The findings unleashes the potential for X-ray computed tomography (CT) to analyze stress or defects noninvasively in embedded 3D-printed medical devices or implants.

Two-photon lithography typically requires a thin glass slide, a lens and an immersion oil to help the laser light focus to a fine point where curing and printing occurs. It differs from other 3D-printing methods in resolution, because it can produce features smaller than the laser light spot, a scale no other printing process can match. The technique bypasses the usual diffraction limit of other methods because the photoresist material that cures and hardens to create structures — previously a trade secret — simultaneously absorbs two photons instead of one.

LLNL researchers describe cracking the code on resist materials optimized for two-photon lithography and forming 3D microstructures with features less than 150 nanometers. Previous techniques built structures from the ground up, limiting the height of objects because the distance between the glass slide and lens is usually 200 microns or less. By turning the process on its head — putting the resist material directly on the lens and focusing the laser through the resist — researchers can now print objects multiple millimeters in height. Furthermore, researchers were able to tune and increase the amount of X-rays the photopolymer resists could absorb, improving attenuation by more than 10 times over the photoresists commonly used for the technique.