They might look like sperm swimming backwards, but red blood cells have become the first living cells to be fitted with an artificial tail. As the tail whips back and forth, the cell moves tail-first at a cool 6 micrometres per second - about 10 times as slow as sperm swim.The secret to the cell’s motion lies in the composition of the tail - a filament of tiny magnetic beads held rigidly together by strands of DNA. When an oscillating magnetic field is applied to the cells, they move through the fluid as their tails bend to align themselves with the constantly reversing direction of the magnetic field.The microscopic swimmers might one day provide a way to direct medicines through the bloodstream to exactly the right spot, says Remi Dreyfus, who created the device with colleagues at France’s Ecole Supérieure of industrial physics and chemistry in Paris. He says that in theory, the filaments could be attached to any cell. But it will be “far in the future” before medical applications emerge, he cautions.You can view a video of a swimming blood cell here (0.8MB .mov file). Unlike sperm, it moves in the direction of the tail, away from the cell.Journal reference: Nature (vol 437, p 862).
