2.4 Floating-electrode dielectric barrier discharge
9 min read•august 21, 2024
(FE-DBD) is a game-changing technique in plasma medicine. It allows for targeted plasma treatment of biological tissues, combining safety and effectiveness in a unique electrode setup.
FE-DBD generates non-equilibrium plasma at atmospheric pressure, using a powered electrode with a dielectric cover and a floating electrode. This configuration enables flexible treatment of irregular surfaces and living tissues, with plasma forming only when near the target.
Fundamentals of FE-DBD
- Floating-electrode (FE-DBD) represents a crucial advancement in plasma medicine, offering targeted and controlled plasma generation for various biomedical applications
- FE-DBD utilizes a unique that allows for direct treatment of biological tissues while maintaining safety and efficacy
Principles of dielectric barrier discharge
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- Dielectric barrier discharge generates non-equilibrium plasma at atmospheric pressure
- Operates by applying high voltage across two electrodes separated by a dielectric material
- Prevents arc formation through charge accumulation on the dielectric surface
- Produces numerous microdischarges distributed over the electrode area
Floating electrode configuration
- Incorporates a powered electrode covered by a dielectric and a floating electrode (typically the treated surface)
- Eliminates the need for a grounded electrode, allowing for more flexible treatment geometries
- Generates plasma only when in close proximity to the target surface
- Enables self-limiting discharge intensity based on the capacitance of the treated object
Key components of FE-DBD
- High voltage power supply delivers alternating current (typically in kHz range)
- Dielectric barrier material (quartz, alumina, or polymers) covers the powered electrode
- Electrode geometry influences plasma distribution and intensity
- Gas composition determines the types of reactive species generated
- Treatment gap between the powered electrode and the floating electrode affects discharge characteristics
FE-DBD vs other plasma sources
- FE-DBD offers unique advantages in plasma medicine compared to conventional plasma sources
- Provides a balance between treatment efficacy and safety for biological applications
Comparison with conventional DBD
- Conventional DBD requires two fixed electrodes, limiting treatment flexibility
- FE-DBD allows for direct treatment of irregular surfaces and living tissues
- Plasma generation in FE-DBD occurs only when in contact with the target, reducing unwanted effects
- Power consumption in FE-DBD tends to be lower due to the self-limiting nature of the discharge
Advantages of FE-DBD
- Enables non-thermal plasma treatment of heat-sensitive materials and living tissues
- Provides precise control over the treatment area and intensity
- Generates a diverse range of reactive species beneficial for biomedical applications
- Allows for portable and handheld device designs for clinical use
- Minimizes the risk of arcing and thermal damage to treated surfaces
Limitations of FE-DBD
- Treatment depth may be limited compared to some other plasma sources
- Requires careful control of operating parameters to maintain consistent plasma characteristics
- May be sensitive to changes in environmental conditions (humidity, temperature)
- Scaling up for large area treatments can be challenging
- Potential for non-uniform treatment due to variations in surface properties of the floating electrode
Physical characteristics
- FE-DBD plasmas exhibit unique physical properties that make them suitable for biomedical applications
- Understanding these characteristics is crucial for optimizing treatment protocols and ensuring safety
Electrical properties
- Characterized by short-duration, high-frequency microdischarges
- Current density typically ranges from 100-1000 A/cm²
- Voltage requirements vary depending on the gap distance and dielectric properties
- Capacitive coupling between the powered electrode and the treated surface influences discharge behavior
- Charge transfer occurs primarily through displacement current rather than conduction current
Gas dynamics in FE-DBD
- Plasma generation creates localized gas heating and expansion
- Convective flows develop due to temperature gradients near the treated surface
- Gas composition changes dynamically during discharge due to dissociation and recombination processes
- Neutral gas temperature remains relatively low (typically <50°C) due to non-equilibrium nature of the plasma
- Pressure waves may be generated by rapid gas heating, potentially influencing treatment effects
