Uniaxial and biaxial mechanical behavior of human amnion
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Uniaxial and biaxial mechanical behavior of human amnion Michelle L. Oyena) Department of Biophysical Sciences and Medical Physics, and Department of Obstetrics, Gynecology and Women’s Health, University of Minnesota, Minneapolis, Minnesota 55455
Robert F. Cook Independent Consultant, Minneapolis, Minnesota 55413
Triantafyllos Stylianopoulos Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455
Victor H. Barocas Department of Biomedical Engineering, University of Minnesota, Minneapolis, Minnesota 55455
Steven E. Calvin Department of Obstetrics, Gynecology and Women’s Health, University of Minnesota, Minneapolis, Minnesota 55455; and Minnesota Perinatal Physicians/Allina Health System, Minneapolis, Minnesota 55407
Daniel V. Landers Department of Obstetrics, Gynecology and Women’s Health, University of Minnesota, Minneapolis, Minnesota 55455 (Received 7 May 2005; accepted 3 August 2005)
Chorioamnion, the membrane surrounding a fetus during gestation, is a structural soft tissue critical for maintaining a successful pregnancy and delivery. However, the mechanical behavior of this tissue membrane is poorly understood. The structural component of chorioamnion is the amnion sublayer, which provides the membrane’s mechanical integrity via a dense collagen network and is the focus of this investigation. Amnion uniaxial and planar equi-biaxial tension testing was performed using cyclic loading and stress-relaxation. Cyclic testing demonstrated dramatic energy dissipation in the first cycle followed by less hysteresis on subsequent cycles. Fractional energy dissipation per cycle was strain dependent, with greatest dissipation at small strain levels. Stress-relaxation testing demonstrated a level-dependent response and continued relaxation after long relaxation times. A nonlinear viscoelastic (separable) hereditary integral approach was inadequate to model the amnion response due to intrinsic coupling of the strain- and time-dependent responses. I. INTRODUCTION
The chorioamnionic (CA) membrane is the strong and resilient tissue that surrounds a fetus during gestation (Fig. 1; right figure after Ref. 1). Premature failure of the chorioamnion, prior to full gestation, accounts for one a)
Address all correspondence to this author. Present address: University of Virginia, Center for Applied Biomechanics, 1011 Linden Ave., Charlottesville, VA 22902. e-mail: [email protected] This paper was selected as the Outstanding Meeting Paper for the 2004 MRS Fall Meeting Symposium Y Proceedings, Vol. 844. DOI: 10.1557/JMR.2005.0382 2902
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J. Mater. Res., Vol. 20, No. 11, Nov 2005 Downloaded: 14 Mar 2015
third of all premature human births and affects 3% of all pregnancies.2 The CA is a bilayer, consisting of a thick and cellular chorion layer3 and a stiff and strong amnion layer, predominantly composed of dense collagen (Fig. 1, center and left). The amnion (A) layer is approximately 20% of the chorioamnion thickness at term but dominates the m
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