Development of Focused Ultrasound System for Skin Tightening Therapy

In this study, a focused ultrasound system for skin tightening therapy was developed. Focused ultrasound has the ability to concentrate acoustic power to generate a steep temperature elevation at the subcutanous tissue and superficial muscular aponeurotic system (SMAS) to cause collagen denaturation, contraction and remodeling. In addition, ultrasound has a great ability of soft tissue penetration for non-invasive treatments. Piezoelectric ceramics elements were cut and then filled with epoxy. After that, the elements were compressed with a designed mold to make them become focused piezoelectric-composite. The transducer was made with a diameter of 10.0 mm, a radius of curvature of 12.0 mm and operated at a frequency of 5.0 MHz. A function generator was connected to a power amplifier to drive the transducer, and a matching circuit was made to achieve a better output power. The electro-acoustic transfer ratio was measured by a radiation force meter. In this study, we used thermo-sensitive phantom to observe the heating effect, an ex vivo porcine model and an in vivo rat model were used to confirm the heating effect and the characteristics of focal zones. We combined the focused ultrasound system with a mechanical scanning system using Labview software. The focused ultrasound system can treat multiple points precisely to reduce the total treatment time by using the mechanical scanning system. The results showed that the electro-acoustic transfer ratio was about 44% and could reach the lower critical solution temperature (LCST) of the thermo-sensitive hydrogel. Experimental studies in ex vivo porcine model and in vivo rat model showed that the focused ultrasound transducer could effectively cause tissue denaturation. In this study, we developed a focused ultrasound system for skin tightening therapy. The manufacturing process of piezoelectric-composite material and the feasibility of effective sonication were verified. The characteristics of focal zones and the heating effects on tissues by the transducer were confirmed.