# Magnetic Self-Healing Composites: Synthesis and Applications
## 4 Applications
### Stretchable Electronics
designed an Fe-doped liquid metal conductive ink combined with a degradable PVA substrate and adhesive fructose. The resulting multifunctional electronic system was able to perform as excellent light-emitting diodes (LED) able to be repaired upon magnetic field irradiation. This material was successfully applied on a crawling robot [126]. Supercapacitors are one of the most promising energy storage candidates as a consequence of the high-power density and large numbers of fast charging-discharging cycles that they can undergo. The introduction of flexibility in supercapacitors allows their use in a large number of portable and wearable lightweight consumer devices, finding applications in diverse fields such as medical, military or civilian fields [127; 128; 129]. Despite the encouraging opportunities, to date, magnetoelectric self-healing supercapacitors have been scarcely approached. As can be observed in Figure 9a, [PERSON] et al. prepared a novel, magnetic, highly stretchable polyacrylamide hydrogel filled with Fe\({}_{3}\)O\({}_{4}\)@Au hybrid NPs. Polypyrrole NPs are built into the hydrogel network acting as electrodes. The Fe\({}_{3}\)O\({}_{4}\)@Au NPs and the hydrogel network are reversibly crosslinked at the gold surface with a disulfide bondeded crosslinker via gold-thiolate bonds, reversibly triggered by remote photo-thermal, magneto-thermal and optical sources. These bonds provide a high multiresponsive head-ability, together with an areal capacitance of 1264 mF-cm\({}^{-2}\) and restorability of 90% of initial capacitances over 10 healing cycles [130]. [PERSON] et al. proved the healing and performance recovery of a yarn-based supercapacitor, which is particularly hard to heal due to its anisotropic wired geometry. In this work, magnetic yarn electrodes can be efficiently reconnected by magnetic attraction between the edges of the magnetic broken fibres, as shown in Figure 9b, while the mechanical properties recovery is attributed to a carboxylated PU supramolecular network electrode cover with abundant hydrogen bonding [131]. Triboelectric nanogenators are a recently attractive choice for wearable devices due to their high energy conversion efficiency using mechanical stimuli [132]. However, the fact that they must endure mechanical forces to generate electronic carriers makes them highly prone to be damaged; thus, self-healing is a promising solution for the long-term loss of functionality of such systems. [PERSON] et al. prepared a magnetic self-healing triboelectric nanogenerator. The healing performance is achieved by means of dynamic disulfide bonds with enhanced mechanical contact of the broken damage promoted by remote magnets (Figure 9). Both the mechanical and electric properties of the built-up electrodes are restored upon healing, and its high flexibility makes this system an interesting candidate for flexible electronics applications such as artificial skin [133]. The combination of triboelectric nanogenerators with supercapacitor systems can drive independent self-chargeable supercapacitors capable of generating their own current and storing it. [PERSON] et al. reported a triboelectric self-charging asymmetric supercapacitor with self-healing capacity. The proposed sandwich structure presents magnetic CoFe\({}_{2}\)O\({}_{4}\) and Fe-decorated reduced graphene oxide that provides magnetic response to the system that can recover its conductive properties after damage thanks to its self-healing properties [125]. Finally, a very promising application of electromagnetic flexible polymeric composites relates to their use as electromagnetic interference (EMI) shields. Electromagnetic radiation is capable of interfering with other electronic devices, disturbing their functioning or even harming people if inadequately handled.