title: Oscillation of the velvet worm slime jet by passive hydrodynamic instability.
abstract: The rapid squirt of a proteinaceous slime jet endows velvet worms (Onychophora) with a unique mechanism for defence from predators and for capturing prey by entangling them in a disordered web that immobilizes their target. However, to date, neither qualitative nor quantitative descriptions have been provided for this unique adaptation. Here we investigate the fast oscillatory motion of the oral papillae and the exiting liquid jet that oscillates with frequencies f~30-60 Hz. Using anatomical images, high-speed videography, theoretical analysis and a physical simulacrum, we show that this fast oscillatory motion is the result of an elastohydrodynamic instability driven by the interplay between the elasticity of oral papillae and the fast unsteady flow during squirting. Our results demonstrate how passive strategies can be cleverly harnessed by organisms, while suggesting future oscillating microfluidic devices, as well as novel ways for micro and nanofibre production using bioinspired strategies.
authors.affiliation: School of Engineering and Sciences, Adolfo Ibañez University, Diagonal las Torres 2640, Peñalolen, Santiago 7941169, Chile.
authors.forename: Andrés
authors.initials: A
authors.lastname: Concha
authors.affiliation: School of Engineering and Sciences, Adolfo Ibañez University, Diagonal las Torres 2640, Peñalolen, Santiago 7941169, Chile.
authors.forename: Paula
authors.initials: P
authors.lastname: Mellado
authors.affiliation: Laboratorio de Genética Evolutiva, Escuela de Ciencias Biológicas, Universidad Nacional de Costa Rica, 86-3000 Heredia, Costa Rica.
authors.forename: Bernal
authors.initials: B
authors.lastname: Morera-Brenes
authors.affiliation: Department of Zoology, Institute of Bioscience, Universidade de Sao Paulo, Sao Paulo, Sao Paulo 11461, Brazil.
authors.forename: Cristiano
authors.initials: C
authors.lastname: Sampaio Costa
authors.affiliation: 1] School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA [2] Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: L
authors.initials: L
authors.lastname: Mahadevan
authors.affiliation: Tropical Biology, Universidad de Costa Rica, 2060 San José, Costa Rica.
authors.forename: Julián
authors.initials: J
authors.lastname: Monge-Nájera