Apparatus for generating pulsed electric fields, and its use

Abstract

The invention relates to an apparatus for generating pulsed electric fields for electroporation of cells, comprising at least two electrodes, at least one of which is partially or fully coated, the coating being characterized by a combination of a suitable dielectric constant, suitable resistivity and suitable dielectric strength.

Description

Device for generating pulsed electric fields and their use The present invention relates to a device for generating pulsed electric fields for electroporation of cells comprising at least two electrodes, at least one of which is partially or completely coated, wherein the coating has a combination of suitable dielectric constant, suitable specific resistance and suitable dielectric strength. The invention further relates to the use of a device according to the invention for electroporating cells and / or for treating foodstuffs and / or for facilitating a subsequent processing step for foodstuffs. The invention further relates to a method for producing a device according to the invention and to a method for operating this device, in particular for electroporation of cells. Pulsed electric fields (PEF) are used to treat food and water. In this process, the food or water to be treated is placed between two electrodes and subjected to electrical pulses. The applied electric field strengths are several tens of kV / cm, and the pulse durations are a few ps. To achieve ideal effects, the fields are applied by a generator within <100 ns. This process involves irreversible electroporation of the cell membranes, leading to the destruction of the biological cells themselves. The pulsed electric fields polarize the medium being treated, thus resulting in the desired electroporation. In electrical engineering terms, this polarization is expressed as reactive electrical power. This process can be used for both food processing and food preservation, as electroporation also irreversibly damages and inactivates bacteria. A good overview is provided by S. Mahnic-Kalamiza et al., "Electroporation in Food Processing and Biorefinery," J. Membrane Biol. (2014) 247, pp. 1279-1304. WO 2012 / 007620 A1 and the publication by Töpfl et al., "High intensity pulsed electric fields applied for food preservation," Chemical Engineering and Procesing 46 (2007), pp. 537-546, describe a collinear flow system for the treatment of liquid media. If such PEF systems are operated continuously, the electrodes will wear out. One effect described in this publication is the parasitic electrolysis of water, which leads to the formation of gas bubbles, which in turn trigger a discharge (arcing) through subsequent electrical voltage pulses. The explosive expansion of this plasma causes cavitation, which leads to the removal of the electrode material, both at the anode and cathode. Another disadvantage is that the food being treated is contaminated by the material removal. Furthermore, the coupling of the electric field pulse and the formation of a plasma result in a local temperature increase directly on the electrode surface. Protein-containing foods in particular are denatured and form a coating on the surface (fouling). Generally, electrodes with good electrical conductivity are used. Stainless steel and titanium materials are often used for food applications. Due to their good electrical conductivity, the application of pulsed electric fields generates active power through the current flow, which, as ohmic resistance heating, leads to an increase in temperature. This unintentionally heats the liquid food being treated and increases energy consumption. The increase in temperature often damages sensitive components of the food, for example, bioactive substances in milk such as lactoferrin, IgA, IgG, TGF-ß1, TGF-ß2, vitamins, or natural flavors in juices. Furthermore, this temperature effect naturally promotes fouling. Coatings of electrodes have been proposed and investigated many times. In S. Kurcevskis, A. Grainys, S. Tolvaisiene and T. Ustinavicius, "High Power Electroporation System in Food Treatment - Review," 2019 IEEE 7th IEEE Workshop on Advances in Information, Electronic and Electrical Engineering (AIEEE), 2019, pp. 1-4, doi: 10.1109 / AIEEE48629.2019.8977026 it is reported that graphene coatings of electrodes have a short lifetime and erode after a few 10 hours of operation. In WO 2012 / 127423 A1 , page 3 line 31 ff. it is reported that an insulating coating of the electrodes to prevent the release of electrode material in the form of ablation particles prevented electroporation or significantly increased the necessary electric fields, so that a technical implementation does not appear possible. In order to suppress the active power that leads to the unwanted temperature increase of the material to be treated, in this case the food, coatings of electrodes have already been considered in the literature, for example in BM Novac, F. Babakhr, IR Smith, L. Pecastaing, R. Ruscassic, AD Ferron, and P. Pignolet, “Demonstration of a Novel Pulsed Electric Field Technique Generating Neither Conduction Currents Nor Joule Effects”, IEEE Trans. Plasma Sci., Vol. 42, No. 1 , pp. 216-228, 2014. It is reported here that the electrodes are to be provided with a coating of dielectric material with high permittivity. In S. Qin et al., "TiG2-Coated Electrodes for Pulsed Electric Field Treatment of Microorganisms," IEEE Transactions on Plasma Science, Special Issue - Pulsed Power Science @ Technology 2016, pp. 1-7, it was shown that electrodes coated with a 2 μm thick TiO2 coating offer similar or better PEF inactivation performance compared to uncoated, conductive electrodes. Furthermore, it was shown that TiO2-coated electrodes lead to a significant reduction in energy losses of approximately 25% during treatment. The TiO2 layers were able to reduce the current during the voltage pulse by only 25%. However, these effects are not stable over the long term because the dielectric and insulating properties of titanium dioxide are adversely affected when in contact with aqueous media (see AV Hippel, RG Breckenridge, FG Chesley, and L.Tisza, “High Dielectric Constant Ceramics,” Industrial and Engineering Chemistry, Vol. 38, no. 11, pp. 1097-1109, Nov. 1946. DE102016216397 A1, paragraph 0013, describes that the electrodes and / or electrode sections are at least partially coated with an insulating layer. This can prevent, for example, deposits from the liquid on the electrodes or electrode sections and / or damage. To ensure that the electric field between the electrodes can develop largely unhindered, a high permittivity (dielectric conductivity) of the coating is recommended. The specific advantages of these coatings are not disclosed. As described above, prolonged treatment of food, especially protein-containing food, leads to undesirable deposits on the electrodes (fouling), usually caused by the denaturation of proteins. DE102018201498 describes a device intended to protect electrodes against deposits. A release device is described that either preventively suppresses deposits and / or subsequently removes existing deposits. One embodiment is surface coatings applied to at least part of the electrode. Non-stick coatings, preferably made of a hydrophobic material, are described as the surface coating: Paragraph

