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.


Exploring hierarchical mechanisms

Imagine a tower build of LEGO, consisting of a number of bricks that together form a new shape. Now imagine that each LEGO brick is a tiny mechanism, in contact with the mechanisms that surround it. What if we can program each individual mechanism with a very simple task, and are able to turn it on or off when we desire. Could we use these tiny mechanisms as cells that create a new, larger mechanism? Can we create a mechanism that is a lawnmower one day, a coffee machine the next, just by switching on or off certain cells?

We want to use the form complexity of 3D printing to create ‘hierarchical mechanisms’, closely related to metamaterials. This is an exploratory assignment, so we are looking for a creative student with an investigative, curious mind. Some inspirational work is shown on this page.

Interested? This assignment is available starting January/February 2021. Contact Kirsten Lussenburg,

Metamaterial mechanisms by Hasso Plattner Institute

Overview ‹ kinetiX — MIT Media Lab
Kinetix Mechanisms by Tangible Media Group

Core Concept: Mechanical metamaterials bend the rules of everyday physics |  PNAS
Textured Mechanical Metamaterials by Yair Shokef’s Research Group

Non-assembly mechanisms for eye surgery

Surgical instruments used in eye surgery are very small, which makes it difficult to produce instruments with high functionality. The bottleneck in the production of eye surgical instruments is the assembly step. Assembly has to be done by hand, because of the small size of the parts. Automation is difficult to implement, due to the relatively small number of specific instruments. As a solution to this problem, the complexity offered by 3D printing can be used. A way to do this is to 3D print entire functioning products or mechanism in one single step, without the need of assembling them afterwards, called non-assembly 3D printing.

A vitrectome is a specific instrument used in eye surgery to remove the vitreous from the eye. It consists of two thin, hollow needles that are inserted into the eye, and a handle containing a vibrating mechanism. In this assignment, you will be working on the design of a non-assembly 3D printed vitrectome mechanism, which should have the same specifications as current vitrectomes.

This assignment will be available from January/February 2021. Interested? Contact Kirsten Lussenburg,

Design of a steerable bone screw

During spinal fusion surgery multiple vertebrae are fused by fixating them together with an internal brace. The brace is connected to a vertebra with pedicle screws. The inside of the bone (cancellous bone) is too weak to achieve sufficient grip. Therefore, screw fixation mainly relies on locations where the screw is in direct contact with the surrounding  layer of the much harder cortical bone. We are developing a steerable bone drill in order to increase the contact area of screws and cortical bone by drilling along the cortical bone layer. An optical sensing system that can differentiate the two types of bone tissue will help the surgeon find and maintain the right drilling trajectory. Furthermore, a novel anchoring device that is flexible during insertion, but becomes rigid once in place will replace straight pedicle screws.

There are multiple graduation projects available related to optical sensing, bone drilling and anchoring.

  • Development of a bone phantom for testing of a steerable drill or screw
    Contact: Merle Losch,
  • Design of a drill prototype to provide directional feedback
    Contact: Merle Losch,
  • Design of  flexible screw that can become incredibly stiff in order to transfer the forces acting of the screw
    Contact: Esther de Kater,

  • Design of a flexible screw that adheres to the bone surface in order to transfer the forces acting on the screw
    Contact: Esther de Kater,

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


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.

Self-Propelling Ovipositor Device

Developed in 2016 by MSc. student Perry Posthoorn

A wasp ovipositor is a needle-like structure composed out of three elements, called valves. A female wasp uses this structure to drill into wood or fruit to deposit eggs inside a living host. The propagation of the ovipositor through the substrate is achieved by a push-pull mechanism, in which one of the valves is pushed while the other two are pulled.

Inspired by the ovipositor of parasitoid wasps, we developed a novel self-propelling Ovipositor Device designed for locomotion through the large intestine (colon). The device contains a miniature electric motor connected to a cylindrical cam. Six sliders are placed around the cam and move forward and backward following the path defined by the cam. Designed for motion through soft environments, the working principle of the propulsion mechanism is that multiple stationary sliders create sufficient friction to allow for a single slider to shuffle forward. In each step, one slider moves forward whereas the others remain stationary relative to the environment, generating a smooth and continuous motion at approximately 1/6 of the speed of a moving slider. The ovipositor mechanism allows a simple and robost construction that can be easily miniaturised to very small dimensions, see our research on self-propelled ovipositor needles.

