Eckhard Kindel

Atmospheric-pressure plasma sources: Prospective tools for plasma medicine

Plasma-based treatment of chronic wounds or skin diseases as well as tissue engineering or tumor treatment is an extremely promising field. First practical studies are promising, and plasma medicine as an independent medical field is emerging worldwide. While during the last years the basics of sterilizing effects of plasmas were well studied, concepts of tailor-made plasma sources which meet the technical requirements of medical instrumentation are still less developed. Indeed, studies on the verification of selective antiseptic effects of plasmas are required, but the development of advanced plasma sources for biomedical applications and a profound knowledge of their physics, chemistry, and parameters must be contributed by physical research. Considering atmospheric-pressure plasma sources, the determination of discharge development and plasma parameters is a great challenge, due to the high complexity and limited diagnostic approaches. This contribution gives an overview on plasma sources for therapeutic applications in plasma medicine. Selected specific plasma sources that are used for the investigation of various biological effects are presented and discussed. Furthermore, the needs, prospects, and approaches for its characterization from the fundamental plasma physical point of view will be discussed.

Antimicrobial treatment of heat sensitive products by miniaturized atmospheric pressure plasma jets (APPJs)

The technological potential of non-thermal plasmas for the antimicrobial treatment of heat sensitive materials is well known. Despite a multitude of scientific activities with considerable progress within the last few years, the realization of industrial plasma-based decontamination or sterilization technology remains a great challenge. This may be due to the fact that an antimicrobial treatment process needs to consider all properties of the product to be treated as well as the requirements of the complete procedure, e.g. a reprocessing cycle of medical instruments. The aim of this work is to demonstrate the applicability of plasma-based processes for the antimicrobial treatment on selected heat sensitive products. The strategy is to use modular, selective and miniaturized plasma sources, which are driven at atmospheric pressure and adaptable to the products to be treated.

Skin decontamination by low-temperature atmospheric pressure plasma jet and dielectric barrier discharge plasma

BACKGROUND Over the past few years, plasma medicine has become an important field in medical science. Cold plasma has proven anti-inflammatory, antimicrobial and antineoplastic effects. AIM To test the decontamination power of two cold plasma sources [low-temperature atmospheric pressure plasma jet (APPJ) and dielectric barrier discharge plasma (DBD)] in vivo on human fingertips. METHODS After 3, 15, 30, 60, 90, 120, 150, 180, 210 and 240 s of spot treatment with the APPJ and DBD, the log reduction factors (RFs) of physiological (PF) and artificially (AF) contaminated flora (Staphylococcus epidermidis and Micrococcus luteus) were calculated. The bacterial load was determined after counting. Tolerance (paresthesia, pain and heat) was measured using a numerical rating scale. FINDINGS Both plasma devices led to a significant reduction in PF and AF. The maximum log reduction factors for PF were 1.3 for the DBD at 210 s and 0.8 for the APPJ at 60 s. For AF, the maximum log reduction factors were 1.7 for the DBD at 90 s and 1.4 for the APPJ at 120 s. Treatment with both devices was well tolerated. CONCLUSION Both the APPJ and DBD were highly effective in eradicating PF and AF from the fingertips of healthy volunteers. No plasma-resistant isolates were observed. Cold plasma appears to have potential for skin disinfection. For hand hygiene purposes, plasma exposure times would need to be reduced significantly by technical means.

Treatment of Candida albicans biofilms with low-temperature plasma induced by dielectric barrier discharge and atmospheric pressure plasma jet

Because of some disadvantages of chemical disinfection in dental practice (especially denture cleaning), we investigated the effects of physical methods on Candida albicans biofilms. For this purpose, the antifungal efficacy of three different low-temperature plasma devices (an atmospheric pressure plasma jet and two different dielectric barrier discharges (DBDs)) on Candida albicans biofilms grown on titanium discs in vitro was investigated. As positive treatment controls, we used 0.1% chlorhexidine digluconate (CHX) and 0.6% sodium hypochlorite (NaOCl). The corresponding gas streams without plasma ignition served as negative treatment controls. The efficacy of the plasma treatment was determined evaluating the number of colony-forming units (CFU) recovered from titanium discs. The plasma treatment reduced the CFU significantly compared to chemical disinfectants. While 10 min CHX or NaOCl exposure led to a CFU log10 reduction factor of 1.5, the log10 reduction factor of DBD plasma was up to 5. In conclusion, the use of low-temperature plasma is a promising physical alternative to chemical antiseptics for dental practice.

