Discharge Mode Enhances the Energy Efficiency of Radiofrequency Microneedle: An In Vivo Porcine Study of Optimized Histological Responses Under Constant Total Energy

Abstract

Objective

To explore the immediate histological effects of insulated (IMRF) and non-insulated (NMRF) radiofrequency microneedles across different discharge modes under a constant total energy, and to evaluate long-term collagen remodeling specifically in the classical discharge mode.

Methods

The backs of Bama pigs (n = 3) were assigned to the classical and sequential discharge modes under IMRF and NMRF treatments at a fixed total energy (1000 mJ). The classical discharge mode group was set as follows: high power and short pulse width (Group A), medium power and medium pulse width (Group B), low power and long pulse width (Group C), and the sequential discharge mode group (ultra-high power and ultra-short pulse width). IMRF and NMRF were used for treatment. The microthermal zone (MTZ) was evaluated and quantified by hematoxylin and eosin (HE) staining immediately after the treatment. Three months after the procedure, the skin lesions were extracted, and the mRNA expression of collagen type I and III was quantitatively evaluated by real-time PCR.

Results

Under the classical discharge mode with constant total energy delivery, a higher power level in IMRF resulted in greater MTZ density (p = 0.014), whereas no significant differences were observed in the depth and width of sub-damage lesions and coagulation zones. In contrast, NMRF failed to produce typical MTZs under any of the three parameter settings. At the 3-month follow-up, type I collagen expression was significantly upregulated in both A and B groups of IMRF (I-A p = 0.002, I-B p = 0.001), while type III collagen expression showed no notable change among all groups (p = 0.671). Under the sequential discharge mode, a sharp increase in single-needle peak power led to the formation of dense MTZs in both IMRF and NMRF. Compared with the medium-power classic mode in the classical discharge mode, the sequential discharge mode resulted in significantly higher MTZ density (IMRF p = 0.002; NMRF p = 0.011). Furthermore, the sub-damage lesion depth was significantly greater with IMRF than with NMRF (NMRF vs. I-B p = 0.017; NMRF vs. IMRF p = 0.01).

Conclusion

MTZ formation is highly dependent on the per-needle power threshold rather than the total energy applied, and is closely associated with the upregulation of type I collagen. The sequential discharge mode, via a “high-power ultrashort pulse width” mechanism, effectively overcomes the activation thresholds of both IMRF and NMRF without increasing the overall thermal load. By generating denser and more stable MTZs, it exhibits promising clinical potential, representing a pivotal direction for future MRF optimization.