Magnetic Self-Healing Composites: Synthesis and Applications

Abstract

Magnetic composites and self-healing materials have been drawing much attention in their respective fields of application. Magnetic fillers enable changes in the material properties of objects, in the shapes and structures of objects, and ultimately in the motion and actuation of objects in response to the application of an external field. Self-healing materials possess the ability to repair incurred damage and consequently recover the functional properties during healing. The combination of these two unique features results in important advances in both fields. First, the self-healing ability enables the recovery of the magnetic properties of magnetic composites and structures to extend their service lifetimes in applications such as robotics and biomedicine. Second, magnetic (nano)particles offer many opportunities to improve the healing performance of the resulting self-healing magnetic composites. Magnetic fillers are used for the remote activation of thermal healing through inductive heating and for the closure of large damage by applying an alternating or constant external magnetic field, respectively. Furthermore, hard magnetic particles can be used to permanently magnetize self-healing composites to autonomously re-join severed parts. This paper reviews the synthesis, processing and manufacturing of magnetic self-healing composites for applications in health, robotic actuation, flexible electronics, and many more.

Keywords: actuators; health; magnetic (nano)particles; magnetic fillers; magnetic self-healing composites; manufacturing; processing; slippery surfaces; stretchable electronic; synthesis.

Figure 2

(a) A scheme showing the effects of the particle size with variations in H_c and M_s, from small superparamagnetic nanoparticles to multidomain domain magnetic (nano)particles. (i) Nanoparticles smaller than 3 nm show superparamagnetic behaviour with Hc = 0, and moderate values of M_s due to the large contribution of paramagnetic atoms on the particle surface. (ii, iii) As the particle size increases, longer relaxation times are observed, stabilizing the blocked state and increasing the H_c. (iv) Lastly, above the critical size for a single-domain formation, the particle is multidomain, which leads to a decrease in H_c. (b) Hysteresis loops of hard (left) and soft (right) self-healing magnetic composites at the same temperature. The saturation magnetization (M_s), the remanence magnetization (M_r) and the coercive field (H_c) are indicated in grey solid spheres. The figure is reprinted under an open access Creative Commons CC BY 4.0 license [29].

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]. Copyright 2021, American Chemical Society.

Figure 1

(a) Scheme depicting the main routes to synthesize magnetic (nano)particles. Diagrams for the preparation of magnetic (nano)particles employing (b) coprecipitation and (c) thermal decomposition approaches [22].

Figure 3

A sketch of the preparation and characterization of the PMMS-COOH-Fe₃O₄ polymer. (a) The chemical structure of the PDMS-COOH polymer. (b) the Schematics for the preparation process. (c) The stress-strain results for both the initial and healed polymers. (d) The self-healing efficiency of the PDMS-COOH at loading weights from 10 to 25 wt%. (e) DSC thermograms of PDMS-COOH and PDMS-COOH-Fe₃O₄ (15 wt%). Adapted with permission from [30]. Copyright 2021, John Wiley and Sons.

Figure 4

(a) The 4cPEG and mPEG-COOH structures of the polymers. (b) On the top is shown the preparation procedure for the Fe₃O₄ particles-cross-linked hydrogel. At the bottom are shown representative pictures at each state. From left to right: Fe₃O₄ dry powder, stabilized Fe₃O₄ NPs in aqueous dispersion before gel assembly, the self-standing solid hydrogel obtained after assembly with 4cPEG, and magnetic attraction of the resulting gel. Adapted with permission from [36]. Copyright 2016, American Chemical Society.

Figure 5

The geometries made by the 3D printing of the AAD-CS-Fe DN hydrogel containing 8 mg·mL⁻¹ nano-Fe₃O₄. (a) A 3D model of the DN hydrogel in the pre-solution just after printing. (b) The 3D geometries made by the 3D printing. From left to right: Quadrangular pyramid, left ear, hexagonal prism, cuboid, nose, letters. The height of the corresponding models is shown in the red box. Adapted with permission from [30]. Copyright 2021, Wiley-VCH.

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.

Figure 8

(a) The preparation of a magnetic anisotropic self-healing hydrogel composed of N-carboxyethyl 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.

Figure 9

(a) A schematic representation of the interface reconstruction process of a magnetic self-healing supercapacitor induced by NIR irradiation [130]. (b) The healing of a yarn-based self-healing supercapacitor with excellent reconnectivity promoted by magnetic interactions. Adapted with permission from [131]. Copyright 2015, American Chemical Society. (c) An artificial skin based on a triboelectric nanogenerator, showing excellent conductive property recovery when the material is submitted to catastrophic damage. Adapted with permission from [133]. Copyright 2017, Elsevier.