Measuring forces in liver cutting for reality-based haptic display

Reality-based modeling of deformable tissues is critical for providing accurate haptic feedback to the surgeon in common surgical tasks such as grasping and cutting organs/tissues. In reality-based modeling, we are interested in modeling tissues as accurately as possible by determining the mechanical properties experimentally and developing a predictive model that is self consistent with the experimentally-determined properties. In this paper, we present the newly developed hardware and software to characterize the mechanical response of pig liver during (ex-vivo) cutting. The macroscopic cutting force-displacement curve shows repeating self-similar units of localized linear loading followed by sudden unloading. The sudden unloading coincides with onset of localized crack growth. This experimental data was used to determine the self-consistent local effective Young´s modulus of the specimens to be used in finite element models. Results from plane-stress and plane-strain finite element analyses reveal that the magnitude of the self-consistent local effective Young´s modulus varies within close bounds.