Mechanics of tissue rupture during needle insertion in transverse isotropic soft tissue.

During robot-assisted percutaneous puncture surgery, a bevel-tipped needle is inserted into a fiber-structured soft tissue, which has transverse isotropic mechanical properties. Tissue rupture may lead to needle bending and insertion error. Therefore, analysis of the mechanics of rupture events in transverse isotropic space is essential for the precise control of needle motion. We analyzed the needle stiffness force and the cutting force, both related to rupture events, which are caused by contact deformation and tissue cutting, respectively. A modified model based on a homogeneous elastic half-space contact force model was used to describe the variation in the stiffness force of the needle. An energy-based maximum stiffness force model was proposed to predict the surface rupture for a needle that is inserted at different orientations. A model for the cutting force was presented based on a solid mechanics theory of unidirectional fiber-reinforced composite material to analyze the effect of the needle tip pose on the cutting force. Experiments on porcine muscle confirmed that the stiffness force and the cutting force were clearly influenced by the insertion orientation angle. The developed models could predict the stiffness force and the cutting force during needle insertion into the transverse isotropic tissue. This method provides a foundation for predicting needle deflection in the transverse isotropic space. Graphical abstract Force modeling for needle insertion in transverse isotropic soft tissue.