Pattern Analysis of 6.78‐MHz Monopolar and 1‐MHz Mono‐/Bipolar Radiofrequency‐Induced Porcine and Rat Skin Reactions

Background Radiofrequency (RF) treatment improves chronologically aged and photodamaged skin with rhytids. The patterns of RF‐induced thermal tissue reactions can vary depending on the tissue resistance and treatment settings. In this study, we aimed to histologically and thermometrically evaluate the patterns of 6.78‐MHz monopolar and 1‐MHz mono‐/bipolar RF‐induced thermal tissue reactions in animal skin in vivo and ex vivo. Methods Various settings of 6.78‐MHz monopolar RF at two different pulse mode characteristics (types S and H) were applied in vivo to minipigs, whereas various settings of 6.78‐MHz monopolar RF or 1‐MHz monopolar or bipolar RF were applied in vivo to rats. Subsequently, samples of the treated tissues were evaluated histologically. Ex vivo, porcine skin samples were treated with 6.78‐MHz monopolar RF, and real‐time noncontact infrared thermometry was used to monitor their surface and deep temperatures. Results In the in vivo porcine skin study, 6.78‐MHz monopolar RF treatments at both pulse characteristics generated similarly effective thermal tissue reactions in the entire dermis and the fibrous septa of subcutaneous fat. However, RF treatment at the type‐S setting delivered RF energy preferentially through the fibrous septa of subcutaneous fat into the muscular fibrous layers. Meanwhile, RF treatment at the type‐H setting induced volumetric thermal reactions in the mid‐ to deep dermis and the fibrous septa of the subcutaneous fat layer. Thirty days post‐treatment, qualitatively increased numbers of thickened and elongated elastic fibers were noted in the lower reticular dermis and the fibrous septa of the subcutaneous fat layer across all experimental settings. RF treatments with three or five stacked passes using two pulse types resulted in different thermometric reactions in the surface and subcutaneous fat areas of ex vivo porcine skin. Additionally, the in vivo rat skin study revealed histopathologic differences based on experimental settings using 1‐MHz RF. Conclusion Our histologic and thermometric pilot experiments demonstrated various patterns of RF‐induced early and late thermal tissue reactions based on the treatment settings, including 6.78‐MHz monopolar, 1‐MHz monopolar, and 1‐MHz bipolar RF delivery.