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

Abstract

3D printing, on all scales, is currently a vibrant topic in scientific and industrial research as it has enormous potential to radically change manufacturing. Owing to the inherent nature of the manufacturing process, 3D printed structures may require additional material to structurally support complex features. Such support material must be removed after printing—sometimes termed subtractive manufacturing—without adversely affecting the remaining structure. An elegant solution is the use of photoresists containing labile bonds that allow for controlled cleavage with specific triggers. Herein, we explore state‐of‐the‐art cleavable photoresists for 3D direct laser writing, as well as their potential to combine additive and subtractive manufacturing in a hybrid technology. We discuss photoresist design, feature resolution, cleavage properties, and current limitations of selected examples. Furthermore, we share our perspective on possible labile bonds, and their corresponding cleavage trigger, which we believe will have a critical impact on future applications and expand the toolbox of available cleavable photoresists.

Bending dynamics of viscoelastic photopolymer nanowires

“…Owing to the high flexibility and the nanoscale spatial resolution of two-photon polymerization direct laser writing (TPP-DLW) lithography, [1][2][3][4][5][6] the application field of nano-and microstructures fabricated by this technique is growing fast. Recent developments cover the areas of photonic devices, [7][8][9] nano-micro-mechanics, [10][11][12] and biomedical applications.…”

Shining Light on Poly(ethylene glycol): From Polymer Modification to 3D Laser Printing of Water Erasable Microstructures

“…[ 11 ] Such post‐DLW erasing is for instance a highly enabling feature for the repair of structural defects, for the selective removal of support structures (e.g., to construct hanging objects) and for the degradation of biomimetic cell culturing scaffolds, once these become redundant. [ 12 ] Hereto, it is essential to design advanced photoresists, applicable to laser lithography, that can introduce the desired programmed cleavage into the finally printed materials. Thus far, only a few examples have been reported in which the controlled erasing of laser written microstructures can be achieved through the use of labile linkers that can be cleaved upon heating, [ 13 ] in the presence of reducing agents, [ 14 ] under basic conditions, [ 15 ] or by using light of a wavelength, which differs from that in the writing process.…”

“…In order to fully expand the potential of erasable direct laser written microstructures to the realm of bioengineering applications, however, the development of photoresists that are susceptible to much milder cleavage conditions is a prerequisite. [ 12,17 ] Indeed, elevated temperatures, chemical additives, and organic solvents all generally suffer from biocompatibility issues and should thus ideally be avoided. In pursuit of more viable methods to effect a sustained hydrogel degradation, enzyme‐labile DLW photoresists have been developed which, although in its infancy, are receiving rapidly increasing attention.…”

“…[ 18 ] Nonetheless, enzymatic cleavable microstructures are limited to specifically tailored peptide‐containing materials and the integration of these responsive elements into synthetic hydrogels is often cumbersome. [ 4b,12,19 ] An alternative biocompatible trigger to cleave 3D microscopic hydrogels can be found in hydrolysis. [ 20 ] In particular, acrylate‐terminated poly(ethylene glycol) (PEG) photoresists have attracted interest because of their susceptibility toward 3D laser printing in the presence of an appropriate photoinitiator, whereas the introduced ester linkages can render the fabricated microstructures prone to hydrolytic cleavage.…”

Enzyme‐Degradable 3D Multi‐Material Microstructures

“…Demand for scaffold materials with smart properties has stimulated substantial interest in designing photoresists with disparate properties. [25,26] The use of enzymes to degrade materials is a highly attractive option for tissue engineering and regenerative medicine. [10,27] Enzymes are highly chemo, regio-and stereoselective with the capability to work under mild, physiological, and aqueous conditions (pH 5-8, ambient temperature 25-37 °C).…”