Direct Cold Plasma Research Articles

Femtosecond laser texturing assisted cold plasma hydrophilization of polytetrafluoroethylene surface

Polytetrafluoroethylene (PTFE) is one of the most widely used engineering polymers, but PTFE-based bonding pairs are prone to failure due to its natural hydrophobicity induced weak interfacial bonding strength. Herein, we propose to improve the hydrophilicity of PTFE surface by femtosecond laser texturing assisted cold plasma modification. Specifically, PTFE surface is firstly textured by femtosecond laser ablation, and then modified by either direct cold plasma treatment or cold plasma induced graft polymerization of acrylic acid. The synergetic treatment roughens the PTFE surface on both micro and nano scales and introduces a large amount of oxygen-containing groups, making the treated surface hydrophilic (water contact angle < 30°). The hierarchically rough and hydrophilic PTFE surface favors its bonding with Cu by forming a mechanically interlocked and robust adhesive interface, and the maximum shearing strength and peeling strength of the bonding pairs were measured to be 2.75 MPa and 6.37 N/mm, respectively. The laser texturing assisted plasma modification enables durable surface hydrophilization and adhesive property improvement for PTFE compared with other previously reported methods, and thereby offers new insights into the fabrication of high-performance PTFE-based bonding components, as well as other functional units that require high-efficiency surface hydrophilization and robust bonding.

Impact of in-package cold plasma treatment on the physicochemical properties and shelf life of button mushrooms (Agaricus bisporus)

Button mushrooms are perishable due to microbial spoilage and browning. The effect of in-package cold plasma CP treatment on the quality and shelf life of button mushrooms is presented. Samples were sealed inside a package with different gas combinations [80% O2 + 10% CO2 + 10% N2, 10% O2 + 10% CO2 + 80% N2, and 10% O2 + 80% CO2 + 10% N2], treated with CP for 15 min at 28 kV and stored at 4 °C for 7 days. Microbiological and physicochemical properties of button mushrooms (control, samples treated with direct cold plasma (DCP), and those packed in three different modified atmospheric packing (MAP) compositions) were analyzed on days 1, 4, and 7 after treatment. Following DCP and in-package CP treatment, the total bacterial count was reduced by 0.93 and 1.14 log CFU/g, while the yeast and mold count was reduced by 1.07 and 1.24 log CFU/g, respectively. In-package CP reduced PPO activity by 29%. Changes in physicochemical properties of button mushrooms were insignificant on day 1. MAP with high oxygen showed larger microbial reductions than the other two gas combinations. At the end of storage, all in-package CP treated button mushrooms maintained significantly (p < 0.05) better quality characteristics than control and DCP-treated mushrooms. The samples treated with CP and kept in a high O2 gas concentration exhibited better quality characteristics. Therefore, in-package CP technology with high O2 concentration can be used as a potential tool for the decontamination and shelf-life extension of button mushrooms.

Cold Plasma Treatment Strategies for the Control of Fusarium oxysporum f. sp. basilici in Sweet Basil

Fusarium wilt of basil (FOB), caused by Fusarium oxysporum f. sp. basilici, is an economically damaging disease of field- and greenhouse-grown sweet basil. Growers have observed a resurgence of FOB and susceptibility in FOB-resistant cultivars. Because currently available chemical, biological, and cultural control methods are costly, unsustainable, ineffective, or challenging to implement, new strategies of FOB control are needed. Cold plasma is becoming an increasingly important experimental technology in the food and agricultural industry for pathogen decontamination. To understand the effect of cold plasma treatment on FOB incidence and severity, experiments were conducted by treating FOB mycelium, inoculated sweet basil seedlings, and seeds with various experimental cold plasma treatment devices, all using helium as a feed gas. Initial results indicated that while the cold plasma jet treatment did not result in a significant reduction in mean mycelial growth rate or virulence of the pathogen, direct cold plasma jet treatments on seedlings, as well as a cold plasma dielectric barrier discharge treatment on seeds, did exhibit varying efficacies against FOB. Control of FOB appeared to be strongly dependent on the exposure time to cold plasma. These findings can aid in the standardization of a cold plasma treatment for the commercial basil seed and transplant industry.

Cold plasma pretreatment – A novel approach to improve the hot air drying characteristics, kinetic parameters, and nutritional attributes of shiitake mushroom

Cold plasma (CP) is a promising novel technology, which can widely be applied to accelerate the drying process and preserve the nutritional values in the foodstuff. Therefore, the aim of this study was to explore the effect of CP pretreatments on hot air drying of shiitake mushroom. Direct CP and cold plasma-activated water (CPAW) was used to treat the mushrooms before drying at 50, 60, and 70 °C. Scanning electron microscopic reports exhibited that both CP and CPAW pretreatment significantly changed the surface topography of shiitake by generating intracellular spaces, larger cavities, and less density, which in turn facilitated the drying process of shiitake. Both CP and CPAW pretreatment accelerated the mass transfer during the drying process, resulting in lower activation energy, drying time and energy requirement compared to Control. Mathematical modeling studies revealed that Page, Parabolic, Logarithmic as well as Midilli and others were the best models to adequately describe the drying kinetics of shiitake. Furthermore, CP pretreatments were better capable of preserving the phenolics, flavonoids, and antioxidant activity than Control. While CP-pretreated mushrooms preserved the highest amount of phenolics (463.30 mg/100 g), flavonoids (100.70 mg/100 g), and DPPH-relative inhibition activity (0.201). Conclusively, CP, as an effective pretreatment strategy, can repeatedly be applicable for the drying of agro-products in terms of improving the drying parameters, energy management as well as protecting the nutritional compounds.

