Rob Lichty
MEDdesign

Biomimicry – Ideas From a Wasp’s Ovipositor

By Rob Lichty
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Rob Lichty

What can an ovipositor can do? How does it relate to space exploration and medical devices? Let’s explore what makes these Ichneumonoidea wasps so interesting.

A number of years ago I was doing research for a particular medical device project.  I needed to get through a hard substrate (perpendicular to bone surface) with as little damage to the surrounding tissue as possible. In my research I came across a really cool wasp with a really cool ovipositor. The mechanism didn’t quite apply to my project and was not being utilized for medical purposes at that time. I always kept the concept in the back of my head but someone beat me to the “punch line,” and I am very glad that they did because it can become a platform to revolutionize the medical device community!

Fig. 1:  Carrot Wasp (Gasteruptiidae sp.) Courtesy Inmagine.com
Fig. 1: Carrot Wasp (Gasteruptiidae sp.) Courtesy Inmagine.com

There are a number of Ichneumonoidea insects in the Genus Megarhyssa, including one in my state of California (Megarhyssa nortoni), with a long ovipositor (ovum – egg; positor – placer). This device is often mistaken for a frightening-long stinger (up to 6″ in some giant Ichneumon), that quickly results in the likelihood of the wasp meeting with the end of a rolled up newspaper. You will be glad to know that these ladies are pretty harmless to humans (only the females lay eggs).

The ovipositor is used to bore through wood and place the wasp’s eggs near (or in) the beetle larva of their choosing. When the eggs hatch, they eat the host larva.

Schematic of the middle region of a typical ovipositor
Fig. 2. Schematic of the middle region of a typical ovipositor [Rahman, M., Fitton, M. & Quicke, D. (1998).
Ovipositor internal microsculpture in the Braconidae
(Insecta, Hymenoptera), Zoologica Scripta 27(4): 319–332.]

The ovipositor is made of two barbed halves interlocked together lengthwise to fashion a single hollow tube.  The two halves can oscillate, or slide, back and forth in opposite directions providing a forward motion without rotary motion or becoming lodged. The penetration has a near net zero force parallel to the ovipositor which could conceivably allow a mechanism with no length limit.

This leads to the possibility of extraterrestrial drilling. There have been only three missions that have successfully drilled into the ground (one Russian and one American mission each to the moon, and one Russian mission to Venus). The difficulty can be directed to hard ground and weaker gravity lessening the ability to push down or to hold a drilling rig stable. The net-zero forces on a properly designed oscillating machine will negate the negative effects of reduced gravity.

This is pretty cool stuff… but what does it have to do with medical devices??

Fig. 3: Sirex ovipositor: Teeth 1 to 4 point proximally (D) and are  “pull-teeth”; teeth 6, 7 and higher point distally (P) and are “push teeth”  [J. F. V. Vincent and M. J. King. The mechanism of drilling by wood wasp  ovipositors. Biomimetics, 3(4):187–201, 1995]
Fig. 3: Sirex ovipositor: Teeth 1 to 4 point proximally (D) and are
“pull-teeth”; teeth 6, 7 and higher point distally (P) and are “push teeth”
[J. F. V. Vincent and M. J. King. The mechanism of drilling by wood wasp
ovipositors. Biomimetics, 3(4):187–201, 1995]

A few years ago, Ferdinando Rodriguez y Baena at Imperial College London looked at the net zero force mechanism and noted that the boring movement is quite gentle to the surrounding areas (in this case, tissue). The team Imperial College created a silicon based “needle” that has 50 micron long teeth and is steerable. The steering mechanism utilizes two linear actuators to reciprocate the two needle halves mated to a rotating mechanism.  The final apparatus allows the needle to crawl along the surface of the brain until it gets to where it needs to be and then a turns to burrow in.  This unit is being called a “Neurosurgery Probe” or a “medical probe.”

But, if they take it a step further and retain the nature of the egg canal, but reassign the use of the tube, then this little robot may one day be utilized to take biopsies, blood samples, deliver drugs, retain fiber optics for visualization or ablation surgery (and why not both?). This “cool ovipositor” just keeps on getting better and better, doesn’t it?

And, in case you want to “bug” everybody you know with your own research and other bugs that may save your life some day, http://bugguide.net and http://www.whatsthatbug.com are good places to start.

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