**6.1. Volume DBD**

Volume DBD (**Figure 4**) with one isolated electrode has been used in the study of Kalghatgi et al. [68]. Plasma can be with direct contact with a treated object (placed between electrodes) but with increasing distance of electrodes, ignition voltage also increases, too. This means that very high voltages need to be used in real applications. Kalghatgi et al. used pulsed discharge with a pulse duration of 1–10 μs. They applied 10 kV in the frequency range of 50–3.5 kHz to HV electrode isolated by quartz glass. The skin was treated from 15 to 120 s.

**Figure 4.** Volume dielectric barrier discharge.

## **6.2. Surface DBD**

Another version of DBD is surface DBD used in Shimizu et al. [23, 69]. Both electrodes were in contact with isolator layer. Each electrode had a thickness in micrometre dimensions. These low dimensions allowed the decrease of ignition voltage to hundreds of volts. During treatment of skin, electrodes were powered by 600 V with an AC frequency of 27 kHz. Electrodes are created by two copper grids each with a thickness of 18 μm with insulation layer between them with thickness of 100 μm. The high-voltage electrode was covered with an insulation layer and the grounded electrode faced the skin samples at a distance of approximately 1.5 mm (**Figure 5**). Thus, there was no risk of electric shock to users, even when touching the surface of the film electrode. The waveform of the applied voltage and corresponding discharge current are shown in **Figure 5**. Holes between electrode lines allowed gas to pass towards the sample (**Figures 5** and **6**). Argon gas was supplied to the microplasma electrode systems with a flow rate of 5 L/min through the tube that was connected to the electrode. The exposure time was usually between 1 and 5 min (**Figure 7**).

**6. Plasma sources used for skin treatment**

118 Advanced Technology for Delivering Therapeutics

**6.1. Volume DBD**

**Figure 4.** Volume dielectric barrier discharge.

exposure time was usually between 1 and 5 min (**Figure 7**).

**6.2. Surface DBD**

Several kinds of plasma sources were used for investigation of transdermal drug delivery so

Volume DBD (**Figure 4**) with one isolated electrode has been used in the study of Kalghatgi et al. [68]. Plasma can be with direct contact with a treated object (placed between electrodes) but with increasing distance of electrodes, ignition voltage also increases, too. This means that very high voltages need to be used in real applications. Kalghatgi et al. used pulsed discharge with a pulse duration of 1–10 μs. They applied 10 kV in the frequency range of 50–3.5 kHz to

Another version of DBD is surface DBD used in Shimizu et al. [23, 69]. Both electrodes were in contact with isolator layer. Each electrode had a thickness in micrometre dimensions. These low dimensions allowed the decrease of ignition voltage to hundreds of volts. During treatment of skin, electrodes were powered by 600 V with an AC frequency of 27 kHz. Electrodes are created by two copper grids each with a thickness of 18 μm with insulation layer between them with thickness of 100 μm. The high-voltage electrode was covered with an insulation layer and the grounded electrode faced the skin samples at a distance of approximately 1.5 mm (**Figure 5**). Thus, there was no risk of electric shock to users, even when touching the surface of the film electrode. The waveform of the applied voltage and corresponding discharge current are shown in **Figure 5**. Holes between electrode lines allowed gas to pass towards the sample (**Figures 5** and **6**). Argon gas was supplied to the microplasma electrode systems with a flow rate of 5 L/min through the tube that was connected to the electrode. The

far, such as volume dielectric barrier discharge (DBD), surface DBD and plasma jet.

HV electrode isolated by quartz glass. The skin was treated from 15 to 120 s.

**Figure 5.** Top view of microplasma electrode, before discharge (left), discharge with Ar gas – 600 V (right) [69].

**Figure 6.** Cross section of microplasma electrode (left); waveforms of microplasma discharge (right) [69].

**Figure 7.** Experimental set-up with microplasma electrode [23].

## **6.3. Plasma jet**

Plasma jets consist usually from a gas nozzle with one, two or three electrodes [70, 71]. The plasma jet can be realised by two ways—active plasma jets (expanding plasma contains free and high energetic electrons) and remote plasma jets (plasma is potential free and consists of relaxing and recombining active species from inside the nozzle) [70]. The plasma jet in **Figure 8** consists of a Pyrex tube and a central tungsten high voltage (HV) electrode. The grounded electrode is an aluminium ring located at the end of the outer surface of the Pyrex tube. The distance between the skin sample and the outlet of the plasma jet was set to 2 mm. The sample was isolated from the holder by a 30-mm thick PVC isolator or without isolator to compare the effect of the conductive layer under the skin surface as the human body is not isolator. The treatment time of the sample was set from several seconds to 1 min. Argon, nitrogen or argon-water vapour gases were introduced into the plasma jet. The waveform of the voltage and current of argon plasma jet is depicted in **Figure 8** [72].

**Figure 8.** Waveform of plasma jet discharge (left) [72] and plasma jet electrode (right).
