Toward a miniaturized needle steering system with path planning for obstacle avoidance.

Percutaneous intervention is among the preferred diagnostic and treatment options in surgery today. Recently, a biologically inspired needle steering system was proposed, where a novel "programmable bevel" is employed to control the tip angle as a function of the offset between interlocked needle segments. The new device, codenamed soft tissue intervention and neurosurgical guide (STING), can steer along arbitrary curvilinear trajectories within a compliant medium, and be controlled by means of an embedded position sensor. In this study, we provide details of our latest attempt to miniaturize the STING, with the design and manufacture of a 4-mm outer diameter (OD) two-part prototype that includes unique features, such as a bespoke trocar and insertion mechanism, which ensure that the segments do not come apart or buckle during the insertion process. It is shown that this prototype can steer around tight bends (down to a radius of curvature of ~70 mm), a performance which is comparable to the best systems in this class. With the need to comply with the specific mechanical constraints of STING, this paper also introduces a novel path planner with obstacle avoidance, which can produce a differentiable trajectory that satisfies constraints on both the maximum curvature of the final trajectory and its derivative. In vitro results in gelatin for the integrated prototype and path planner demonstrate accurate 2-D trajectory following (0.1 mm tracking error, with 0.64 mm standard deviation), with significant scope for future improvements.