Biaxial Mechanical Response of Bioprosthetic Heart Valve Biomaterials to High In-plane Shear

[+] Author and Article Information
Wei Sun, Michael S. Sacks, Tiffany L. Sellaro

Engineered Tissue Mechanics Laboratory, Department of Bioengineering

William S. Slaughter

Department of Mechanical Engineering, University of Pittsburgh, Pittsburgh, PA

Michael J. Scott

Edwards Lifesciences, Irvine, CA

J Biomech Eng 125(3), 372-380 (Jun 10, 2003) (9 pages) doi:10.1115/1.1572518 History: Received April 15, 2002; Revised February 03, 2003; Online June 10, 2003
Copyright © 2003 by ASME
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(a) A schematic of the biaxial specimen showing the specimen axes (X1−X2 axes) and material axes (i.e. X1−X2 axes), which was aligned at a 45° angle with respect to the specimen axes. (b) Experimental protocols of stress-control biaxial testing, where the labels indicate the ratios of the normal Lagrangian stress in the specimen axes coordinate system (T11:T22).
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A representative biaxial mechanical response for each component, with peak shear stresses of 400 kPa and peak shear strains of ±0.10. One novel feature observed was that the mechanical response to the T11:T22=1:0 and 0:1 were quite different from the other protocols. Labels indicate the ratios of the normal Lagrangian stress in the specimen axes coordinate system (T11:T22).
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Representative biaxial response for the in-plane shear response before and after glutaraldehyde fixation, which affected the low-stress (<250 kPa), whereas the remaining higher stress region were comparable.
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Results for the seven parameter Fung model (Q7) applied to (a) the subdivided data set I (r2=0.980) and data set II, demonstrating very good fits (r2=0.963). Inset-biaxial protocols for each set.
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Predictive capability results for the equal-biaxial protocol 1:1 by fitting the seven parameter model (Q7) to the T11:T22=1:0.1 and 0.1:1 protocols only. Even though equal-biaxial protocol lies within the stress and strain ranges used for parameter determination, the interpolated result is poor. For illustration purposes the peak values of S11,S12 and S22, which were 1.4e+5,0.4E+5, and 1.2E+5 kPa, respectively, were truncated.
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Representative response functions for (a) S12 vs. E11 and E12, with E22=0.2, indicating that S12 had a relatively weak dependence on E11. In contrast, the S12 vs. E12 and E22 with E11=0.18 responses shown in (b) indicated that S12 had a strong dependence on both E12 and E22.
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In-plane shear fit results for the eight parameter model (Eq. (5)) fit to (a) data set I only and predicting the set II response, and (b) all data simultaneously. As expected, the fit to set I only demonstrated a better fit to both the inner test protocols (set I), but also demonstrated reasonable predictive capabilities.




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