Stress relaxation and stress-strain characteristics of porcine amniotic membrane

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 AMsamples were prepared at four different AMregions 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 ± 0.99 MPa and 6.26 ± 2.69 MPa. The average of the relaxation coefficient for the fast and slow relaxation phases are 12.8 ± 4.4 s and 37.0 ± 7.7 s, 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.