Inductive sensing of magnetic microrobots under actuation by rotating magnetic fields.

The engineering space for magnetically manipulated biomedical microrobots is rapidly expanding. This includes synthetic, bioinspired, and biohybrid designs, some of which may eventually assume clinical roles aiding drug delivery or performing other therapeutic functions. Actuating these microrobots with rotating magnetic fields (RMFs) and the magnetic torques they exert offers the advantages of efficient mechanical energy transfer and scalable instrumentation. Nevertheless, closed-loop control still requires a complementary noninvasive imaging modality to reveal position and trajectory, such as ultrasound or X-rays, increasing complexity and posing a barrier to use. Here, we investigate the possibility of combining actuation and sensing via inductive detection of model microrobots under field magnitudes ranging from 100 s of microtesla to 10 s of millitesla rotating at 1 to 100 Hz. A prototype apparatus accomplishes this using adjustment mechanisms for both phase and amplitude to finely balance sense and compensation coils, suppressing the background signal of the driving RMF by 90 dB. Rather than relying on frequency decomposition to analyze signals, we show that, for rotational actuation, phase decomposition is more appropriate. We demonstrate inductive detection of a micromagnet placed in two distinct viscous environments using RMFs with fixed and time-varying frequencies. Finally, we show how magnetostatic selection fields can spatially isolate inductive signals from a micromagnet actuated by an RMF, with the resolution set by the relative magnitude of the selection field and the RMF. The concepts developed here lay a foundation for future closed-loop control schemes for magnetic microrobots based on simultaneous inductive sensing and actuation.

Screen-Printed Resistive Tactile Sensor for Monitoring Tissue Interaction Forces on a Surgical Magnetic Microgripper.

With the recent development of novel miniaturized magnetically controlled microgripper surgical tools (of diameter 4 mm) for robot-assisted minimally invasive endoscopic intraventricular surgery, the surgeon loses feedback from direct physical contact with the tissue. In this case, surgeons will have to rely on tactile haptic feedback technologies to retain their ability to limit tissue trauma and its associated complications during operations. Current tactile sensors for haptic feedback cannot be integrated to the novel tools primarily due to size limitations and low force range requirements of these highly dextrous surgical operations. This study introduces the design and fabrication of a novel 9 mm2, ultra-thin and flexible resistive tactile sensor whose operation is based on variation of resistivity due to changes in contact area and piezoresistive (PZT) effect of the sensor's materials and sub-components. Structural optimization was performed on the sub-components of the sensor design, including microstructures, interdigitated electrodes, and conductive materials in order to improve minimum detection force while maintaining low hysteresis and unwanted sensor actuation. To achieve a low-cost design suitable for disposable tools, multiple layers of the sensor sub-component were screen-printed to produce thin flexible films. Multi-walled carbon nanotubes and thermoplastic polyurethane composites were fabricated, optimized, and processed into suitable inks to produce conductive films to be assembled with printed interdigitated electrodes and microstructures. The assembled sensor's electromechanical performance indicated three distinct linear sensitivity modes within the sensing range of 0.04-1.3 N. Results also indicated repeatable and low-time responses while maintaining the flexibility and robustness of the overall sensor. This novel ultra-thin screen-printed tactile sensor of 110 µm thickness is comparable to more expensive tactile sensors in terms of performance and can be mounted onto the magnetically controlled micro-scale surgical tools to increase the safety and quality of endoscopic intraventricular surgeries.

Design and Comparison of Magnetically-Actuated Dexterous Forceps Instruments for Neuroendoscopy.

Robot-assisted minimally invasive surgical (MIS) techniques offer improved instrument precision and dexterity, reduced patient trauma and risk, and promise to lessen the skill gap among surgeons. These approaches are common in general surgery, urology, and gynecology. However, MIS techniques remain largely absent for surgical applications within narrow, confined workspaces, such as neuroendoscopy. The limitation stems from a lack of small yet dexterous robotic tools. In this work, we present the first instance of a surgical robot with a direct magnetically-driven end effector capable of being deployed through a standard neuroendoscopic working channel (3.2 mm outer diameter) and operate at the neuroventricular scale. We propose a physical model for the gripping performance of three unique end-effector magnetization profiles and mechanical designs. Rates of blocking force per external magnetic flux density magnitude were 0.309 N/T, 0.880 N/T, and 0.351 N/T for the three designs which matched the physical model's prediction within 14.9% error. The rate of gripper closure per external magnetic flux density had a mean percent error of 11.2% compared to the model. The robot's performance was qualitatively evaluated during a pineal region tumor resection on a tumor analogue in a silicone brain phantom. These results suggest that wireless magnetic actuation may be feasible for dexterously manipulating tissue during minimally invasive neurosurgical procedures.