## 4 Applications
### Flexible Electronics  
Conductive and flexible materials have garnered attention for their conductivity, stretchability, and tensile strength. SMPNCs have emerged as promising candidates in the field of flexible materials in electronics, offering unique properties that can revolutionize various electronic applications [291]. These materials can adapt to curvilinear surfaces by changing shape or modifying physical properties like stiffness, enabling specific functions  
Figure 27: **(a)** Schematic illustration of LAA with thrombi and the magnetic-induced 4D transformation process of transcatheter LAA closure (scale bar = 10 mm). Reproduced with permission from ref. [278]. Copyright 2021 American Chemical Society. **(b)** Magnetically activated shape-recovery process of 4D printed occlusion devices. Reproduced with permission from ref. [279]. Copyright 2019 John Wiley and Sons. **(c)** Illustration of NIR controlled shape-memory “double umbrella” structure atrial septal defect (ASD) occlusion device in an isolated pig heart. Reproduced with permission from ref. [80]. Copyright 2023 American Chemical Society. **(d)** 3D-printed stent showing shape recovery ex vivo within a porcine intestinal segment using NIR light irradiation. Reproduced with permission from ref. [100]. Copyright 2022 John Wiley and Sons. **(e)** Schematic representation of the direct writing printing technique and the shape-recovery process of the 4D intravascular stent controlled by a magnetic field. Reproduced with permission from ref. [281]. Copyright 2016 American Chemical Society. **(f)** Design and fabrication of bone tissue scaffolds using 4D printing technology. Reproduced with permission from ref. [285]. Copyright 2020 Elsevier. **(g)** Magnetic field-stimulated the shape-recovery process of scaffolds for bone repair. Reproduced with permission from ref. [286]. Copyright 2019 Elsevier. in diverse applications [29; 292]. The incorporation of nanofillers imparts multifunctionality of SMPs, boosting performance and responsiveness in electronic systems. In the context of wearable electronics, semitransparent conductors play a vital role, enabling integration into various devices and applications such as artificial skins, photovoltaics, and touchscreens [292]. Notably, a visibly semitransparent SMP/Ag composite, combining cross-linked SMP polycyclooctene with electrospun Ag nanofibers, has been developed for such applications [293]. Furthermore, flexible semitransparent electrodes, incorporating silver nanowires (AgNWs) in a mercapto-ester-based ultraviolet-curable polymer, have been utilized in organic photovoltaic devices and wearable heaters [294; 295]. [PERSON] et al. designed a conductive, semitransparent SMP composite with UV-curable resin and AgNWs, showcasing its potential as a strain sensor and electronic skin capable of detecting touch, pressure, and bending (Figure 28a) [292]. Additionally, [PERSON] et al. used AgNWs to create a temperature-sensing device, where AgNPs formed a conductive network within the SMP matrix, enabling dramatic resistance reduction upon thermal-induced shape recovery [296]. [PERSON] et al. developed a rubber-based electrically conductive strain sensor using epoxidized natural rubber (ENR), carboxymethyl chitosan (CMCS), dopamine (DA), and multi-walled carbon nanotubes (CNTs) [297]. The composite, affixed to the index finger joint with tape as shown in Figure 28b, demonstrated changes in the recorded current signal during finger movements, indicating the sensor's potential for monitoring body motions. In another study, [PERSON] and colleagues utilized CNTs as conductive filaments in thermoplastic polyurethane fibers to create a wearable strain sensor, demonstrating reliable and repeatable performance with superior sensitivity across a wide tensile strain range (0.1% to 50%) [298]. This sensor architecture detected various deformation modes--including tension, bending, torsion--and human motions such as finger bending, breathing, and phonation.