E. Stoffels

Plasma needle for in vivo medical treatment: recent developments and perspectives

In this paper we describe the hitherto unravelled facts on the interactions of a cold atmospheric plasma with living cells and tissues. A specially designed source, plasma needle, is a low-power discharge, which operates under the threshold of tissue damage. When applied properly, the needle does not cause fatal cell injury which would result in cell death (necrosis). Instead, it allows precise and localized cell removal by means of the so-called cell detachment. In addition, plasma can be used for bacterial disinfection. Because of mild treatment conditions, plasma disinfection can be performed in vivo, e.g. on wounds and dental cavities. Presently, one strives to obtain a better control of the operating device. Therefore, plasma has been characterized using a variety of diagnostics, and a smart system has been designed for the positioning of the device with respect to the treated surface.

Cold Atmospheric Plasma: Charged Species and Their Interactions With Cells and Tissues

Cold atmospheric plasma (CAP) treatment of living tissues becomes a popular topic in modern plasma physics and in medical sciences. The plasma is capable of bacterial inactivation and noninflammatory tissue modification, which makes it an attractive tool for wound healing and the treatment of skin diseases and dental caries. There are still many open issues with regard to the mechanisms of action of the plasma on bacteria and mammalian cells and tissues, both from the biological and the physical perspective. For example, the chemistry of CAP and the exact roles of various plasma constituents in tissue treatment are not yet fully resolved. In this paper, we shall concentrate on the charged species (electrons and ions) in the plasma. The selected physical properties of typical atmospheric plasma sources will be discussed; experiments will be confronted with theoretical considerations, and several biomedical aspects of CAP treatment will be surveyed.

Plasma treatment of dental cavities: a feasibility study

Much effort is invested in the development of tissue-saving methods in dentistry. Cleaning and sterilization of infected tissue in a dental cavity or in a root channel can be accomplished using mechanical or laser techniques. However, with both approaches, heating and destruction of healthy tissue can occur. Recently, a nonthermal atmospheric plasma (plasma needle) has been developed. In this work, the interactions of this plasma with dental tissue is studied, and its capability of bacterial inactivation is tested. A plasma needle is an efficient source of various radicals, which are capable of bacterial decontamination; however, it operates at room temperature and thus, does not cause bulk destruction of the tissue. Plasma treatment is potentially a novel tissue-saving technique, allowing irregular structures and narrow channels within the diseased tooth to be cleaned.

Superficial treatment of mammalian cells using plasma needle

Interactions of a small-size, non-thermal plasma (plasma needle) with living cells in culture are studied. We have demonstrated the non-destructive character of the plasma needle: under moderate conditions (low-power and low concentration of molecular species) the plasma needle does not heat biological samples and does not induce cell death. Treatment of living cells is restricted to the cell exterior (membrane). As a result of the interactions of plasma radicals with cell adhesion molecules, cell attachment is temporarily interrupted; the loose cells can be removed, reattached or transferred. This effect may prove very useful in fine surgery, where a part of the tissue must be removed with high-precision, without damage to the adjacent cells and without inflammatory reaction.

Deactivation of Escherichia coli by the plasma needle

In this paper we present a parameter study on deactivation of Escherichia coli (E. coli) by means of a non-thermal plasma (plasma needle). The plasma needle is a small-sized (1 mm) atmospheric glow sustained by radio-frequency excitation. This plasma will be used to disinfect heat-sensitive objects; one of the intended applications is in vivo deactivation of dental bacteria: destruction of plaque and treatment of caries. We use E. coli films plated on agar dishes as a model system to optimize the conditions for bacterial destruction. Plasma power, treatment time and needle-to-sample distance are varied. Plasma treatment of E. coli films results in formation of a bacteria-free void with a size up to 12 mm. 104–105 colony forming units are already destroyed after 10 s of treatment. Prolongation of treatment time and usage of high powers do not significantly improve the destruction efficiency: short exposure at low plasma power is sufficient. Furthermore, we study the effects of temperature increase on the survival of E. coli and compare it with thermal effects of the plasma. The population of E. coli heated in a warm water bath starts to decrease at temperatures above 40°C. Sample temperature during plasma treatment has been monitored. The temperature can reach up to 60°C at high plasma powers and short needle-to-sample distances. However, thermal effects cannot account for bacterial destruction at low power conditions. For safe and efficient in vivo disinfection, the sample temperature should be kept low. Thus, plasma power and treatment time should not exceed 150 mW and 60 s, respectively.

