Christoph Keplinger1

1, University of Colorado-Boulder, Boulder, Colorado, United States

Soft robotic systems are currently limited by the soft actuators that power them. They predominantly rely on fluidic actuators, which limit speed and efficiency. Electrically powered muscle-mimetic actuators, such as dielectric elastomer actuators (DEAs) offer high performance actuation but they come with their own challenges. Being driven by high electric fields, DEAs are prone to failure by dielectric breakdown and electrical ageing. More importantly, DEAs are hard to scale up to deliver high forces, as large areas of dielectric are required (e.g. in stack actuators), which are much more likely to experience premature electrical failure, following the Weibull distribution for dielectric breakdown.
Here an overview is presented of a new class of self-sensing, high-performance artificial muscles, termed Hydraulically Amplified Self-healing ELectrostatic (HASEL) transducers. HASEL actuators harness an electro-hydraulic mechanism to activate soft hydraulic architectures, and combine the versatility of soft fluidic actuators with the muscle-like performance and self-sensing abilities of DEAs, while simultaneously addressing critical challenges. HASEL actuators autonomously self-heal from electrical and mechanical damage, and thus feature reliable and scalable performance. Several different designs and fabrication strategies, as well as prototypical applications are introduced; a specific geometry of HASEL is shown to linearly contract upon activation with voltage, thereby closely mimicking biological muscle. These results indicate that HASEL actuators promise to enable robust and versatile actuation in next- generation soft robotic devices.