Extremely Flexible Hydrogel Particles (IMAGE) University of North Carolina Health Care Caption These extremely flexible hydrogel particles 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. Credit Image courtesy Timothy J. Merkel and Joseph M. DeSimone, University of North Carolina at Chapel Hill. Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.