Novel, High-Resolution, Subtractive Photoresist Formulations for 3D Direct Laser Writing Based on Cyclic Ketene Acetals

Direct laser writing (DLW) is an innovative technology based on two-photon polymerization processes which allow the 3D printing of architectures with arbitrary complexity at the (sub)micrometer scale. While most of the research interest in this field relies on additive manufacturing, subtractive approaches can be extremely helpful in nano/microfabrication, allowing the preparation of expendable scaffolds, replaceable parts, and for the protection of fragile structures. In this study, we show that the simple addition of 2-methylene-1,3-dioxepane, a cyclic ketene acetal compound, to a series of different acrylate-based photoresists results in functional formulations that allow the 3D-printing of degradable poly(ester-co-acrylate) microstructures via DLW. These latter could be degraded reliably under mild conditions compatible with other photoresists and materials of common use in the fabrication of MEMS, thus opening new opportunities to design novel fabrication procedures. In addition, the possibility of using different acrylate mixtures without affecting the degradability, allows the users to choose between a broad range of properties for the printed structures to fit their needs, without affecting the degradability. Finally, the authors show the potential of these photoresists in the fabrication of shadowing masks on 3D objects and their selective degradation employing a photobase.