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TECHNICAL PAPERS: Cell

Heat-Induced Changes in the Finite Strain Viscoelastic Behavior of a Collaagenous Tissue

[+] Author and Article Information
S. Baek, P. B. Wells, K. R. Rajagopal

Departments of Biomedical and Mechanical Engineering, Texas A&M University, College Station, TX 77843-3120

J. D. Humphrey

Departments of Biomedical and Mechanical Engineering, Texas A&M University, College Station, TX 77843-3120jhumphrey@tamu.edu

Pseudoelasticity is a term coined by Fung (9) to denote the nearly strain-rate independent behavior, with little hysteresis, of tissues under cyclic loads.

J Biomech Eng 127(4), 580-586 (Jan 14, 2005) (7 pages) doi:10.1115/1.1934222 History: Received April 29, 2004; Revised January 14, 2005

Supra-physiological temperatures are increasingly being used to treat many different soft tissue diseases and injuries. To identify improved clinical treatments, however, there is a need for better information on the effect of the mechanics on the thermal damage process as well as the effect of the incurred damage on the subsequent mechanical properties. In this paper, we report the first biaxial data on the stress relaxation behavior of a collagenous tissue before and after thermal damage. Based on a two-dimensional finite strain viscoelastic model, which incorporates an exponential elastic response, it is shown that the thermal damage can significantly decrease the characteristic time for stress relaxation and the stress residual.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Comparison of the stress responses during equibiaxial stretching tests for the native (T11=▵,T22=◻) and the thermally treated (T11=▴,T22=∎) tissue. The thermal treatment was isothermal heating with an isometric constraint at λ1=λ2=1.03 and temperature of 75°C for 15min. (a) T22 versus λ2 before and after heating; (b) T11 versus λ1 before and after heating.

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Figure 2

Normalized membrane stress relaxation data for a native (panel a) and a thermally treated (panel b) tissue. The thermal treatment was isothermal heating with an isometric constraint at λ1=λ2=1.03 and temperature of 75°C for 15min.

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Figure 3

Experimental data and theoretical fits for a representative group I stress relaxation test. Experimental data are shown for the native tissue (T11=▵,T22=◻) and thermally treated tissue (T11=▴,T22=∎). The theoretical fit is shown by solid lines. Note that a single set of material parameters provided the fits to all native data, whereas a different set of values provided the fit to all thermally treated data. (a) Native tissue; (b) thermally treated tissue.

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Figure 4

Experimental data and theoretical fits for a representative group II stress relaxation test. Experimental data are shown for the native tissue (T11=▵,T22=◻) and thermally treated tissue (T11=▴,T22=∎). The theoretical fit is shown by solid lines. (a) Native tissue; (b) thermally treated tissue.

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Figure 5

Experimental data and theoretical fits for a representative group III stress relaxation test. Experimental data are shown for the native tissue (T22=◻) and thermally treated tissue (T22=∎). The theoretical fit is shown by solid lines. (a) Native tissue; (b) thermally treated tissue.

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Figure 6

Equilibrium shrinkage ξ1e and ξ2e for the isometric constraint of λ1=λ2=1.03 used in this work (×) versus that for free shrinkage heating (엯) and isotonic heating (◇) from Harris and Humphrey (10). Their samples were heated at temperatures ranging from 65to75°C with different biaxial isotonic constraints (0–21.3N∕m) and different durations (600–7200s).

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