Stick, unstick, restick sticky films in the colon.
The main challenge in designing diagnostic devices able to move along the colon is their locomotion method. Manipulating friction with the colonic surface is a key requirement for their safe and atraumatic propagation. One possible solution is to generate friction by means of adhesive forces. For this reason, a diagnostic device can be covered with mucoadhesive films that are able to stick on the colonic surface by generating high static friction. For a smooth transition from static to dynamic regime, the mucoadhesive films should unstick just before the initialisation of motion. Experiments have shown that promoting cohesive fracture of the films by controllable air introduction does not lead to friction reduction sufficient for smooth unsticking. Introducing water at the film-colon interface, however, reduces the static friction significantly, and makes the device to unstick and slide smoothly without leaving film fragments on the colonic surface behind. If unsticking is initiated by means of air or water introduction, a new film is required each time the device is required to restick. As an alternative, the possibility of coating the device with environmentally-sensitive mucoadhesive polymers that can respond reversibly to external stimuli and alter their properties is discussed.