Introducing notched flexible needles with increased deflection curvature in soft tissue

Robotics-assisted needle steering can enhance the accuracy of needle-based medical interventions, especially when the designated target locations are obscured by obstacles. However, the steering techniques using standard needles are not capable of achieving high curvatures and cannot follow tightly curved paths inside tissue. In this work, we introduce a new notched steerable needle with improved curvature. The notched needle is developed by carving a series of small notches on a regular needle shaft. The notches decrease the needle's flexural rigidity and increase the maximum achievable curvature. First, we develop a model of the notched needle deflection inside soft tissue using the finite element method (FEM). The model relates the needle radius of curvature to the number of notches and their locations on the needle shaft. Next, the capability of the notched steerable needle in achieving high curvature and the model's accuracy in predicting needle curvature are validated by performing several needle insertion experiments on a tissue phantom. The results demonstrate that our newly developed needles can achieve a minimum radius of curvature of 198 mm, which is 67% better than standard needles, enabling future research in needle steering in tight spaces.