Hydrogels for Actuators

In microsystem technology research a material with such a diversity and significance like silicon in microelectronics has not been established for the last 20 years. Recently in microfluidics and in special imaging systems hydrogels get ready to take this place. Here we present a review on hydrogel based microsystems with actuator or sensor-actuator functionalities. Automatic microfluidic systems based on the sensor-actuator properties of hydrogels offer functionalities which have not been yet realised with other systems or actuators. The functional principles of the basic elements are described on the example of hydrodynamic transistors, pumps and tunable microlenses. In the field of microelectromechanical microfluidic systems hydrogels provide a unique multi-functionality. We describe the basic principles applied on an electronic control for hydrogel actuators and also on the basic components for microfluidics: microvalve, micropump and hydrodynamic transistors. Furthermore, the first hydrogel-based highly integrated microsystem, a high-resolution tactile display containing 4,225 individually controllable actuator pixels, is reviewed. In the last two Sections we discuss essential physical phenomena und design rules, which have to be considered to avoid malfunctions of the designed devices.