A finite element model of skin deformation. II. An experimental model of skin deformation.

Skin flap design has traditionally been based on geometric models which ignore the elastic properties of skin and its subcutaneous attachments. This study reviews the theoretical and experimental mechanics of skin and soft tissues (I) and proposes a mathematical model of skin deformation based on the finite element method (III). Finite element technique facilitates the modeling of complex structures by analyzing them as an aggregate of smaller elements. This paper gives the results of an animal model developed to study the deformation and mechanical properties of skin, including its viscoelastic properties (hysteresis, creep, and stress relaxation). A new skin extensometer, constructed with digital stepper motors and controlled with a microcomputer, is described to measure these properties for both skin and its subcutaneous attachments. Deformation grids quantitated from photographs with a digitalizing tablet are presented, and computer software is introduced to standardize and analyze them (II). The mathematical model is used to simulate wound closures such as the ellipse and rectangular advancement flap. In addition, a series of mathematical experiments performed to simulate deformation of a strip of skin are described; the relationships between the various elastic constants are investigated; and a comparison of these simulations with actual deformation is presented. Limitations of the model and areas for future investigation are discussed (III).