Category Archives: Interventional Devices

Ovipositor MRI-Needle

Developed in 2020-2021, diameter 0.8 mm.

Female parasitic wasps pass their eggs through an organ called the ovipositor into their hosts, which sometimes hide in a solid substrate such as wood. The ovipositor has the shape of a tube and consists of three slender, parallel-positioned segments, called valves. The wasp can push and pull the valves with respect to each other in a reciprocating manner. A groove-and-tongue mechanism interlocks the valves along their length. The push-pull motion of the valves has two functions. First, it keeps the unsupported length of the individual valves low. Second, moving the individual valves forward one by one while pulling the others provides stability to the wasp’s ovipositor and prevents buckling. The push and pull forces produce a net force near zero, enabling a self-propelled motion.

Inspired by the wasp ovipositor, we developed a self-propelled Ovipositor MRI-Needle with a diameter of 0.8 mm that can be used inside an MRI system. Our needle consists of six parallel needle segments and an actuation unit. The design of the actuation unit is based on the so-called click-pen mechanism of a ballpoint pen. The actuation unit allows you to actuate the needle that consists of six parallel Nitinol segments by just a translating motion. We 3D-printed the components of this actuation to be able to test it inside an MRI system. The video below shows the movement of the needle segments actuated by the actuation unit:

The prototype was tested with success in ex-vivo human prostate tissue in a preclinical 7-Tesla MRI system at the Amsterdam University Medical Centres. The results showed that the needle tip was visible in MR images and that the needle was able to self-propel through tissue.

This project, in which we developed a self-propelled wasp-inspired needle that can be used inside an MRI system, is part of Project 4 of the MEDPHOT programme funded by the Netherlands Organization for Scientific Research (NWO). MEDPHOT focusses on the development of photonics-based technologies that can enable earlier diagnosis and tailored treatment of diseases in the pulmonology, urology, and gastroenterology fields and translate these technologies to their clinical environments. The goal of Project 4 is to develop a novel transperineal laser ablation platform for an accurate treatment of prostate tumours under MRI.


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.



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.)



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.

Pulze Hammer II: Catheter

Developed in 2017-2018, diameter 2 mm

We want to go deeper into the human body, using incisions that are smaller or even non existent. For this purpose we need small flexible tools that are able to deliver sufficient forces without buckling.

In an effort to facilitate high force delivery in a small flexible medical instrument, the pulze catheter prototype (2 mm) has been developed. Buckling is prevented by using a dynamic loading method, in which a high-speed indenter collides with the non-moving target. The flexible prototype consists of a distal spring-loaded indenter, which is manually actuated using a compliant (re)load mechanism, allowing for loading, locking, and (re)loading of the prototype while inserted in the body.

We are currently testing this catheter ex-vivo. Further development of this crossing prototype may in time allow for performing surgery deep inside the body.


Novel Shooting Mechanism for Tissue Puncturing

In nature multiple animals have developed intriguing shooting mechanisms for food capture, defence, and reproductive reasons. Think for example on the amazing tongue shooting capability of the chameleon and the appendage strike of the mantis shrimp.

For a full overview of innovative and interesting shooting mechanisms in nature, we would like to refer to: Shooting Mechanisms in Nature: A Systematic Review by Sakes et al. [2016]

These shooting mechanisms can offer inspiration for new ideas on the technological development of fast acceleration mechanisms in medicine. High-speed shooting mechanisms can, for example, be used for the endovascular treatment of Chronic Total occlusions (CTOs). CTOs are heavily calcified and are thus difficult to puncture and cross with the small (0.36 mm) guidewire. The required force to puncture the CTO is often higher than the buckling force of the guidewire due to the low bending stiffness (EI) and long (unsupported) length (L). As a result, the guidewire often buckles. Buckling in turn causes procedural failure since the CTO cannot be crossed. Buckling of the crossing tool may be prevented by using a high-speed crossing tools as this increases the buckling resistance of the guidewire and potentially minimizes the puncture force of the CTO.

With this in mind an innovative high-speed crossing tool was developed using nature’s shooting mechanisms as inspiration. The crossing tool (OD 2 mm) incorporates an innovative spring-driven indenter and decoupling mechanism for high-speed puncturing of the proximal cap. First tests have been very promising. The prototype hit the CTO with an average speed of 3.4 m/s and was able to deliver a maximum force of 20 N (without buckling), which is well over the required 1.5 N to puncture the CTO. Additionally, the device was tested on CTO models made out of calcium and gelatine of different consistency. Puncture was achieved with on average 2.5 strikes for heavily calcified (77 wt% calcium) CTO models.

We feel that with continued development of this technique it will become possible to deliver high forces in ultra thin devices, such as guidewires, and as such increase the success rate of the the endovascular treatment of CTOs and other minimal invasive applications.

For a video of the prototype hitting a fixed surface, please see: Velocity_Max_10fps (Converted), which is slowed down 1000x.

Ovipositor Needle I – Self-Propelling through Tissue

Developed in 2014, thickness 2 mm.

Wasp ovipositors  are thin and flexible needle-like structures used for laying eggs inside wood or larvae.  Wasp ovipositors are composed out of  longitudinal segments, called “valves”, that can be actuated individually and independently of each other with musculature located in the abdomen of the insect. In this way the wasp can steer the ovipositor along curved trajectories inside different substrates without a need for rotatory motion or axial push.

Inspired by the anatomy of wasp ovipositors, we developed an Ovipositor Needle containing a 2 mm thick “needle” composed out of four sharp and polished stainless steel rods, representing four ovipositor valves. The four valves can be individually moved forward and backward by means of  electromechanical actuators mounted in a propulsion unit that is standing on four passive wheels. If the needle is inserted into a gel that represents tissue, and if the four valves are sequentially moved forward and backward, the friction behaviour around the valves in the gel will result in a net pulling motion that drives the needle forward through the gel. The ovipositor needle is therefore self-propelling, meaning that it does not need a net pushing motion for moving forward through tissue like normal needles do.

Ovipositor Needle I is part of the  WASP project that focuses on the development of steerable needles for localized therapeutic drug delivery or tissue sample removal (biopsy). In a new prototype that is currently under development, we aim to extend the self-propelled needle with steering capabilities at an outer diameter of just 1 mm.



Flexible Endovascular Horse Morcellator

Cushing’s disease is a naturally occurring progressive pituitary disorder that can be found in multiple species, including dogs, donkeys, horses, and humans. In horses, treatment of Cushing’s disease is aimed at controlling and reducing the severity of the clinical signs using oral medication, rather than removing the tumor from the pituitary gland (which is often performed in humans), due to the fact that to date surgical removal has been technically impossible. Therefore, a new paradigm in pituitary surgery in horses was developed in close collaboration with expert veterinarian Johannes van der Kolk of the Faculty of Veterinary Medicine of the University Utrecht. In contrast to the human vascular system, multiple superficial veins in the horse, like the facial vein, can provide direct access to the pituitary gland. This superficial vein was used to guide an innovative flexible morcellator towards the pituitary gland. Once arrived at the pituitary gland, this morcellator uses a flexible drive cable to actuate a rotating cutting blade at the tip of the instrument to resect and subsequently remove the pituitary tumors. First cadaver experiments have proven successful in inserting this instrument and removing pieces of pituitary tumor. Further research needs to be done before clinical application of the instrument can take place. Nevertheless, continued development of this approach may in time improve the quality of life of horses suffering from Cushing’s disease.




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.