3-D inks that can be erased selectively

Adding chemically selective subtraction to multi-material 3D additive manufacturing

SEM images showing the selective cleavage of MSEA-, ESEA-, and ISEA-based 3D microstructures. The glass substrate was sequentially immersed in NaHCO3 at 50 °C, then, in K2CO3 at RT and finally, in KF at RT (scale bars = 20 μm). (Bottom left) Schematic representation of a glass substrate containing four model structures composed of MSEA (blue Eiffel tower), ESEA (red Aztec pyramid), ISEA (purple bridge) and PETA (green Asian temple)

Existing photoresists for 3D laser lithography that can be removed after development in a subtractive manner typically suffer from harsh cleavage conditions. Here, we report chemoselectively cleavable photoresists for 3D laser lithography based on silane crosslinkers, allowing the targeted degradation of 3D printed microstructures under mild conditions.

Three bifunctional silane crosslinkers carrying various substitutions on the silicon atom are synthesized. The photoresists are prepared by mixing these silane crosslinkers with pentaerythritol triacrylate and a two-photon photoinitiator. The presence of pentaerythritol triacrylate significantly enhances the direct laser written structures with regard to resolution, while the microstructures remain cleavable.

For the targeted cleavage of the fabricated 3D microstructures, simply a methanol solution including inorganic salts is required, highlighting the mild cleavage conditions. Critically, the photoresists can be cleaved selectively, which enables the sequential degradation of direct laser written structures and allows for subtractive manufacturing at the micro- and nanoscale.

The direct structuring of soft matter in three dimensions via direct laser writing (DLW), also referred to as 3D laser lithography or 3D laser printing, has revolutionized the field of micro-optics1,2,3,4.

SEM images of polymer lines and 3D structures written on a glass substrate. Polymer line composed of a 100 mol% ISEA, b 97.5 mol% ISEA and 2.5 mol% PETA, and c 100 mol% PETA (scale bars = 200 nm). d Woodpile structure composed of 97.5 mol% ISEA and 2.5 mol% PETA (scale bars = 1 and 4 μm, respectively). e Fragment of a Greek temple with multiple columns holding up an entablature composed of 97.5 mol% ESEA and 2.5 mol% PETA (scale bar = 10 μm)

This light-based micro- and nanoscale printing method is based on a multi-photon polymerization of a photoresist employing a femtosecond laser, in which two (and occasionally more) photons are absorbed simultaneously. Due to the nonlinearity of the multi-photon process, the chemical reaction occurs exclusively within the focal spot of the laser and allows for locally defined crosslinking.

Thus, DLW is capable of fabricating complex 3D structures on the submicron length scale. This high resolution—in some instances sub-diffraction resolution by exploiting STED principles5,6,7,8—is particularly attractive for applications where sophisticated structures with high precision are required, including optical metamaterials, biomedicine, microfluidics, and microelectronic1,9,10,11,12. To date, there exists no other 3D manufacturing approach on the submicron length scale that would be even remotely as versatile.

Read more: 3-D inks that can be erased selectively

Source: nature.com