# Magnetic Self-Healing Composites: Synthesis and Applications
## 5 Perspectives  
Self-healing materials are able to repair autonomously or under the action of a stimulus after damage and recover lost material properties, thus extending the lifetime of these materials and related products. Self-healing magnetic composites can recover both their mechanical properties and magnetic functional properties. In applications such as electronics, robotics and health care, derived systems are able to recover their sensory functions and actuation performance. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Application** & **Fabrication Method** & **Self-Healing Mechanism** & **Magnetic Filler** & **References** \\ \hline \multirow{4}{*}{Actuators} & \multirow{2}{*}{Mixing} & Disulfide bonds & Nd\({}_{2}\)Fe\({}_{4}\)B & [86] \\ \cline{3-5}  & & Boronic ester & CoFe\({}_{2}\)O\({}_{4}\) & [87] \\ \cline{2-5}  & \multirow{2}{*}{Surface eng.} & Metal-ligand complex & Fe\({}_{3}\)O\({}_{4}\)@CNC & [88] \\ \cline{3-5}  & & Hydrogen bonds & Fe\({}_{3}\)O\({}_{4}\) & [93] \\ \hline \multirow{4}{*}{Biomedical} & \multirow{2}{*}{Mixing} & Imide bonds & Fe\({}_{3}\)O\({}_{4}\)@DF-PEG-DF & [106] \\ \cline{3-5}  & & Schiff base & Fe\({}_{3}\)O\({}_{4}\) & [102] \\ \cline{2-5}  & \multirow{2}{*}{Mixing + external magnetic field} & Schiff base & CIPs & [76] \\ \cline{3-5}  & & Intermolecular diffusion & Fe\({}_{3}\)O\({}_{4}\)@PSSMA@SiO\({}_{2}\) & [77] \\ \hline Slippery surfaces & Mixing & Intermolecular diffusion & Oil-based ferrofluid & [145] \\ \hline \multirow{4}{*}{Stretchable electronics} & \multirow{2}{*}{Mixing} & Hydrogen bonds & Fe\({}_{3}\)O\({}_{4}\)@SiO\({}_{2}\) & [124] \\ \cline{3-5}  & & Magnetic cubes & [133] \\ \cline{3-5}  & & Metal-ligand complex & Fe\({}_{3}\)O\({}_{4}\)@MoS\({}_{2}\) & [140] \\ \cline{3-5}  & & Imide bonds & Fe\({}_{3}\)O\({}_{4}\)@MWCNTs & [137] \\ \cline{3-5}  & & Diels-Alder & Fe\({}_{3}\)O\({}_{4}\)@rGO & [138] \\ \cline{3-5}  & & Disulfide bonds & Fe\({}_{3}\)O\({}_{4}\)@MoS\({}_{2}\)@rGO & [139] \\ \hline \multirow{2}{*}{Surface eng.} & \multirow{2}{*}{Hydrogen bonds} & ZnFe\({}_{2}\)O\({}_{4}\)@MWCNTs & [123] \\ \cline{3-5}  & & Disulfide bonds & Fe\({}_{3}\)O\({}_{4}\)@Au & [130] \\ \hline Additive manufacturing & \multirow{2}{*}{Intermolecular diffusion} & Nd\({}_{2}\)Fe\({}_{4}\)B & [125] \\ \cline{3-5}  & & Fe-GaIn & [126] \\ \hline Electrodeposition & Hydrogen bonds & Fe\({}_{3}\)O\({}_{4}\)@Stainless Steel & [131] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The different self-healing mechanisms, magnetic fillers and fabrication methods reported for the evaluated magnetic self-healing application fields. Magnetic (nano)particles have been introduced in thermally reversible polymer networks as a mechanism for remotely applying a thermal response using inductive or irradiative heating. Such a thermal stimulus can speed up the healing kinetics and increase the healing efficiency by activating the thermoreversible crosslinks or interactions. This thermal stimulus could also be used to achieve the thermal depolymerization of the reversible covalent polymer network for reprocessing or for reversible adhesion by the remote application of an alternating magnetic field; conversely, this stimulus could start a (frontal) polymerization reaction during synthesis or later during use. Similarly, inductive heating could also be used to activate other chemical or physical processes such as the shape-memory effect for improved damage closure or for actuation or locomotion. The use of magnetic (nano)particles or components further improves the healing performance of the self-healing materials and structures, as it can bring the damaged surfaces back into contact, thus, closing the damaged volume. Soft magnetic particles can be embedded into a self-healing matrix to close large damage during the healing treatment in the presence of an external magnetic field. Contact between damaged surfaces and the alignment of the damaged areas remain major challenges in self-healing materials and composites.