[0014] reveals: "Hydrophobic materials reduce the adhesion of denatured food components and preventively suppress the formation of deposits of these undesirable degradation products. Hydrophobic surface coatings are those that are water-repellent, meaning water beads up and rolls off them. Hydrophobic surfaces have a water contact angle of over 90°, which can be measured, for example, with a contact angle goniometer." No further information is given on the design of the surface coating as a clearance holder. While such hydrophobic coatings can reduce the adhesion between deposits and the electrode surface, they do not prevent the deposits themselves. Furthermore, such coatings cannot exert their effect on electrodes that wear out during long-term operation due to the erosion described above. Against this background, the object of the present invention was to provide a device for generating pulsed electric fields for the electroporation of cells and / or the treatment of foodstuffs, which has a long-term stable electrode, but at the same time offers a suitable property window for a preferred energy-saving mode of operation and good efficiency. Furthermore, low temperatures should preferably be ensured during operation in order to expose the material to as little heat as possible. This object is achieved by a device for generating pulsed electric fields for electroporation of cells, comprising at least two electrodes, of which at least one is partially or completely coated, wherein the coating - has a dielectric constant DK of 5 - 50, preferably 7 - 40, more preferably 10 - 30 under standard conditions and at a frequency of 1 MHz, - a specific resistance of > 10 10 sqm, preferably > 10 11 sqm, more preferably > 10 12 Qm at standard conditions and a frequency of 1 MHz and - has a dielectric strength of > 20 V / pm, preferably > 30 V / pm, more preferably > 40 V / pm under standard conditions. A "device for generating pulsed electric fields for the electroporation of cells" within the meaning of this text is an arrangement of components specifically designed to effect corresponding electroporation. This term therefore does not include devices that generate pulsed electric fields but for which it cannot be ruled out that individual or a few cells (accidentally) enter the effective range of the pulsed electric fields, so that electroporation of these cells cannot be ruled out. A "device for generating pulsed electric fields for the electroporation of cells" is therefore designed to treat a large number of cells accordingly. In this text, "electroporation" preferably refers to irreversible electroporation. A partially coated electrode can be coated on only one side, e.g., the side facing the other electrode. For a partially coated electrode, it is preferred that at least the areas of highest stress, i.e., those areas of the electrode where the largest electric fields occur, are coated. It has surprisingly been found that a relatively low dielectric constant is sufficient for the coating used according to the invention to achieve good electroporation results and, on the other hand, to provide electrodes with a significantly longer service life than uncoated electrodes and, in some cases, even those used in the prior art. Furthermore, the coating according to the invention enables good electroporation results with a relatively low electrical energy per unit of treated material, in particular a food product to be treated. The relationship between the dielectric constant and the field strength in the coating can be estimated with reference to Figure 1 according to the usual rules of electrostatics. In Figure 1, E= applied field strength, Ei= field strength in the coating, ei=DK of the coating, e2= DK of the liquid di= thickness of the coating, d2= thickness of the liquid layer, Ei(coating)=E*(di / d2*e2) / (ei+2*di / d2*e2) In order to reliably avoid voltage breakdowns during electroporation, the dielectric strength of the layer material should be significantly higher, preferably at least twice as high, more preferably at least 10 times as high as the field strengths occurring in the coating. Examples for specific coatings and arrangements: di=10 pm, d2=1 cm => di / d2=10 -3 e2=100 (as an example of a liquid with a particularly high DK) Coating I: di = 10 pm DLC coating with ei=3 E = 10 kV: Ei = 313 V E = 30 kV: Ei = 938 V Coating II: di = 10 pm S13N4 with ei=12 E = 10 kV: Ei = 82 V E = 30 kV: Ei = 246 V Coating III: di=10pm ZrO? with ei=30 E = 10 kV: Ei = 33 V E = 30 kV: Ei= 99 V Coating IV: di=10 pm T1O2 with ei=100 E = 10 kV: Ei = 10 V E = 30 kV: Ei = 30 V Although TiO2 performs best in terms of electrical parameters, its high interaction with water makes it unsuitable as an electrode coating. SiSn4 exhibits the best barrier properties against water and chloride ions. ZnO2 has a water absorption of < 0.01% and a higher dielectric constant. In addition to the material parameters, the defect-free nature of the coating is of utmost importance. Therefore, deposition is preferably carried out under vacuum (PVD, CVD), as this produces the best coating qualities. In many cases, it is preferred that the device according to the invention has more than two electrodes. In this way, the alternating