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.

Living organisms ubiquitously display colors that adapt to environmental changes, relying on the soft layer of cells or proteins. Adoption of soft materials into an artificial adaptive color system has promoted the development of material systems for environmental and health monitoring, anti-counterfeiting, and stealth technologies. Here, a hydrogel interferometer based on a single hydrogel thin film covalently bonded to a reflective substrate is reported as a simple and universal adaptive color platform. Similar to the cell or protein soft layer of color-changing animals, the soft hydrogel layer rapidly changes its thickness in response to external stimuli, resulting in instant color change. Such interference colors provide a visual and quantifiable means of revealing rich environmental metrics. Computational model is established and captures the key features of hydrogel stimuli-responsive swelling, which elucidates the mechanism and design principle for the broad-based platform. The single material-based platform has advantages of remarkable color uniformity, fast response, high robustness, and facile fabrication. Its versatility is demonstrated by diverse applications: a volatile-vapor sensor with highly accurate quantitative detection, a colorimetric sensor array for multianalyte recognition, breath-controlled information encryption, and a colorimetric humidity indicator. Portable and easy-to-use sensing systems are demonstrated with smartphone-based colorimetric analysis.

Many living organisms track light sources and halt their movement when alignment is achieved. This phenomenon, known as phototropism, occurs, for example, when plants self-orient to face the sun throughout the day. Although many artificial smart materials exhibit non-directional, nastic behaviour in response to an external stimulus, no synthetic material can intrinsically detect and accurately track the direction of the stimulus, that is, exhibit tropistic behaviour. Here we report an artificial phototropic system based on nanostructured stimuli-responsive polymers that can aim and align to the incident light direction in the three-dimensions over a broad temperature range. Such adaptive reconfiguration is realized through a built-in feedback loop rooted in the photothermal and mechanical properties of the material. This system is termed a sunflower-like biomimetic omnidirectional tracker (SunBOT). We show that an array of SunBOTs can, in principle, be used in solar vapour generation devices, as it achieves up to a 400% solar energy-harvesting enhancement over non-tropistic materials at oblique illumination angles. The principle behind our SunBOTs is universal and can be extended to many responsive materials and a broad range of stimuli.

Electrocaloric cooling technologies, enabled by the discovery of the giant electrocaloric effect in dielectrics more than a decade ago, represents a zero-globalwarming-potential, environment-benign cooling alternative. Benefited from its nature as an electricity-driven capacitor, the electrocaloric working body renders the great advantages in the energy efficiency and the device integration. The decade-long efforts on advancing the technology revealed many promising material candidates with matured manufacturing protocols, as well as intriguing device prototypes for applications beyond the traditional vapor compression based cooling. This article presents the recent advances in electrocaloric cooling technologies, from material improvements to device demonstrations. The environmental impact and the energy efficiency of the technology were evaluated by the total effective warming impact and the material COP, respectively. In addition to the current progresses achieved by the decade-long research effort, the existing challenges and potential opportunities brought by the electrocaloric refrigeration will be discussed.

The recent finding of large electrocaloric effect in several ferroelectric polymers creates unique opportunity for developing compact size solid state cooling cycles beyond the traditional mechanical vapor compression cycles. Here, we show that, by employing regeneration process with solid state regenerators, a chip scale Electrocaloric Oscillatory Refrigeration (ECOR) can be realized. A prototype ECOR is fabricated and characterized. More than 6 K temperature span is obtained near room temperature between the hot and cold sides of a 2 cm long device. Finite volume simulation validates the test results and shows the potential high performance of the ECOR.