Radiofrequency (RF) energy can be emitted into the skin, either non- or invasively, via a monopolar mode that utilizes an active electrode and a grounded electrode or via a bipolar mode that employs two active electrodes. In this experimental study of RF tissue reactions, bipolar RF energy was emitted in vivo to micropig skin at varying microneedle penetration depths, signal amplitudes and conduction times. Immediately after RF treatment, skin samples exhibited RF-induced coagulation columns of thermal injury, separately generated around each microneedle in the dermis. In ex vivo bovine liver tissue, the thermal coagulation columns were found to be concentrated maximally around the pointed tips of each electrode. After a RF conduction time of 2 seconds, the individual areas of thermal coagulation began to converge with neighboring RF-induced coagulation columns; the convergence of coagulation columns was found to start from the tips of neighboring electrodes.

Optical pulses from picosecond lasers can be delivered to the skin as single, flat-top beams or fractionated beams using a beam splitter or microlens array (MLA). In this study, picosecond neodymium:yttrium aluminum garnet laser treatment using a single flat-top beam and an MLA-type beam at the wavelengths of 532 nm and 1,064 nm were delivered on ex vivo genotype-regulated, pigmented micropig skin. Skin specimens were obtained immediately after treatment and microscopically analyzed. Single flat-top beam treatment at a wavelength of 532 nm and a fluence of 0.05-J/cm² reduced melanin pigments in epidermal keratinocytes and melanocytes, compared to untreated controls. Additionally, 0.1 J/cm²- and 1.3 J/cm²-fluenced laser treatment at 532 nm elicited noticeable vacuolation of keratinocytes and melanocytes within all epidermal layers. Single flat-top beam picosecond laser treatment at a wavelength of 1,064 nm and a fluence of 0.18 J/cm² also reduced melanin pigments in keratinocytes and melanocytes. Treatment at 1,064-nm and fluences of 1.4 J/cm² and 2.8 J/cm² generated increasing degrees of vacuolated keratinocytes and melanocytes. Meanwhile, 532- and 1,064-nm MLA-type, picosecond laser treatment elicited fractionated zones of laser-induced micro-vacuolization in the epidermis and dermis. Therein, the sizes and degrees of tissue reactions differed according to wavelength, fluence, and distance between the microlens and skin.