3D printing via direct laser writing involves a computer-controlled focused laser beam that acts as a pen and creates the desired structure in the printer ink — a photoresist. In this way, any three-dimensional form down to the size of a few micrometers can be created.
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 movable after the printing process and can change their shapes by an external signal. A printing process for such movable structures has been developed.
Special materials — stimulus-responsive polymers whose properties can be modified by external signals — were used for the printer ink. The chemical compound poly(N-isopropysycraymide) changes its shape considerably when the temperature is raised only slightly above room temperature. The 3D structures produced in this way are functional in aqueous environments and thus ideal for applications in biology and biomedicine.
The method can be used to manufacture complex structures in which, as a result of external stimulation, the moving parts do not all react in the same way, but show different but precisely defined reactions. This is made possible by grayscale lithography, where the photoresist is not exposed with the same intensity at all points but is exposed in a graded manner. This allows the desired material properties, and thus the strength of the movement at a certain temperature change, to be set very precisely. With computer simulations, the resulting movements can be precisely predicted and therefore allow a rational design of complex 3D structures.