Ratchetting of porcine skin under uniaxial cyclic loading.

Skin soft tissue (e.g., porcine skin) was tested in vitro under uniaxial cyclic loading, and its biomechanical responses were investigated to realize some basic properties which are very significant in assessing the fatigue life of skin soft tissue. The results show that a cyclic accumulation of peak and valley strain, which can be terminologically called as ratchetting in terms of material science of metals, occurs in the porcine skin during cyclic tension-unloading, tension-tension and compression-unloading tests. Observed ratchetting of porcine skin depends on load level and loading orientation greatly and also presents remarkable rate dependence due to the viscosity of skin soft tissue. The ratchetting is much more remarkable during the test at lower loading rate than that at higher loading rate. Moreover, some basic properties of porcine skin were also investigated by monotonic tension, compression and creep tests in order to address the ratchetting more comprehensively. Finally, collagen fiber bundles in the porcine skin and their variation during monotonic and cyclic tension tests were observed microscopically in term of standard iron-hematoxylin staining method. The observations are useful to realize the micro-mechanism of ratchetting deformation.