A system was developed to mimic the natural environmental condition of the liver for ex vivo mechanical testing. The system maintains the structural integrity of the liver post mortem by perfusing the organ with physiologic solutions at appropriate pressures and temperature (39 C). Adjusting the heights of the perfusate reservoirs kept the pressures to the hepatic artery and the portal vein at 100-120 mmHg and 15-20 mmHg respectively.

Mechanical testing was performed using the VESPI (Visco-Elastic Soft-Tissue Property Indentation) device. Large strain (>30%) indentations typical of surgical manipulations and diagnostic palpations were applied to the organ using a known load and displacements were recorded over time. These creep tests were performed on whole porcine livers in vivo, ex vivo perfused, and ex vivo unperfused on the same locations. In vitro tests on a sectioned lobe under warm ischemic conditions were also done. Biopsies were taken for histology on the ex vivo states over time and compared against an in vivo control.

Initial results indicate over a 50% difference in the steady state strain response of the liver between the in vivo and ex vivo unperfused states. A 17% difference is noted between the in vivo and the ex vivo perfused states. The in vitro condition did not achieve a steady state response within 5 minutes of load application. Both the in vivo and the ex vivo perfused conditions show good repeatability over time within the same location, whereas the ex vivo unperfused state drastically changes with time. Histological evaluations of the samples over time suggest that structural integrity was maintained in the perfused state but that cellular dissociation was more severe in the unperfused condition.

Since human's can detect differences in force as small as 10%, it is clear that ex vivo testing alone is not sufficient to accurately characterize the mechanical behavior of soft tissues. After minor modifications (changes in perfusate and pressure as suggested by histology) are applied, the ex vivo perfusion system is one method for obtaining the desired results in an accessible, ethical, and controlled manner.