Mechanical properties of the skin of Xenopus laevis (Anura, Amphibia)

Abstract

The skin of the aquatic pipid frog, Xenopus laevis, was examined for specific biomechanical features: 1) thickness, 2) maximal strain at break (epsilon f), 3) tensile strength (sigma m), 4) modulus of elasticity (E, stiffness), and 5) the area under the stress-strain curve (W) (breaking energy, toughness). Skin freshly removed from dorsal, ventral, and lateral areas of the body was subjected to uniaxial tension. In both sexes, the dorsal skin is thicker than the ventral. The skin of male frogs was consistently thinner in all body regions than that of females. Most biomechanical parameters showed a considerable range of values in both males (epsilon f = 59-63%, sigma m = 15-16.5 MPa, E = 33.5-38.4 MPa, W = 3.8-4.5 MJ/m3) and females (epsilon f = 102-126%, sigma m = 11.5 MPa, E = 10.4-12 MPa, W = 5.2-6.7 MJ/m3). The disparate epsilon f values in males (low) and females (high) might reflect sexual dimorphism. Static stress-strain curves were typically J-shaped; with the exception of a "toe," the curves rose approximately linearly with increasing strain. The skin of X.laevis, although heterogeneous in structure, possesses features similar to those found in tissues with aligned collagen fibers such as tendons or fish skin. However, in anurans, the skin seems to play a more passive mechanical role during locomotion than in fish.

J-shaped stress-strain diagram of collagen fibers: Frame tension of triangulated surfaces with fixed boundaries

“…3. From the snapshots, we confirm that the variable σ is locally ordered when H/H 0 = 1 for κ = 1 while it is globally J-shaped stress and strain diagram [1][2][3][4]. The canonical model is defined as…”

“…The mechanical properties of macroscopic membranes, such as human skin, have been extensively studied experimentally for a long time [1][2][3]. One interesting mechanical property is the stress-strain diagram.…”

Testes físico-mecânicos e físico-químicos do couro da tilápia vermelha

“…Segundo Hoinacki (1989), essa arquitetura das fibras colágenas é muito importante para a resistência do couro. Greven et al (1995) também afirmaram que a quantidade de espessas camadas de fibras colágenas tem efeito sobre as propriedades mecânicas da pele. Segundo Vademécum... (2004), os valores de referência para couros curtidos ao cromo para vestuário, independentemente do tipo de recurtimento, deve ser de no máximo 60% para o alongamento na ruptura, no mínimo de 25N/mm 2 de resistência à tração ou tensão e, no mínimo, 35N/mm para a resistência de rasgamento progressivo.…”

Sex and weaponry: The distribution of toxin‐storage glands on the bodies of male and female cane toads (Rhinella marina)

“…Thus, the toxin‐containing glands may serve additional functions other than deterrence of predators. In some anurans (but apparently not in cane toads: Schwinger et al., 2001), males and females differ in skin thickness (Greven, Zanger, & Schwinger, 1995, for Xenopus laevis ); such a difference might impose selection on a range of functions that are conferred by glandular secretions and on the structures that produce glandular secretions. …”