Fluorescent hydrogel actuators with simultaneous morphing- and color/brightness-changes enabled by light-activated 3D printing

Gradient cross-linking hydrogels capable of shape-morphing and fluorescence-color changes have practical significance in the fields of anti-counterfeiting, implantable sensors and smart wearable devices. However, it remains challenging to fabricate the gradient hydrogel actuators in a green, efficient and controllable manner, limited in the design and processing conditions. Herein, we merge the intriguing characteristics of light-activated 3D printing process with shape-morphing properties to fabricate a new fluorescent hydrogel actuator that can self-actuate in response to temperature, meanwhile, the synchronous color/brightness changes as a function of temperature can be well realized by those hydrogels doped with lanthanide ions. Remarkably, this kind of fluorescent hydrogel actuator can also perform as an information carrier to reveal the concealed information in two ways: i) specific UV light irradiation to read out the information, ii) self-morphing with the increase of temperature to display the information. Based on these excellent properties, the 3D-printed fluorescent hydrogel actuators with gradient cross-linking structures provide new insights in designing and fabricating novel soft robots. In addition, the light-activated 3D printing should guide the future intelligent manufacturing for fluorescent hydrogel actuators with the advantages of low cost, high efficiency, high accuracy, as well as the tailorable shapes and programmable actuations.