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.

Ovipositor Device, showing the six sliders, brass frame and front cap

Ovipositor Device assembly, showing the internal electric motor and cam

Ovipositor Device, close up of brass frame with guiding grooves

Ovipositor Device covered with flexible 3D printed surfaces

Ovipositor Device covered with flexible 3D printed surfaces

Ovipositor Device covered with flexible 3D printed surfaces

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

Publications

• Scali M. (2020). Self-Propelling Needles – From Biological Inspiration to PercutaNeous Interventions. PhD-thesis, TU Delft, ISBN 978-94-6366-282-6, 185 p.