Characterizing the Biomechanical Response of Liver

Motor vehicle collisions can result in life threatening liver injuries. Dummies are utilized to study injury in motor vehicle collisions; however, no crash test dummies are currently equipped to represent individual solid organs. This has increased the use of finite element models to help reduce these injuries; however, accurate material models need to be established to have accurate injury assessment using these models. This thesis presents a total of 4 studies that explore the biomechanical response of liver. The research on bovine liver is geared to understanding whether or not liver tissue can be frozen prior to testing and what environmental temperature the liver should be tested at. The first study utilized two bovine livers that were each divided in half and one half was tested at 75°F while the other half was tested at 98°F. A total of 24 tensile failure tests were performed on the parenchyma. It was determined that there were no statically significant differences between failure stresses and strains between the testing temperatures. To test the effects of freezing, tensile tests were performed on the parenchyma of a single bovine liver that was divided in half. One half was frozen and then thawed prior to tensile testing while the other was tested fresh. It was determined that freezing reduces average failure strain by 50%. The research on human liver was geared toward understanding the rate dependence during uniaxial tension tests and unconfined compression tests. Samples were constructed of only the parenchyma. A total of 7 livers were used to create the 51 tensile specimens and a total of 6 livers were used to obtain the 36 unconfined compression specimens. For the uniaxial tensile tests, average failure stresses ranged from 40.21 to 61.02 kPa while average failure strain ranged from 24% to 34%. For the unconfined compression tests, average failure stresses ranged from -165 to -203 kPa while average failure strain ranged from -46% to -61%. It is expected that the results presented in this thesis will: 1) Help establish correct transportation and procurement methodology for soft tissue mechanical testing. 2) Provide tension and compression material response of the human liver at multiple strain rates for use as material properties and injury tolerance values to validate finite element models.