Real red blood cells owe their astonishing agility to their “biconcave” or tyre-like shape. To create synthetic particles with the same agility, Samir Mitragotri of the University of California and his team got their inspiration from the way real red blood cells acquire their final shape in the body.
They start out as spherical cells which then collapse into mature red blood cells following exposure to various substances. Similarly, Mitragotri’s team found that if they added small balls made of a polymer called PLGA to a particular solvent, the spheres would collapse into a biconcave shape.
The researchers coated these 7-micrometre across, tyre-shaped particles, in a layer of protein. When they dissolved away the polymer core, a soft biodegradable protein shell was left behind with the same mechanical properties as red blood cells.
“The soft protein shell makes them squishy and elastic,” says Mitragotri. “They can squeeze through capillaries smaller than their own diameter, just like real blood cells.”
The fake cells also seem to share red blood cells’ ability to transport substances. One of the proteins Mitragotri added to the surface of the imitation blood cells was haemoglobin, the molecule that binds to oxygen in the lungs, later releasing it elsewhere in the body.