This study demonstrates soft, epidermal resistive strain gauges capable of tracking finger joint angle during dexterous manipulation tasks. Intrinsically stretchable, biphasic, gallium-based metal films embedded in an elastomeric substrate allow for extremely thin (<50 µm) and skin-conforming wearable sensors with outstanding robustness. The sensors sustain repeated cycling to 50% strain and are insensitive to normal pressure up to 100 kPa. Following a calibration phase, we recorded flexions of a human finger using the soft sensors and compared their joint angle estimation to that of a commercial marker-based visual motion tracking system. The accuracy of our system (defined as the mean angular deviation between our sensors' output and the reference system) was below 9° over a set of 11 different grasping and motion tasks. We demonstrate the scalability and wearability of our technology with a three-finger sensing system used to track the fine movements of a pianist hand. Our soft technology is a promising candidate for implementation of truly wearable proprioceptive sensing systems.

Elastic electronic surfaces will integrate stiff thin film devices onto compliant polymer substrates. These surfaces may be stretched once or many times, by up to tens of percent strain. One way to make such an elastic electronic surface is to distribute rigid subcircuit islands over the polymer surface, and then fabricate active devices on the islands. These islands need to be interconnected with stretchable metallization. We describe stretchable interconnects made of stripes of thin gold film patterned on elastomeric membranes. These membranes can be stretched by up to twice their initial length and maintain electrical conduction. We review the fabrication of these conductors, present their electrical and mechanical properties, and summarize our model for their extreme stretchability. Using such stretchable interconnects, we made the first elastic circuit, an inverter of thin film transistors. The circuit remains functional when stretched and relaxed by 12% strain.