Plastic hexahedral FEM for surgical simulation

Area of Science:

• Computational mechanics
• Biomedical engineering
• Surgical simulation

Background:

• Soft-tissue manipulations are integral to surgery.
• Excessive force during surgery can cause plastic deformation, impacting surgical outcomes.
• Accurate modeling of tissue deformation is crucial for effective surgical simulation.

Purpose of the Study:

• To extend the finite element method (FEM) for modeling tissue plasticity in surgical simulations.
• To develop a hexahedral mesh-based approach for simulating large plastic deformations in soft tissues.
• To enhance the open-source Simulation Open Framework Architecture (SOFA) with hyperelastic and plastic deformation capabilities.

Main Methods:

• Extended volumetric FEM to model tissue plasticity using hexahedral thick shells or embedded organs.
• Integrated plasticity into the SOFA framework (Caribou) by factoring deformation gradients into elastic and plastic components.
• Implemented techniques to avoid re-meshing, such as limits on element twist and plasticity bounds, while enforcing volume preservation.

Main Results:

• Developed a hexahedral FEM that overcomes limitations of tetrahedral FEM for surgical simulation.
• Extended hyperelastic FEM to include stretching plasticity in hexahedral elements.
• Demonstrated that high-order accurate blended-vertex deformation allows coarse hex meshes to model large deformations without re-meshing.
• Verified volume preservation for significant deformations and compared different plasticity models.

Conclusions:

• Generated hexahedral meshes can be directly used for finite element analysis of plastic deformation.
• The developed method provides accurate simulations of tissue plasticity suitable for surgical applications.
• The enhanced SOFA framework with Caribou offers a robust tool for advanced surgical simulation.