Philippe Marmottant, Olivier Vincent and Catherine Quilliet
Laboratoire de Spectrométrie Physique
CNRS / Université de Grenoble
140 av de la Physique 38042 Grenoble
marmotta@spectro.ujf-grenoble.fr
A process difficult to perform within the channels of a miniaturized lab, called Lab on a chip, is the sudden transfer
of a small sample of fluid in a closed container. This operation is naturally found in the vegetal kingdom when
considering the aquatic carnivorous plants Utricularia (common name bladderwort). This plants are gifted with
suction traps (Skotheim 2005): a contact opens a door, the trap sucks in liquid, and then the door closes
hermetically, all this sequence within the impressive time of a few milliseconds, barely visible with the naked eye.
We present an on-going experimental study of the biomechanics of the trap. The motion of the trap door is
recorded by a high-speed camera. We could record the natural activation of the trap (using different fresh water
crustaceans), and then provoked activation of the trap with a fine needle. With this artificial triggering, we could
focus on the succession of the two distinct phases of the suction : first the door opens, and second the door closes
hermetically after suction. The motion is therefore di fferent from the close-only traps of the Venus flytrap (Forterre
2005). We also record the associated fluid motion. We find that the door is curved inwards at opening, and that an
intense flow of liquid (1 m/s) is generated during a very short time (0.4 ms).
These observations are interpreted with a biomechanical approach involving elasticity and flow. The door opening is
described as a buckling of the door under the a preexisting pressure, because of a softening of the door following
the touch of sensitive trigger hairs. The door closure results from the equilibration of pressures, and from the fact
that the relaxed shape of the door is the closed position.
An original behavior was also recorded: after a few hours the trap activates spontaneously . If the precise biological
function of this phenomenon is unclear, it expresses the fact that the sensibility of the plant increases considerably
at time of 5 hours, and is trigger by very small fluctuations.
We conclude by the presentation of a simple analytical model that will prove useful for the design of a biomimetic
reproduction of the trap, and its implementation in a microfluidic circuit as a miniaturised pipette.
References
[1] Skotheim, J. M. and Mahadevan, L. Physical Limits and Design Principles for Plant and Fungal Movements
Science, 2005, 308, 1308-1310.
[2] Forterre, Y.; Skotheim, J. M.; Dumais, J. and Mahadevan, L. How the Venus flytrap snaps Nature, 2005, 433,
421-425.