Plasma temperature and density
- Electron temperature reaches 1-10 eV, while ion and neutral gas temperatures remain near ambient
- Electron density typically ranges from 10¹⁴ to 10¹⁶ cm⁻³
- Ion density is generally lower than electron density due to rapid recombination
- Temperature gradients exist within the plasma, with higher temperatures near the powered electrode
- Plasma density decreases rapidly with distance from the dielectric surface
Reactive species generation
- Production of reactive species is a key feature of FE-DBD for biomedical applications
- Understanding and controlling species generation is crucial for optimizing treatment outcomes
Types of reactive species
- Reactive oxygen species (ROS) include O, O₃, OH, H₂O₂, and ¹O₂
- Reactive nitrogen species (RNS) comprise NO, NO₂, and ONOO⁻
- Charged particles electrons and various positive and negative ions
- Metastable species (excited state atoms and molecules with relatively long lifetimes)
- UV photons generated by electronic transitions in the plasma
Factors affecting species production
- Applied voltage and frequency influence the electron energy distribution
- Gas composition determines the primary reactive species generated
- Humidity levels affect the production of OH radicals and other water-derived species
- Surface properties of the treated object can modify local electric fields and species formation
- Treatment time and duty cycle impact the accumulation of long-lived reactive species
Measurement techniques
- (OES) identifies excited species and their relative concentrations
- Mass spectrometry detects neutral and ionic species in the plasma afterglow
- Laser-induced fluorescence (LIF) measures specific reactive species with high spatial resolution
- Chemical probes and indicators (DPPH, KI-starch) quantify certain reactive species in liquid environments
- Electron paramagnetic resonance (EPR) spectroscopy detects and quantifies free radicals
Biomedical applications
- FE-DBD has shown promising results in various biomedical fields
- The unique properties of FE-DBD plasmas enable targeted treatments with minimal collateral damage
Wound healing
- Promotes tissue regeneration through stimulation of growth factors and cytokines
- Enhances microcirculation and oxygenation of wound beds
- Provides antimicrobial effects against a broad spectrum of pathogens
- Modulates inflammation and accelerates the healing process
- Improves outcomes for chronic wounds (diabetic ulcers, pressure sores)
Sterilization and decontamination
- Inactivates bacteria, viruses, and fungi on surfaces and in liquids
- Effective against antibiotic-resistant strains (MRSA, VRE)
- Penetrates biofilms and inactivates embedded microorganisms
- Decontaminates heat-sensitive medical devices and instruments
- Potential for air and water purification applications
Cancer treatment potential
- Selectively induces apoptosis in cancer cells while sparing healthy tissue
- Enhances the efficacy of chemotherapy drugs through increased cellular uptake
- Modulates the tumor microenvironment to suppress cancer growth
- Potential for targeting circulating tumor cells in blood
- Shows promise in combination with immunotherapy approaches
FE-DBD in plasma medicine
- FE-DBD interacts with biological systems in complex ways
- Understanding these interactions is crucial for developing safe and effective treatments
Interaction with biological tissues
- Generates localized electric fields that can influence cell membrane potential
- Delivers reactive species that modify the redox balance of cells and tissues
- Produces UV radiation that may have both beneficial and harmful effects
- Creates localized pressure waves that can enhance drug delivery and cellular uptake
- Modifies surface properties of tissues, potentially affecting cell adhesion and migration
Cellular response mechanisms
- Activates intracellular signaling pathways (MAPK, NF-κB) involved in stress response and adaptation
- Induces production of heat shock proteins and other protective molecules
- Modulates gene expression related to cell proliferation, differentiation, and apoptosis
- Alters cellular metabolism and energy production
- Triggers release of growth factors and cytokines that influence neighboring cells
Safety considerations
- Requires careful control of to avoid thermal damage
- Potential for DNA damage from UV radiation and reactive species must be assessed
- Long-term effects of repeated treatments need further investigation
- Possible induction of oxidative stress in healthy tissues surrounding the treatment area
