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 locally, within the segments, by miniature electric motors controlled by a computer. This will, however, result in a device much too large for surgical applications. Alternatively, the actuators can be stored in a handle so that larger motors can be used in combination with steering cables that transfer the motion to the snake-like tip. Although feasible, using electric actuators controlled by a computer will result in a complex and expensive system requiring additional safety measures to ensure reliability during surgery.
In a desire to create a simpler system that combines high safety with small dimensions, we explored an alternative follow-the-leader approach by using a mechanical memory. Following the design approach of our MultiFlex, the MemoFlex 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 and the pathway is fixed in the pre-bent shape and therefore not adjustable. In parallel with the development of our MemoSlide, we therefore continued this research with an improved prototype, the MemoFlex 2, which solves these issues with an entirely different shape memory mechanism. We will keep you posted about this new development!
- Henselmans P.W.J. (2020). Mechanical Snakes – Path Following Instruments for Minimally Invasive Surgery. PhD-thesis, TU Delft, ISBN 978-94-6402-213-1, 177 p.
- Henselmans P., Smit G., Breedveld P. (2019). Mechanical follow-the-leader motion of a hyper-redundant surgical instrument: proof-of-concept prototype and first tests. Proc. Inst. Mech. Eng. Part H: Journal of Engineering in Medicine, 10 p.