Category Archives: Self-Propelled Devices

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.)

Publications

Ovipositor Needle II – Self-Propelling & Steering through Tissue

Developed in 2016, diameter 1.2 mm (tip) & 0.75 mm (body).

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 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 new Ovipositor Needle with a diameter of 1.2 mm at the tip and 0.75 mm along the body. The needle consists of six superelastic Nickel Titanium (NiTi) wires (Ø 0.25 mm, length 160 mm) concentrically arranged around a seventh NiTi wire. The seven wires are interconnected at the tip with a flower-shaped ring (Ø 1.2 mm, length 2.0 mm), manufactured for minimal resistance during propulsion. The ring has a central hole to which the central wire is glued and six holes through which the six other wires can slide back and forth.

Each proximal end of the six movable wires is connected to a stepper motor, in which a leadscrew-slider mechanism converts rotational motion into linear motion. During an experiment, the needle was inserted in a stationary tissue-mimicking phantom, placed on a cart with low-friction wheels. The wires were sequentially moved back and forth inside the phantom, generating a net pulling motion of the phantom towards the actuation unit, and resulting in the needle moving forward inside the phantom. Different sequences of wire actuation were used to achieve both straight, curved and S-shaped trajectories.

In a follow-up 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.

Ovipoistor Needle II is, to our knowledge, world’s thinnest self-propelled-steerable needle. Our novel bio-inspired steering and propulsion mechanism allows for the design of extremely long and thin 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.

Ovipositor Needle II is part of the WASP project that focuses on the development of steerable needles for localized therapeutic drug delivery or tissue sample removal (biopsy). We are currently  working on further miniaturization to diameters <0.5 mm.

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

Publications

Media

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.

 

Publications