Credit:
Extremely flexible hydrogel particles that resemble red blood cells in size and shape. To date, attempts to create effective red blood cell mimics have been limited because synthetic particles tended to be quickly filtered out of the circulatory system due to their stiffness. In testing, these flexible particles remained in circulation up to 30 times longer than stiffer ones. Image courtesy Timothy J. Merkel and Joseph M. DeSimone, University of North Carolina at Chapel Hill.