Plasma is an ionized gas containing a mixture of neutral atoms, molecules, ions, and electrons. Medical applications utilize Cold Atmospheric Plasma (CAP), which maintains a gas temperature near room temperature, typically below 40°C. This low temperature allows CAP to be applied directly to living tissues without causing thermal damage.
A plasma needle is a specialized CAP device engineered for highly focused and localized medical treatment. It generates a stable, non-thermal plasma plume at its tip. This design bridges the gap between traditional surgical instruments and advanced plasma therapies, enabling minimally invasive procedures.
Defining the Dimensions
The size of plasma needles involves differentiating between the physical device and the active plasma plume it generates. The physical device is often designed as a compact, pen-like, or handheld unit for easy manipulation. These devices connect to a power supply and a gas delivery system, which may be housed in a separate desktop unit.
The active component, the plasma plume—the “needle” referred to in the name—is exceedingly small to ensure high precision. The diameter of this plasma plume is generally in the sub-millimeter to few-millimeter range, often reported to be around 0.1 millimeters up to 3 millimeters. This diminutive scale is a deliberate design choice, allowing the device to treat highly localized areas.
The length of the plasma plume can be controlled by adjusting the gas flow rate and the applied voltage. Some plasma jets, which are closely related to the needle concept, can produce a stable plume up to several centimeters in length. However, the active therapeutic zone immediately outside the device remains tightly focused. This small, controlled size makes the plasma needle distinct from larger cold plasma devices designed to treat broader surface areas.
The Mechanism of Cold Plasma Generation
Creating a stable, focused, non-thermal plasma jet at atmospheric pressure requires specialized engineering. The core challenge is generating a high density of chemically reactive species without significantly raising the gas temperature. This is achieved by creating a non-equilibrium state where electrons are highly energetic, but the heavier ions and neutral gas particles remain cool.
A common method for generating the plasma needle involves Dielectric Barrier Discharge (DBD) or micro-plasma jets. The device typically uses a needle-like electrode housed within a dielectric (insulating) material, such as a ceramic tube. An inert gas, like helium or argon, is flowed through this setup while a high-frequency alternating current voltage is applied.
The high voltage creates an electrical discharge that ionizes the gas, but the dielectric barrier prevents the formation of a hot arc. This results in a continuous stream of microdischarges expelled from the tip as a focused jet of cold plasma. This mechanism produces a variety of reactive oxygen and nitrogen species (RONS) that are the primary agents responsible for the biological effects.
Precision Targeting in Clinical Settings
The specific dimensions of the plasma needle are essential for targeted medical treatments. The ability to generate a sub-millimeter plasma plume is crucial when treating small, irregularly shaped, or delicate biological structures. This high spatial resolution ensures that the therapeutic effects are confined exactly where they are needed.
Oncology and Wound Care
In oncology research, the small plasma plume allows for the selective induction of cell death in cancerous cells while sparing surrounding healthy tissue. This precision is also invaluable in dermatology and wound care. The focused stream of reactive species can decontaminate a localized area, reducing the microbial load without causing collateral damage.
Enhanced Drug Delivery
Furthermore, the focused plasma stream can be used to temporarily disrupt the skin’s outer layer, the stratum corneum, to enhance drug delivery. By creating micro-channels or modifying the lipid barrier, the needle allows therapeutic agents to penetrate more deeply into the tissue. This localized, non-destructive interaction provides an unparalleled level of control for diverse applications like treating dental cavities or targeting specific biofilms.