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October 5, 2005

The first microscopic artificial swimmer is based on spermatozoid swimmers

CNRS and ESPCI (1) researchers have made the first artificial micro-swimmer produced to date. Like a spermatozoid, the micro-swimmer has a head (a red blood cell) and a tail (flexible magnetic filament). Placed in an oscillating magnetic field, the tail beats in the direction of the field, propelling the micro-swimmer. This discovery could be used to carry and position cells placed in front of the micro-swimmer, because direction and speed of movement are adjustable. These results were published in Nature on October 6, 2005.

Natural microscopic swimmers, from bacteria to  spermatozoids, use molecular motors to rotate or beat a filament. On a scale of just a few microns, swimming is only efficient if the two half-periods of the swimmer's movement are not superimposed, in other words, if the "forward" and "backward" movements do not follow the same route. This property, developed by physicists during the 1950s, is the main difference with the macroscopic world, because of the importance of viscosity on a small scale. Natural micro-swimmers respect this principle.

 

Researchers at the "laboratoire Liquides ioniques et interfaces chargées" (Ionic liquids and charged interfaces laboratory) (CNRS/ESPCI/University Paris 6)(2) have produced and studied a spermatomorphic swimmer, the head of which is a red blood cell and the tail a flexible magnetic filament. They made the filament of paramagnetic particles (which attract each other when placed in a magnetic field), connected sequentially by DNA strands. By adjusting the number and length of the strands, they were able to duplicate the flexibility of natural filaments. Using an alternating magnetic field, the researchers imitated the spermatozoid's swimming movement. As the field changes directions, the filament swivels to follow it. It is therefore deformed, creating a wave which is propagated along the length of the filament (see diagram) propelling the micro-swimmer.

 

This micromachine is the first version obtained so far of a self-propelling  microscopic system. It generates new prospects in understanding the subtleties of swimming on a microscopic scale, because researchers can vary the field frequency, length of filament etc. This type of micro-swimmer could also be used in  applications requiring cell positioning or for moving infinitely small quantities of fluid (when the micro-swimmer is fixed, the liquid is moved around it).

 
micro-nageur

© CNRS-Rémi Dreyfus. Image available from the CNRS photo library: phototheque@cnrs-bellevue.fr

The time interval between each image is 5 milliseconds.
The white arrows represent the direction of the magnetic field.


 
 

(1) Ecole supérieure de physique et de chimie industrielle.
(2) in association with the "Laboratoire de physique et mécanique des milieux

 hétérogènes" (CNRS/ESPCI/University Paris 6 and 7) and a team from Harvard University.

Bibliography:

Microscopic artificial swimmers, Rémi Dreyfus, Jean Baudry, Marcus L. Roper, Marc Fermigier, Howard A.Stone, Jérôme Bibette, Nature, 6 October 2005.

Contacts:

Researcher contact information:
Jérôme Bibette
Tel: 01 40 79 52 19 ou 06 85 13 75 36, E-mail: jerome.bibette@espci.fr

Press contact:
Claire Le Poulennec
Tel: 01 44 96 49 88, E-mail: claire.le-poulennec@cnrs-dir.fr


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