Bioactuators based on stimulus-responsive hydrogels and their emerging biomedical applications

The increasingly intimate bond connecting soft actuation devices and emerging biomedical applications is triggering the development of novel materials with superb biocompatibility and a sensitive actuation capability that can reliably function as bio-use-oriented actuators in a human-friendly manner. Stimulus-responsive hydrogels are biocompatible with human tissues/organs, have sufficient water content, are similar to extracellular matrices in structure and chemophysical properties, and are responsive to external environmental stimuli, and these materials have recently attracted massive research interest for fabricating bioactuators. The great potential of employing such hydrogels that respond to various stimuli (e.g., pH, temperature, light, electricity, and magnetic fields) for actuation purposes has been revealed by their performances in real-time biosensing systems, targeted drug delivery, artificial muscle reconstruction, and cell microenvironment engineering. In this review, the material selection of hydrogels with multiple stimulus-responsive mechanisms for actuator fabrication is first introduced, followed by a detailed introduction to and discussion of the most recent progress in emerging biomedical applications of hydrogel-based bioactuators. Final conclusions, existing challenges, and upcoming development prospects are noted in light of the status quo of bioactuators based on stimulus-responsive hydrogels.