E-Mail IMAGE: Power transmitted through the conductive silver-hydrogel composite actuated the shape-memory alloy muscle of this stingray-inspired soft swimmer. view more Credit: Soft Machines Lab, College of Engineering, Carnegie Mellon University In the field of robotics, metals offer advantages like strength, durability, and electrical conductivity. But, they are heavy and rigid--properties that are undesirable in soft and flexible systems for wearable computing and human-machine interfaces. Hydrogels, on the other hand, are lightweight, stretchable, and biocompatible, making them excellent materials for contact lenses and tissue engineering scaffolding. They are, however, poor at conducting electricity, which is needed for digital circuits and bioelectronics applications.