Scientists are hopeful that jelly-like synthetic "hydrogel" nanoparticles could be the first step towards artificial blood being developed.
The particles, which measure six micrometres (0.006 millimetres) across, are highly flexible like real red blood cells and could end up being used in the fight against cancer.
Hydrogel's flexibility mean that they stay in circulation longer before they are filtered, slipping through narrow capillaries or microscopic pores in organs.
Researchers are excited by the medical potential of the particles, but they are yet to be tested for their ability to transport oxygen or carry anti-cancer drugs.
If it comes through such tests with flying colours, it could create an endless supply of man-made blood.
Up to now the most promising studies for synthetic blood involve red blood cells being derived from stem cells.
A US company has developed a "pharming" process to produce blood cells from stem cells taken from umbilical cords which it hopes can be used in the field.
Scientists have also succeeded in creating red blood cells from spare IVF embryos but attempts to mimic nature with an artificial way of carrying oxygen around the body have not proved successful.
Lack of flexibility has been the major stumbling block. Real blood cells gradually become stiffer during their life and are eventually filtered out of the circulation when they can no longer bend enough to pass through pores in the spleen.