Antimicrobial efficacy of non‐thermal plasma in comparison to chlorhexidine against dental biofilms on titanium discs in vitro – proof of principle experiment

AIM Dental biofilms play a major role in the pathogenesis of peri-implant mucositis. Biofilm reduction is a pre-requisite for a successful therapy of peri-implant mucosal lesions. In this study, we evaluated the effect of three different plasma devices on the reduction of Streptococcus mutans (S. mutans) and multispecies human saliva biofilms. MATERIAL AND METHODS We assessed the efficacy of three different non-thermal atmospheric pressure plasma devices against biofilms of S. mutans and saliva multispecies grown on titanium discs in vitro in comparison with a chlorhexidine digluconate (CHX) rinse. Efficacy of plasma treatment was determined by the number of colony forming units (CFU) and by scanning electron microscopy. The results were reported as reduction of CFU (CFU(untreated) -CFU(treated) ). RESULTS The application of plasma was much more effective than CHX against biofilms. The maximum reduction of CHX was 3.36 for S. mutans biofilm and 1.50 for saliva biofilm, whereas the colony forming units (CFU) reduction of the volume dielectric barrier discharge argon plasma was 5.38 for S. mutans biofilm and 5.67 for saliva biofilm. CONCLUSIONS Treatment of single- and multispecies dental biofilms on titanium discs with non-thermal atmospheric pressure plasma was more efficient than CHX application in vitro. Thus, the development of plasma devices for the treatment of peri-implant mucositis may be fruitful.

Efficacy of chlorhexidine, polihexanide and tissue-tolerable plasma against Pseudomonas aeruginosa biofilms grown on polystyrene and silicone materials.

Background: The formation of biofilms is crucial in the pathogenesis of many acute and subacute microbial infections, including chronic wounds and foreign-body-related infections. Topical antimicrobial therapy with chemical antiseptics or physical treatment with tissue-tolerable plasma (TTP) may be promising to control bacterial infection. Methods: We assessed the efficacy of 0.1% chlorhexidine digluconate (CHX), 0.02 and 0.04% polihexanide (polyhexamethylene biguanide, PHMB) and of TTP against Pseudomonas aeruginosa SG81 biofilm grown in microtitre plates (polystyrene) and on silicone materials in an artificial wound fluid. Results: Overall, PHMB was as effective as CHX in reducing the total amount of biofilm (gentian violet assay) and in reducing the bacterial metabolism in biofilms (XTT assay). TTP also led to a significant reduction in colony-forming units. Conclusion: The antimicrobial activity of PHMB in biofilms is comparable to that of CHX. TTP could become an interesting physical alternative to chemical antisepsis in the future.

The hairline plasma: An intermittent negative dc-corona discharge at atmospheric pressure for plasma medical applications

A cold atmospheric pressure plasma source, called hairline plasma, for biological and medical applications has been developed. Using the physical effect of the negative dc corona discharge, a nanosecond pulsed microplasma has been created. The device produces a very thin (d∼30 μm) plasma filament with a length of up to 1.5 cm. Due to this geometrical parameters this plasma is particularly suitable for the treatment of microscopic cavities. The low plasma temperature allows to treat the human skin without any heating or painful irritation.

Cold plasma is well‐tolerated and does not disturb skin barrier or reduce skin moisture

Background: Cold plasma, a new treatment principle in dermatology based on ionic discharge delivering reactive molecular species and UV‐light, exhibits strong antimicrobial efficacy in vitro and in vivo. Before implementing plasma as new medical treatment tool, its safety must be proven, as well as assessing skin tolerance and patient acceptance.

In Vitro Killing of Clinical Fungal Strains by Low-Temperature Atmospheric-Pressure Plasma Jet

Plasma medicine is an expanding focus and offers new aspects of therapy combining potent physical partial efficacies, like such as ultraviolet, infrared, and reactive species and particles, and nowadays, many successful treatments of different illnesses have been described. Fungal skin and nail infections pose significant therapeutic and economical problems. To test the plasma susceptibility of clinical strains of the most frequently encountered fungal species involved in dermatomycosis, clinical isolates of Trichophyton interdigitale, Trichophyton rubrum, Microsporum canis, and Candida albicans were irradiated by a cold atmospheric pressure plasma jet. Punctual plasma irradiation eradicated fungal growth of all species with the largest inactivation zones with most progress in the first 15 s of treatment, treating C. albicans and least progress in that of , the lowest being M. canis. No isolate exhibited resistance to plasma treatment. Plasma treatment also completely eradicated reproductive fungal elements of T. interdigitale in dandruff of patients with tinea pedis ex vivo and in the environment in contaminated shoes. Accordingly, cold plasma seems suited to antifungal in vivo treatment of fungal skin infections and decontamination of environmental infective material.

Antimicrobial Effects of UV and VUV Radiation of Nonthermal Plasma Jets

Radio-frequency-driven plasma jets in argon at atmospheric pressure have been shown to emit a significant amount of UV and VUV radiation. There is an increasing interest in the use of UV and VUV photons in many fields of research and in industry, in particular for life-science applications. In order to study the antimicrobial effect of plasma-emitted UV and VUV radiation, microbiological tests and plasma diagnostics are combined. In particular, quantitative values of irradiance are estimated. The VUV emission of the plasma jet is dominated by the emission of argon excimer (Ar2). The recorded spectra between 115 and 180 nm also include several atomic emission lines of nitrogen and oxygen. The UV emissions are due to molecular bands of NO, OH, and N2. The best antimicrobial effect is observed by means of direct plasma treatment. UV and VUV emissions have a lower effect, and there is no difference observed between these two components.