Direct Laser Writing of Bioinspired Architectures with Novel Polysaccharide-Based Photoresists

The polysaccharide cellulose is next to chitin the most abundant biopolymer on earth and is considered an almost inexhaustible source of raw material for the increasing demand of environmentally friendly and biocompatible products.^[1,2] We recently synthesized a bio-based photoresist, where a photo-reactive cellulose derivative is dissolved in an organic solvent together with a photoinitiator.<br/><br/>This novel photoresist is curable by two-photon absorption at 780 nm in a direct laser writing (DLW) system (Nanoscribe Photonic Professional GT). With this setup, two-dimensional architectures with a linewidth of less than 250 nm and a minimum line distance of 500 nm are achieved. Our bio-based photoresist allows three-dimensional structuring of cellulose on the µm scale via DLW.^[3] Curing of our cellulose derivative is generally possible in liquid and solid state via two-photon absorption.<br/><br/>In contrast to common photoresists, which are based on polymers sourced from mineral oil, our approach conserves resources through replacing those polymers by sustainable materials such as polysaccharides. The presented research includes the functionalization of polysaccharides to enable photo-crosslinking for generating biopolymer-based hierarchical architectures. This chemical modification is a prerequisite for the fabrication of two- and three-dimensional structures by DLW. Disorder on the nano-scale is created by the surface roughness of the DLW-fabricated structures and can be tuned via the concentration of the photoinitiator. An additional degree of disorder is introduced through a self-assembled tilting and twisting of the written structures during the development process. This enables manufacturing of bioinspired photonic patterns.<br/><br/>Moreover, this polysaccharide-based photoresist enables manufacturing of manifold biomimetic architectures, which consist entirely of a natural bulking material. Additionally, this bio-based photoresist is curable via one-photon absorption with a UV-lamp (365 nm) in liquid as well as in dried state. Our resist opens up a new class of photo-curable polymers based on sustainable and renewable materials.<br/><br/><br/><b>References</b><br/>[1] D. Klemm, et al., Angew. Chem. Int. Ed. 2005, 44, 3358.<br/>[2] M. Rothammer, et al., Adv. Optical Mat. 2021, 9, 2100787.<br/>[3] M. Rothammer, et al., Cellulose 2018, 25, 6031.