The paper “Adding Chemically Selective Subtraction to Multi-Material 3D Additive Manufacturing” in Nature Communications can be found here: https://www.nature.com/articles/s41467-018-05234-0.

Three-dimensional (3D) printing is an additive manufacturing method, where a digital model is turned into a physical object. 3D printing is perhaps similar in societal impact to Gutenberg's 2D printing press invented in the 1440s. As a printing method that can create complex and intricate designer products, 3D printing is currently the subject of substantial interest in the scientific and industrial communities due to its enormous potential to radically transform current manufacturing. Some estimate that by 2030, 10% of all manufactured goods will be 3D printed.

3D printing with light has numerous advantages over traditional 3D printing techniques. In addition to being substantially faster, it is also capable to create higher-resolution prints. An important aspect for current and future applications of 3D printing using light is to extend the range of available resists. For many applications, it is beneficial when specific elements within a 3D printed object consist of a material, which is removable after finalizing its fabrication. Combining additive and subtractive fabrication techniques, also referred to as hybrid manufacturing, is particularly interesting for applications where the 3D printed material acts as support structure or natural damage results in a short lifetime and requires replacement.

In our recent paper in Nature Communications, we report the combination of chemically selective subtraction with multi-material 3D additive manufacturing. Specifically, we employ 3D laser lithography, which is a particular type of 3D printing allowing the fabrication of micro- and nano-sized structures. In analogy to established strategies for degradable soft materials, we prepared crosslinkers with labile linkages based on silyl ethers that undergo cleavage under mild yet specific conditions. Three bifunctional silane crosslinkers having various substitutions on the silicon atom were prepared using a facile and rapid one-step synthesis. 3D printed materials made of these silane crosslinkers were degraded using only inorganic salts (i.e., NaHCO₃, K₂CO₃ or KF) in methanol. In addition, our set of silane crosslinkers enables the targeted degradation of individual structures in a consecutive and selective fashion. As a proof of concept, we sequentially subjected a single substrate with 3D microstructures made of different photoresists to three conditions: (1) a saturated solution of NaHCO₃ in MeOH at 50 °C, (2) a saturated solution of K₂CO₃ in MeOH at room temperature (RT), and (3) a saturated solution of KF in MeOH at RT.

Due to the mild, efficient and selective nature of the cleavage process, we suggest that silane-based photoresists hold large potential for the fabrication of a variety of complex and multifunctional 3D structures that are presently inaccessible using current state of the art photoresists and/or subtractive manufacturing methodologies.