Magnetically-driven robotic capsule navigation for colonoscopic procedures

Soft-tethered magnetic capsules have the potential to become the gold standard for diagnosing colorectal cancer; thus, simplifying and reducing the risk and discomfort of traditional colonoscopy. To ensure that the magnetic forces and torques applied on the capsule are safe for the patient and sufficient to translate the capsule, the interaction between the colon and the soft-tethered magnetic capsule must be better understood. Additionally, existing magnetic navigation control frameworks need further development to account for realistic in vivo conditions while maintaining clinically acceptable procedure times. The first aim of this work is to develop a magnetic robotic platform to experimentally test magnetic navigation strategies under realistic ex vivo scenarios. The second aim is to characterize the resistance to overcome when pulling a soft-tethered capsule along the colon. Finally, the last aim is to present various control frameworks which enable the soft-tethered capsule to navigate the colon in a robust, safe, and rapid manner. This work presents an analytical model, validated in ex vivo conditions, for the resistance forces introduced by the tether-colon interaction. Such forces are the main resistance to overcome during navigation and grow exponentially as a function of the friction coefficient and the contact angle. Additionally, we demonstrate that a tangential space force control framework allows for a more reactive navigation. A set of robot motion primitives are presented which maximize the local increase in navigation force by accounting for the effect magnetic forces have on the capsule-colon interaction resistance. The motion primitives overcome previously impregnable realistic scenarios while reducing the stress on the colon walls. These findings suggest that the resistance introduced by the tether must be reduced and that the novel motion primitives have the potential to allow for effective in-vivo navigation.