- Need for standardized protocols and safety guidelines for clinical applications
Device design and optimization
- Optimizing FE-DBD devices is crucial for achieving desired treatment outcomes
- Various design parameters can be adjusted to tailor the plasma characteristics
Electrode configurations
- Planar electrodes provide uniform treatment over flat surfaces
- Cylindrical or needle electrodes enable focused treatments and penetration into cavities
- Multi-electrode arrays allow for larger treatment areas and complex geometries
- Mesh electrodes can be used for treating porous materials or creating specific plasma patterns
- Flexible electrode designs adapt to curved surfaces for improved contact
Power supply requirements
- High voltage AC sources (typically 1-20 kV) with frequencies ranging from kHz to MHz
- Pulsed power supplies offer control over plasma characteristics and reduce heat generation
- Impedance matching networks optimize power transfer and plasma stability
- Feedback control systems maintain consistent plasma parameters during treatment
- Safety features (current limiting, arc detection) prevent electrical hazards
Gas composition effects
- Noble gases (, ) lower breakdown voltage and enhance plasma stability
- Oxygen admixtures increase production of reactive oxygen species
- Nitrogen-containing gases generate reactive nitrogen species for specific applications
- Humidity levels influence OH radical production and overall plasma chemistry
- Gas flow rates affect species transport and treatment uniformity
Diagnostic techniques
- Accurate diagnostics are essential for characterizing FE-DBD plasmas and optimizing treatments
- Various methods provide complementary information about plasma properties
Optical emission spectroscopy
- Identifies excited species through analysis of characteristic emission lines
- Provides information on relative species concentrations and electron temperature
- Enables spatially and temporally resolved measurements of plasma emission
- Can be used to monitor plasma stability and uniformity during treatment
- Requires careful calibration and interpretation due to complex plasma dynamics
Electrical characterization methods
- Voltage and current waveform analysis reveals discharge characteristics
- Lissajous figures quantify power consumption and energy transfer
- Electrical models help predict plasma behavior under different operating conditions
- Impedance measurements provide insights into plasma-surface interactions
- Time-resolved electrical diagnostics capture fast events in individual microdischarges
Chemical species detection
- Mass spectrometry identifies and quantifies neutral and ionic species
- Fourier-transform infrared spectroscopy (FTIR) detects molecular species in the gas phase
- Laser-induced breakdown spectroscopy (LIBS) measures elemental composition of treated surfaces
- Colorimetric and fluorometric assays quantify specific reactive species in liquids
- Gas chromatography analyzes long-lived species and byproducts in the plasma afterglow
Current research trends
- FE-DBD research is rapidly evolving to address challenges and expand applications
- Interdisciplinary approaches are driving innovation in plasma medicine
Novel FE-DBD configurations
- Microplasma arrays for high-resolution patterning and selective treatments
- Liquid-phase plasmas for direct treatment of biological fluids and cell cultures
- Plasma jets with floating electrode designs for enhanced penetration and directional control
- Surface dielectric barrier discharge (SDBD) configurations for large-area treatments
- Hybrid systems combining FE-DBD with other plasma sources for tailored effects
Combining FE-DBD with other therapies
- Plasma-activated media for indirect treatment and drug delivery applications
- Synergistic effects with photodynamic therapy for enhanced
- Integration with electroporation techniques for improved cellular uptake of drugs
- Combination with cold atmospheric plasma (CAP) for multi-modal plasma medicine
- Plasma-assisted wound dressings for controlled release of antimicrobial agents
Emerging biomedical applications
- Dental applications for biofilm removal and tooth whitening
- Ophthalmology treatments for corneal disorders and dry eye syndrome
- Dermatological therapies for skin rejuvenation and acne treatment
- Targeted drug delivery using plasma-induced transdermal transport
- Neurological applications for stimulating nerve regeneration and treating brain disorders
Challenges and future directions
- Addressing key challenges will be crucial for the widespread adoption of FE-DBD in clinical settings
- Future research directions aim to expand the capabilities and understanding of FE-DBD technology
