Finite element modeling of human skin using an isotropic, nonlinear elastic constitutive model

The collagen network in skin is largely responsible for the nonlinear mecha nical stress-strain response of skin. We hypothesize that the force-stretch response of collagen is governed by the entropies of long-chain molecules. We show that a constitutive model derived From the: statistical mechanics of long-chain molecules. corresponding to the fibrous collagen network in s kin, captures the mechanical response of skin. A connection between the phy siologically meaningful parameters of network molecular chain density and f ree length of collagen fibers and the constitutively significant parameters of initial modulus and limiting stretch is thus established. The relevant constitutive law is shown to have predictive capabilities related to skin h istology by replicating in vivo and in vitro experimental results. From fin ite element simulations, this modeling approach predicts that the collagen network in hypertrophic scars is more dense and the constituent collagen fi bers have shorter free lengths than in healthy skin. Additionally, the mode l is shown to predict that as rat skin ages, collagen network density incre ases and fiber free length decreases. The importance of knowledge of the in situ stress state for analyzing skin response and validating constitutive laws is also demonstrated. (C) 2000 Elsevier Science Ltd. All rights reserv ed.