Killing of S. mutans Bacteria Using a Plasma Needle at Atmospheric Pressure

Streptococcus mutans (S. mutans) bacteria were killed using a low-power millimeter-size atmospheric-pressure glow-discharge plasma or plasma needle. The plasma was applied to a culture of S. mutans that was plated onto the surface of an agar nutrient in a Petri dish. S. mutans is the most important microorganism for causing dental caries. A spatially resolved biological diagnostic of the plasma is introduced, where the spatial pattern of bacterial colonies in the sample was imaged after plasma treatment and incubation. For low-power conditions that would be attractive for dentistry, images from this biological diagnostic reveal that S. mutans was killed within a solid circle with a 5-mm diameter, demonstrating that site-specific treatment is possible. For other conditions, which are of interest for understanding plasma transport, images show that bacteria were killed with a ring-shaped spatial pattern. This ring pattern coincides with a similar ring in the spatial distribution of energetic electrons, as revealed by Abel-inverted images of the glow. The presence of the radicals OH and O was verified using optical-emission spectroscopy

Reattachment and Apoptosis After Plasma-Needle Treatment of Cultured Cells

Nonthermal plasmas can be used to locally influence cell adhesion: cells can be removed from their surroundings without causing necrosis. In fact, cells remain alive and can reattach within hours. This phenomenon may, in the future, be used for microsurgical procedures. Another method to remove cells is to induce apoptosis or programmed cell death. This type of cell death is preferred above necrosis, which may cause inflammation reactions. When the detached cells are allowed to reattach and grow, it is important to know their condition. Therefore, long-term effects of plasma-needle treatment were assessed, with special focus on reattachment and apoptosis. The cells were treated using a plasma needle. This device generates a small (1-mm diameter) plasma at atmospheric pressure. To avoid any heat effects, it is important that the plasma temperature is at or below physiological temperature. This is the case for the plasma needle

Electrical and optical characterization of the plasma needle

The plasma needle is a source to create a non-thermal radiofrequency plasma at atmospheric pressure. To improve the ease of working on biological samples, a flexible plasma probe was designed. In the new configuration, the needle was confined in a plastic tube through which helium flow was supplied. The new set-up was characterized by impedance measurements and emission spectroscopy. Impedance measurements were performed by means of an adjustable matching network; the results were modelled. The discharge was found to be entirely resistive; the measured voltage was in the range 140–270 Vrms and it was in excellent agreement with model results. From the resistance, the electron density was estimated to be 1017 m−3.Optical measurements showed substantial UV emission in the range 300–400 nm. Active oxygen radicals ( and ) were detected. Furthermore, the influence of helium flow speed was investigated. At low flow speeds, the density of molecular species in the plasma increased.UV emission and density of active species are important factors that determine the performance of plasma in the treatment of biological materials. Therefore, the new characterization will help us to understand and optimize the interactions of atmospheric plasma with cells and tissues.

Plasma treatment of mammalian vascular cells: a quantitative description

For the first time, quantitative data was obtained on plasma treatment of living mammalian cells. The nonthermal atmospheric discharge produced by the plasma needle was used for treatment of mammalian endothelial and smooth muscle cells. The influence of several experimental parameters on cell detachment and necrosis was tested using cell viability assays. Interruption of cell adhesion (detachment) was the most important cell reaction to plasma treatment. Treatment times of 10 s were enough to detach cells in the cultured cell sheet. Under extreme conditions, cell necrosis occurred. Cell detachment without necrosis could be achieved at low voltages. It was shown that the thickness of the liquid layer covering the cells was the most important factor, which had more influence than treatment time or applied voltage. The results show no remarkable differences between the responses of the two cell types.

The effects of UV irradiation and gas plasma treatment on living mammalian cells and bacteria: a comparative approach

Living mammalian cells and bacteria were exposed to irradiation from narrow-band UV lamps and treated with a nonthermal gas plasma (plasma needle). The model systems were: Chinese Hamster Ovary (CHO-K1) cells (fibroblasts) and Escherichia Coli bacteria. UV irradiation can lead to cell death (necrosis) in fibroblasts, but the doses that cause such damage are much higher than those needed to destroy Escherichia Coli. The usage of UV radiation in combination with active oxygen radicals lowers the UV dose sufficient to kill the cells. However, in any case the fibroblasts seem to be fairly resistant to UV radiation and/or radicals. Possibly, the lamps may be used for decontamination of infected wounds. The most important active species in an atmospheric plasma are the radicals; the role of UV is less pronounced. Treatment of CHO-K1 cells with the plasma needle can lead to cell necrosis under extreme conditions, but moderate doses cause only a temporary interruption of cell adhesion. Plasma needle may be used for fine tissue treatment (e.g., controlled cell removal without inflammation) and also for bacterial decontamination.