Fracture Mechanics Model of Needle Cutting Tissue

This work develops a needle insertion force model based on fracture mechanics, which incorporates the fracture toughness, shear modulus, and friction force of the needle and tissue. Ex vivo tissue experiments were performed to determine these mechanical tissue properties. A double insertion of the needle into the tissue was utilized to determine the fracture toughness. The shear modulus was found by applying an Ogden fit to the stress-strain curve of the tissue achieved through tension experiments. The frictional force was measured by inserting the needle through precut tissue. Results show that the force model predicts within 0.2 N of experimental needle insertion force and the fracture toughness is primarily affected by the needle diameter and needle edge geometry. On average, the tearing force was found to account for 61% of the total insertion force, the spreading force to account for 18%, and the friction force to account for the remaining 21%.