Normalization of hydrogel swelling behavior for sensoric and actuatoric applications.

Hydrogels can be used for sensor or actuator applications depending on their swelling behavior: highly sensitive hydrogels are better suited for sensors while hydrogels with lower sensitivity are more suitable for precision actuators. The identification of an appropriate material for a specific application is however tedious, since different measures for swelling are used in literature. To overcome this drawback, an approach for the generalization of hydrogel swelling is presented in the current research. In order to obtain the normalized form of swelling data, the reference point is extracted from the stimulus-swelling-curve. For isotropic swelling of different hydrogel materials, the Hencky strain is applied as generalized swelling parameter. Together with the stimulus ratio, a normalized sensitivity parameter is derived. In the present work, different kinds of stimuli such as temperature, pH, ions and light with their respective swelling mechanisms are considered. The Temperature Expansion Model allows Finite Element simulation of hydrogels with the described responsivenesses in their normalized forms. It is shown that the normalized swelling and the derived sensitivities can be used to assess hydrogels in their suitability for the application in sensors or actuators. The normalized forms can also be used in the design process to choose adequate materials for an envisioned application. [ABSTRACT FROM AUTHOR]