MemoFlex 1 – Mechanical Surgical Snake

Developed in 2016-2017, diameter Ø5 mm

During complex surgical procedures such as in skull-base surgery, there is a need to reach difficult-to-reach locations via narrow anatomic corridors. Performing surgery along complex 3D pathways requires a snake-like instrument that memorizes the 3D shape of the followed pathway and shifts the shape backward as the instrument moves forward. This snake-like method of locomotion is called “follow-the-leader locomotion”, in which the head is the “leader” and the body follows the pathway of the head, see the following animations:

Follow-the-leader locomotion requires a segmented multi-steerable instrument as well as a memory in which the angles of the segments can be stored and shifted. In robotic approaches, the actuation usually occurs by a range of electric motors controlled by a computer. Although feasible, this will result in a very complex system requiring additional safety measures to ensure reliability during surgery.

In a desire to create a simpler system, we explored an alternative follow-the-leader approach by using a mechanical memory. Following the design approach of our MultiFlex, the MemoFlex 1 contains a 12 cm long, Ø5 mm multi-steerable tip with 14 segments that can be controlled individually in 28 Degrees of Freedom. Using 56 steering cables, the tip is connected to a bendable handle. When the handle is bent in a certain shape, the shape is mirrored and replicated by the tip.

The shape memory is a pre-bent stainless steel rod that slides through the bendable handle, driven by a crank. As the rod slides through the handle, its shape is detected by a 3D-printed compliant helicoid insert that makes the handle follow the shape of the rod precisely. The mechanism replicates the handle-shape to the tip which will then maneuver along a curved pathway equivalent to the shape of the pre-bent rod. The shape of the pre-bent rod can be derived from CT or MRI-images.

Our novel copy-and-replication mechanism shows promising results. Yet, the prototype has a high mechanical complexity. We therefore continued this research with an improved prototype, the MemoFlex 2, which contains aan improved shape memory mechanism and a strongly simplified compliant 3D-printed tip.