A biodegradable low-voltage soft actuator with exceptional energy density and ultrafast response

Soft actuators that integrate biodegradability, responsiveness to human-safe stimuli, and high actuation performance are highly desirable for next-generation biomedical devices. However, current systems fail to realize these attributes within a single platform. Here, we propose a microfibrillated cellulose (MFC)–based soft actuator incorporating a poly(ethylene glycol) (PEG) network to suppress crystallinity and ionic liquid (IL) aggregation. This design enhances ionic conductivity, forms abundant ion transport channels, and reduces interfacial resistance. Operated at 1 volt, the actuator achieves a record-high energy density of 64.4 kilojoules per cubic meter and the fastest response time of 1 second among reported ionic electroactive polymers (IEAPs) under the same conditions. Such materials are biocompatible and biodegradable in various physiological environments. Device-level demonstrations show that an actuation-enabled sciatic nerve cuff enables high-fidelity signal transmission in vitro with a signal-to-noise ratio of 40 decibels and stable real-time in vivo neural recording with evoked responses of up to ~150 microvolts, supporting minimally invasive bioelectronic interfacing.