Background: Recently, amniotic membrane (AM) as scaffold is accumulating much more attention in tissue engineering. It is well-known that the mechanical properties of the scaffold inevitably affect the biological process of the incorporated cells.
Objective: This study investigates the stress relaxation and stress-strain characteristics of AM, which have not been sufficiently elucidated before.
Methods: Porcine AM samples were prepared at four different AM regions and at three different directions. Ramp-and-hold and stretch-to-rupture tests were conducted on a uniaxial tensile apparatus. A nonlinear viscoelastic model with two relaxation coefficients is proposed to fit the ramp-and-hold data. Rupture strain, rupture stress, and elastic modulus of the linear portion of the stress-strain curve are used to characterize the strength properties of the AM.
Results: Sample direction has no significant effect on the mechanical properties of the AM. Samples at the ventral region has the maximum rupture strength and elastic modulus, respectively, 2.29±0.99MPa and 6.26±2.69MPa. The average of the relaxation coefficient for the fast and slow relaxation phases are 12.8±4.4s and 37.0±7.7s, respectively.
Conclusions: AM is a mechanically isotropic and heterogeneous material. The nonlinear viscoelastic model is suitable to model the AM viscoelasticity and potential for other biological tissues.
Keywords: Amniotic membrane; mechanical characteristics; mechanical heterogeneousness; nonlinear visceoelastic model; stress relaxation.