Investigating the potential of non-thermal microwave as a novel skin penetration enhancement method

Microwaves (MW), a part of the electromagnetic spectrum at 0.3–300 GHz, affect human body in different ways through its thermal and athermal effects, including fluidization of cell membranes and liquid crystalline systems. Due to presence of such structures in skin barrier, it was decided here to investigate the potential of athermal MW as skin penetration enhancer. In this investigation, nitrofurazone was chosen as the model penetrant and its permeation through rat skin was studied in vitro at 45 and 90 min exposure intervals using MW intensities of 3, 15, 30, 60, 120 W at 2450 MHz. Results revealed that at 30 °C and 45 min exposure, 3 W MW does not affect permeation of nitrofurazone (P = 0.148), while higher intensities increased its flux significantly (P < 0.05) in a intensity-dependent manner up to 2.7 times. When the duration of exposure increased to 90 min, the enhancement ratio also increased to reach a maximum of 3.3. Applying 60 W MW at 25, 30, 37 and 42 °C resulted in a parabolic relationship between temperature and enhancement ratio. The present results reveal that microwave can act as a skin penetration enhancement method and that its effect depends on applied intensities, exposure time and temperature.