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.