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Research Papers

Freezing-Induced Fluid-Matrix Interaction in Poroelastic Material

[+] Author and Article Information
Bumsoo Han1

Department of Mechanical and Aerospace Engineering, University of Texas at Arlington, Arlington, TX 76019bhan@uta.edu

Jeffrey D. Miller, Jun K. Jung

Department of Mechanical and Aerospace Engineering, University of Texas at Arlington, Arlington, TX 76019

1

Corresponding author.

J Biomech Eng 131(2), 021002 (Dec 09, 2008) (8 pages) doi:10.1115/1.3005170 History: Received October 22, 2007; Revised August 06, 2008; Published December 09, 2008

Freezing of biological tissue is emerging in various biomedical applications. The success of these applications requires precise control of the tissue functionality, which is closely associated with the microstructure of the extracellular matrix (ECM). In the present study, the spatiotemporal effects of freezing on the ECM were experimentally and theoretically investigated by approximating biological tissue as a poroelastic material saturated with interstitial fluid. The experiments with type I collagen gel showed that its matrix underwent two distinct levels of structural changes due to freezing: enlarged pore structure of the matrix and increased collagen fibril diameters. The extent of these changes was augmented as the freezing temperature was lowered. The theoretical model suggested that the interstitial fluid might be transported toward the unfrozen region from the phase change interface due to the volumetric expansion associated with the water-ice phase change, and the transported fluid could interact with the matrix and enlarge its pore structure. The model also illustrated the effects of matrix structural properties on this interaction including initial porosity, hydraulic conductivity, and elastic modulus. These results imply that an identical macroscopic freezing protocol may result in different microstructural alterations of poroelastic materials depending on the structural properties of the matrix. This may be relevant to understanding the tissue-type dependent outcomes of cryomedicine applications and be useful in designing cryomedicine applications for a wide variety of tissues.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 9

Effects of elastic modulus and hydraulic conductivity on porosity and interstitial fluid pressure: profiles at t=600s. The same macroscopic freezing condition induces different microstructural changes depending on poroelastic material specific properties. The elastic modulus for (b) is 110mmHg and the hydraulic conductivity for (c) is 7×10−11m2∕smmHg, respectively.

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Figure 8

Effects of initial porosity on the freezing-induced porosity change: porosity profiles at t=600s. By the identical macroscopic freezing condition, poroelastic material with different initial porosities results in different porosity changes during freezing.

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Figure 7

Spatiotemporal dilatation and interstitial fluid pressure profiles during freezing. Corresponding to the freezing-induced porosity change, poroelastic material experiences local dilatation up to 8% and significantly increased interstitial fluid pressure.

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Figure 6

Spatiotemporal porosity profiles during freezing. In the frozen region, the porosity increases along the freezing direction, which indicates the microstructure of collagen matrix swells. Near the phase change interface, a thin layer of the unfrozen region is also dilated due to the excess water from the phase change.

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Figure 5

Temperature profiles, the location of phase change interface, and the interstitial fluid velocity at the interface during freezing of poroelastic material

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Figure 4

Quantified alteration of collagen gel matrix microstructure after freezing∕thawing (n=3 for each freezing temperature): (a) void area ratio and (b) fibril diameter. The void area ratio increases in the frozen region, and the increase in the void area ratio is augmented with lowering the freezing temperature. The fibril diameter also increases after freezing∕thawing, whose extent is also augmented with lowering the freezing temperature.

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Figure 3

Typical SEM micrographs of collagen gel: (a) unfrozen, (b) frozen to −20°C, and (c) frozen to −40°C. The unfrozen gel has a dense matrix structure of thin collagen fibrils, but the frozen ones have a coarse matrix of thick collagen fibrils. The scale bars are 10μm.

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Figure 2

Top view of collagen gel after freezing∕thawing on a directional solidification stage. The unfrozen portion (i.e., UF3 and UF4) is translucent, but the frozen portion (F1 and F2) is transparent.

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Figure 1

Schematic of freezing-induced interstitial fluid transport. Due to the volumetric expansion associated with freezing of water, the interstitial fluid is expected to transport from the phase change interface to the unfrozen region.

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