Category Archives: Snake-like Instruments

MemoFlex 2 – Mechanical Cam-Following Snake

Developed in 2018-2020, diameter Ø8 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 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 memoryFollowing our  HelicoFlex design, the MemoFlex II contains an Ø8 mm multi-steerable tip with 14 segments controlled by 56 steering cables in 28 Degrees of Freedom. The novel compliant frame of the tip is entirely non-assembly 3D printed out of one single part, creating an easy-to-make construction with a large range of snake-like motion possibilities.

The mechanical shape memory consists of four 3D printed plates (two for the horizontal plane and two for the vertical plane) containing curved grooves representing the required pathway of the tip. The four plates are mounted in a rotatable blue cylinder that is surrounded by a static exoskeleton. When the instrument is moved forward, the cylinder turns around, driven by a cam in the exoskeleton, and the curved grooves move along a set of ball bearings, each bearing connected to one of the steering cables, causing the tip to move along the shape of the curved grooves. The pre-programmed groove-shape can be derived preoperatively from CT or MRI-images.

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HelicoFlex – advancing steering with 3D printing and minimal assembly

Developed in 2019-2020, diameter Ø8 mm

In minimally invasive surgery, instrument maneuverability is limited by the use of small incisions. Increasing the number of degrees of freedom (DOF) of the instrument shaft is beneficial for many surgical interventions. However, increasing DOF usually leads to high mechanical complexity, issues with sterilisation and too large cost price for disposable use.

In an attempt to reduce manufacturing time we propose the first fully 3D-printed handheld, multi-steerable instrument: the HelicoFlex. The instrument is mechanically actuated and is fitted with a compliant shaft containing five serially-controlled segments enabling high maneuverability in 10 degrees of freedom.

Our new, compliant segment design merges the functions of four helicoids and a continuum backbone combining high torsion and axial stiffness with low bending stiffness. Five such compliant segments were combined to form the shaft of the HelicoFlex. Following the control design strategy of our older MultiFlex and HelixFlex devices, a compliant control handle was designed that mimics the shaft structure.

The entire frame of the HelicoFlex consists of only three complex-shaped 3D printed components that are printed without a need for any support material in the compliant section. The use of minimal-assembly 3D printing drastically decreases assembly time. Our 3D printed shaft features four working channels that facilitate combined use with flexible instruments such as biopsy forcipes. With its 10 degrees of freedom, our HelicoFlex showed a fluid motion in performing single and multi-curved paths.

Video adapted from Culmone, C., et al. (2020). Plos one, 15(5), e0232952 licensed under CC BY 4.0

Publications

Culmone, C., Henselmans, P. W., van Starkenburg, R. I., & Breedveld, P. (2020). Exploring non-assembly 3D printing for novel compliant surgical devices. Plos one15(5), e0232952.

Culmone, C., Smit, G., & Breedveld, P. (2019). Additive manufacturing of medical instruments: A state-of-the-art review. Additive Manufacturing27, 461-473.

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.

Publications

MemoSlide – Moving like a Mechanical Snake

Developed in 2016-2017, 13 cm wide, 20 cm long, and 10 cm high.

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 able 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 relatively low-cost follow-the-leader system that combines high safety with small dimensions, we explored an alternative follow-the-leader approach by using a mechanical memory inspired by the technology of mechanical calculators such as Charles Babbage’s Difference Engine.

MemoSlide features two mechanical memory registers: a static register (green in the design drawing below) and a moveable register (red) in which the angles of 11 tip segments can be stored, the angles represented by 11 small Ø3 mm ball-bearings that can slide sideways through slots in the brass top plate . The two registers are mutually coupled via a system of ball-bearings and cams underneath the brass top plate. Both registers can be locked and unlocked, and the moveable register can be shifted one segment forward or backward relative to the static register. The position of the first tip segment can be controlled by turning the blue steering wheel. Turning the crank around the steering wheel then results in  a sequence of locking, unlocking and shifting motions, controlled by the four brass cams  at the corners of the device, to memorize and shift the position of the ball bearings backward along the registers. The movie below shows an example in which MemoSlide is programmed with a sinusoidal shape that is shifted backward along the device (and then forward again, as the device works in two directions).

Although in principle suited for controlling the shape of a snake-like surgical device, MemoSlide is in its current configuration still too complex and limited to 2D pathways. Based on our experience with MemoSlide, we are currently developing a new mechanical system suited for memorizing 3D shapes and sufficiently simple for integration in the handle of a snake-like  surgical device. We will keep you posted!

Publications

Media

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]

 

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MultiFlex – Tentacle from Steel

 

 

Developed in 2008-2009, diameter 5 mm, steering range: ±200º in all directions.

The MultiFlex is what we call a multi-steerable instrument. Based on the Cable-Ring mechanism applied in the Endo-Periscope III, the MultiFlex does not contain just one, but five steering segments serially stacked on top of each other. Each of these segments can be actuated in two Degrees of Freedom (DOF) by its own set of four steering cables, resulting in a total of 20 steering cables and a 10-DOF maneuverable tip capable of making a wide range of 3D shapes and curves. This level of maneuverability gives the instrument the ability to steer around anatomic strucures, making it world’s first instrument of this kind developed at 5 mm dimensions.

By using the Cable-Ring mechanism, all actuation cables could be positioned at the same diameter. Consequently, the increase in maneuverability does not affect the outer diameter of the instrument, which is still equal to Ø5 mm with a complexity similar to the Endo-Periscope III. The control handle of the MultiFlex has a  structure similar to the tip, yet its dimensions are scaled-up for a better fit to the surgeon’s hand.

 

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