A chemical reaction driven untethered volume changing robotic capsule for tissue dilation

Robotic capsules provide an alternative route of entry to the gastrointestinal tract with minimal discomfort to patients. As capabilities of milli to micro robots progress, the potential of using robotic capsules not just for inspection, but for surgical procedures increase. To aid operations in the intestine, the capsule could be used to expand the site of surgery and anchoring to the intestinal walls to keep itself in place. This paper presents an untethered robotic capsule that can provide volumetric expansion using a chemical reaction without on-board electronic components. The expansion is based on the reaction between chemicals that are safe for ingestion, operated with magnetic fields and temperatures that are within safe limits. The capsule was able to expand greater than the diameter of the small intestine for 44 minutes and provided 0.27 N of anchoring force. A theoretical model of the reaction process was built and simulated to predict the behavior of the capsule expansion and validated through the experiments. The design and the simulation presented in this paper can be used for fabricating capsules to specific clinical needs. The work also opens up the possibility of untethered technologies that are remotely and chemically programmed for in-vivo surgical applications.