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Single-celled predator extends its ‘neck’ with the help of origami

The cell is held by two micropipettes to lengthen the neck.

The organism is held by two micropipettes to lengthen the “neck”

Elliot Flaum and Manu Prakash/Stanford University

Imagine if your neck was so extendable that your head could reach your local store while sitting on the couch. That would be the human equivalent of what a single-celled predator can do, and now the long-standing mystery of how it can extend its “neck” more than 30 times the length of its “body” has been solved.

This organism’s cell membrane is folded into a series of folds that can only unfold and fold in one way, Eliott Flaum of Stanford University and his colleague Manu Prakash have discovered, allowing it to extend and fold back without becoming tangled. . “We found out most of this by playing with a piece of paper,” Prakash says.

tear smell It is a single-celled organism, or protist, that lives in fresh water and hunts its prey with its extraordinarily extendable neck-like protuberance. Its name means “swan’s tear,” because of its swan-like neck and tear-shaped body.

Although cell membranes are very flexible, they are not elastic and cannot stretch. So, How L. smell Extending its neck to such a length has been a mystery since it was first seen under a microscope in the 16th century. “We compared it to many other organisms and it is much larger in this extent,” says Prakash. “That’s the riddle.”

He and Flaum were intrigued when they saw L. smell on samples they collected from a swamp six or seven years ago, and set out to solve the mystery. Flaum used several different techniques to image the exterior structure of L. smell and its internal cytoskeleton, made up of structures called microtubules. “We tried a lot of different ways of looking at it to understand what was happening,” she says.

This revealed that the cell membrane of L. smell It folds into 15 folds, and each fold spirals around the cell, forming a helical structure. Prakash calls this folding pattern “curved fold origami” or “Lacrigami”.

But how L. smell Unfold and refold this huge area of ​​cell membrane without getting tangled? What Prakash and Flaum discovered is that because of the way folds are stabilized by bands of microtubules connected to them, an entire fold cannot unfold at once. Instead, only one point of a fold can be deployed or retracted at any time.

As these points move in parallel upward in each of the 15 folds, the cell membrane unfolds in an orderly manner, extending the neck. Reversing the process shortens the neck.

“Instead of folding randomly, like you would crumple paper, it has a guide rail to fold it the same way every time,” Flaum says.

The folding and unfolding is driven by hairs or cilia that cover the entire surface of the cell, says Prakash. It requires energy to unfold and refold, unlike a spring, but it needs very little because cell membranes bend easily.

To his knowledge, no one had discovered this folding pattern before. “When we realized this, I always thought that someone playing with paper would have discovered this origami,” says Prakash. “It’s pretty simple.” Anyone can do it with a piece of paper and some tape, he says.

“The clever origami design of its neck makes the cilia effective for high-speed and long-distance hunting,” write Leonardo Gordillo and Enrique Cerda of the University of Santiago de Chile in an accompanying paper. “The origami-like protrusion mechanism identified by Flaum and Prakash has the potential to inspire new strategies in soft matter engineering.”

In fact, Prakash and Flaum are currently working on developing medical robots based on “Lacrigami”. “If you had a small microrobot in a very small space and it could suddenly extend, it would be enormously useful in microsurgery,” she says. “But we did this work because it is simply beautiful and a mystery to solve. “We didn’t think it was useful in any way.”

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