An evaluation of electrocoagulation and thermal diffusion following radiofrequency microneedling using an in vivo porcine skin model

Abstract

Background: Few studies exist that examined the role of radiofrequency microneedling (RFMN) in skin electrocoagulation. This research utilized a porcine model to understand bipolar dermal delivery from an RFMN device.

Aims: The objective of this study was to elucidate and compare the dermal thermal effects of a RFMN device producing 1 and 2 MHz signal amplitudes, with respective voltage and current gradients, utilizing noninsulated and insulated needles by examining the histologic effects on porcine skin.

Methods: Two separate animal studies were conducted to evaluate the electrocoagulation and thermal diffusion effects using the RFMN device. The electrocoagulation effects were assessed histologically using hematoxylin and eosin (H&E) staining, and heating effects were assessed through thermal imaging.

Results: Histology results of the thermal injury induced by insulated needles demonstrated that 2 MHz resulted in a narrow and concentrated coagulation zone as compared to 1 MHz. Further, the 1 MHz insulated needle resulted in ovular shaped tissue coagulation as compared to 2 MHz tissue coagulation that was columnar. Finally, full thermal diffusion occurs seconds after the set RF conduction time.

Conclusion: The findings showed that 1 MHz insulated needle produces larger coagulations with an increase in power level, the 1 MHz noninsulated array was comparable to the 2 MHz insulated array with similar histologic features, and heat dissipates seconds after the set conduction time.

Keywords: dermal heating; electrocoagulation; microneedling; radiofrequency; skin tightening.

FIGURE 1

RFMN Device. A, Device design. B, Handpiece side view with attached microneedle cartridge. C, Microneedle cartridge with protruding needles into dermal layer. D, Illustration of noninsulated microneedles (top) and insulated microneedles (bottom)

FIGURE 2

Image processing technique for area analysis of nonuniform shapes using ImageJ. A, H&E image of RFMN event. B, Threshold color to show electrocoagulation. C, Raw selection of threshold color. D, Electrocoagulation with the reduction of noise for area analysis

FIGURE 3

Tissue reactions after 1 MHz bipolar radiofrequency (RF) treatment using insulated microneedle electrodes on in vivo porcine skin. Porcine skin shows thermal injury in the dermis induced by radiofrequency with set parameters—1 MHz invasive bipolar RF, power level 4(A), 5(B), 6(C), 7(D), 8(E), conduction time of 600 ms, penetration depth of 2 mm using a electrosurgical microneedling unit

FIGURE 4

Tissue reactions after 2 MHz bipolar RF treatment using insulated microneedle electrodes (A‐E) and 1 MHz invasive bipolar RF using noninsulated microneedle electrodes (F‐J) on in vivo porcine skin. Porcine skin shows thermal injury similarities when using 2 MHz insulated microneedle electrode RF compared to 1 MHz noninsulated microneedle electrode RF in the dermis with set parameters—2 MHz (A‐E) and 1 MHz (F‐J) invasive bipolar RF, power level 4(A, F), 5(B, G), 6(C, H), 7(D, I), 8(E, J), conduction time of 600 ms, penetration depth of 2 mm using a electrosurgical microneedling unit

FIGURE 5

Representation of thermal temperature images under IR camera based off electrode placement of RFMN system. A, Representation after 800 ms RF conduction time. B, Representation after a few seconds of thermal dispersion. C, Representation of thermal zones for RFMN system

FIGURE 6

Thermal temperature images of application area using insulated microneedle electrodes at RF conduction time of 800 ms and at power level 10. A, 1 s, (B) 2 s, (C) 8 s, and (D) 10 s