Integrated circuits (ICs) are the key to powerful microarchitectures for lab on a chip applications. High actuator densities can enable the control of several thousand of reactions executed in parallel on a single chip. Hydrogels can act as self‐contained sensor–actuator materials, which control fluid flows depending on local physicochemical conditions. A concept is described for the preparation of highly integrated circuits based on stimuli‐sensitive hydrogels. The concept allows to adjust the working point and fulfill the free swelling condition of the hydrogels, which is favorable for the dynamic performance of the actuators. The components are polymerized on a glass substrate, which is also used to seal the microfluidic system. Therefore, the hydrogel integration is conducted within the standard microfluidic system set‐up procedure. For a first demonstration integration densities of microfluidic valves of up to 172 gels cm−2 in a single microfluidic circuit are realized. Furthermore, control of microfluidic valves fabricated by the demonstrated high integration procedure via an optoelectrothermic transducer setup is shown.

By the integration of smart materials, hydrogel-based LoCs even differ from other LoC approaches, as they bring more diverse functionality on the chip and reduce external equipment for fluid transport and decision-making. [52,53] Regarding the level of external control, two fundamental platforms exist: microelectromechanical and chemofluidic hydrogel-based LoCs. The first includes electronically controlled microvalves, [54,55] micropumps, [56] switchable storages, [57] filters, adjustable membranes, [58] and bioreactors [59][60][61] all based on hydrogel components. Chemofluidic integrated circuits introduce direct feedback control to chemical and physical parameters by combining both actuator and sensor properties on hydrogel material level for the LoC technology. There is a comprehensive choice of self-regulating components including chemomechanical valves, [62][63][64][65] chemostats, [66,67] thermostats, [68] pumps, [69][70][71][72][73] and adjustable filters. [74] The recent development of a universal circuit element, the chemofluidic transistor, [75,76] allows exclusive chemical control and via a set of logic operations the realization of a complete self-powered and selfcontrolling information-processing system on one integrated circuit chip. [76][77][78][79][80] However, stimuli-responsive hydrogels are materials with complex physics and behavior. The fabrication of gel-based LoC needs sophisticated technology. Moreover, the correct design of hydrogel-based components must respect parameters reaching from multidomain thermodynamics, swelling kinetics, mechanical properties of the soft materials over fabrication to functional design. To emphasize the versatility of hydrogels, numerous reviews have been published, highlighting to a different extent the material classification, [81][82][83][84][85][86][87] hydrogel behavior, [88][89][90] fabrication methods, [91][92][93][94][95][96][97] and the application range. [52,[98][99][100][101][102][103][104] The unique characteristic of this tutorial review is not only that it provides an up-to-date overview of the research field of hydrogel-based components in microfluidics, it also gives best practice suggestions to take action into the area of material selection, patterning methods, and device design. These aspects are compiled into the formulation of five design rules. Furthermore, the most important scaling laws and supporting simulation methods are presented to the future designers of hydrogelbased components for microfluidics. Therefore, this tutorial review is addressed to those who want to learn more about Stimuli-sensitive hydrogels have an outstanding potential for miniaturized, integrated sensor, and actuator systems and especially for lab-on-chip technology, but the application is still in its infancy. One major reason may be that design and realization of hydrogel-based systems are exceptionally complex and demanding. Here, the design parameters of a key component, the hydrogel-based valve, are discussed in their entirety. Key developments in the fields...

The mechanics of medical endoscopes have not fundamentally changed over the last 40 years. Most endoscopes are manually operated through Bowden cables to control the head of the device, which is known to have major limitations. We propose a shape memory alloy actuated setup to enable computer-aided control. Before a complex manufacturing of porotypes is established, the design needs to be evaluated for feasibility. In this work, an efficient design approach is highlighted, where the thermal properties for an asymmetric cross-section of the endoscope is modeled with finite elements in the transient electro-thermo-mechanical domain and the results are then transferred to a network model to efficiently evaluate operation procedures. With the proposed model approach, a fast but detailed description is established which focuses on the optimization of dimensional and material parameters and models efficiently the impact of complex dynamic operating regimes.