Fabrication of 3D Functional Nanocomposites Through Post‐Doping of Two‐Photon Microprinted Nanoporous Architectures

Two-photon lithography (TPL) enables the fabrication of complex 3D structures with sub-micrometer precision. Incorporation of new functionalities into TPL-printed structures is key to advance their applications. A prevalent approach to achieve this is by directly adding functional nanomaterials into the photoresist (called "pre-doping"), which has several inherent challenges including material compatibility, light scattering, and nanoparticle agglomeration. Here, a conceptually different "post-doping" strategy is proposed, where the functionality of the TPL-printed architectures is achieved by impregnating functional materials into their nanoporous 3D mimics. Using the principle of polymerization-induced phase separation, TPL printing of complex microarchitectures with well-defined nanoporous structures having pores of ≈420 nm is realized, which allows spontaneous impregnation of functional liquids via capillary effect. Importantly, unlike the "pre-doping" approach that requires printing optimization for each photoresist, this strategy is highly versatile in terms of functionalities possible. As a proof-of-concept, the impregnation of several functional liquids into TPL-printed porous microstructures is demonstrated: a fluorinated-lubricant, an ionic liquid, and three types of fluorescent liquids, conferring the microstructures with slippery, conductive, and localized fluorescence properties, respectively. Such versatility to fabricate complex microstructures with tailorable and localized functionalities is expected to open new possibilities in wide fields including bionics, electronics, and cell biology.