field generation can be optimized by suitable placement of the electrodes. It is particularly preferred that several electrodes are operated simultaneously with one voltage supply. Thus, in a tubular collinear treatment chamber, the differently polarized electrodes can be alternately connected in series in order to increase the treatment intensity and thus the throughput. Likewise, Operate multiple treatment chambers with a single power supply by connecting the electrode pairs of the individual treatment chambers in parallel. Mixed configurations, such as parallel connection of series circuits, are also preferred. These circuits allow the required treatment intensity to be ideally adjusted to the material being treated, given the given power supply. A device according to the invention is preferred, wherein the coating of the electrode comprises at least two elements selected from the group consisting of Si, C, O, N, Ti, Zr, Ta, Sr, Zn, Nb, H, Mg and Al or consists of two or more of these elements. A device according to the invention is also preferred, wherein the coating comprises or consists of titanate, titanium oxide, zirconate, zirconium oxide, silicon oxide, nitride, particularly preferably selected from the group consisting of amorphous titanium dioxide, rutile, silicon nitride, zirconium dioxide and / or steatite. The person skilled in the art will ensure that the materials of the coating meet the above-described parameters according to the invention.For example, the person skilled in the art will not use coating material with a dielectric constant of >50 as a pure substance, but will mix such material with coating material of a suitable lower dielectric constant, naturally also taking into account the other parameter ranges mentioned above. The preferred materials mentioned for the coating to be used according to the invention have proven to be particularly suitable for achieving the property windows of dielectric constant (DK), specific resistance and dielectric strength that are important for the invention. A particularly preferred material for the coating is SisN4, especially preferably in amorphous form. A device according to the invention is preferred, wherein the coating is a coating deposited from the gas phase, preferably in a PVD or CVD process, more preferably in a PE-CVD or sputtering process, wherein more preferably the deposition has taken place under low-pressure conditions. For the purposes of this application, low-pressure conditions exist when the pressure is < 1 mbar. It has been found that the required property window for the coatings according to the invention can be achieved particularly easily and reliably using PVD or CVD processes, in particular PE-CVD or sputtering processes. In particular, this allows for the reliable production of largely defect-free coatings. According to the invention, it is preferred that the coating to be used according to the invention on the electrodes of the device according to the invention is amorphous. “Amorphous” in the sense of this text means X-ray amorphous, i.e., when characterizing a TEM lamella, less than 5% of the examined area (100 nm x 100 nm) is crystalline and preferably no crystallinity can be determined by XRD. Here again, it is particularly possible to achieve the property window according to the invention, even in the preferred combinations, with amorphous coatings to be used according to the invention (in particular also in the preferably described forms). Accordingly, it is also preferred that a device according to the invention for generating pulsed fields with a preferred amorphous coating on the electrode for the coating has a dielectric constant DK of 5-30, preferably 7-30, more preferably 8-25 and particularly preferably 10-20 under standard conditions and a frequency of 1 MHz. Such dielectric constants, although surprisingly low, nevertheless ensure the successful operation of the device according to the invention. The device can thus be operated with particularly long-term stability and energy efficiency. According to the invention, a device according to the invention is preferred, wherein the coating has a specific resistance > 10 9 sqm, preferably e 10 1 ° m², more preferably > 10 11 Qm at standard conditions and a frequency of 1 MHz. The high retention of the specific resistance is an expression of the property of the coating used in the invention to produce little, preferably no, water vapor upon contact with water. absorb water. This, in turn, increases the durability of the coating used on the electrode, which in turn protects the electrode for longer. Accordingly, a device according to the invention is preferred, wherein the coating has a dielectric strength of > 10 V / pm, preferably 20 V / pm, more preferably 30 V / pm under standard conditions after three months of working conditions. The preservation of the dielectric strength upon contact with water is also proof of the high quality of the coating used according to the invention and also contributes to the preservation of the coating and thus of the electrode under stress. “Working conditions” within the meaning of this application are those described in Example 1. According to the invention, a device according to the invention is