Evaluation and simulation of the multiaxial mechanical behavior of native and engineered soft tissues is becoming more prevalent. In spite of this growing use, testing methods have not been standardized and methodologies vary widely. The strong influence of boundary conditions were recently underscored by Waldman et al. [2002, J. Materials Science: Materials in Medicine 13, pp. 933–938] wherein substantially different experimental results were obtained using different sample gripping methods on the same specimens. As it is not possible to experimentally evaluate the effects of different biaxial test boundary conditions on specimen internal stress distributions, we conducted numerical simulations to explore these effects. A nonlinear Fung-elastic constitutive model (Sun et al., 2003, JBME 125, pp. 372–380, which fully incorporated the effects of in-plane shear, was used to simulate soft tissue mechanical behavior. Effects of boundary conditions, including varying the number of suture attachments, different gripping methods, specimen shapes, and material axes orientations were examined. Results demonstrated strong boundary effects with the clamped methods, while suture attachment methods demonstrated minimal boundary effects. Suture-based methods appeared to be best suited for biaxial mechanical tests of biological materials. Moreover, the simulations demonstrated that Saint-Venant’s effects depended significantly on the material axes orientation. While not exhaustive, these comprehensive simulations provide experimentalists with additional insight into the stress–strain fields associated with different biaxial testing boundary conditions, and may be used as a rational basis for the design of biaxial testing experiments.

1.
Lanir
,
Y.
, and
Fung
,
Y. C.
, 1974, “
Two-Dimensional Mechanical Properties of Rabbit Skin. I. Experimental System
,”
J. Biomech.
0021-9290,
7
(
1
), pp.
29
34
.
2.
Lanir
,
Y.
, and
Fung
,
Y. C.
, 1974, “
Two-Dimensional Mechanical Properties of Rabbit Skin. II. Experimental Results
,”
J. Biomech.
0021-9290,
7
(
2
), pp.
171
82
.
3.
Sacks
,
M. S.
, and
Sun
,
W.
, 2003, “
Multiaxial Mechanical Behavior of Biological Materials
,”
Annu. Rev. Biomed. Eng.
1523-9829,
5
, pp.
251
284
.
4.
Sacks
,
M. S.
, 2000, “
Biaxial Mechanical Evaluation of Planar Biological Materials
,”
J. Elast.
0374-3535,
61
, pp.
199
246
.
5.
Waldman
,
S. D.
, and
Lee
,
J. M.
, 2002, “
Boundary Conditions During Biaxial Testing of Planar Connective Tissues: Part 1: Dynamic Behavior
,”
J. Mater. Sci.: Mater. Med.
0957-4530,
13
, pp.
933
938
.
6.
Waldman
,
S. D.
,
Sacks
,
M. S.
, and
Lee
,
J. M.
, 2002, “
Boundary Conditions During Biaxial Testing of Planar Connective Tissues: Part II: Fiber Orientation
,”
J. Mater. Sci. Lett.
0261-8028,
21
, pp.
1215
1221
.
7.
Horgan
,
C. O.
, 1983, “
Recent Developments Concerning Saint-Venant’s Principle: An Update
,”
Appl. Mech. Rev.
0003-6900,
42
, pp.
295
302
.
8.
Miller
,
K. L.
, and
Horgan
,
C. O.
, 1995, “
End Effects for Plane Deformation of an Elastic Anisotropic Semi-Infinite Strip
,”
J. Elast.
0374-3535,
38
, pp.
261
316
.
9.
Choi
,
I.
, and
Horgan
,
C. O.
, 1977, “
Saint-Venant’s Principle and End-Effects in Anisotropic Elasticity
,”
J. Appl. Mech.
0021-8936,
44
, pp.
424
430
.
10.
Billiar
,
K. L.
, and
Sacks
,
M. S.
, 2000, “
Biaxial Mechanical Properties of the Natural and Glutaraldehyde Treated Aortic Valve Cusp—Part I: Experimental Results
,”
J. Biomech. Eng.
0148-0731,
122
(
1
), pp.
23
30
.
11.
Nielsen
,
P. M. F.
,
Hunter
,
P. J.
, and
Smaill
,
B. H.
, 1991, “
Biaxial Testing of Membrane Biomaterials: Testing Equipment and Procedures
,”
J. Biomech. Eng.
0148-0731,
113
, pp.
295
300
.
12.
Sun
,
W.
,
Scott
,
M. J.
, and
Sacks
,
M. S.
, “
Finite Element Implementation of a Generalized Fung-Elastic Constitutive Model for Planar Tissues
,”
Biomechanics and Modeling in Mechanobiology
, (to be published).
13.
Sun
,
W.
,
Sacks
,
M. S.
, and
Scott
,
M. J.
, 2003, “
Numerical Simulations of the Planar Biaxial Mechanical Behavior of Biological Materials
,” in
ASME Summer Bioengineering
, Miami, FL.
14.
Sun
,
W.
,
Sacks
,
M. S.
,
Sellaro
,
T. L.
,
Slaughter
,
W. S.
, and
Scott
,
M. J.
, 2003, “
Biaxial Mechanical Response of Bioprosthetic Heart Valve Biomaterials to High In-Plane Shear
,”
J. Biomech. Eng.
0148-0731,
125
, pp.
372
380
.
15.
Fung
,
Y. C.
, 1993,
Biomechanics: Mechanical Properties of Living Tissues
,
2nd ed.
,
Springer Verlag
, New York, p.
568
.
16.
Sacks
,
M. S.
,
Smith
,
D. B.
, and
Hiester
,
E. D.
, 1997, “
A Small Angle Light Scattering Device for Planar Connective Tissue Microstructural Analysis
,”
Ann. Biomed. Eng.
0090-6964,
25
(
4
), pp.
678
689
.
17.
Billiar
,
K. L.
, and
Sacks
,
M. S.
, 1997, “
A Method to Quantify the Fiber Kinematics of Planar Tissues Under Biaxial Stretch
,”
J. Biomech.
0021-9290,
30
(
7
), pp.
753
756
.
18.
Langdon
,
S. E.
,
Chernecky
,
R.
,
Pereira
,
C. A.
,
Abdulla
,
D.
, and
Lee
,
J. M.
, 1999, “
Biaxial Mechanical/Structural Effects of Equibiaxial Strain During Crosslinking of Bovine Pericardial Xenograft Materials
,”
Biomaterials
0142-9612,
20
(
2
), pp.
137
153
.
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