Toward Active Cannulas: Miniature Snake-Like Surgical Robots

We have developed a new class of continuously flexible snake-like robots, called active cannulas, that consist of several telescoping pre-curved superelastic tubes. The devices derive bending actuation not from tendon wires or other external mechanisms, but from elastic energy stored in the backbone itself. This allows active cannulas to have a small diameter and a high degree of dexterity, which should enable them to navigate through complex anatomy to sites inaccessible by current surgical robotic devices. Active cannulas may also enhance patient safety because their inherent compliance mitigates potential trauma from inadvertent tool-tissue collision. A consequence of our design is that dexterity improves with miniaturization. A kinematic description of active cannula shape requires a model of the elastic interaction of telescoping pre-curved flexible tubes, and we derive a two-"link" beam mechanics-based model. Experiments using curved nitinol tubes and wires validate the model.