Nonlinear deformations of soft tissues for surgery simulation

Soft tissue deformation is of great importance to virtual reality based surgery simulation. This paper presents a new methodology for modelling of nonlinear soft tissue deformation from the physicochemical viewpoint of soft tissues. This methodology converts soft tissue deformation into nonlinear chemical-mechanical interaction. Based on this, chemical diffusion of mechanical load and non-rigid mechanics of motion are combined to govern the dynamics of soft tissue deformation. The mechanical load applied to a soft tissue to cause a deformation is incorporated in chemical diffusion and distributed among mass points of the soft tissue. A chemical diffusion model is developed to describe the distribution of the mechanical load in the tissue. Methods are established for construction of the diffusion model on a 3D tissue surface and derivation of internal forces from the distribution of the mechanical load. Real-time interactive deformation of virtual human organs with force feedback has been achieved by the proposed methodology for surgery simulation. The proposed methodology not only accommodates isotropic, anisotropic and inhomogeneous materials by simply modifying diffusion coefficients, but it also accepts local and large-range deformation.