Neurosurgery could benefit from robot-assisted minimally invasive approaches, but existing robot tools are insufficiently small and compact. Magnetic actuation is an attractive approach to medical robotics because it allows small, modular serial mechanisms to be remotely actuated. Despite these advantages, magnetic actuation is relatively weak compared to alternative actuation methods. In this paper, we introduce a novel analytical model for magnetic serial robots, use this model to design two prototypes, and then demonstrate that a 4-mm-diameter prototype without any internal mechanical transmission can produce forces up to 0.181 N: high enough to perform delicate microsurgical tasks. We also demonstrate that the robot can achieve a closed-loop step response rise time of 0.71 seconds with an overshoot of 7.8%: sufficiently fast for surgical motions while maintaining a tip precision of less than 2 mm during a worst-case dynamic motion. These experiments provide strong evidence for the feasibility of directly-driven magnetic tools for neurosurgical applications, and they motivate future investigations in this area.

Dexterity is demanded for an endoscopic tool to handle complicated procedures in neurosurgery, e.g., removing diseased tissue from inside the deep brain along a tortuous path. Current robotic tools are either rigid or lack wristed motion ability at the tip, leading to limited usage in minimally invasive procedures. In this paper, a hybrid steerable robot with a magnetic wristed forceps is proposed to provide enhanced dexterity for endoscopic epilepsy surgery. A set of three precurved Nitinol tubes with concentric deployment, called a concentric tube robot (CTR), serves as a 6 degrees-of-freedom (DoF) robotic positioner. The magnetic wristed forceps is composed of a rotational wrist joint, and forceps at the tip, both of which are actuated remotely by magnetic fields. The magnetic wrist and forceps provide an extra rotational DoF and a gripping DoF on top of the CTR, respectively. The magnetic wrist and gripper are designed to have a hollow channel along their common axis, inside which a soft tube is deployed as a second functional tool for irrigation or suction. An electromagnetic navigation system (eMNS) with 8 coils is used to create the quasi-static magnetic fields. Experimental characterization of the robot kinematics is performed and the results show the mean motion error of CTR is 2.8 mm. The workspace is also analyzed and results indicate that the proposed hybrid robot has a significantly larger reachable area compared to the one of the CTR alone. Mock epilepsy procedures are performed on a brain phantom to validate the feasibility of the hybrid robot for neurosurgery applications.

Magnetic torsion springs are capable of producing unique and useful torque-displacement responses that are not possible with elastic springs. Millimeter-scale magnetically-actuated robots, which are gaining increasing interest in biomedical applications, would benefit from the use of magnetic torsion springs. However, existing magnetic torsion springs are difficult to fabricate at that scale and can only produce sinusoid-like responses. Here we show that the magnets embedded in the links of a robot for actuation purposes can also be leveraged to produce torsion spring-like behavior. This Simultaneous Magnetic Actuation and Restoring Torque (SMART) spring design can enable switching or pop-up behaviour in millimeter-scale magnetically-actuated mechanisms. A novel analytical model, validated both numerically and experimentally, is used to design constant-stiffness and nonlinear bistable SMART springs. These springs are integrated into a novel 3.5 mm diameter magnetic robot manipulator.