## 4 Applications
### Flexible Electronics
Utilizing multifunctional shape-memory RGO/ethylene-vinyl acetate composites, [PERSON] and coworkers developed strain sensing by the swelling-ultrasionating and one-step twisting method [46]. This composite demonstrated exceptional stretchability up to 130% strain, high sensitivity (gauge factor of 7.3), and a broad linear working range up to 70% strain [46]. [PERSON] et al. engineered a flexible strain sensor from a shape-memory hydrogel composite embedded with Fe\({}_{3}\)O\({}_{4}\) nanoparticles, demonstrating the ability to control the illumination of an LED system through stretching, indicating higher sensitivity than its non-magnetic counterpart [299]. The composite exhibited reliable performance, maintaining its strain sensing capabilities over 500 cycles before and after its initial shape recovery. In a separate study, [PERSON] and colleagues developed a smart tactile sensor using 4D printing technology, capable of adjusting its measuring range, sensitivity, and shape to accurately sense unstructured objects [183]. This 4D-printed tactile sensor (4 DPS) demonstrated superior performance over traditional devices by effectively adapting to both spherical dome and saddle surfaces (Figure 28c). The sensor's ability to program temporary shapes during the shape-memory process enabled it to adjust sensing performance for various complex body parts and joints, demonstrating enhanced versatility and applicability. [PERSON] and colleagues developed highly flexible electrodes using silver nanowires (AgNWs) on transparent polyacrylate substrates, capable of bending up to 16% while maintaining low surface resistance [300]. This composite was employed as a substitute for conventional indium-doped tin oxide (ITO) substrates in light-emitting diode devices, demonstrating enhanced flexibility and repeated bending capability. A similar technique was utilized to create light-emitting devices from a CNT/poly(tert-butyl acrylate) composite, which possessed a glass transition temperature (T\({}_{\text{g}}\)) of approximately 56 \({}^{\circ}\)C [301]. The resulting device exhibited up to 45% linear strain stretchability while retaining its electroluminescent properties at 8 V, demonstrating its flexibility and functional durability. SMP composites are also widely used to construct electric switches for various devices. [PERSON] et al. developed a thermosensitive switch using a thermosetting shape-memory polyimide (PI)/reduced graphene oxide (rGO) nanocomposite (TCPI/rGO) for high-temperature warning devices [236]. As illustrated in Figure 28d, the nanocomposite film, initially set in a temporary shape with one end bent, was integrated into a circuit. Upon exposure to high temperature or NIR light, it reverted to its original two-dimensional shape, completing the circuit to light a bulb and signal an alarm. This demonstrates the potential application of these films in intelligent high-temperature early warning systems. Using rGO/SMPU/polyurethane foam, [PERSON] and coworkers engineered a temperature sensor that demonstrated a swift response to temperature changes, as indicated by the rapid dimming of a bright yellow light (within 1 s) emitted by a bulb [302]. This dimming occurred as the sensor expanded due to heating, resulting in an increase in electrical resistance, reflecting its practical and efficient temperature detection capabilities. [PERSON] and coworkers also designed a high-temperature warning circuit based on the transparency and shape-changing properties of a nanocomposite [270]. In their demonstration, a stretched, opaque SiO\({}_{2}\)/EVA composite film was connected to a switch via a thin wire in a circuit with a lightbulb and battery. Upon exposure to hot air at 85 \({}^{\circ}\)C, the composite film gradually shrunk and increased in transparency. This shape recovery triggered the circuit, serving as a visual high-temperature alert.