R E J Sladek

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.

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.

Plasma-Needle Treatment of Substrates With Respect to Wettability and Growth of Escherichia coli and Streptococcus mutans

In this paper, surface modification of various materials exposed to a nonthermal atmospheric plasma is investigated. The used source is the plasma needle: a radio-frequency-driven nonthermal atmospheric microplasma. A number of substrates (Perspex and polystyrene) were treated with the plasma needle. The modification of materials was subsequently identified as hydrophilization of the surface and was experimentally validated by water-contact-angle measurements. Furthermore, the effect of this modification on the growth of two bacterial species, which are the Escherichia coli and Streptococcus mutans, is studied. The bacteria were cultured on treated and nontreated polystyrene 96-well plates; the growth of E. coli on the treated substrates was enhanced, while for S. mutans, it was reduced. An explanation of these effects is provided

Plasma interactions with living cells

Summary form only given. In pursuit of minimum-invasive surgery one has to develop techniques, that allow specific cell removal or rearrangement without influencing the whole tissue. In conventional or laser surgery individual cells undergo accidental cell death (necrosis), which is followed by inflammation and may lead to permanent tissue damage. In contrast, cold plasma techniques allow cell removal without necrosis. At the Eindhoven University a suitable small-size plasma source has been developed (plasma needle) and several potentially beneficial plasma-cell interactions have been identified. These reactions include: cell detachment without affecting cell viability, induction of apoptosis (programmed cell death), and altering cell proliferation rate. So far the tests have been performed on cells in culture (mouse fibroblasts or human epithelial cells of lung carcinoma), but recently we have introduced a new model: tissue engineered skin. The effect of plasma-induced cell detachment has been already identified in this model. At present we check for early markers of tissue damage and differentiation of keratinocytes after plasma treatment. In parallel, we continue the study on mouse fibroblasts. MTT assay for long-term viability has been performed. Cell proliferation rate has been monitored using the BrdU assay (a marker for newly formed DNA). A strong link between the plasma properties and triggered cell reactions is expected. Moderate cell damage, which leads to (reversible) detachment or apoptosis, may result from interactions with plasma-produced radicals. The ROS (reactive oxygen species) are known to play an important role in these processes. We have shown that plasma radicals can exist in the liquid phase (cell culture medium). Micro-molar concentrations of ROS from the plasma have been detected using a fluorescent probe in combination with (confocal) LIF, and correlated with gas-phase plasma properties. We conclude that ROS concentrations are within the safe range: the radicals can trigger specific cell reactions, but are unable to kill the cells.

Power outflux from the plasma: an important parameter in surface processing

In this work we characterize a low-power radio-frequency atmospheric plasma (plasma needle) in terms of dissipated (input) and emitted power per unit surface (power outflux). The plasma is a non-thermal source, used for treatment of biological tissues and other vulnerable surfaces. A calibrated thermal probe is used to determine the power emitted from the plasma towards treated surfaces. Transmission of the emitted plasma power through various media (solid layers, fluids and physiological media) is studied for a broad range of plasma conditions. These data give insight into various contributions to the power outflux (thermal conduction, radiation and energetic species), as well as the penetration depth of the plasma into treated objects. The power outflux is shown to be a very important parameter, which determines the performance of the plasma tool. For the effectiveness and reproducibility of the process the power outflux is much more important than the nominal power setting. Thus, a thermal probe should become a standard control unit in surface processing reactors.

Towards Plasma Surgery: Plasma Treatment of Living Cells

The physical, biological and technical background for high-precision plasma surgery is prepared in a multi-disciplinary team. The aim of the research is to achieve controlled removal of diseased cells and bacteria without harming the healthy rest of the tissue. For this purpose, a small, cold, flexible and non-toxic plasma is developed (the plasma needle) and tested on cultured cells and bacterial samples. The needle is an atmospheric discharge induced by a radio-frequency voltage applied to a metal pin. This plasma operates at room temperature, in the milliwatt power regime; it poses no risk of thermal or electrical damage to living tissues. Several beneficial responses of living cells to plasma treatment have been already identified. Plasma does not cause accidental cell death (necrosis), which leads to inflammation and tissue damage. Instead, it allows to detach cells from each other and from the scaffold, and thus to remove them in a non-destructive way. Moreover, plasma is capable of bacterial inactivation. I parallel, we have determined the electrical and optical properties of the plasma and found a method of precise positioning of the plasma needle with respect to the treated tissue.

Investigation of possibilities of plasma treatment for dental caries

Much effort is invested in 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 laser techniques, but in addition to being too expensive, lasers cannot perform superficial treatment of an irregular surface. Recently, a non-thermal atmospheric plasma has been developed and its interactions with living objects have been studied [E. Stoffels, 2002]. Plasma is an efficient source of various radicals, capable of bacterial decontamination, while it operates at room temperature and does not cause bulk destruction of the tissue. Plasma treatment is potentially a novel tissue-saving technique, allowing to clean irregular structures and narrow channels within the diseased tooth.