3-D Printing Metal (IMAGE) California Institute of Technology Caption Two-photon lithography is used to 3-D print structures out of a liquid material, creating chemical bonds that harden into a solid material. Credit Greer Lab/Caltech Usage Restrictions For use in news stories 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.