# Magnetic Self-Healing Composites: Synthesis and Applications
## 4 Applications
### Actuators
In addition to magnetic fields, near-infrared-light (NIR) irradiation has been studied as a stimulus for magnetic self-healing elastomers using magnetic particles as photothermal conversion agents. [PERSON] et al. developed multi-stimulus-responsive biomimetic soft microactuators based on a hierarchically structured metal-ligand-crosslinked supramolecular elastomer embedded with a 3D interconnected magnetic nanohybrid network [88]. The prepared microrobots exhibit great self-healing performance at room temperature and can be actuated upon NIR light and magnetic field exposure as illustrated in Figure 6d,e (reversible capture actuation and butterfly wing actuation, respectively). Another well-known remote actuation method is the use of the shape memory effect. Shape-memory polymers can \"memorize\" a permanent shape conformation. When the material is subsequently manipulated and deformed, it undergoes a change from this temporary fixed state to the memorized permanent shape under the application of an external trigger, such as heat or light [89]. This actuation method has been combined with self-healing and magnetic properties to enhance its functionalities, resulting in so-called  
Figure 6: (**a**) A cargo transport task accomplished by a soft self-healing actuator under the presence of external magnetic fields; (**b**) a multiterrain carrier able to move forward using magnetic leg tilts; (**c**) magnetically controlled artificial soft tendrils. Adapted with permission from [86]. Copyright 2021, John Wiley and Sons; (**d**) mimosa-inspired magnetically driven capture-and-release actuation; and (**e**) synthetic butterfly wing healing under NIR irradiation and subsequent recovery of the vibratory actuation. Adapted with permission from [88]. Copyright 2019, John Wiley and Sons. shape-memory-assisted self-healing (SMASH) [90; 91; 92]. [PERSON] et al. reported a magnetic shape-memory self-healing elastomer with embedded spherical nanoparticles NPs with an average particle size of 12.3 nm prepared via in situ radical polymerization [93]. The hydrogen bond interactions between NPs and polymer chains provide the great self-healing response. Inspired by the interfacial adhesion chemistry of mussel threads, [PERSON] et al. designed a multiresponsive composite with self-healing capacity provided by metallo-supramolecular interactions at the surface of the magnetic particles when combined with cathecol-telechelic end-capped poly(\(\varepsilon\)-caprolactone). This material combines thermal, magnetic and light responsiveness for actuation as illustrated in Figure 7a [51]. Despite the manifested interest in the combination of shape-memory and self-healing properties for magnetic actuators, to date, no studies of SMASH have been reported for soft robotics. SMASH-based systems could exhibit interesting applicability for soft actuators, mostly due to using the combination of both magnetic actuation and shape memory to accomplish much greater motion degrees of freedom. Despite the clear advantages, SMASH capability is still restricted to narrow damage below 1 mm size. [PERSON] et al. took another approach to obtain large damage recovery using magnetostriction of the broken surfaces (Figure 7b). This magnetically driven self-healing method enabled the repair of wide damage areas (several millimetres) by promoting the closure of the damage surfaces by an external magnetic field [56]. This approach is particularly interesting to develop soft robotics systems that perform their actuation duties in harsh, aggressive environments. Figure 7: **(a)** Magnetic self-healing composite actuation using the shape-memory response under heating caused by a remote alternating magnetic field (adapted with permission from [51]. Copyright 2018, American Chemical Society); **(b)** magnetostriction-aided large damage healing (damage gap size of 4 mm-5 mm; adapted with permission from [56]. Copyright 2020, Elsevier; and **(c)** magnetic swimmer autonomously repaired “on-the-fly” using printed magnetic microparticles strips. Adapted with permission from [94].