Paper Filters (IMAGE) Rice University Caption Rice University bioengineers stacked paper filters to culture heart valve cells in collagen and hyaluronan, both natural hydrogels, to see how they influenced calcification of the model. Credit Madeline Monroe/Rice University 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.