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HelixFlex – Squid-like motion by helical steering

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

Nature exhibits two inherently different approaches for creating maneuverable structures: the endo- or exoskeleton approach, and the hydrostatic skeleton approach. An endo- or exoskeleton  is a rigid structure  connected by joints that enable motion, for example in our own body.  A hydrostatic skeleton, however, is a compliant structure solely contructed out of soft tissues, for example in the tentacle of a squid or in the trunk of an elephant.

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.

Inspired by nature’s hydrostatic skeleton approach, the multi-maneuvrable 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. Simultanuous actuation of these 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 (see movie).

To our knowledge, the HelixFlex is the first instrument that uses simultaneous actuation of parallel- and helical-routed cable layers, and therefore a patent is pending.

*Left: A section view of the Loliginidae squid tentacle showing the differently orientated muscle layers. Right: the steerable tip of HelixFlex containing multiple differently orientated cable layers.
Left: A section view of the Loliginidae squid tentacle showing the differently orientated muscle layers. Right: the steerable tip of HelixFlex containing multiple differently orientated cable layers. [1]




Biopsy Harvester – High-Speed Tissue Cutting

Current minimally invasive laparoscopic tissue harvesting techniques for pathological purposes involve taking multiple imprecise and inaccurate biopsies, usually using a laparoscopic forceps or other assistive devices. Potential hazards, e.g. cancer spread when dealing with tumorous tissue, call for a more reliable alternative in the form of a single laparoscopic instrument capable of repeatedly taking a precise biopsy at a desired location. Therefore, the aim of this project was to design a disposable laparoscopic instrument tip, incorporating a centrally positioned glass fibre for tissue diagnostics; a cutting device for fast, accurate and reliable biopsy of a precisely defined volume and a container suitable for sample storage.

Inspired by the sea urchin’s chewing organ, Aristotle’s lantern, and its capability of rapid and simultaneous tissue incision and enclosure by axial translation, we designed a crown-shaped collapsible cutter operating on a similar basis. Based on a series of in vitro experiments indicating that tissue deformation decreases with increasing penetration speed leading to a more precise biopsy, we decided on the cutter’s forward propulsion via a spring. Apart from the embedded spring-loaded cutter, the biopsy harvester comprises a smart mechanism for cutter preloading, locking and actuation, as well as a sample container.

A real-sized biopsy harvester prototype was developed and tested in a universal tensile testing machine at TU Delft. In terms of mechanical functionality, the preloading, locking and actuation mechanism as well as the cutter’s rapid incising and collapsing capabilities proved to work successfully in vitro. Further division of the tip into a permanent and a disposable segment will enable taking of multiple biopsies, mutually separated in individual containers. We believe the envisioned laparoscopic opto-mechanical biopsy device will be a solution ameliorating time demanding, inaccurate and potentially unsafe laparoscopic biopsy procedures.




The FORGUIDE mechanism enables making a shaft-guide out of cheap standard parts that is rigidified by creating a laminate that consists of a spring, cables and expandable tube. The connection between these three layers is obtained by friction. The bench tests showed that the FORGUIDE prototype FGP-01 of only 5.5 mm diameter could provide flexural rigidities up to 1541 Ncm2 , which far exceeds the flexural rigidity of flexible endoscopes. Furthermore, a bending radius of almost 1 cm could be achieved in the compliant state with the FGP-01 without losing the ability to rigidify.


Flexible endoscopes are used for diagnostic and therapeutic interventions in the human body for their ability to be advanced through tortuous trajectories. However, this very same property causes difficulties as well. For example, during surgery a rigid shaft would be more beneficial since it provides more stability and allows for better surgical accuracy. In order to keep the flexibility and obtain rigidity when needed, a shaft guide with controllable rigidity could be used. On this page we introduce the PlastoLock shaft-guide concept, which uses thermoplastics (Purasorb PLC 7015) that are reversibly switched from rigid to compliant by changing their temperature from 5 to 43 degrees Celcius. These materials were used to make a shaft that can be rendered flexible to follow the flexible endoscope and rigid to guide it.  A feasibility study shows the great potential of this concept in terms of achievable flexural rigidity, miniaturization, and simplicity.