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There are different strategies to contain the healing agents inside the material such as hollow fibers or a microvascular network filled with a crosslinking agent, microspheres or microcapsules of crosslinking agent and superparamagnetic nanoparticles, as is shown in Figure 3.3 [34]. The mechanism to heal the sample is similar in cases of hollow fiber, microspheres or microcapsules and microvascular network: once the crack propagates, the container is broken and releases the crosslinking agents; they fill the crack and then repair the structure. In the case of super paramagnetic nanoparticles dispersed in the matrix, the self-healing mechanism is activated through the application of an external magnetic field that induces a vibration in the particles. Therefore, the temperature increases and facilitates the self-healing.

Figure 3.3 Self-healing illustration of common encapsulation methods, (a) hollow fibers inside a polymer, (b) Microspheres/microcapsules, (c) microvascular network, and (d) superparamagnetic nanoparticles (Reprinted from Yang et al. [34], open access).