preferred, wherein the coating has a layer thickness d at points on the electrode where the highest electric field strengths occur, between 0.5 pm - 100 pm, preferably 1 pm - 20 pm, more preferably 1 pm - 10 pm, more preferably 1 pm - 5 pm. A further preferred lower limit for the layer thickness range is 1.2 pm. In collinear arrangements, the areas where the highest field strengths occur are particularly the areas that are directly or adjacent to the necessary insulators that separate the electrodes from each other. In the case of the coplanar electrode arrangement, these are areas with a particularly small distance between the electrodes. It has been found that the preferred layer thickness for the layer to be used according to the invention, particularly in the preferred embodiments, enables a good compromise between the insulating and protective properties of the coating and, at the same time, the efficiency of the electrode in generating the alternating fields. According to the invention, a device according to the invention is preferred, wherein the coating on the side facing away from the electrode has an anti-fouling layer, preferably in the form of a hydrophilic coating, more preferably as a PE-CVD coating and / or as a hydrogel and / or wherein the device is designed so that a flowable mass, in particular a liquid, is arranged between the two electrodes and / or wherein the device has a conveying device in order to pass material to be treated between the electrodes. An anti-fouling layer within the meaning of the present invention is a coating that counteracts protein adsorption. An anti-fouling layer within the meaning of the present invention is one in which the adsorption of the protein bovine serum albumin (BSA) is <30 wt.%, preferably <20%, preferably <10%, as measured by QCM-D (quartz crystal microbalance with dissipation monitoring) (see Measurement Example 3). The anti-fouling layer, which is preferably provided additionally on the coating, helps to reduce the adsorption of proteins during operation of the device according to the invention and thus to increase the durability of the electrode. The preferred alternative or additional variant that the device is designed so that a flowable mass, in particular a liquid, is arranged between the two electrodes ensures good operability of the device according to the invention, namely during the electroporation of cells. The material to be treated is placed between the electrodes, allowing the alternating fields to optimally affect the cellular material contained in the treated material. The material to be treated may be solid (e.g., potatoes), but in this case, it is preferred according to the invention for the material to be treated to be placed between the electrodes in a liquid such as water. A flowable mass is present in the sense of the present invention if the main medium (or carrier medium) of this mass has a viscosity of <= 5 * 10 4 mPa s, preferably <= 5 * 102 mPa s, measured according to EN ISO 3219 A “liquid” in the sense of this text is present if the viscosity is <= 5 * 10 4 mPa s, preferably <= 5 * 10 2 mPa s measured according to EN ISO 3219. In the alternative or additional embodiment in which the device has a conveyor device for conveying the material to be treated between the electrodes, any means that ensures material flow can be used as the conveyor device. In the simplest case, this could be a pipe with a gradient, but pumps or other suitable components can also be used. With this conveying device preferably provided according to the invention, it is possible to operate the device according to the invention in a continuous process and to achieve a high throughput of material to be treated. According to the invention, a device according to the invention is preferred, wherein a food is preferably selected from the group consisting of vegetables, in particular potatoes, sweet potatoes, beetroot, celery, carrots, cabbage, turnips, pumpkin, root parsley, horseradish, radish, wasabi, salsify, parsnip, Jerusalem artichoke, ginger, okra; sugar cane, rhubarb, asparagus, fennel, bamboo shoots, quinoa, cassava, peppers, chili, tomatoes, onion vegetables, in particular vegetable onions, garlic, leeks, shallots, wild garlic; pulses; coffee cherries; coffee beans; beans, cocoa beans; soybeans; peas; chickpeas; lentils; lupin seeds; edible mushrooms, in particular button mushrooms, chanterelles, porcini mushrooms, truffles; cereals, in particular oats, wheat, barley, rice, corn;Fruits, in particular grapes, citrus fruits, in particular oranges, limes, lemons, grapefruits, kumquats, tangerines, clementines, apricots, peaches, nectarines, pineapples, apples, pears, cherries, pomegranates, quinces, mangoes, sea buckthorn fruits; berries, in particular elderberries, blackberries, currants, raspberries, cranberries, strawberries; sweet chestnuts; olives; sunflower seeds; rapeseed; walnuts; linseed; hemp seeds; pine nuts; pistachios; peanuts; safflower seeds; shea nuts; pumpkin seeds; juice, in particular fruit juices, in particular fruit juices of the above-mentioned fruits; drinking water; sugar water; honey, mash; seasoning; protein-containing foods, in particular milk-containing foods, liquid egg, algae, insects in various