initial strike and restrike are presented.

Investigation of Surface Flashover on Dielectrics Enhanced by Excimer Laser Processing

One of the factors that contributes to surface flashover on dielectrics is the existence of defects on the surface of the material. For our studies, excimer laser processing was utilized on alumina dielectrics in an attempt to substantially increase the threshold voltages for flashover. Through excimer laser processing, the surface material melts and re-crystallizes to form a uniform surface structure. The defects on the dielectric surface can be minimized, reducing charge trapping, leading to higher flashover voltages. Two sets of samples were tested. The first set of samples was processed using the laser and the second set was not. The samples were then stressed under high voltage to induce surface flashover. Analysis of the effects of the excimer laser processing was performed and are shown