Viscoelastic Characterization of Perfused Liver: Indentation Testing and Preliminary Modeling

Computer-aided medical technologies are currently restricted by the limited understanding of the mechanical response of solid abdominal organs to finite loading conditions typical of surgical manipulation [5]. This limitation is a result of the difficulty in acquiring the necessary data on whole organs. To develop a constitutive model capable of predicting complex surgical scenarios, multiple testing modalities need to be simultaneously obtained to capture the fundamental nature of the tissue’s behavior under such conditions. In vivo tests are essential to obtain a realistic response, but their inherent difficulty and unknown boundary conditions makes them an impractical approach. Ex vivo tests are easy to control, but the response is unrealistic. A perfusion apparatus was previously developed that obtained near in vivo conditions for whole livers while allowing the ease of ex vivo testing [3]. This work presents the results from complete viscoelastic testing of whole-perfused livers with surgically relevant time-dependant indentation loading profiles to 35% nominal strain. These results will aid in the development of a constitutive model for the liver whose parameters can be related to the physical constituents of the tissue. As an intermediate modeling step, a 1D rheological modeling tool was used to identify the form and initial parameters for a constitutive model.