Velvet worms shoot slime out of two nozzles on either side of their head, as shown in the picture on the right, through strong muscle contractions. When the velvet worms eject their sticky slime, the fluid solidifies to form fibres, trapping their prey. This process is reversible as the dried fibres can be dissolved in water and re-drawn into new ones. This would be extremely useful for humans to recreate as a potential key step in the quest for more easily recyclable plastic materials.
The first stage is to fully understand the structure of the slime and learn what causes it to solidify. In this study, published recently in Small, researchers used a range of techniques, including small angle neutron and X-ray scattering (SANS and SAXS) at ISIS. They looked at how the components of the slime interact with one another on the nanoscale under native conditions, after reconstitution and following mechanical agitation. Slime samples were collected from worms collected in Australia by encouraging them to eject slime into sample tubes.
“Small angle scattering is a particularly well-suited technique for studying biological soft matter as it can look at the nanoscale structures under real-world conditions," explains beamline scientist Najet Mahmoudi. “By combining SAXS in the Materials Characterisation Laboratory with SANS on Sans2d, and using both light and heavy water during hydration, we could distinguish between different fractions of free proteins and nanoglobule condensates of lipids and proteins in the slime."
Previous experiments had suggested that the slime formed fibres from proteins stored in nanoglobules. However, in this study the researchers found that only a small fraction of the proteins aggregated into nanoglobules with the rest existing as free proteins in the liquid phase. This was the case even after shaking in the absence of air, where no fibres formed, implying that the exposure to air or other interfaces and directional drawing of the material might be required for fibres to form.
“The slime did not form fibres under our experimental conditions, so it could be that it needs exposure to air or directional drawing for this to happen" explains Dr Alexander Bär from the University of Kassel. “It was interesting for us to see that the nanoglobules were not aggregating into fibres, as this is what we expected to see."
To investigate this system further and look at what happens when the slime is exposed to air, the researchers hope to use neutron and X-ray reflectometry.
The full paper can be found online at DOI: 10.1002/smll.202300516