Investigation of the spatial resolution of a laser-based stimulation process for light-addressable hydrogels with incorporated graphene oxide by means of IR thermography

The development of lab-on-chip (LoC) devices has led to a demand of new microactuator technologies. Light-responsive hydrogels are promising candidates as actuator materials for this type of applications. These are polymers that change their water content and volume significantly upon illumination with a light source. For proper operation, the spatial resolution of the stimulation process is an important parameter. To investigate this resolution, poly(N-isopropylacrylamide) (PNIPAAm) hydrogels with incorporated graphene oxide (GO) were monitored with an infrared (IR) camera during illumination with a laser source. The GO nanoparticles convert the absorbed light energy into heat and for temperatures above the lower critical solution temperature (LCST), the polymer collapses. Therefore, the desired actuated area has to have a temperature above the LCST. A mathematical model was used to fit the recorded spatial temperature profiles in order to obtain the width at the LCST and to evaluate the temporal progression of the stimulated area. The results enable the development of new stimulation strategies and enhance the understanding of the spatial resolution of light-addressable hydrogels. Furthermore, the required stimulation time for different laser powers is presented.