title: Stress relaxation and stress-strain characteristics of porcine amniotic membrane.
abstract: 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.
authors.affiliation: Graduate School of Science and Engineering, Yamagata University, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Kikuchi
authors.affiliation: Graduate School of Science and Engineering, Yamagata University, Japan.
authors.forename: Zhonggang
authors.initials: Z
authors.lastname: Feng
authors.affiliation: Graduate School of Science and Engineering, Yamagata University, Japan.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Kosawada
authors.affiliation: Graduate School of Medical Science, Yamagata University, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Sato
authors.affiliation: Graduate School of Medical Science, Yamagata University, Japan.
authors.forename: Takao
authors.initials: T
authors.lastname: Nakamura
authors.affiliation: Integrative Bioscience and Biomedical Engineering, Graduate School of Waseda University, Japan.
authors.forename: Mitsuo
authors.initials: M
authors.lastname: Umezu
mesh_terms: D000650:Amnion / Q000502:physiology*; D000818:Animals; D001696:Biomechanical Phenomena; D055119:Elastic Modulus / Q000502:physiology; D004548:Elasticity; D008954:Models, Biological; D017711:Nonlinear Dynamics; D013314:Stress, Mechanical; D013312:Stress, Physiological; D013552:Swine; D054457:Tissue Scaffolds; D014783:Viscosity
keywords: Amniotic membrane; mechanical characteristics; mechanical heterogeneousness; nonlinear visceoelastic model; stress relaxation