The replica red blood cells look just like the real deal (Image: Nishit Doshi) Spot the difference: these are the real blood cells (Image: Stone/Getty)

You can’t get blood from a stone, but it seems you can make imitation red blood cells from polymers.


Just like real blood cells the pretenders can squeeze through spaces much smaller than their own diameter and absorb and release substances to order, including oxygen.

They could be used to disperse drugs, or the contrast agents used in medical imaging, throughout the body with fewer side effects than direct injection.

The fake cells could also be given to people who have lost blood instead of a blood transfusion.

Biodegradable tyre

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.

Oxygen carriers

“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.

In test tube experiments, the researchers found that their haemoglobin-coated particles picked up oxygen when there was a lot around and released it later when the concentration was lower. If the squishy particles do the same thing when injected in animals, they could be given to people instead of a blood transfusion.

To see if the protein shells could also carry drugs, Mitragotri’s team exposed them to the anti-clotting drug heparin. Sure enough, the particles soaked up the heparin and then released it later on when they were moved to an area of lower concentration.

Drug delivery

Mitragotri reckons that the particles could provide a way to get drugs into the body at a more constant concentration, or substances such as iron oxide nanoparticles, which increase contrast in magnetic resonance imaging.

When agents are injected directly, the concentration tends to be highest at the site of injection – dropping in concentration the further away they get. This scenario isn’t ideal as it can cause an adverse reaction at the injection site, and lead to a shortage of the drug elsewhere.

The team also created mimics of the misshapen, crescent-like blood cells that people with sickle cell disease produce. “We could study them to understand how diseased cells flow in the bloodstream, which is currently quite difficult to do,” says Mitragotri.

Elastic shape

It’s not the first attempt at artificial red blood cells, but these are the only ones so far to have the shape and elasticity of real cells, says Mitragotri.

Joseph DeSimone, who developed fake blood cells last year, calls the new research “exciting”. “All in all, this is great progress in tackling an important problem,” he says.

Next the team want to look at exactly how the particles behave in an animal, particularly whether they circulate in the same way as their natural counterparts.

Journal reference: Proceedings of the National Academy of Sciences, DOI: 10.1073_pnas.0907127106