They may never pose a challenge to Olympic superstar Michael Phelps, but the "microswimmers" developed by researchers in Spain and the United Kingdom could break a long-standing barrier to improving delivery of medications for cancer and other diseases.

A collaboration of British and Iranian physicists has created an armada of self-propelled polystyrene balls about as wide as a strand of your hair. Their efforts are moving toward self-propelled nanoswimmers that could navigate narrow channels such as the human circulatory system.