Screw-tip Soft Magnetically Steerable Needles

We present a new paradigm in steerable needles comprising flexible tubing with a screw tip and a permanent magnet near the tip. The needle is rotated at its proximal end as the primary mechanism of insertion, rather than being pushed, enabling the screw tip to pull itself through the tissue as it is steered via magnetic torque. Our design enables turns with tighter curvature than previous designs, and it circumvents a well-known problem with existing steerable needles: it is challenging to turn more than 90 degrees without inducing damage. We evaluate our needle via human-in-the-loop robot-assisted magnetic steering in a brain-simulating gel tissue phantom, wherein we achieve a radius of curvature of 29 mm with 210 degrees of turning for a needle with a functional lumen. In a needle without the lumen we achieve a minimum radius of curvature of 10.1 mm. We further evaluate the needle in ex-vivo ovine brain via open-loop steering. We characterize the steerability of the needles as a function of independent parameters. The results demonstrate a needle that promises significantly improved steerability and safety, particularly for use in delicate tissues that create the greatest challenges for existing designs.