stages of development and meat in the area of ​​influence of the generated pulsed fields. The above list naturally only includes parts of the foodstuffs named. These foods have proven to be particularly suitable for treatment with the device according to the invention in the context of electroporation of the cells contained in the food or, for example, in the case of drinking water germs. A foodstuff within the meaning of this application is a good intended for consumption or oral ingestion by humans or animals, or a part of a good intended for such consumption. Part of the invention is the use of a device according to the invention for the electroporation of cells and / or for the treatment, in particular for the pasteurization of foodstuffs and / or for the cooking of foodstuffs and / or for facilitating a subsequent processing step for foodstuffs, in particular for improving sliceability and / or for simplifying moisture reduction and / or for improving pressability, extractability and / or juicability and / or lauterability and / or filterability. The device according to the invention can particularly effectively demonstrate its advantages when used according to the invention. The coating applied according to the invention on the electrode(s) results in a significant extension of the electrodes' service life without significantly negatively impacting the treatment outcome of the device according to the invention. Accordingly, the device according to the invention can be used for a variety of processes in the food industry. Examples of such applications include moisture reduction before frying processes, before drying processes, and / or before freeze-drying. The use according to the invention makes it possible to facilitate the desired moisture reduction for the subsequent processing step. Improving pressability or extractability, for example, when pressing olives, especially during cold pressing, is also a suitable, helpful approach for the use according to the invention. Part of the invention is also a method for producing a device according to the invention, comprising the steps a) providing an electrode, b) coating the electrode with one or more layers, as explained above, and c) inserting the coated electrode into a device for generating pulsed electric fields. With this method according to the invention it is possible to provide the device according to the invention. Part of the invention is also a method for electroporation of cells, comprising the steps a) providing a device according to the invention, b) providing cells and c) subjecting the cells to pulsed electric fields generated by the device, so that electroporation is effected. It is obvious to those skilled in the art that cells must be provided for electroporation. Within the scope of the method according to the invention, it is often possible for the "provided" cells to be present in the form of cell aggregates in foodstuffs, such as potatoes or other fruits, in the form of cell components in juices, or even in the form of contaminants such as microorganisms in drinking water. A method according to the invention is preferred, wherein the electroporation is carried out for the preservation and / or cooking of foodstuffs and / or for preparation to facilitate a subsequent processing step, in particular for improving the sliceability and / or for simplifying the moisture reduction and / or for improving the pressability and / or extractability and / or juicability and / or clarifyability and / or filterability of a foodstuff. The advantages of the device according to the invention can be used particularly well in the method according to the invention. Measurement examples: Measurement example 1: A PEF structure analogous to the Nest / e application PCT / EP2012 / 063218 Example 1 is used. Instead of the generator used there, the electrical measuring setup as sketched in Fig. 2 is used, where UDC=50 kV, R=20 MQ, C=50 nF, PEF=pulse electric field electrodes, Gap=spark gap with an electrode distance of 20 mm. If the spark gap hasn't ignited, the capacitor and the PEF chamber (also a capacitor) are charged via resistor R to a voltage of 25 kV. At 25 kV, the spark gap ignites, and the two capacitors discharge with a current of up to 60 A, with the high discharge current flowing for only 1 ps. If the discharge voltage drops below 3 kV, the spark gap is extinguished, and the cycle begins again. The treatment duration in the chamber is 3 months. The erosion of the electrodes is characterized gravimetrically by weighing the electrodes before, after the operating period and after removal of the fouling layer. Measurement example 2: Dielectric strength The dielectric strength is determined according to ASTM D149. Measurement example 3: QCM-D The quartz crystal microbalance with dissipation (QCM-D) enables the investigation of the adsorption of biomolecules in the pg / crrF range on quartz crystal surfaces (sensors). The measurement principle is based on the frequency change of the sensors (acoustic resonator) in response to molecular interactions on the crystal surface. The layers to be analyzed were applied to the QCM-D sensor crystals and subsequently investigated with bovine serum albumin (BSA) for adsorption and desorption kinetics. The BSA concentration in aqueous solution was 1 mg / ml with 1.4 mmol / l tris(hydroxymethyl)aminomethane hydrochloride and 0.9 g / l NaCl at a pH of 7. After approximately 50 min, the aqueous BSA solution was replaced with deinonated water. An example of adsorption and desorption kinetics is shown in Figure 3. Implementation examples: Embodiment 1 (not according to the invention): Titanium grade 1 was used as the electrode material. The electrodes were used without any additional coating. The electrodes were tested in long-term operation for three months according to Example 1. Municipal water was used as the liquid food. In cases of doubt, "municipal water" is defined as a 0.9 wt.