Development and evaluation of a titanium-based planar ultrasonic scalpel for precision surgery

This paper introduces a titanium-based planar ultrasonic microscalpel. The concept of silicon-based planar ultrasonic transducers has already been proven, but they are not yet suitable for clinical use due to material failure. The main objective of this work was to develop a smaller, lighter, and more cost-effective ultrasonic scalpel that could be used as an alternative or supplementary device to current surgical instruments. Various prototypes were fabricated and characterized, differing in bonding by three epoxy adhesives and two solder pastes as well as three variations in tip design. The instruments were designed to operate in the frequency range of commercial instruments and to generate a longitudinal displacement amplitude. The electro-mechanical characterization through impedance analysis and vibration measurements was complemented by an in vitro cutting trial and an acute in vivo animal experiment in comparison to commercial ultrasonic and electrosurgical devices. The operating frequency was around 40 kHz and 48 kHz depending on whether matched or unmatched operation was used. Unmatched operation turned out to be more suitable, achieving displacement amplitudes of 25.3 μm and associated velocity amplitudes of up to 7.9 m/s at an electrical power of 10.2 W. The cutting ability was demonstrated in vivo by successful dissection even under anticoagulation. The geometry of the instrument tip was found to have a major influence on cutting performance by affecting the resonance behaviour and tissue penetration.