Standardization issues
- Developing standardized protocols for plasma characterization and
- Establishing reproducible treatment parameters across different device designs
- Creating reference materials and calibration standards for plasma diagnostics
- Harmonizing terminology and reporting methods in plasma medicine research
- Implementing quality control measures for FE-DBD devices and treatments
Scaling up for clinical use
- Designing larger-scale FE-DBD systems for treating extensive areas
- Developing automated treatment systems for consistent and efficient application
- Addressing regulatory requirements for medical device approval
- Conducting large-scale clinical trials to establish efficacy and safety
- Creating user-friendly interfaces and controls for clinical staff
Potential long-term effects
- Investigating the cumulative effects of repeated plasma treatments on tissues
- Assessing the potential for plasma-induced mutations and carcinogenesis
- Studying the impact on the microbiome and long-term immune responses
- Evaluating the effects on and tissue regeneration over extended periods
- Monitoring for potential systemic effects resulting from localized plasma treatments
Key Terms to Review (18)
Argon: Argon is a colorless, odorless, and inert gas that belongs to the noble gases group in the periodic table, with the atomic number 18. Due to its inertness, argon is commonly used in various applications, especially in plasma technology where it acts as a filler gas in dielectric barrier discharge systems, enabling the production of plasma while minimizing reactions with other substances.
Atmospheric Pressure Plasma Jet: An atmospheric pressure plasma jet is a non-thermal plasma source that operates at room temperature and generates plasma in an open-air environment. It is used for various applications, including surface modification, sterilization, and biomedical treatments. The jet consists of ionized gas that flows out from a nozzle, creating reactive species that can interact with surfaces or biological materials without causing thermal damage.
Bactericidal activity: Bactericidal activity refers to the ability of a substance or treatment to kill bacteria, effectively reducing their population and preventing them from multiplying. This is crucial in various applications, including medical treatments, food preservation, and sanitation, as it helps control bacterial infections and contamination. Understanding how different methods achieve bactericidal effects can inform their effective use in different environments.
Cancer treatment: Cancer treatment refers to the various medical approaches used to combat cancer, including surgery, radiation therapy, chemotherapy, and emerging therapies like plasma medicine. The goal is to eradicate cancer cells, shrink tumors, and improve the overall health and quality of life for patients. In recent years, plasma medicine has been recognized as a promising avenue for cancer treatment due to its ability to selectively target and destroy cancer cells while sparing healthy tissues.
Dielectric Barrier Discharge: Dielectric Barrier Discharge (DBD) is a type of electrical discharge that occurs between two electrodes separated by a dielectric material, allowing the generation of non-thermal plasma at atmospheric pressure. This technique is significant because it enables stable plasma generation without the need for high voltages while producing reactive species useful for various applications such as medical treatments, surface modifications, and sterilization.
Dosimetry: Dosimetry is the measurement and assessment of the dose delivered by ionizing radiation or other forms of energy in medical treatments. It plays a crucial role in ensuring that the correct amount of energy is administered to achieve therapeutic effects while minimizing damage to surrounding healthy tissues. This measurement is particularly important when using techniques like floating-electrode dielectric barrier discharge, which involves plasma and electric fields to interact with biological tissues, and in personalized plasma medicine, where dosimetry is tailored for individual patient needs.
Electrical Breakdown: Electrical breakdown occurs when an insulating material becomes conductive due to the application of a sufficiently high voltage, resulting in a sudden discharge of electricity. This phenomenon is essential in understanding the behavior of dielectric materials in high-voltage environments, as it can lead to various forms of plasma generation and influence the operation of devices like dielectric barrier discharges.
