Traffic Control Of Cells (IMAGE) University of Freiburg Caption Researchers developed a hydrogel whose stiffness and permeability to cells can be controlled with light. Credit Graphic: Jo Richers 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.