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

Abstract

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.

It's in the Fine Print: Erasable Three‐Dimensional Laser‐Printed Micro‐ and Nanostructures

“…di(meth)acrylates), while DLW applications often require tri‐ or tetrafunctional crosslinkers (e.g. pentaerythritol triacrylate (PETA)) to fabricate structures with fine details …”

“…With regard to spatial control, cleaving a material can be divided into three categories: 1) no spatial control, 2) partial spatial control, and 3) complete spatial control (Figure ). No spatial control (category 1) is the easiest to achieve and requires a photoresist that can be degraded by a homogeneous external condition, such as pH, temperature, specific additives, or enzymes . Complete cleavage without spatial control is particularly interesting, for example in drug delivery, when the cargo is only transported by a direct‐laser‐written structure and cleavage is used for controlled cargo release .…”

“…A large body of work has been established that extensively exploits the controlled cleavage of networks via labile moieties, such as gels, solid‐phase organic synthesis, drug‐delivery systems, and biodegradable polymers, among others . However, research regarding cleavable 3D printed materials fabricated in the submicron range is still challenging and only a few examples have been reported so far, which will be discussed in the next Section . Consequently, the translation of existing knowledge for the next generation of DLW photoresists is of significant value for the design of degradable micro‐ and nano‐sized printed 3D materials.…”

“…Because microstructures fabricated via DLW can be used as templates, orthogonal cleavable materials enable the design of new materials that are currently inaccessible. Some of us recently reported a cleavable photoresist system based on labile silane crosslinkers that allow the chemoselective degradation of multiple 3D printed microstructures under mild conditions . Three crosslinkers containing methyl, ethyl, or isopropyl substituents on the silicon atom were mixed with a two‐photon photoinitiator and PETA.…”

“…While acid‐cleavable materials are thoroughly described in the literature, there is only a limited number of examples based on base‐labile linkages. Commonly employed photoresists in DLW are multifunctional polyesters, such as PETA, poly(ethylene glycol) diacrylate, pentaerythritol tetraacrylate, among others. Although polyesters can gradually degrade in harsh conditions, the required basic pH values are often impractical for many applications.…”