Investigation at the nano level

Researchers on the trail of animal glue

2023/03/08 by

An international team of researchers with the participation of TU Darmstadt has come a step closer to uncovering the secret of an amazing adhesive from the animal world. So-called velvet worms, a group of animals with some unusual properties, hunt with this secretion. The new findings could help develop reusable biomaterials for medical or industrial purposes.

A representative of the species Euperipatoides rowelli expelling secretion through the mucous papillae

The Australian velvet worm species Euperipatoides rowelli preys on smaller insects and defends itself by expelling a sticky fluid from two nozzles on its head. In contact with surfaces and by pulling, tensile fibres are instantly formed in the secretion. The more the trapped animal wriggles, the firmer these become.

To study the mucus, Professor Emanuel Schneck from the Department of Physics at the TU Darmstadt and researchers from the University of Kassel worked with neutron beams, which behave like the waves of light. From the directional dependence in which these waves are deflected by the sample, they were able to calculate how the sticky substance is structured. To their astonishment, they found that although uniformly sized nanospheres are present in the mucus, large proteins, from which the tensile fibres are formed, are not stuck in these globules but float freely in the secretion.

New insights through neutron measurements

“Until now, it was thought that most of the proteins were incorporated into the nanospheres and that fibres would then form from these globules when they were pulled on,” Professor Schneck explained. “My research colleagues Professor Georg Mayer, head of the Department of Zoology at the University of Kassel, and department member Dr Alexander Bär have already been studying the functioning and structure of the mucus since 2012. The neutron measurements now provide completely new insights, on the basis of which the common thesis of how the secretion works must be revised.”

The researchers also acted on the secretion with ultrasound. This allowed them to generate shear forces in the absence of ambient air and without bringing the substance into contact with other surfaces. No fibres were formed, and the inner structure of the mucus hardly changed either. Their conclusion: It takes more than just mechanical action on the secretion for free proteins to assemble into stable fibres.

The scientists now suspect that the nanospheres and adjacent surfaces serve as points of attachment where the proteins accumulate and associate to form tension-resistant fibres. Drying of the secretion by ambient air could additionally drive the change in shape of the mucus.

The researchers have thus come a great deal closer to their goal of researching the substance so well that its mechanisms of action can be reproduced. Synthetically produced materials that exhibit these mechanisms of action could be of great use, for example, as recyclable and naturally compatible adhesives in medicine or industry.

The publication

The study entitled “The internal structure of the velvet worm projectile slime: A small-angle scattering study” was published in the journal “Small” on 24.02.2023:

In addition to the TU Darmstadt and the University of Kassel, researchers from the Institut Laue-Langevin in Grenoble (France), the Rutherford Appleton Laboratory in Didcot (Great Britain), the University of Quebec at Montreal (Canada), McGill University in Montreal and Heinrich Heine University Düsseldorf were also involved.