Effects of clamping force on carrying energy ability of a harmonic scalpel

The carrying energy of a harmonic scalpel determines biological tissue coagulation quality, and is related to the clamping force between the blade of a harmonic scalpel and the biological tissue. The objective of this study is to investigate the effect of clamping force on the carrying energy ability of a harmonic scalpel. First, the carrying energy model of a harmonic scalpel transducer is developed, which is regarded as a mass-spring-damper oscillator. Then, the characteristic parameters at various clamping forces are determined by a least-square parameter identification method, which represent the carrying energy ability of harmonic scalpel. Furthermore, the carrying energy ability relative to clamping force is evaluated by coagulating biological tissue in vitro. The results show that mass, force resistance and stiffness of mass-spring-damper oscillator increase with increasing clamping force, which reflects the increase of the harmonic scalpel carrying energy ability. This trends plateaus with the continuous increase of clamping force. Correspondingly, the coagulation depth of biological tissue increases with the increase of clamping force, and an optimal clamping force exists. The results of the histological investigations are in good agreement with carrying energy under different clamping force conditions.