Design of a Bone Marrow Harvesting Device

Bone marrow is a soft and fatty tissue located within the porous bone structure at the centre of the larger bones. During bone marrow biopsies, also called trephine biopsies, a 1-2 cm long sample of the bone and bone marrow is taken to check, amongst others, for blood cell abnormalities. A Jamshidi needle is used to collect the bone marrow by pushing the needle through the rigid cortical outer layer of the bone such that it will be located within the softer cancellous bone. During retrieval of the needle, the biopsy sample sometimes remains inside the incision. This requires manual removal of the sample using forceps, and possibly a second biopsy has to be taken.

During this project, you would first look into current instruments used to perform a bone marrow biopsy after which you will design a novel device that could be used for harvesting bone marrow samples.

Interested? Contact Esther de Kater,

Wasp-Inspired Tissue Transportation Device

Developed in 2017-2018, diameter 6 mm. 

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 and deposit eggs inside a living host. The propagation of eggs through the ovipositor is achieved by a smart push-pull mechanism, in which some valves are pushed while other valves are pulled, using surface- and direction-dependent friction with the egg to make it move forward. Inspired by the ovipositor of parasitoid wasps, we developed a novel tissue transportation device that can transport tissue samples at a precisely controlled speed without any risk of clogging.

The developed mechanism consists of an outer tube surrounding six semi-cylindrical blades that make a reciprocal forward/backward motion, driven by a miniature electric motor with a cam, similar to our Self-Propelling Ovipositor Device. Tissue samples are transported using a friction differential between the tissue and the blades, at a speed which is set by the surgeon. We tested the device with various tissue-mimicking gels as well as with compacted minced meat, using different motion sequences of the blades. In all cases the substance was transported reliably, showing that the ovipositor principle is well-suited for tissue transportation and a useful alternative to conventional aspiration (suction)-based devices that are prone to clogging.

The BBC made a nice animation showing the working principle of the device. In a new research project within Dutch Soft Robotics we are currently equipping the device with a flexible steering section to facilitate tissue transport from difficult-to-reach locations in the human body.



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.


Variable Friction Catheter

In cardiovascular interventions, Catheters are typically inserted in the radial or femoral artery and are navigated through the arteries to the heart, where the interventions are performed.  In order to safely reach the heart,  catheters  (and guidewires) used during these procedures need to be able to easily follow the curves in the  vascular  system,  while  creating  as  little  friction  as  possible to avoid damaging the blood vessel inner wall.  While low friction is beneficial during navigation, it makes holding the catheter at a specific location in open spaces, such as inside the heart, difficult during the execution of the surgical procedure. Thus, it limits the force transmission capability of the catheter. In this project, we look forward to developing a new variable friction catheter which can be modulated to have low friction while navigating and high friction while performing the surgical task to ensure optimal performance and outcomes in both cases.

The assignment is currently available with compatible literature review assignments. Interested? Contact Mostafa Atalla:  

SIGMA Catheter – steering inside the Heart

Developed in 2016-2017, diameter Ø3 mm, lumen Ø1 mm

In recent years, steerable catheters have been developed to combat the effects of the dynamic cardiac environment. However, current solutions are bound to a number of limitations: (1) low torsion, (2) shaft shortening, (3) high unpredictable friction, and (4) coupled tip-shaft movements. These effects make it very hard to steer in tortuous blood vessel and inside the heart.

In order to tackle these limitations we developed a novel multi-steerable catheter prototype with four degrees of freedom. The tip has two steering segments that can be steered in all directions, controlled by two joysticks on the handle: one for the thumb and one for the index finger. The prototype features automatic lock of the steering angle once the joystick is released.

To solve the four limitations mentioned above we used eight miniature Bowden-cables inside of the flexible shaft for independent omnidirectional steering of each tip segment. As each segment can steer in all directions, twisting the shaft is not needy for directing the catheter tip, which solves the issue with low torsion (1). The issue with shaft shortening (2) is solved with the Bowden-cables which are axially incompressible. The Bowden cables generate very low predictable friction (3) and coupled tip-shaft movements (4) are absent as the Bowden-cables transfer the joystick motions directly to the tip without influencing the shaft.

The ability to steer inside the heart with a variety of complex shapes and curves opens great possibilities for complex catheter interventions. We evaluated our SIGMA catheter in a transparent 3D printed heart, based on MRI-images and created by the company Materialize, as well as ex-vivo in a beating porcine heart at the LifeTec Group. Both evaluations show very promising results and superior behaviour as compared to conventional steerable catheters.


