A Computational Model of Scalp Skin for in Vivo Material Characterization and Reconstructive Surgery Simulation

A computational model is formulated for the in vivo mechanical characterization of human scalp skin and the simulation of reconstructive surgical procedures on the scalp. The scalp flaps are represented as isotropic, hyperelastic and homogeneous plane membranes undergoing large deformations. The time independent elastic potential has the form proposed by Tong and Fung [1] and is defined in terms of the strain invariants or the components of the Green-Lagrange strain tensor through three or five parameters. In order to simulate the complex geometry and loading conditions of the system, the domain is discretized and the problem is solved using the finite element method. An inverse procedure formulated [2] to identify the model parameters and the pre-existing stress state of the skin from load-displacement curves of in vivo scalp flaps obtained using the experimental methodology developed by Raposio and Nordström [3]. It is shown that the information content of the experimental data currently available does not allow the derivation of all parameters with no indeterminacy. The indeterminacy does not affect the simulation of a reconstructive surgery procedure performed under conditions similar to those of the experimental tests. However, it may affect simulations performed under different conditions. An investigation is then performed, using synthetic data, to identify which are the experimental measurements that could lead to a better estimate of all unknown parameters.