% NaCl solution in water. A clear erosion of the electrodes was visually observed. The areas of the electrodes where the highest field strengths act are the most eroded. Example 2: Description of the Si3N4 coating Titanium Grade 1 is used as the electrode material. The electrodes were coated as follows: Description of the Si3N4 coating The silicon nitride coating is deposited using low-pressure sputtering technology. The reactor measures 0.5 m x 0.5 m x 0.5 m. A sputtering magnetron with a diameter of 3 inches was used. Silicon is used as the target material. The distance between the target and the substrate is 5 cm. Initially, the reactor is evacuated to a base pressure of 1*10-5 mbar, and then nitrogen is introduced into the reactor at a flow rate of 80 sccm. After the magnetron is ignited, a self-bias voltage of 300 V is applied at a plasma power of 400 W. After a sputtering time of 30 minutes, a layer thickness of approximately 1,200 nm Si3N4 is achieved. The XPS analysis of the coating reveals the following atomic composition: N = 52.7%; Si = 43.5%; O = 3.8%, with approximately 10 nm of the coating removed by Ar sputtering in the XPS before the measurement begins. The deposited coating had a DK of 11.5 at a frequency of 1 MHz, the specific resistance was 10 13 -10 14 Qm, the dielectric strength was 45 V / pm and the layer thickness was approximately 1200 nm. The electrodes were tested in long-term operation for 3 months according to Example 1. City water was used as the liquid food. After long-term operation for 3 months, the deposited coating had a DK of 14 at a frequency of 1 MHz, the specific resistance was 10 12 -10 13 Qm, the dielectric strength 45 V / pm and the layer thickness approx. 1,200 nm. The erosion of the electrodes could not be detected within the measurement accuracy of 1 mg. Visually, no erosion could be detected either. The coating proved to be suitable for long-term electroporation use. Example 3: BaTiO3 coated PEF electrodes The titanium electrodes were coated with a 2 pm thick, crystalline barium titanate coating, which was sputtered from a barium titanium target in low-pressure plasma. The dielectric constant of this coating was 2000 for frequencies below 1 Hz and approximately 200 for 1 MHz. The coated electrodes were characterized as described in Example 1. The coating proved unsuitable for electroporation applications. Example 4: TiO2 coated PEF electrodes The titanium electrodes were sputtered with a 2 μm thick, crystalline TiO2 layer. The dielectric constant of the coating was 70 at a frequency of 1 MHz. When the electrodes were characterized according to Example 1, a preservative effect was found. However, the insulating effect of the TiO2 coating decreased after just 2 hours of operation, resulting in a significant increase in the current intensity in the PEF chamber. A measurement of the specific electrical resistance yielded a value in the range of 106 Ωm. The coating proved to be unsuitable for permanent electroporation use. Example 5: Description Deposition of the acrylic acid layers of the antifouling layer In addition to Example 2, plasma polymer acrylic acid layers were deposited on Si4N3 layers as follows: The plasma polymer acrylic acid layers (ppAA) are produced using low-pressure plasma polymerization of acrylic acid. For this purpose, a 360 l plasma reactor is evacuated to a base pressure of 5*10-3 mbar, and then sufficient acrylic acid vapor is introduced into the reactor to achieve a pressure of 0.03 mbar. A high-frequency plasma (13.56 MHz) is ignited using a plasma electrode (35 x 35 cm) positioned 7 cm above the chamber floor. The titanium electrodes to be coated are attached to a stainless steel plate 7 cm above the plasma electrode. After a process time of 160 s, the following layer thicknesses (on the electrode opening facing the pulsed electric field) and contact angles were obtained. Table 2: Properties of ppAA layers depending on the plasma power Long-term operation according to Example 1 using milk as the liquid food resulted in visually detectable fouling on the electrode surface of samples 1 and 2. This fouling did not differ significantly from the fouling observed when using a Si4N3-coated Ti electrode without a plasma-polymer acrylic acid coating. The plasma-polymer acrylic acid layer was dissolved under the influence of the aqueous medium. The best anti-fouling properties were observed in Sample 3 (95% reduction in deposits). No fouling was visually detectable. Minor deposits were found in Sample 4 (80% reduction in deposits).

