Novel Photoresist Developed

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Researchers in the -3D Matter Made to Order- Cluster of Excellence expand possibilities of three-dimensional printing of the tiniest microstructures

Researchers of Karlsruhe Institute of Technology (KIT) and Heidelberg University have developed a novel photoresist for two-photon microprinting. For the first time, it can be used to produce three-dimensional microstructures with cavities in the nano-range. The researchers of the joint -3D Matter Made to Order- Cluster of Excellence also investigated how this porous quality can be controlled during the printing process and how this affects the light scattering structures of the microstructures.

The light microscopy image using dark field illumination illustrates the strong light scattering of the printed cuboid on the left side. The latter is caused by the porosity of the nanostructure (right).

Photoresists are printing inks used to print the tiniest microstructures in three dimensions by so-called two-photon lithography. During printing, a laser beam is moved in all spatial directions through the initially liquid photoresist. The photoresist hardens in the focal point of the laser beam only. Complex microstructures can be gradually built up in this way. Possible areas of application include the production of micro-optics, so-called metamaterials, and micro-scaffolds for experiments with single biological cells.

To expand the spectrum of applications, new printable materials are required. This is the starting point for the scientists of the Cluster of Excellence. Using conventional photoresists, it was possible to print transparent, glassy polymers only, according to the researchers. For the first time, the new photoresist makes it possible to print three-dimensional microstructures from porous nanofoam. This polymer foam has cavities of 30 to 100 nm in size, which are filled with air.

The photoresist is transparent prior to the printing process. Owing to increased light scattering, the numerous tiny air holes in the porous microarchitectures make them appear white and are highly reflective. Another factor that opens up new applications is the extremely large internal surface area of the porous material. It might be useful for filtration processes on the smallest space, for highly water-repellent coatings, or for the cultivation of biological cells. The researchers used electron microscope analyses and optical experiments to determine how best to use the new photoresist. They demonstrated how the cavities in printed structures are distributed and how their formation - such as their size - can be controlled by varying the printing parameters, especially the intensity of the laser pulses. To make the interior of the printed structures visible, they were first embedded into a synthetic resin and then cut into extremely thin slices (60-100 nm). Series of these slices can then be recorded as individual images in a scanning electron microscope and re-assembled into a 3D volume.

In the current collaboration of the Cluster of Excellence, the Heidelberg researchers are working on electron microscopy of new - especially beam-sensitive - carbon-materials and the Karlsruhe scientists in the fields of chemistry and physics. The results of the research were published in the journal -Advanced Materials-.

In the -3D Matter Made to Order- (3DMM2O) Cluster of Excellence, scientists of Karlsruhe Institute of Technology and Heidelberg University conduct interdisciplinary research into innovative technologies and materials for digital scalable additive manufacturing processes to enhance the precision, speed, and performance of 3D printing. Work is aimed at completely digitising 3D manufacture and materials processing from the molecule to the macrostructure. In addition to funding as a Cluster of Excellence under the Excellence Strategy competition launched by the federation and the federal states, 3DMM2O is financed by the Carl Zeiss Foundation.

F. Mayer, D. Ryklin, I. Wacker, R. Curticean, M. ─îalkovsk├oe, A. Niemeyer, Z. Dong, P. A. Levkin, D. Gerthsen, R. R. Schr÷der, M. Wegener: 3D Two-Photon Microprinting of Nanoporous Architectures. Advanced Materials 2020


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