Soft phototactic swimmer based on self-sustained hydrogel oscillator

Abstract

Oscillations are widely found in living organisms to generate propulsion-based locomotion often driven by constant ambient conditions, such as phototactic movements. Such environment-powered and environment-directed locomotions may advance fully autonomous remotely steered robots. However, most man-made oscillations require nonconstant energy input and cannot perform environment-dictated movement. Here, we report a self-sustained soft oscillator that exhibits perpetual and untethered locomotion as a phototactic soft swimming robot, remotely fueled and steered by constant visible light. This particular out-of-equilibrium actuation arises from a self-shadowing–enabled negative feedback loop inherent in the dynamic light–material interactions, promoted by the fast and substantial volume change of the photoresponsive hydrogel. Our analytical model and governing equation unveil the oscillation mechanism and design principle with key parameters identified to tune the dynamics. On this autonomous oscillator platform, we establish a broadly applicable principle for converting a continuous input into a discontinuous output. The modular design can be customized to accommodate various forms of input energy and to generate diverse oscillatory behaviors. The hydrogel oscillator showcases agile life-like omnidirectional motion in the entire three-dimensional space with near-infinite degrees of freedom. The large force generated by the powerful and long-lasting oscillation can sufficiently overcome water damping and effectively self-propel away from a light source. Such a hydrogel oscillator–based all-soft swimming robot, named OsciBot, demonstrated high-speed and controllable phototactic locomotion. This autonomous robot is battery free, deployable, scalable, and integratable. Artificial phototaxis opens broad opportunities in maneuverable marine automated systems, miniaturized transportation, and solar sails.

An Autonomous Soft Actuator with Light‐Driven Self‐Sustained Wavelike Oscillation for Phototactic Self‐Locomotion and Power Generation

“…It typically occurs in certain living organisms, such as insects, jellyfish, or zooplankton, that are considered to be related to navigation or photosynthesis 65,66. Very recently, Zhao et al reported a swimmer robot based on a photosensitive hydrogel oscillator showing negative phototactic movement (away from the light source) in water driven by a laser 4. They further developed an artificial phototropic system based on hydrogels or a series of photoresponsive polymers that can autonomously aim and align in the incident light direction in three dimensions 67.…”

“…Examples include the involuntary beating of the heart muscle, neuron impulses, cell cycling, water waves, etc., which can be regarded as a type of persistent motor that continuously outputs mechanical work. The unique characteristics of oscillation as well as its potential for various applications (e.g., soft robots for walking or swimming, self‐cleaning surfaces, and energy coupling) inspire us to devise novel types of artificial self‐oscillating actuators with self‐sustained autonomous motion under a constant environment 3–8. However, at present, most of the smart actuators for converting external environmental stimuli into mechanical deformation can only produce unsustainable single motion under constant stimulation, which lacks the autonomy compared with self‐oscillation in nature 9–19.…”

Recent Advances in Photoactuators and Their Applications in Intelligent Bionic Movements

“…[30,70,74] Recently, He's group reported an Au NPs-embedded PNIPAm (AuNPs/PNIPAm) hydrogel pillar, and it can oscillate under constant light owing to a builtin feedback loop ( Figure 2C). [75] The oscillating displacement was about 0.3 mm corresponding to an oscillation temperature from ≈30 to 34 °C ( Figure 2D). They also adopted other photothermal agents (GO, polyaniline) and poly(2-(diethylamino) ethyl methacrylate) hydrogel to achieve the full-automatic phototaxis movements.…”

“…Reproduced with permission. [75] D) the oscillation displacement and temperature as a function of time for the AuNP/PNIPAm hydrogel. Reproduced with permission.…”

Kirigami‐Design‐Enabled Hydrogel Multimorphs with Application as a Multistate Switch

“…Morphing materials have promising applications in biomedical devices, flexible electronics, soft robotics, and so forth. [ 1–5 ] Many efforts have been made to realize controllable deformations of intelligent materials including liquid crystalline elastomers and shape‐memory polymers. [ 6,7 ] Among these materials, hydrogels have received increasing attention owing to their similarity to soft bio‐tissues and multiresponsiveness to external stimuli.…”