Experiments were carried out with various flexible 3D-printed structures attached to the outer surface of each slider to generate direction-dependent friction for further enhancement of grip. Tests in plastic tubes showed fast and fluent self-propelled motion. Locomotion in a colon was succesfully achieved with an improved 3D-printed outer surface in which the tangential spacing between the sliding structures was decreased so that the colonic wall does not flex between them. The improved prototype was able to self-propel ex-vivo through a porcine colon without any visual damage to the colonic wall.

(Featured image adapted from “Braconid Wasp Ovipositing” by Katja Schulz is licensed under CC BY 2.0.)


NWO – Spine Stabilization

This research project is funded by the Netherlands Organization for Scientific Research NWO and conducted in collaboration with Philips Research, DEAM, Karolinska University Hospital in Sweden, Amsterdam University Medical Center and Reinier de Graaf Hospital in Delft.

Spinal fusion is the surgical procedure of stiffening parts of the spinal column with screws and rods to, among others, reduce back pain for patients affected by multiple diseases. Vertebrae have an outer layer of hard cortical bone surrounding the softer core that consists of cancelous bone. The strength of the connection between vertebra and screw mainly relies on the contact area with the cortical bone, but drilling close to this cortical bone layer is risky, as it can lead to cortical breaches. These breaches can have severe complications, especially since important neural and vascular structures run along the spinal column.

This research will focus on creating a better fixation of the screws and preventing complications that can arise due to cortical breaches by developing a steerable bone drill with an optical sensing system in the tip. This allows the surgeon to drill a curved path along the cortical bone layer while getting real time information about the location of the drill. Regular stiff screws will not fit this curved hole, thus a new anchoring device will be developed that is flexible when introduced to the curved hole and that can become rigid to generate the needed fixation.


Our aim in ‘Project Inspiration’ is to quickly develop an emergency mechanical ventilator, inspired by a mechanical ventilator from the 60’s. A team of staff members and students, led by Gerwin Smit, has developed a new ventilator, that can be manufactured anywhere in the world. More information can be found at:


Miniature Biopsy Needle for Ductoscopy

In ductoscopy, the milk ducts of the breast are investigated using a so-called ductoscope. The ductoscope consists of a handle with three canals: (1) for insertion of the micro-endoscope, (2) for insertion of a tool, and (3) the irrigation canal to expand the milk duct, and a hollow tube that is inserted in the milk duct.

In case a lesion is found during this procedure, a biopsy procedure is performed using a biopsy basket. Unfortunately, this procedure is very unreliable and difficult to perform, often resulting in the need for a follow-up procedure.

In an effort to overcome this challenge, we have developed a biopsy needle that can be used during the ductoscopy procedure. The biopsy needle consists of two concentric cutting blades with a rectangular cut-out at the distal tip. By counter-rotating the cutting blades, a biopsy can be obtained, similar to the way a scissor works. The cutting blades are actuated using a handle in which the counter-rotating motion of the blades is transferred to an axial translation (see below).

In a proof-of-principle experiment, a milk duct phantom was manufactured out of gelatin. The biopsy needle was able to reliably obtain biopsy samples from this phantom. Furthermore, the biopsy needle was also successfully combined with the ductoscope.


  • Sakes A., Snaar K., Smit G., Witkamp A.J., and Breedveld P. (2018). Design of a Novel Miniature Breast Biopsy Needle for Ductoscopy. Biomedical Physics & Engineering Express. Accepted.

Devices for autonomous intraluminal surgery

This research is part of the AuTonomous intraLuminAl Surgery Innovative Training Network ( ATLAS-ITN) and has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 813782 .

The goal of this project is to develop smart, flexible robots that autonomously propel themselves through complex, deformable, tubular structures. This calls for seamless integration of sensors, actuators, modelling and control.

Two early-stage researchers, Fabian Trauzettel (ESR 1) and Chun-Feng Lai (ESR 12), will be based at TU Delft, while two others, Di Wu (ESR 11) and Zhen Li (ESR 13) will have TU Delft as their secondary institution. They will focus on multi-steerable catheter technology, follow-the-leader control, control of multi-DOF catheters in unknown environments, and path planning / real-time re-planning. Details of their projects can be found here.

Research in the network will be conducted at KU Leuven, TU Delft, University of Strasbourg, Politecnico di Milano, Università di Verona, Scuola Superiore Sant’Anna Pisa, and UPC Barcelona.

Solving medical problems through nature’s ingenuity