Stimuli-responsive materials have attracted a lot of interest in the research field of new materials due to their alterable properties compared with traditional materials. A variety of stimuli including humidity, heat, light, magnetic field, electricity, pressure, pH and mechanical force have been investigated for their potential to change structural shapes, dimensions and functionalities. The responsiveness and reactions of stimuli-responsive materials promote their potential applications in various areas involving soft actuators, sensors, biomedical therapy, optical investigation and many others. Moreover, the rapid revolution of additive manufacturing (AM) accelerates the development for design and fabrication of stimuli-responsive materials with complex geometries and high resolution, which broadens the application of stimuli-responsive materials enormously. Among the driving energy for different stimuli-responsive materials, the untethered remote control and wireless manipulation can be achieved by light or magnetic stimuli, which provide the potential application in enclosed or in-vivo environments. The study of untethered stimuli-responsive materials opens a new avenue for fabricating smart structures and actuators. In this dissertation, two parts based on the untethered stimuli-responsive materials are included: the light-responsive structures and the magnetic-responsive materials.

In the first part of this dissertation, the light-responsive reconfigurable structures with complex geometries and multi-level functions are proposed and studied. The selectively kirigami-patterned reconfigurable structures based on light-responsive material are reported, and their applications in biomimetic actuators and flexible electronics field are explored. More than a dozen sophisticated kirigami patterns are fabricated, programmable shape transformations from planar sheets are achieved reversibly under light illumination with finite element analysis guidance. Three biomimetic actuators composed of reconfigurable structures are generated with programmable and remote actuation. Furthermore, to extend the functions of this strategy to the flexible electronics field, a reconfigurable monopolar antenna is demonstrated. Three states of the antenna can be regulated and switched by light with different power densities. The results pave a facile scheme to realize the flexible and intricate design of light-controlled actuators with multiple functions.

The second part of this dissertation is about magnetic-responsive materials. Obvious advantages such as untethered control, strong penetrability, and excellent biocompatibility can be achieved by magnetic driving force compared with other stimuli. In chapter 4, with the assistance of the direct ink writing (DIW) method, a soft Polydimethylsiloxane (PDMS) matrix with iron microparticles is designed, and various gradient structures are fabricated. Some simple motions such as bending, twisting, and crawling are performed under the control of an external magnetic field. In the next chapter 5, to further optimize the structures and programming of magnetic-responsive materials, a new origami-inspired method is introduced and studied. The approach can not only lead to the simplification of the manufacturing of magnetic-responsive actuators, but also provide another way to define the inner property of magnetic-responsive materials. The various actuators with complex geometries indicate that this scheme can promote innovations for the development of magnetic-responsive soft actuators and extend the applications of soft actuators driven by magnetic energy. In the last chapter 7, a new scheme to fabricate magnetic-responsive bistable structures is promoted, the snap-through behavior of the actuator can be achieved and regulated by the external magnetic field. Moreover, a biomimetic Venus flytrap actuator is designed, and a quick response to the magnetic field is performed.

In summary, this dissertation focuses on the design and manufacturing of structures and devices based on untethered stimuli-responsive materials. Two untethered stimuli including light and magnetic field, are characterized and studied. The untethered control, wireless manipulation and programmable actuation are demonstrated by various structures with flexible designs and complex geometries. Multiple devices, including deformable structures, biomimetic actuators and the flexible antenna, are performed and they all show great potential for future practical applications of untethered stimuli-responsive materials.