# Magnetic Self-Healing Composites: Synthesis and Applications
## 4 Applications
### Stretchable Electronics  
Flexible electronics are a rapidly growing field due to their capacity to experience high deformations while keeping their electric functionality. They find use in technological applications such as wearable electronics and sensors [114; 115], health care systems [116] and flexible batteries and supercapacitors [117]. There are two predominant manufacturing strategies for the mentioned systems: intrinsic flexible and conductive polymers or hybrid composites containing a soft elastomeric substrate with interconnected conductive particles dispersed. The most popular choices among the latter include multiwalled carbon nanotubes (MWCNTs) and graphene due to their great mechanical properties, flexibility, high conductivity and anisotropy [118]. Thus, multiple conductive polymers as well as particle fillers embedded within soft elastic polymeric matrices have been explored and optimized for the desired applications. Magnetic particles have also been combined with flexible electronics to improve the material performance or enable an extra functionality as magnetoelectronic systems [119; 120]. Thus, the formulation of self-healing, magneto- and electro- responsive systems drives the conceptualization, production and utilization of state-of-the-art, multi-stimuli-triggered smart materials. As a consequence of their inherent softness, stretchable electronics are also prone to lacerative damage or perforations that can limit their lifespans and utility. In addition, damage can yield the percolated conductive particle microstructures of filled polymeric composites, thus deteriorating the conductive response. In response, self-healing has been proposed as a solution to overcome the vulnerability of their conductive composites [121; 122]; however, this process should restore not only the initial mechanical properties of the cured material but also the recombination of the conductive filler network. Thriving studies on conductive polymers applied to magnetoelectric self-healing composites have recently been proposed in the literature. [PERSON] et al. developed an ultrasoft self-healing hydrogel with magnetic and conductive properties by dispersing MnFe\({}_{2}\)O\({}_{4}\) NPs within a conductive polyaniline (PAni) matrix. NP aggregation was prevented using nanofibrillated cellulose (NFC) as a dispersant. Similarly, [PERSON] et al. prepared a biocompatible, remouldable composite hydrogel with conductive, magnetic and self-healing response by introducing a ZnFe\({}_{2}\)O\({}_{4}\)/MWCNT/Polypyrrole hybrid structure within a dynamic reversible hydrogel composed of a polyvinyl alcohol/borax double network. The hydrogen bonding between matrix and filler serves as an additional tool for mechanical strengthening [123]. He et al. embedded Fe\({}_{3}\)O\({}_{4}\) NPs in a supramolecular network filled with imidazolium-based ionic liquids as a self-healing electronic sensor. Since the conductivity of ionic liquids is higher as the temperature increases, the exploitation of magnetic hyperthermia to improve the sensing performance was successfully confirmed in  
Figure 8: (**a**) The preparation of a magnetic anisotropic self-healing hydrogel composed of N-carboxymethyl chitosan and aldehyde hyaluronic acid crosslinked by dynamic imine covalent bonds. Adapted with permission from [76]. Copyright 2018, American Chemical Society. (**b**) The welding of two self-healing hydrogels with different structural colours. Adapted with permission from [77]. Copyright 2020, Elsevier. this study [124]. One promising route towards an enhanced self-healing performance was introduced by [PERSON] et al., consisting of the interactions among permanent magnetic particles (e.g., Nd\({}_{2}\)Fe\({}_{14}\)B microparticles) as an assisted healing driving force for self-healing graphitic inks. The formulated inks exhibit an impressive recovery of large damages in approximately 50 ms without any stimulus, restoring the conductivity and electrochemical properties [125]. Similarly, [PERSON] et al.