Claims

Claims 1 . Device for generating pulsed electric fields for electroporation of cells, comprising at least two electrodes, of which at least one is partially or completely coated, wherein the coating - has a dielectric constant DK of 5 - 50, preferably 7 - 40, more preferably 10 - 30 under standard conditions and at a frequency of 1 MHz, - a specific resistance of > 10 10 sqm, preferably > 10 11 sqm, more preferably > 10 12 Qm at standard conditions and a frequency of 1 MHz and - has a dielectric strength of > 20 V / pm, preferably > 30 V / pm, more preferably > 40 V / pm under standard conditions.

2. Device according to claim 1, wherein the coating of the electrode comprises at least two elements selected from the group consisting of Si, C, O, N, Ti, Zr, Ta, Sr, Zn, Nb, H, Mg and Al or consists of two or more of these elements.

3. Device according to claim 1 or 2, wherein the coating comprises or consists of titanate, titanium oxide, zirconate, zirconium oxide, silicon oxide, nitride, particularly preferably selected from the group consisting of amorphous titanium dioxide, rutile and silicon nitride, zirconium dioxide and / or steatite.

4. Device according to one of the preceding claims, wherein the coating is a coating deposited from the gas phase, preferably in a PVD or CVD process, more preferably in a PE-CVD or sputtering process, more preferably the deposition being carried out under low-pressure conditions.

5. Device according to one of the preceding claims, wherein the coating is amorphous.

6. Device according to claim 5, wherein the coating has a dielectric constant DK of 5-30, preferably 7-30, more preferably 8-25 and particularly preferably 10-20 at standard conditions and a frequency of 1 MHz.

7. Device according to one of the preceding claims, wherein the coating has a specific resistance > 10 9 Qm, preferably > 1 O 10 sqm, more preferably > 10 11 Qm at standard conditions and a frequency of 1 MHz.

