Researchers from the German universities of Heidelberg and Stuttgart have developed a new type of “ink” that enables 3D printing of electrochemically switchable, conducting polymers using a light-based process. This innovation allows so-called redox polymers to be fabricated through digital light processing (DLP), producing complex two- and three-dimensional structures that can be electrochemically manipulated to change color.
The work, conducted within the Research Training Group “Mixed Ionic-Electronic Transport: From Fundamentals to Applications,” is supported by both universities and opens up new possibilities for producing 3D printed optoelectronic devices.
Digital Light Processing Enables Fast Fabrication of Complex Structures
Digital light processing (DLP) is a 3D printing technique in which a light-sensitive “ink” is solidified layer by layer into a three-dimensional object through selective exposure to UV light. Compared with other AM methods, DLP allows for rapid production of intricate structures. “Although the technology has already been successfully used in dentistry, for example, until now DLP printing of conducting polymers for applications in optoelectronics has been challenging,” explains Prof. Eva Blasco for Molecular Systems Engineering and Advanced Materials of Heidelberg University.
The research teams developed a methacrylate-based ink containing redox-active carbazole groups, which allow the polymer chains to donate or accept electrons. This property makes the materials electrically conductive and enables color changes based on their oxidation or reduction state. Using this photoconducting ink, the researchers successfully fabricated structures that can be electrochemically manipulated even after printing, maintaining switchable properties. “This research was made possible by a close, interdisciplinary cooperation in our labs in Heidelberg and Stuttgart,” emphasize Christian Delavier and Svenja Bechtold, both doctoral researchers in the Research Training Group.
The carbazole-containing ink was used to 3D print two-dimensional pixel arrays, checkerboard patterns, and a multi-layered three-dimensional pyramid. Initially almost transparent, these structures turned light green under electrochemical stimulation, then dark green, and finally nearly black. “This process is completely reversible and can be controlled down to the pixel level depending on the structure. Control in the third dimension, i.e., with respect to the architectures’ height, is especially exciting,” added Sabine Ludwigs, Professor, Institute of Polymer Chemistry at the University of Stuttgart.
Prof. Blasco and Prof. Ludwigs noted that combining high-resolution, light-based 3D printing with redox polymers opens new possibilities for manufacturing pixel displays or actuators in soft robotics, where volume can be electrochemically switched.
Related Advances in DLP 3D Printing
The potential of high-resolution DLP 3D printing extends far beyond the color-changing redox polymers developed at Heidelberg and Stuttgart. Researchers around the world are pushing the boundaries of this technology to produce increasingly complex, functional structures.
For example, teams at Lawrence Livermore National Laboratory and the University of California, Santa Barbara, have created a dual-wavelength resin system for DLP printing. Their method allows the simultaneous fabrication of permanent structures and degradable supports in a single resin formulation, eliminating the need for resin swaps or manual support removal. The approach, enabled by a custom-built dual-wavelength DLP printer, streamlines production of intricate 3D objects.
Similarly, researchers at the University of Texas at Austin, led by Zachariah A. Page, have developed a multicolor DLP resin system that enables rapid fabrication of freestanding structures using dissolvable supports. By combining UV- and visible-light-responsive chemistries, the team produced materials with distinct solubility profiles, significantly simplifying post-processing and expanding design possibilities.
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Featured image shows Visualization of a 3D printed pyramid displaying electrochromic behavior. Image via University of Stuttgart.
