Parametric investigation of multi-pulsed cryogen spray cooling for skin protection during hyperthermal laser lipolysis through in vitro experiment and numerical simulation

Nowadays laser lipolysis has been a widely accepted modality to remove fat. Transcutaneous hyperthermal laser lipolysis has attracted researchers’ interest because of its non-invasive nature and high efficiency. However, the possible thermal damage of skin tissue owing to the competitive absorption of laser energy between water and adipose tissue limits its application, which necessitates the development of efficient skin cooling technology. An in vitro laser experiment of streaky pork under 1210 nm laser irradiation with different power (E) and irradiation (t) proved that the epidermis temperature will exceed the safety threshold of 47 °C when E = 6W and t ≥ 5s, or E ≥ 9W and t ≥ 3s. To protect skin from thermal injury, the multi-pulsed cryogen spraying cooling (MP-CSC) by using R134a was introduced and numerical simulation was conducted to optimize cooling and laser parameters by simplifying the skin tissue to a multi-layered model. The simulation results suggest that hyperthermal laser lipolysis with a power of 6W∼9W and an irradiation duration of 7s can be realized for an area as large as 3 × 7.2 mm², by coupling MP-CSC with a pulse duration of 10 ms, a pulse delay of 2000 ms and a pulse number of 5. In this sense, the MP-CSC has great potential to prompt transcutaneous hyperthermal laser lipolysis.