Characterizing Soft Materials Using an Indentation Device
A surgical simulation device enables surgeons to practice surgery on a virtual patient. Coupling the simulation device with haptic feedback can enable the surgeon to sense how much pressure is required to make an incision into soft tissue, such as the brain. To accurately provide the surgeon with force-feedback information, the material properties of soft tissues will need to be incorporated into the haptic system software. However, soft tissue material properties are currently not well understood. We fabricated an indentation device to characterize the mechanical behavior of soft materials at low strain rates, typical of surgical procedures. During testing, a sample is placed on a z-axis stage that translates vertically upward until it compresses against a spherical indenter tip with a 5 mm radius. Measurements of the indenter displacement and the force applied to the sample surface were used to calculate the elastic modulus, which is a material property that quantifies stiffness. The biomaterial polydimethylsiloxane (PDMS) was selected to validate the force-displacement measurements by comparing the calculated elastic modulus with values reported in the literature. The indentation device was then used to characterize the elastic modulus of pig brain tissue.