Shape Programming via Direct Laser Writing*

Photochemical shrinkage during laser-induced polymerization can cause residual stresses in materials that can be exploited for fabricating shape morphing structures. In this work, we show that direct laser writing, a method based on two-photon polymerization, can be used to create pre-programmed planar sheets that evolve into complex 3D geometries upon triggering. The method allows for direct production of structures in the cm-range with sub-micron resolution.

We fabricate self-bending biomimetic lotus flowers and shark skins to demonstrate precise control over inhomogeneous and anisotropic shape morphing behavior. Resulting curvatures are locally controlled through variations in laser writing- and geometrical parameters. We conduct microexperiments to quantify the driving factors for the shape transformations: Residual stresses, capillary action, and adhesive forces.

A comprehensive mechanical model based on beam bending theory is presented to determine local bending curvatures analytically. Dynamic finite element simulations are implemented to capture the polymerization process and predict the resulting global deformations. The analytical and numerical predictions are in good accordance with the experimental results.