Hydrogel-Based Microfluidic Systems

Over the last ten years, microfluidic technologies have gained considerable importance. However, realising highly integrated microsystems is a major challenge, which so far has only been solved insufficiently. Here, we present an innovative approach to fabricate low-cost, integrable mi- crofluidic platforms. As active elements, photopolymerised hydrogels based on Poly(N-isopropylacrylamide) (PNIPAAm) are introduced. PNIPAAm is temperature-sensitive. Heated in water above its lower crit- ical solution temperature (LCST), it reversibly changes from a swollen to a shrunken state (volume change in the order of 90%) and can, via an electrothermic interface, be employed as electrothermally switchable actuator. Varying specific parameters in the swelling agent, for example varying its alco- hol concentration, can shift the LCST. So not only micropumps or microvalves, but also valves with an appointed threshold value, so-called chemostats or chemical transistors, can be realised. Using the example of a microchip performing enzymatic endpoint analyses, we investigate characteristic be- haviour of active elements based on PNIPAAM and show the ability of integrating different fluidic operations like fluid transportation, metering, valving and mixing into one fully polymeric microchip.