Effect of cold plasma on polyphenol oxidase inactivation in cloudy apple juice and on the quality parameters of the juice during storage

Direct cold plasma treatment has been investigated as an alternative non-thermal technology as a means of maintaining and improving quality of fresh cloudy apple juice. Process variables studied included type of plasma discharge, input voltage and treatment time on polyphenol oxidase (PPO) inactivation. Spark discharge plasma at 10.5 kV for 5 min was the best treatment, with near total inactivation of PPO achieved, although good PPO inactivation was also recorded using shorter treatment times. Residual activity (RA) of PPO was 16 and 27.6% after 5 and 4 min of treatment respectively. This PPO inactivation was maintained throughout the storage trials, but decreased with samples treated for a shorter time. Plasma treatment improved key quality parameters of Golden delicious cloudy apple juice, with retention of critical quality parameters during extended storage trials. Color was the most noticeable change, which was enhanced with retention of a greener color. An increase of 69 and 64% was obtained in the total phenolic content after 4 and 5 min of treatment, respectively. Therefore, cold plasma was demonstrated to be a good alternative to traditional heat treatments for enhanced quality retention of fresh cloudy apple juice and over its storage.

How Does Plasma Activated Media Treatment Differ From Direct Cold Plasma Treatment?

The aim of the paper is to investigate the optimum condition for generation of Plasma Activated Media (PAM), where it can deactivate the cancer cells while minimum damage for normal cells. Over past few years, cold atmospheric Plasma-Activated Media (PAM) have shown its promising application in plasma medicine for treatment of cancer. PAM has a tremendous ability for selective anti-cancer capacity in vitro and in vivo. We have analyzed the radicals in air using the optical emission spectroscopy and in culture media using chemical analysis. Further, we have tested the toxicity of PAM using MTT assay. We observed that more cancer cell death is for the Ar plasma followed by the Ar-N2 plasma, and the least cell death was observed for the Ar-O2 plasma at all treatment times both by direct treatment and through PAM treatment. The concentration of the RNS species is high for Ar-N2 plasma in gas as well as inside the culture media compared to that for pure Ar plasma. However, the difference is significantly less between the Ar plasma treatments and the Ar-N2 plasma treatments, showing that ROS is the main factor contributing to cell death. Among all three feeding gas plasmas the best system is Ar-O2 plasma for direct treatments towards the cancer cells. In addition, the best system for PAM preparation is Ar-N2 at low time treatments (1 min and 2 min) because it has no effect on normal cells, but kills the cancer cells.

The Application of the Cold Atmospheric Plasma-Activated Solutions in Cancer Treatment.

Over the past five years, the cold atmospheric plasma-activated solutions (PAS) have shown their promissing application in cancer treatment. Similar as the common direct cold plasma treatment, PAS shows a selective anti-cancer capacity in vitro and in vivo. However, different from the direct cold atmospheric plasma (CAP) treatment, PAS can be stored for a long time and can be used without dependence on a CAP device. The research on PAS is gradually becoming a hot topic in plasma medicine. In this review, we gave a concise but comprehensive summary on key topics about PAS including the development, current status, as well as the main conclusions about the anti-cancer mechanism achieved in past years. The approaches to make strong and stable PAS are also summarized.

Stabilizing the cold plasma-stimulated medium by regulating medium's composition.

Over past several years, the cold plasma-stimulated medium (PSM) has shown its remarkable anti-cancer capacity in par with the direct cold plasma irradiation on cancer cells or tumor tissues. Independent of the cold plasma device, PSM has noticeable advantage of being a flexible platform in cancer treatment. Currently, the largest disadvantage of PSM is its degradation during the storage over a wide temperature range. So far, to stabilize PSM, it must be remained frozen at −80 °C. In this study, we first reveal that the degradation of PSM is mainly due to the reaction between the reactive species and specific amino acids; mainly cysteine and methionine in medium. Based on this finding, both H2O2 in PSM and the anti-cancer capacity of PSM can be significantly stabilized during the storage at 8 °C and −25 °C for at least 3 days by using phosphate-buffered saline (PBS) and cysteine/methionine-free Dulbecco’s Modified Eagle Medium (DMEM). In addition, we demonstrate that adding a tyrosine derivative, 3-Nitro-L-tyrosine, into DMEM can mitigate the degradation of PSM at 8 °C during 3 days of storage. This study provides a solid foundation for the future anti-cancer application of PSM.