Laser-based 3D printing can now be used to produce any structure on a micrometer scale. However, for many applications, especially in biomedicine, it would be advantageous if the printed objects were not rigid but switchable. Researchers at the Karlsruhe Institute of Technology (KIT) have already been able to print microstructures that change shape under the influence of temperature or light. The results were published in the journal Communications of nature.
3D printing has established itself as a technology with numerous fields of application. Direct laser engraving is considered a particularly promising method: a computer-controlled focused laser beam acts as a pen and creates the desired structure in the printer's paint, which is a photoresist here. In this way, any three-dimensional shape up to a size of a few micrometers can be created. "However, for many applications, particularly in biology and biomedicine, it would be desirable not only to produce rigid structures, but also active systems that are still mobile after the printing process, for example, that can change their shapes through an external signal," emphasizes. Professor Martin Bastmeyer of the KIT Zoological Institute and Institute of Functional Interfaces. In cooperation with the group of Professor Martin Wegener at the Institute of Applied Physics and Institute of Nanotechnology at KIT, as well as with the chemists from Karlsruhe and Heidelberg, a printing process has now been developed for these mobile structures. Special materials, ie, stimulus-sensitive polymers whose properties can be modified by external signals, are used for printer ink. The chemical compound poly (N-isopropisycraymide) considerably changes its form when the temperature is raised only slightly above room temperature. The 3D structures produced in this way are functional in aqueous environments and therefore ideal for applications in biology and biomedicine.
"We developed the method in such a way that we can also fabricate complex structures in which, as a result of external stimulation, the moving parts do not react in the same way, but they show different, but precisely defined reactions," explains Marc. Hippler, first author of the study. This is possible thanks to grayscale lithography, where the photoresist is not exposed to the same intensity at all points, but is exposed in a gradual manner. This allows the desired properties of the material and thus the resistance of the movement at a certain temperature change to be defined very accurately. With computer simulations, the resulting motions can be precisely predicted and therefore allow a rational design of complex 3D structures.
The workgroups around Martin Bastmeyer and Martin Wegener went one step further: instead of temperature, the focused light is used as a control signal. For the first time, this allows targeted control of individual microstructures in a complex three-dimensional arrangement. This feature can be used, for example, in microfluidic systems. Since the used photoresist can be changed at room temperature, there are additional applications in basic biological research, for example, the targeted mechanical manipulation of individual cells.
The interdisciplinary study was conducted as part of the "3D Matter Made to Order" cluster of excellence, a joint research association of the Karlsruhe Institute of Technology and the University of Heidelberg. PhD students at KIT's Karlsruhe School of Optics and Photonics (KSOP) were also involved.
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