Histological evaluation of monopolar and bipolar radiofrequency microneedling treatment in a porcine model

Background and Objective: Fractional radiofrequency microneedling (FRM) is widely used as an option for skin rejuvenation, however there is a lack of histological evidence for the various energy delivery systems available. The objective was to assess thermal denaturation of tissue and the wound healing response in monopolar mode versus bipolar mode. Histological analysis was performed to demonstrate the efficacy of automatic impedance feedback system in monopolar mode. Study Design and Methods: In this study, the acute thermal effects caused by monopolar FRM treatment to the dorsal skin of pigs were assessed histologically by hematoxylin & eosin (H&E) staining. Then, one session of either monopolar or bipolar FRM was used to treat one or the other side of the pig using varying power levels and pulse widths. The acute and chronic tissue reactions were assessed using H&E, immunofluorescence, and western blot analysis at 0, 14, 30, and 90 days after treatment. The efficacy of the impedance feedback system was also monitored histologically. Results: High-energy FRM treatment produced tissue loss and necrosis. The power level and pulse duration significantly affected the coagulation amount. Histopathology at 0, 14, 30, and 90 days showed that the skin tissue reaction was more pronounced for bipolar compared to monopolar FRM. Immunofluorescence showed the expression of TGF-β, Ki67, MMP3, and elastin increased dramatically with both modes, but were higher in the bipolar FRM treated side. The automatic impedance feedback system could effectively adjust the output energy. Conclusions: We found that bipolar FRM produced greater thermal effects, more collagen coagulation, and more pronounced molecular changes compared with monopolar mode in a porcine animal model.