HelixFlex : bioinspired maneuverable instrument for skull base surgery

In 2013 I joined as visiting research fellow the lab of Prof. Paul Breedveld at the bio-mechanical department of in TU Delft (The Netherlands) where I worked on the design and development of a new instrument for improving dexterity during endonasal skull surgery. This experience taught me a lot about mechanical design and instrument manufacturing.

The pituitary gland is cradled in the sella turcica. Endoscopic endonasal surgery (EES) targeting pituitary gland adenomas involves rigid instruments that are inserted through the nostrils. Bone of the sphenoid sinus and sella turcica have to be removed in order to reach the gland.

The pituitary gland is cradled in the sella turcica. Endoscopic endonasal surgery (EES) targeting pituitary gland adenomas involves rigid instruments that are inserted through the nostrils. Bone of the sphenoid sinus and sella turcica have to be removed in order to reach the gland.

Endoscopic surgical treatment of most skull base pathologies, including certain pituitary tumors, is severely impaired by current instruments lack of maneuverability. In this context there is the need for instruments that are able to provide a stable shaft position, while both the orientation and the position of the end-effector can be independently controlled.

HelixFlex device:  Developed in 2013-2014, diameter 5 mm, steering range: ±150º in all directions.

HelixFlex device: Developed in 2013-2014, diameter 5 mm, steering range: ±150º in all directions.

Conventional steerable designs, based on rigid links and hinged mechanisms, are best comparable with nature’s endo- or exoskeleton approach. These conventional  designs have proven  to be highly effective at large dimensions, as for example in the scales of an excavator. At the smaller dimensions needed for minimally invasive surgery, however, the fabrication of such hinged structures becomes increasingly difficult. The muscular hydrostatic skeleton in the arms of Loliginid squid consists out of differently orientated muscle layers (see Figure). Simultaneous contraction of these muscle layers results in a flexible, fluent motion. This led to the development of a new principle of steering via simultaneous actuation of multiple, differently orientated cable layers.

Top: Top: section view of the Loliginidae squid tentacle showing the differently orientated muscle layers. Bottom: the steerable tip of HelixFlex containing multiple differently orientated cable layers. [1]

Top: Top: section view of the Loliginidae squid tentacle showing the differently orientated muscle layers. Bottom: the steerable tip of HelixFlex containing multiple differently orientated cable layers. [1]

Inspired by nature’s hydrostatic skeleton approach, the multi-maneuverable tip of the HelixFlex consists of a single compliant segment, and incorporates three different cable layers: one with parallel cables and two with helically-oriented cables. 

HelixFlex prototype being manually actuated by the authors: (a) showing the independent control of the tip’s position, (b) showing the independent control of the tip’s orientation, (c) showing the tip’s capability of deforming in multiple planes at once.

HelixFlex prototype being manually actuated by the authors: (a) showing the independent control of the tip’s position, (b) showing the independent control of the tip’s orientation, (c) showing the tip’s capability of deforming in multiple planes at once.

Simultaneous actuation of cable layers is accomplished via a similarly shaped  joystick in the handle of the instrument. By manually controlling this joystick, the user can control the movement of HelixFlex’ tip in four Degrees of Freedom, resulting in a  fluent motion that greatly reflects the motion of squid tentacles (check out this movie of the Helixflex skillfully maneuvered by Prof. Breedveld)


References:

Gerboni, G., Henselmans, P.W.J., Arkenbout, E.A., van Furth, W.R., Breedveld, P. (2015), “HelixFlex: A Bioinspired Maneuverable Instrument for Skull Base Surgery.”Bioinspiration & Biomimetics 10, no. 6, 066013

Patent : WO 2015105421 A1, title "Industrial or medical tool with steering cables", inventors: P. Breedveld, P. Henselmans, G. Gerboni, E. Arkenbout, W. F. Wouter.

More info on BITE group website