8. Device according to one of the preceding claims, wherein the coating has a dielectric strength of > 10 V / pm, preferably 20 V / pm, more preferably 30 V / pm under standard conditions after three months in water at 20 °C.

9. Device according to one of the preceding claims, wherein the coating has a layer thickness d at locations on the electrode where the highest electric field strengths occur between 0.5 pm - 100 pm, preferably 1 pm - 20 pm, more preferably 1 pm - 10 pm, more preferably 1 pm - 5 pm.

10. Device according to one of the preceding claims, wherein the coating on the side facing away from the electrode has an anti-fouling layer, preferably in the form of a hydrophilic coating, more preferably as a PE-CVD coating and / or as a hydrogel, and / or wherein the device is designed such that a flowable mass, in particular a liquid, is arranged between the two electrodes and / or wherein the device has a conveying device in order to pass material to be treated between the electrodes.

11. Device according to one of the preceding claims, wherein a food is preferably selected from the group consisting of vegetables, in particular potatoes, sweet potatoes, beetroot, celery, carrots, cabbage, turnips, pumpkin, root parsley, horseradish, radish, wasabi, salsify, parsnip, Jerusalem artichoke, ginger, okra; sugar cane, rhubarb, asparagus, fennel, bamboo shoots, quinoa, cassava, peppers, chili, tomatoes, onion vegetables, in particular vegetable onions, garlic, leeks, shallots, Wild garlic; pulses; coffee cherries; coffee beans; beans, cocoa beans; soybeans; in particular potatoes, sweet potatoes, beetroot, celery, carrots, cabbage, turnips, pumpkin, root parsley, horseradish, radish, wasabi, salsify, parsnip, Jerusalem artichoke, ginger, okra; sugar cane, rhubarb, asparagus, fennel, bamboo shoots, quinoa, cassava, peppers, chili, tomatoes, onion vegetables, in particular sweet onions, garlic, leeks, shallots, wild garlic; pulses; coffee cherries; coffee beans; beans, cocoa beans; soybeans; peas; chickpeas; lentils; lupin seeds; edible mushrooms, in particular button mushrooms, chanterelles, porcini mushrooms, truffles; cereals, in particular oats, wheat, barley, rice, corn; Fruits, in particular grapes, citrus fruits, in particular oranges, limes, lemons, grapefruits, kumquats, mandarins, clementines, apricots, peaches, nectarines, pineapples, apples, pears, cherries, pomegranates, quinces, mangoes, sea buckthorn fruits;Berries, in particular elderberries, blackberries, currants, raspberries, cranberries, strawberries; sweet chestnuts; olives; sunflower seeds; rapeseed; walnuts; linseed; hemp seeds; pine nuts; pistachios; peanuts; safflower seeds; shea nuts; pumpkin seeds; juice, in particular fruit juices, in particular fruit juices of the above-mentioned fruits; drinking water; sugar water; honey, mash; seasoning; protein-containing foods, in particular milk-containing foods, liquid egg, algae, insects in various stages of development and meat in the area of ​​influence of the generated pulsed fields.

12. Use of a device according to one of the preceding claims for the electroporation of cells and / or for cooking foodstuffs and / or for treating, in particular for pasteurizing foodstuffs and / or for facilitating a subsequent processing step for foodstuffs, in particular for improving sliceability and / or for simplifying moisture reduction and / or for improving pressability, extractability and / or juicability and / or clarifyability and / or filterability.

13. A method for producing a device according to any one of claims 1-11, comprising the steps of: a) providing an electrode, b) coating the electrode with one or more layers as defined in any one of claims 1-10 and c) Inserting the coated electrode into a device for generating pulsed electric fields.

14. A method for electroporation of cells, comprising the steps of: a) providing a device according to any one of claims 1-10, b) providing cells, and c) subjecting the cells to pulsed electric fields generated by the device to effect electroporation.

15. The method according to claim 14, wherein the electroporation is carried out for the preservation and / or cooking of food and / or for preparation to facilitate a subsequent processing step, in particular for improving the sliceability and / or for simplifying the moisture reduction and / or for improving the pressability and / or extractability and / or juicability and / or clarifyability and / or filterability of a food.

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