Evaluation of dielectric elastomers to develop materials suitable for actuation.

Electroactive polymers based on dielectric elastomers are stretchable and compressible capacitors that can act as transducers between electrical and mechanical energies. Depending on the targeted application, soft actuators, sensors or mechanical-energy harvesters can be developed. Compared with conventional technologies, they present a promising combination of properties such as being soft, silent, light and miniaturizable. Most of the research on dielectric elastomer actuators has focused on obtaining the highest strain, either from technological solutions using commercially available materials or through the development of new materials. It is commonly accepted that a high electrical breakdown field, a low Young's modulus and a high dielectric constant are targets. However, the interdependency of these properties makes the evaluation and comparison of these materials complex. In addition, dielectric elastomers can suffer from electromechanical instability, which amplifies their complexity. The scope of this review is to tackle these difficulties. Thus, first, two physical parameters are introduced, one related to the energy converted by the dielectric elastomer and another to its electromechanical stability. These numbers are then used to compare dielectric elastomers according to a general and rational methodology considering their physicochemical and electromechanical properties. Based on this methodology, different families of commercially available dielectric elastomers are first analyzed. Then, different polymer modification methods are presented, and the resulting modified elastomers are screened. Finally, we conclude on the trends enabling the choice of the most suitable modification procedure to obtain the desired elastomer. From this review work, we would like to contribute to affording a quick identification method, including a graphic representation, to evaluate and develop the dielectric materials that are suitable for a desired actuator.

Feasibility of a Dielectric Elastomer Augmented Aorta.

Although heart transplantation is a gold standard for severe heart failure, there is a need for alternative effective therapies. A dielectric-elastomer aorta is used to augment the physiological role of the aorta in the human circulatory system. To this end, the authors developed a tubular dielectric elastomer actuator (DEA) able to assist the heart by easing the deformation of the aorta in the systole and by increasing its recoil force in the diastole. In vitro experiments using a pulsatile flow-loop, replicating human physiological flow and pressure conditions, show a reduction of 5.5% (47 mJ per cycle) of the heart energy with this device. Here, the controlled stiffness of the DEA graft, which is usually difficult to exploit for actuators, is perfectly matching the assistance principle. At the same time, the physiological aortic pressure is exploited to offer a prestretch to the DEA which otherwise would require an additional bulky pre-stretching system to reach high performances.