This thesis includes the development, construction and testing of internal organ phantoms, with focus on the liver, for biomechanical testing. Phantoms have various biomedical applications such as surgical simulations, minimally invasive surgery, soft tissue characterization, diagnostic tools and instrumentation calibration. However, there is little work present in literature regarding phantoms and the work that is currently available does not account for the non-linear viscoelastic properties as well as the Glisson’s capsule. In this work, three different phantoms are presented: a fluid-filled phantom, a perfused phantom and a hydrogel-based liver phantom. A testing apparatus is designed, built and used to measure the force-displacement data during the indentation of the phantom.
The first phantom that is designed and constructed follows the basis of a fluid-filled vessel. It is composed of a linear low-density polyethylene (LLDPE) bag filled with different fluids namely: water, a 1:1 water/glycerine mixture and glycerine. The phantoms are subjected to quasi-static loading as well as relaxation testing. The effect of density and viscosity, its size, and confined and unconfined boundary conditions are characterized.
The second phantom is designed to investigate the effects of hepatic macrocirculation on the biomechanical properties of the liver. The phantom is made of two-part silicone (Smooth-On, ECOFLEX 00-30), and contains a network of conduits to model the large blood vessels in the liver. A perfusion system that captures the general features of the human hepatic circulation is used to help investigate the effects of the different flow parameters such as pressure and flow rate on the biomechanical characteristics of the liver. The perfusion system is designed to reproduce comparable pressures to the human portal vein and hepatic artery.
The third phantom is made of two parts, a hydrogel inner layer with a LLDPE outer layer. The idea behind this phantom is to represent the organ as accurately as possible by accounting for the capsule that surrounds the organ as well as the biphasic (solid and fluid) nature of the organ. A biphasic poroviscoelastic model is used to model the hydrogel while the LLDPE uses a non-linear hyperelastic and viscoelastic model. Modeling is done in ABAQUS to fit the experimental data obtained from quasi-static indentation and relaxation testing using a parametric study.
In conclusion, phantoms replicating the non-linear viscoelastic properties observed in organs are presented and characterized.