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, CD31-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.
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