Compact Magnetic Twisted String Actuated Forceps for Stronger Robot-Assisted Neuroendoscopy

Robot-assisted minimally invasive surgical approaches have grown in popularity among many medical fields such as general, gynecology, cardio-thoracic, ENT, and pediatric surgery 1. As procedures strive to minimize trauma to surrounding tissues surgical tools must drasti- cally decrease in size. Consequently, researchers turn to alternative actuation methods to meet size constraints, resulting in scaling issues such as friction. Magnetic actuation presents a viable alternative to con- ventional cable-actuated tools (daVinci Surgical System) as forces and torques can be applied wirelessly through biological tissues 2. Many magnetic robots at the mil- limeter scale such as forceps and mobile microrobots can only achieve a few millinewtons of force, smaller than required for surgical interventions 3. These surgical tools require micro-transmission methods such as gear train systems, smart biomaterials, and twisted string actuators (TSA), to leverage the output of a magnetic system. TSAs are powerful, simple, compact, and have a high transmission ratio. Meaning that low-torque inputs are converted into large output-forces. Previous work implemented TSAs to augment the gripping force of a surgical gripper for neurosurgery applications, achieving a peak gripping force of 1.09 N using a 20 mT applied field 4. The gripper, axially 55 mm long, required an extended length to enable the high output force. This work presents an improved forceps design 17 mm long by 3.5 mm wide (Fig. 1), that is a 3.25-fold reduction in length compared to the prior iteration while maintaining a similar blocking force of 1.05N. This improves the clinical feasibility of magnetically actuated surgical forceps as the tool can be articulated in confined spaces while generating enough force to manipulate tissue. In this paper, the tool design, operating principle, magnetic and TSA model, and mechanical testing are presented. Clinical feasibility is demonstrated through ex-vivo and in-vivo experimentation and the integration of a concentric tube robot (CTR) system.