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When biology and technology intersect, we usually talk about bionics. The mouthparts of ants could, for example, help to improve needle holders during endoscopic procedures. Dr Benjamin Wipfler and colleagues from various disciplines recently conducted a STUDY and explained in more detail what it is all about in our interview:
What is special about the mouthparts of the red wood ant?
Unlike all other winged insects, ants have jaws that allow movement in the joint. We can imagine it like a door: the door leaf hangs in the frame with two joints, which means it can only move along a single path. It does not need to be stabilised when closing, but all the force flows into the closing process. In the case of the ants, one of the door's hinges is partially unhinged and therefore allows play. If you want to close the door now, it becomes much more complicated and requires more force. I have to stabilise and guide the door leaf from several sides so that it arrives in exactly the right position in the frame. It becomes impossible to throw it shut quickly.
How do these characteristics give them an advantage in their habitats?
We don't know exactly why the ants did this. There are several hypotheses: Colleagues in 2020 suggested that this play in the joint allows the ants to carry their eggs with a more gentle grip. Another advantage is a wider opening angle of the jaws and improved force transmission from the muscle to the jaws.
Can you explain the three evolutionary design principles that you have derived from the ant's biting apparatus?
In addition to the jaw principle of the "unhinged door", we were able to derive two more: In insects, the jaws move primarily to the sides and not up and down as in us humans. However, the axis of the jaw is not parallel to the axis of the head as in humans, but is tilted both horizontally and vertically. Therefore, the jaws do not open directly to the sides, but rather diagonally backwards. We could imagine this as if the main movement of chewing in humans was no longer horizontal, but an oblique, vertical movement from top right to bottom left. We are also familiar with this shift in the axis from other insects.
Finally, the third principle is the transfer of force from the muscle to the jaws. This is the same functional principle as with scissors. The longer the handle and the shorter the cutting edge of a pair of scissors, the more force is transferred. However, the movement becomes slower and slower the more the force transmission is increased by changing these distances. The same principles apply in the insect jaw: The further the distance between the muscle insertion and the joint axis, the more force is transmitted. Predatory insects that hunt soft prey usually have a smaller force transmission, but this allows them to close very quickly. Animals that have to chew very hard things such as seed capsules tend to use a lot of force. The movement in the ant's joint changes the transmission of force during the closing process of the jaws. When the jaws are wide open, little force is transmitted, whereas the value increases the further the jaws close. This makes sense insofar as most of the force is needed just before closing when chewing hard objects.
What advantages can be gained from this for medical endoscopy?
We have transferred these three principles to an endoscopic needle holder. This is a rod-like device with small grippers at the tip, which is used to suture all incisions made in the body with a needle and thread after an operation.
[3D model 1]
Every time the surgeon loses the needle during suturing or it slips, a new grip must be applied, which is very difficult due to poor visibility and the very confined space and can lead to complications. A firm grip on the needle is therefore very important. At the same time, the needle holder cannot become larger or wider and therefore more effective, as it still has to fit through the small entry holes in the body. We were able to show that the force transmission and thus the stability of the needle against movement increases if we transfer the three functional principles of the ant jaw that we investigated to such needle holders.
How exactly can these properties be transferred to medical devices and thus to operations?
We have designed three new models, each of which utilises one of the three principles. The first model allows movements in the joint: the needle holder not only performs the classic closing movement of scissors, but is supplemented by an additional forward and backward movement. This clamps the needle in the needle holder, which provides additional stability.
[3D model 2]
The second model is based on the principle of the tilted axis of rotation: The opening movement no longer goes upwards, but diagonally to the side. The arms of the needle holder act like door wedges that hold the needle in place.
The third design has an increased distance between the base of the power cable and the axis of rotation, which greatly increases the power transmission. This was particularly tricky as we had to achieve this without widening the entire bracket. In the end, we solved the problem by replacing the classic pin that holds the two parts of the scissors together with a rounded guide rail on which one of the needle holder arms is guided in a circular motion. This projects the joint axis onto a virtual point outside the actual needle holder, allowing us to achieve the advantage of higher force transmission without spreading the needle holder. We were able to show that these three newly developed models are about two to three times as effective as the commercial original model when it comes to preventing rotation and movement of the needle in the holder.
Which disciplines were involved in the project and how did they work together?
Our most important resource was an extremely interdisciplinary team. It consisted of surgeons and doctors from Brandenburg University Hospital, mechanical engineers from the University of Bayreuth, a functional morphologist from Greifwald and myself as an evolutionary biologist. This extreme versatility in the team, the different ways of thinking and approaches really helped us.
What happens now?
Ants' jaws are a good model for gripping tools in confined spaces. In principle, even more effective models could be designed using the principles we have shown, or there is also the possibility of combining the three approaches. Of course, the new models must be explicitly tested for their application. We would be delighted if someone took up our approaches and developed a finished product. The project has raised so many exciting new questions about insect jaws and their movement and function that I will continue to work on them for quite some time.