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Research Papers

Effect of Preservation Period on the Viscoelastic Material Properties of Soft Tissues With Implications for Liver Transplantation

[+] Author and Article Information
Sina Ocal

College of Engineering, Koc University, Istanbul, 34450, Turkeysinocal@ku.edu.tr

M. Umut Ozcan

College of Engineering, Koc University, Istanbul, 34450, Turkeyuozcan@ku.edu.tr

Ipek Basdogan

College of Engineering, Koc University, Istanbul, 34450, Turkeyibasdogan@ku.edu.tr

Cagatay Basdogan1

College of Engineering, Koc University, Istanbul, 34450, Turkeycbasdogan@ku.edu.tr

1

Corresponding author.

J Biomech Eng 132(10), 101007 (Oct 01, 2010) (7 pages) doi:10.1115/1.4002489 History: Received April 13, 2010; Revised August 23, 2010; Posted September 01, 2010; Published October 01, 2010; Online October 01, 2010

The liver harvested from a donor must be preserved and transported to a suitable recipient immediately for a successful liver transplantation. In this process, the preservation period is the most critical, since it is the longest and most tissue damage occurs during this period due to the reduced blood supply to the harvested liver and the change in its temperature. We investigate the effect of preservation period on the dynamic material properties of bovine liver using a viscoelastic model derived from both impact and ramp and hold experiments. First, we measure the storage and loss moduli of bovine liver as a function of excitation frequency using an impact hammer. Second, its time-dependent relaxation modulus is measured separately through ramp and hold experiments performed by a compression device. Third, a Maxwell solid model that successfully imitates the frequency- and time-dependent dynamic responses of bovine liver is developed to estimate the optimum viscoelastic material coefficients by minimizing the error between the experimental data and the corresponding values generated by the model. Finally, the variation in the viscoelastic material coefficients of bovine liver are investigated as a function of preservation period for the liver samples tested 1 h, 2 h, 4 h, 8 h, 12 h, 24 h, 36 h, and 48 h after harvesting. The results of our experiments performed with three animals show that the liver tissue becomes stiffer and more viscous as it spends more time in the preservation cycle.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 5

The stress relaxation modulus of bovine liver measured at 1 h, 2 h, 4 h, 8 h, 12 h, 18 h, 24 h, 36 h, and 48 h after harvesting (filtered experimental data for three animals)

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Figure 6

The stress-relaxation response of bovine liver is estimated via curve fitting a Prony series with N=2 and N=3 to the experimental data (dashed) collected 1 h after harvesting (only the first 20 s of the data are displayed for comparison)

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Figure 7

The storage (a) and loss (b) moduli estimated through the stress relaxation response are compared to that of the optimization process (the solid curves represent the solution obtained locally) for the experimental data collected 1 h after harvesting (dashed)

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Figure 8

The storage (a) and loss (b) moduli of bovine liver estimated through the optimization process for the preservation periods of 1 h, 2 h, 4 h, 8 h, 12 h, 18 h, 24 h, 36 h, and 48 h

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Figure 9

(a) The variation in the long term (steady state) elastic modulus of bovine liver as a function of preservation period for three different animals (E∞=0.45∗T+4.1 and R2=0.98). (b) The variation in the settling time of bovine liver as a function of preservation period (settling time=80.3∗ log(T)+333.3 and R2=0.90).

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Figure 4

The storage (a) and loss (b) moduli of bovine liver measured at 1 h, 2 h, 4 h, 8 h, 12 h, 18 h, 24 h, 36 h, and 48 h after harvesting (raw experimental data for one animal)

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Figure 3

The flow-chart of the optimization process for estimating the viscoelastic material coefficients of soft organ tissues

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Figure 2

The set-up for conducting ramp and hold experiments to characterize the stress relaxation modulus of bovine liver

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Figure 1

The set-up for conducting impact experiments to determine the storage and loss moduli of bovine liver

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