Ali A., Sakes A., Arkenbout E.A., Henselmans P., Starkenburg R. van, Szili-Torok T., Breedveld P. (2019). Catheter steering in interventional cardiology: mechanical analysis and novel solution. Proc. Inst. Mech. Eng. Part H: Journal of Engineering in Medicine, 12 p.


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 and deposit eggs inside a living host. The propagation of the ovipositor through the substrate is achieved by a smart push-pull mechanism, in which one of the valves is pushed while the other two are pulled, using the surface-dependent friction properties with the soft substrate to move forward.

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.)


Ovipositor Needle II – Self-Propelling & Steering through Tissue

Developed in 2016-2019, diameters ranging from 1.2 mm to 0.4 mm. 

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 and deposit eggs inside a living host. The propagation of the ovipositor through the substrate is achieved by a smart push-pull mechanism, in which one of the valves is pushed while the other two are pulled, using the surface-dependent friction properties with the soft substrate to move forward. Inspired by the ovipositor of parasitoid wasps, we developed a series of self-propelled steerable Ovipositor Needles with ultrathin diameters ranging from 1.2 mm to 0.4 mm.

Our first Ovipositor Needle prototype consists of six super elastic Nickel Titanium (NiTi) wires concentrically arranged around a seventh NiTi wire. The seven wires are interconnected at the tip with a small flower-shaped ring (Ø 1.2 mm) manufactured for minimal resistance during propulsion. The ring has a central hole to which the central wire is glued, surrounded by six concentric holes through which the six other wires can slide back and forth. Each proximal end of the six movable wires is connected to a miniature stepper motor, in which a leadscrew-slider mechanism converts rotational motion into linear motion.

We performed a series of experiments in which the needle was inserted in tissue-mimicking gel phantoms. The wires were sequentially moved back and forth, resulting in the needle moving forward inside the phantom using the surface-dependent friction properties between the wires and the gel. Different sequences of wire actuation were used to achieve both straight, curved and S-shaped trajectories.

In our second Ovipositor Needle prototype we changed the shape of the interlocking ring from cylindrical to conical to investigate the effect of pre-curved wires. We found out that pre-curved wires facilitate steering, however, at the drawback of a slightly larger tip diameter due to the use of a conical flower-ring.

In a final series of Ovipositor Needle prototypes, the flower-shaped ring was replaced by an thin-walled shrinking tube, glued to one of the outer wires, ultimately resulting in ultrathin 0.4 mm needle diameters three times the size of a human hair. The prototypes were tested in multi-layered gel phantoms with varying stiffness properties and artificial membranes, representing different organs and tissues. In a final series of ex-vivo experiments the needles were evaluated with success in porcine liver, kidney and brain tissue.

This project, in which we developed world’s thinnest self-propelled-steerable needles, shows the strength of a novel bio-inspired approach leading to a new generation of needles that can be used to reach deep targets inside the body without a risk of buckling and with the possibility to correct the trajectory. Our needles were developed within the WASP project that focused on the development of steerable needles for localized therapeutic drug delivery or tissue sample removal (biopsy). In a follow-up project, funded by the Netherlands Organization for Scientific Research (NWO) we will develop the needles further towards clinical application in urological interventions under MRI.

(Picture at the top adapted from “Braconid Wasp Ovipositing” by Katja Schulz is licensed under CC BY 2.0.)



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.

Entry point detection for spinal fusion surgery

Multiple diseases can require patients to undergo spine surgery. At the BITE group, we are developing a novel probe that allows for the surgeon to steer through the bone along a secure drilling trajectory, avoiding nerves and blood vessels that run along the spinal column. To help the surgeon find and maintain the right trajectory, an optical sensing system based on Diffuse Reflectance Spectroscopy (DRS) will be integrated into the probe to differentiate the tissue ahead of the tool tip, thereby providing positional feedback for the surgeon in real time.

In the scope of the proposed graduation project, a probe prototype will be designed that enables the surgeon to sense the correct entry point for spine drilling procedures. Its usability for guidance will be assessed through drilling tests on a bone phantom/ex-vivo animal bone.

This assignment will be available from September 2021. Interested? Contact Esther de Kater, or Merle Losch,

Solving medical problems through nature’s ingenuity