ProjectsSwitchable, bistable microactuator systems based on stimuli-responsive polymers
Stimuli-responsive hydrogels are highly interesting materials for generating microactuator systems, as they offer interesting properties for manipulating cells and microfluidic devices. Current hydrogel based microactuators, however, are very simple and the issue of bistability in their function is largely unexploited; therefore applications have not quite matured yet. We here propose a novel strategy to achieve light switchable, bistable microactuator systems using stimuli-responsive polymers whose response to a specific stimulus (heat) can be modulated by molecular switches. The microactuator systems will be made of thermoresponsive polymers that is in a swollen, hydrated phase below the lower critical solution temperature, and in a shrunken phase at higher temperatures. In our first conceptual approach, bistability will be introduced by changing the lower critical solution temperature through introducing photoswitches; the system will then operate at one work temperature. Our second approach is dynamic, because we will change the local temperature; but in addition, we will also modulate the lower critical solvent temperature (LCST) by switching the hydrogel with light. We will investigate different types of heating stimuli, including Joule heating, magnetic heating and optical heating. A current disadvantage of using merely thermally responsive hydrogels to control the microactuator system is that cross-talks between individual microactuators can be expected through heat gradients. We hypothesize that light might be a much better controllable stimulus as it can be brought into microsystems with high spatial precision, reducing the cross-talk between the individual microactuators and thus increasing the functionality of the whole microactuator system. The final microactuator system will consist of an array of microactuators in different shapes and configurations. As applications, we will explore their suitability in microfluidics and cell sorting devices. A significant disadvantage of state-of-the-art microfluidic and cell sorting devices is that their properties are predefined during their fabrication. Although some dynamics can be added by microvalves or external steering forces, the flexibility of the devices is still limited. Our dynamic microactuator system will instead be based on switchable, bistable microactuator systems that will add dynamic flexibility into microfluidic and cell sorting devices by the cooperative action of individual microactuators.
This project is funded by the German Research Foundation (DFG) and part of the Priority Program 2206 “Cooperative Multistage Multistable Microactuator Systems".