Electrode Configuration: Electrode configuration refers to the arrangement and design of electrodes within plasma generation systems, which is crucial for determining the characteristics and performance of the resulting plasma. The specific layout influences factors such as the electrical field distribution, energy efficiency, and stability of the discharge, directly impacting applications in areas like surface treatment, biomedical applications, and material processing. Understanding electrode configuration helps optimize various plasma generation methods for effective and safe use in diverse environments.
Floating-electrode dielectric barrier discharge: Floating-electrode dielectric barrier discharge (FE-DBD) is a plasma generation technique that uses a dielectric barrier to separate the electrodes and allow for the formation of a discharge without direct electrical contact. This method is significant in applications such as surface treatment, sterilization, and medical therapies, due to its ability to produce non-thermal plasma at atmospheric pressure. The unique feature of the floating electrode is that it allows for the potential of the discharge to vary dynamically, enhancing its effectiveness for various applications.
Gas flow rate: Gas flow rate refers to the volume of gas that passes through a given cross-sectional area per unit time, typically measured in liters per minute (L/min) or cubic centimeters per minute (cc/min). This measurement is crucial in various applications as it affects the efficiency and performance of plasma systems, influencing parameters like discharge stability, energy input, and reaction dynamics in processes involving gas plasma interactions.
Glow Discharge: Glow discharge is a type of electrical discharge characterized by a low-pressure gas ionization that produces a luminous glow. This phenomenon occurs when a gas becomes ionized due to the application of an electric field, creating a plasma state that can be utilized in various applications, including generating plasmas for treatments, enhancing surface properties, and purifying air and water.
Helium: Helium is a colorless, odorless, tasteless, non-toxic gas that is the second lightest and second most abundant element in the universe, primarily formed during nuclear fusion in stars. In the context of floating-electrode dielectric barrier discharge, helium serves as an important working gas due to its unique electrical and thermal properties, which enhance plasma generation and stability, leading to various applications in medical and industrial fields.
Ionization: Ionization is the process by which an atom or molecule gains or loses an electric charge, typically through the removal or addition of electrons. This fundamental transformation is crucial in understanding how plasmas are formed and manipulated, as ionized particles become integral to various applications in medicine and technology.
Langmuir Probe: A Langmuir probe is a diagnostic tool used to measure the electron temperature, electron density, and potential in a plasma. It consists of a small electrode that is inserted into the plasma and collects current from the charged particles, allowing for an analysis of the plasma's properties. This information is crucial for understanding the behavior and characteristics of plasmas, especially in applications like floating-electrode dielectric barrier discharges.
Optical Emission Spectroscopy: Optical emission spectroscopy (OES) is an analytical technique used to determine the elemental composition of materials by analyzing the light emitted from excited atoms and ions. This method is particularly valuable in plasma diagnostics as it helps characterize the physical and chemical properties of various plasma sources, aiding in understanding their interactions with biological tissues and monitoring plasma treatment processes.
Plasma-induced apoptosis: Plasma-induced apoptosis is a form of programmed cell death triggered by reactive species generated from non-thermal atmospheric pressure plasma. This process is significant in biomedical applications, especially in cancer treatment, where targeted destruction of malignant cells is desired. The mechanisms of plasma-induced apoptosis involve oxidative stress and activation of specific cellular pathways that lead to cell death, making it an important area of research in therapeutic strategies using plasma technology.
Treatment parameters: Treatment parameters refer to the specific settings and conditions that are adjusted during therapeutic procedures to optimize outcomes. In the context of floating-electrode dielectric barrier discharge, these parameters play a crucial role in determining the effectiveness of plasma applications in medicine, influencing factors such as energy delivery, frequency, and duration of exposure.
Wound Healing: Wound healing is a complex biological process through which the body repairs damaged tissues following injury. This process involves a series of overlapping phases including hemostasis, inflammation, proliferation, and remodeling, all of which are essential for restoring skin integrity and function. The interaction between cells, extracellular matrix, and various signaling molecules is crucial for effective healing, and the use of advanced technologies can enhance these processes significantly.