Influence of cutaneous appendages on bipolar radiofrequency hyperthermia on facial skin rejuvenation

Abstract The current academic literature on the mechanisms underlying skin tissue thermotherapy predominantly employs a homogeneous layer structure that overlooks the microstructural electrothermal effects of cutaneous appendages. This study aims to investigate the influence of cutaneous appendages on bipolar radiofrequency (RF) hyperthermia of facial skin. Two-dimensional finite element method models were developed to represent skin tissue with and without cutaneous appendages (appendage model or homogeneous model). The architecture of the cutaneous appendages was constructed on the basis of sagittal images derived from light micrographs of longitudinal sections of the female cheek in the appendage model. The COMSOL Multiphysics 6.0 software suite was employed to analyze the electrothermal responses of homogeneous model and appendage model. Porcine skin tissue and self-developed bipolar RF heating platform were used to conduct ex vivo experiments. Under the simulation conditions of 4.84 W RF power, 2.4 mm electrode spacing, and 200 s −1 heating duration, the maximum temperature was observed at a depth of 2.23 mm in the appendage model (45.2 °C), while the homogeneous model reached a peak temperature of 46.8 °C at a depth of 1.86 mm. Under identical conditions, ex vivo experiments resulted in a peak temperature of 45.2 °C at a tissue depth of 2.19 mm. The simulated temperature distribution was found to closely resemble that of the appendage model. Due to the differences in electrical conductivity between various cutaneous appendages—such as hair follicles, sebaceous glands, and sweat glands—and the surrounding epidermal and dermal tissues, the distribution of electrostatic fields exhibits nonlinear characteristics. Cutaneous appendages influence the distribution of static electric fields and obstruct the flow of electrical current and power absorption. This enhanced accuracy makes the appendage model a valuable tool for further investigation of hyperthermia.