A SINGLE INTEGRAL FINITE STRAIN VISCOELASTIC MODEL OF LIGAMENTS AND TENDONS

A general continuum model for the nonlinear viscoelastic behavior of s oft biological tissues was formulated. This single integral finite str ain (SIFS) model describes finite deformation of a nonlinearly viscoel astic material within the context of a three-dimensional model. The sp ecific form describing uniaxial extension was obtained, and the idea o f conversion from one material to another (at a microscopic level) was then introduced to model the nonlinear behavior of ligaments and tend ons. Conversion allowed different constitutive equations to be used fo r describing a single ligament or tendon at different strain levels. T he model was applied to data from uniaxial extension of younger and ol der human patellar tendons and canine medial collateral ligaments. Mod el parameters were determined from curve-fitting stress-strain and str ess-relaxation data and used to predict the time-dependent stress gene rated by cyclic extensions.