title: Structural characterization and viscoelastic constitutive modeling of skin.
abstract: A fascinating material, skin has a tensile response which exhibits an extended toe region of minimal stress up to nominal strains that, in some species, exceed 1, followed by significant stiffening until a roughly linear region. The large toe region has been attributed to its unique structure, consisting of a network of curved collagen fibers. Investigation of the structure of rabbit skin reveals that it consists of layers of wavy fibers, each one with a characteristic orientation. Additionally, the existence of two preferred layer orientations is suggested based on the results of small angle X-ray scattering. These observations are used to construct a viscoelastic model consisting of collagen in two orientations, which leads to an in-plane anisotropic response. The structure-based model presented incorporates the elastic straightening and stretching of fibrils, their rotation towards the tensile axis, and the viscous effects which occur in the matrix of the skin due to interfibrillar and interlamellar sliding. The model is shown to effectively capture key features which dictate the mechanical response of skin.
  
  
  
  Examination by transmission and scanning electron microscopy of rabbit dermis enabled the identification of the key elements in its structure. The organization of collagen fibrils into flat fibers was identified and incorporated into a constitutive model that reproduces the mechanical response of skin. This enhanced quantitative predictive capability can be used in the design of synthetic skin and skin-like structures.
authors.affiliation: University of California San Diego, La Jolla, CA 92093, USA.
authors.forename: Vincent R
authors.initials: VR
authors.lastname: Sherman
authors.affiliation: Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai 200072, People's Republic of China.
authors.forename: Yizhe
authors.initials: Y
authors.lastname: Tang
authors.affiliation: University of California San Diego, La Jolla, CA 92093, USA.
authors.forename: Shiteng
authors.initials: S
authors.lastname: Zhao
authors.affiliation: University of California San Diego, La Jolla, CA 92093, USA; Department of Materials, ETH Zurich, 8093 Zürich, Switzerland.
authors.forename: Wen
authors.initials: W
authors.lastname: Yang
authors.affiliation: University of California San Diego, La Jolla, CA 92093, USA. Electronic address: mameyers@ucsd.edu.
authors.forename: Marc A
authors.initials: MA
authors.lastname: Meyers
mesh_terms: D000818:Animals; D003094:Collagen / Q000502:physiology* / Q000648:ultrastructure*; D019245:Compressive Strength / Q000502:physiology; D055119:Elastic Modulus / Q000502:physiology*; D005260:Female; D006244:Hardness / Q000502:physiology; D066298:In Vitro Techniques; D008954:Models, Biological; D011817:Rabbits; D012867:Skin / Q000648:ultrastructure*; D012879:Skin Physiological Phenomena; D013314:Stress, Mechanical; D013718:Tensile Strength / Q000502:physiology; D014783:Viscosity
chemical_list: D003094:Collagen
keywords: Collagen; Constitutive equation; Dermis; Rabbit; Viscosity