In vivo skin reactions from pulsed‐type, bipolar, alternating current radiofrequency treatment using invasive noninsulated electrodes

Abstract Background Bipolar, alternating current radiofrequency ( RF ) conduction using invasive noninsulated electrodes consecutively generates independent tissue coagulation around each electrode and then, the converged coagulation columns. Methods Two pulsed‐type RF models at the on‐time pulse width/pulse pack of 30 and 40 milliseconds were designed to amplify the early stage of RF ‐induced tissue reaction using hairless mouse skin in vivo. Then, structural and ultrastructural changes were evaluated in hairless mouse skin samples at baseline and immediately 1 day, 3 days, 7 days, and 14 days after treatment. Results Immediately after pulsed‐ RF treatment, a few chrysanthemum‐like zones of electrothermal coagulation and hypereosinophilic collagen fibers were found in the dermis and dermo‐subcutaneous fat junction. Histochemical staining for periodic acid‐Schiff and immunohistochemical staining for type IV collagen revealed marked thickening of basement membranes. Transmission electron microscopy demonstrated that pulsed‐ RF treatment resulted in higher electron‐dense and remarkably thicker lamina densa, as well as increases in anchoring fibrils, compared with untreated control specimens. Furthermore, CD 31‐positive blood vessels were smaller in size with a slit‐like luminal appearance, without excessive damage to endothelial cells. Conclusion Our data indicated that pulse‐type, bipolar RF energy induces structural and ultrastructural changes in basement membranes and vascular components in hairless mouse skin.