Dynamic analysis of soft tissues using a state space model

Research on the biomechanical behavior of soft tissues has drawn a lot of recent attention due to its application in tumor pathology, rehabilitation, surgery and biomaterial implants. In this study a finite element (FE) model is applied to represent soft tissues and phantoms with complex geometry and heterogeneous material properties. A solid 3D mixed u-p element S8P0 (8-node for displacement and 1-node for internal pressure) is implemented to capture the near-incompressibility inherent in soft tissues. A dynamic analysis of soft tissues' response to excitation is explored in which, the second order differential equation representing the soft tissues in FE necessitates a time-consuming numerical solution procedure. Moreover, the second-order representation is complicated in estimating the tissue mechanical properties by inverse procedure. Thus, a state space (SS) model is used to equivalently represent soft tissues by transforming the second-order differential equation into a system of linear first-order differential equations. The linear and time-invariant SS representation of soft tissues for general dynamic analysis can reduce the computational cost and a provide framework for the "forward" simulation and "inverse" identification of soft tissues.