Instrumentation for Testing Soft Tissue Undergoing Large Deformation: Ex Vivo and In Vivo Studies

Abstract

Biomechanical property of soft tissue derived from experimental measurements is critical to develop a reality-based soft-tissue model for minimally invasive surgical training and simulation. In our research, we have focused on developing a biomechanical model of the liver with the ultimate goal of using this model for local tool-tissue interaction tasks and providing feedback to the surgeon through a haptic (sense of touch) display. In this paper, we present two devices that we have designed and built, namely, ex vivo and in vivo testing devices. We used them to measure the experimental force and displacement data of pig liver tissue. The device for ex vivo experiments uses a PC-based control system to control the motion of the probe and acquire the experimental force and displacement data. The force resolution for ex vivo testing was 0.002N (as per the resolution information provided by the manufacturer) and the probe velocity ranged from 0.1mm∕s to 25.4mm∕s. The device was designed so that it could be easily used for both small probe (tissue sample larger than the indenting probe surface area) testing as well as large probe (tissue sample smaller than the indenting probe surface area) testing. The device for in vivo experiments used a microcontroller-based instrumentation to control the motion and acquire and store the data on a multimedia memory disk. This device is designed for the purpose of acquiring experimental force and displacement data in vivo. The primary challenge in the design of the device for in vivo experiments was the limited workspace for device operation. The force resolution for in vivo testing was 0.015N and the displacement resolution was 0.02mm. The sampling frequency for data acquisition for in vivo testing was 50Hz.