Material: Erodium (Stork bill) awn
Trigger: heat
The Erodium awn consists of fiber-cells that are oriented along the awn. The cell wall of these elongated cells consists of cellulose micro fibrils that are coiled around the cell, embedded within a water-absorbing matrix.
This unique structure causes each cell to coil upon dehydration and to uncoil when hydrated. As a result, the entire awn undergoes the coiling-uncoiling motion.
In nature, the difference in humidity between night (wet) and day (dry) drives the repetitive motion and the drilling of the seed into the soil. Here, the heat of the lamp dries the wan, while periodic dripping of water drives the uncoiling.
The Racah Institute of Physics (The Hebrew University)
Omri Shaltiel
Eran Sharon
This is an enlarged imaging of the repetitive motion of an Erodium awn. As it is dried, by the heat from tha lamp, it coils into a tight helix. Then it gets wet and uncoiled, before being dried again, and so on...