|The concept of artificial muscle made from onion epidermal cell.|
(Credit: Shih Lab, National Taiwan University)
Just one well-placed slice into a particularly pungent onion can send even the most seasoned chef running for a box of tissues. Now, this humble root vegetable is proving its strength outside the culinary world as well - in an artificial muscle created from onion cells. Unlike previous artificial muscles, this one can either expand or contract to bend in different directions depending on the driving voltage applied. The finding is published in the journal Applied Physics Letters.
The onion epidermis - the fragile skin found just beneath the onion's surface - is a thin, translucent layer of blocky cells arranged in a tightly-packed lattice. The researchers thought that onion epidermal cells might be a viable candidate for the tricky task of creating a more versatile muscle that could expand or contract while bending. To date, artificial muscles can either bend or contract, but not at the same time.
The researchers treated the cells with acid to remove the hemicellulose, a protein that makes the cell walls rigid. Then, they coated both sides of the onion layer with gold. When current flowed through the gold electrodes, the onion cells bent and stretched much like a muscle.
The scientists intentionally made the top and bottom electrodes a different thickness so that the cell stiffness becomes asymmetric from top to bottom. The asymmetry gave the researchers control over the muscle's response: a low voltage made them expand and flex downwards, towards the thicker bottom layer. A high voltage, on the other hand, caused the cells to contract and flex upwards, towards the thinner top layer.
To demonstrate their device's utility, the researchers combined two onion muscles into a pair of tweezers, which they used to pick up a cotton ball. In the future, they hope to increase the lifting power of their artificial muscles.
Based on material originally posted by American Institute of Physics.