M.Sc Thesis

M.Sc StudentEshel Hagai
SubjectEffects of Strain Level and Proteoglycan Depletion on
Preconditioning and Viscoelastic Responses
of Rat Skin
DepartmentDepartment of Biomedical Engineering
Supervisor PROFESSOR EMERITUS Yoram Lanir


The mechanical response of rat dorsal skin was experimentally studied under cyclic uniaxial ramp stretches to various strain levels. Special emphasis was paid to the effects of the preconditioning protocol on the stress-strain relation-ship, and to the effects of strain level and proteoglycan (PG) depletion, on viscoelasticity and preconditioning responses. The results show that preconditioning significantly reduced both the slope of the low strain stress-strain relation-ship, and the stress levels at consecutive stretch cycles. Following a 10 min rest there was a significant partial recovery. Stress decay due to preconditioning was significant at all strain levels, and increased with strain. Stress relaxation was significant at all strain levels, but varied little with strain. Statistical analysis of the data reveled that preconditioning is unaffected by PG depletion, that relaxation is affected by depletion at low and intermediate strain levels, and that recovery is unaffected by PG depletion. These results are consistent with the following notion: (1) skin consists of three mechanical components which determine its response: elastin and proteoglycan which dominate the low strain response and are effected by the strain level, and collagen which dominates the high strain response and is unaffected by strain level and PG depletion; (2) the viscoelasticity of elastin and PG vs. that of collagen are similar, so that rat skin can be regarded as quasilinear viscoelastic.