Drops (IMAGE) Penn State Caption Self-healing reverse filter allows large particles through, but excludes smaller particles and gases. Credit Tak-Sing Wong/Birgitt Boschitsch, Penn State Usage Restrictions Non commercial use only 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.