Reversible Supramolecular Assembly of Velvet Worm Adhesive Fibers via Electrostatic Interactions of Charged Phosphoproteins

Velvet worms secrete a fluid hunting slime comprised of a dispersion of nanoglobules that form microfibers under small mechanical shear forces, facilitating the rapid formation of stiff biopolymeric fibers. Here, we demonstrate that the nanoglobules are held together and stabilized as a dispersion by electrostatic interactions reminiscent of coacervate-based natural adhesives. Variation of ionic strength and pH affects the stability of nanoglobules and their ability to form fibers. Fibers mainly consist of large (similar to 300 kDa), highly charged proteins, and current biochemical analysis reveals a high degree of protein phosphorylation and presence of divalent cations. Taken together, we surmise that polyampholytic protein sequences, phosphorylated sites, and ions give rise to transient ionic cross-linking, enabling reversible curing of ejected slime into high-stiffness fibers following dehydration. These results provide a deeper understanding of velvet worm adhesive fibers, which may stimulate new routes toward mechanoresponsive and sustainable materials.