Multi-photon multi-material 3D laser printing of stimulus-responsive architectures

We review our work on multi-photon 3D laser micro- and nanoprinting of stimulus-responsive multi-material architectures. We emphasize (i) work for actuation under aqueous conditions and (ii) work for actuation under ambient conditions. Part (i) is based on hydrogels and has previously been published (M. Hippler et al., Nature Commun. 10, 232 (2019)). Here, the degree of cross-linking can be controlled by laser exposure dose (“gray-tone lithography), allowing us to obtain multi-material architectures from just a single photoresist. The Young’s modulus and the thermal expansion coefficient can be different by as much as about a factor of ten. Part (ii) is based on liquid-crystal elastomers (unpublished). Here, during the 3D printing process and in a dedicated sample cell, we apply a quasi-static electric field, allowing us to define the direction of the liquid-crystal director for each voxel in three dimensions. Large reversible and repeatable actuation is obtained.