DLP 3D printing with conductive polymers: color-changing structures from Heidelberg and Stuttgart

Researchers at the Universities of Heidelberg and Stuttgart have developed a resin formulation that enables electrochemically switchable, conductive polymers to be three-dimensionally printed using Digital Light Processing (DLP). The work links polymer-chemical material development with precise, light-based 3D printing and targets optoelectronic components whose properties can be specifically altered after printing.

DLP is one of the resin-based 3D printing processes in which UV light cures a liquid “ink” layer by layer. The technology is already established in dentistry and prototyping, but has so far been difficult to use for conductive polymers with tunable electrochemical behavior. Prof. Eva Blasco from the Institute for Molecular Systems Engineering and Advanced Materials in Heidelberg emphasizes that, particularly in the field of optoelectronics, the direct printing of functional materials has so far been missing.

“While the technology is already being used successfully in dentistry, it has so far been difficult to use it for conductive polymers with applications in optoelectronics and to print them directly,” explains Prof. Dr. Eva Blasco.

The teams in Heidelberg and at the Institute of Polymer Chemistry in Stuttgart, led by Prof. Sabine Ludwigs, therefore formulated a methacrylate-based resin that incorporates carbazole units into the polymer chain. These redox groups can accept and donate electrons, making the material conductive and causing its color to change depending on the oxidation state. Crucially, this functionality survives the DLP process: the printed structures remain electrochemically addressable and can be switched afterward. Doctoral researchers Christian Delavier and Svenja Bechtold point to the close collaboration between the laboratories, which brought together materials chemistry, printing process and electrochemical characterization.

“This was made possible by close, interdisciplinary collaboration in our laboratories in Heidelberg and Stuttgart,” emphasize Christian Delavier and Svenja Bechtold, who are working on their dissertations within the framework of the research training group.

“This process is fully reversible and can be controlled pixel by pixel depending on the structure. The control in the third dimension, i.e. with respect to the height of the architectures, is particularly exciting,” emphasizes Sabine Ludwigs.

The team demonstrated two-dimensional pixel arrays, checkerboard patterns and a multilayer 3D pyramid. Starting from nearly transparent components, an applied potential successively generates light green, dark green and almost black states – fully reversible and controllable down to individual pixels or defined height regions. This makes it particularly interesting to realize different switching states within a single component in the third dimension.

The combination of high-resolution DLP and redox polymers opens up prospects for 3D-printed pixel displays, adaptive optical elements or soft-robotics actuators in which volume, color or conductivity are controlled electrochemically. The project is part of the research training group “Mixed Ionic-Electronic Transport” and was funded by the DFG; the results were published in “Advanced Functional Materials.”