Researchers from Karlsruhe Institute of Technology introduced functional 3D hetero-microstructures based on pNIPAM
Stimuli-responsive microstructures play a major role in creating adaptable systems in soft robotics and biosciences. The materials must be compatible with aqueous environments and enable the manufacturing of 3D structures in order to be used in such applications. Poly(N-isopropylacrylamide) (pNIPAM) is a polymer that shows a significant response to changes in temperature. Materials that react differently with respect to a stimulus are required to create complex actuation patterns. Now a team of researchers from Karlsruhe Institute of Technology developed functional 3D hetero-microstructures based on pNIPAM. The team varied the local exposure dose in 3D laser lithography to demonstrate that the material parameters can changed as desired in a single resist formulation. The team analyzed this approach for sophisticated 3D architectures with large-amplitude and complex responses.
The team found that the experimental results were consistent with numerical calculations. The team used these calculations to predict the actuation response. Moreover, a local temperature increase was induced by two-photon absorption of focused light to achieve a spatially controlled response. Stimulus-responsive polymers whose properties can be modified by external signals are used for printer ink. pNIPAM changes its shape considerably when the temperature is raised only slightly above room temperature and the resulting 3D structures are functional in aqueous environments and can be used for applications in biology and biomedicine. According to the researchers, the new method can be used to manufacture complex structures in which the moving parts do not react in the same way due to external stimulation. Moreover, these structures show different and precisely defined reactions.
This property is attributed to grayscale lithography in which the photoresist is not exposed with the same intensity at all points, instead is exposed in a graded manner. This in turn offers desired material properties and the strength of the movement at a certain temperature change can be set high accuracy. Moreover, computer simulations can be used to predict the resulting movements to allow a rational design of complex 3D structures. The team used focused light, instead of temperature, as a control signal. This enabled targeted control of individual microstructures in a complex, 3D arrangement. The findings of the research were published in the journal Nature Communications on January 16, 2019.
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