Compensating for distortions in complex structures 3D printed by two-photon polymerization

Two-photon polymerization (2PP) is an additive manufacturing technique exploiting two-photon-absorption-induced photo-polymerization to fabricate three-dimensional complex geometries at the micrometric scale. Applications span various fields from photonics to bio-scaffolds to microrobotics. Unfortunately, even when using ultra-low-shrinkage polymeric resins, distortions occur, thereby compromising the dimensional fidelity and expected performance of the printed structures.

This work examines the physical sources of the distortions arising in 2PP 3D-printed structures. A primary distortion (due to a refractive index mismatch between the immersion medium of the objective and the polymeric resin) causes an overall stretching, whereas a secondary distortion (related to a saturating voxel growth during hatching and slicing) leads to an additional thickness on individual features within a structure. Two prints are thus devised to evaluate the stretching factor and saturated voxel height, and a straightforward technique is proposed to pre-compensate for distortions in the initial design of a structure. Finally, this methodology is shown to successfully eliminate all distortions in complex structures such as lattices and triply periodic minimal surfaces (TPMS).