Study of soft tissue cutting forces and cutting speeds.

A versatile equipment to study the cutting of soft tissue with surgery scalpel was designed and constructed. Experiments were performed with pig liver (ex-vivo) to measure the blade-tissue interaction forces at cutting speeds ranging from 0.1 cm/sec-2.54 cm/sec. The experimentally measured force-displacement curves reveal that the liver cutting process was made up of a sequence of repeating local units with similar features. Each local unit was comprised of a linear deformation phase followed by a crack growth phase. A method was developed to quantify the deformation resistance of the tissue during each local deformation phase in cutting. This deformation resistance was presented in the form of a self-consistent local effective Young's modulus (LEYM), and was determined by post-processing force-displacement data with finite element models. Values for LEYM were determined from plane-stress finite element model and plane-strain finite element model. The plane-stress LEYM values were within a close bound of the plane-strain values. Results of the self-consistent LEYM at different cutting speeds show that the tissue's resistance to deformation decreased as the cutting speed increased.