# Magnetic Self-Healing Composites: Synthesis and Applications
## 4 Applications
### Biomedical  
Hydrogels have attracted great attention for biomedical applications in recent years. Their properties, similar to the extracellular matrix, such as high water content, biodegradability, suitable viscoelasticity, biocompatibility and porous framework, make them promising candidates for applications such as tissue engineering and bioimaging [95]. Tailoring factors such as concentration, molecular weight, functionality and stoichiometric ratio permit the tunability of their mechanical properties, which in turn influences their processing conditions and may guide cell fate processes [96]. The stimulus-responsive behaviour of reversible polymer networks has attracted much attention in addition to their self-healing ability. Dynamically crosslinked polymer networks allow novel routes towards the formulation of stimuli-responsive hydrogels that enable versatile adaptation to the surrounding environmental conditions. Conventional crosslinked hydrogels undergo several degradation mechanisms during their lifespan, such as mechanical failure and complex biodegradation controllability, that hinder their use in long-term applications. The ability to recuperate their mechanical properties under certain stimuli makes self-healing hydrogels better candidates for some in vivo biomedical applications that need sufficiently long mechanical durability to accomplish their tasks [97]. This is especially useful for minimally invasive operations performed by injectable hydrogels that perform, for example, as tissue-engineered scaffolds [98; 99], wound dresses [100; 101] or drug or cell delivery carriers [102; 103]. Regularly, the extrusion of soft hydrogels through a nozzle requires mechanisms to undergo reversible sol-gel transitions such as pH or temperature (de)polymerizations or mechanical thixotropy to lower the system viscosity during the extrusion time [97]. The incorporation of dynamic crosslinks demonstrates self-healing hydrogels as excellent candidates to undergo these triggered transitions and heal the internal structure after injection. Furthermore, the incorporation of magnetic particles (mostly iron oxides due to their biocompatibility) within crosslinked hydrogels provides thermosensitivity when submitted to an alternating external magnetic field, finding use in minimally invasive therapeutic interventions and controlled drug release [104; 105]. As a result, the formulation of self-healing dynamically crosslinked hydrogels embedded with magnetic particles is a little-explored field that can combine the advantages of the previously referred systems. A magnetic self-healing hydrogel was reported for the first time by [PERSON] et al. that dispersed Fe\({}_{3}\)O\({}_{4}\) NPs within a dynamic hydrogel composed of chitosan and telechelic difunctional poly(ethylene glycol) [52]. Following this seminal work, several similar hydrogel matrix systems with embedded magnetic particles for biomedical applications have been reported. The most attractive application reported is their exploitation as chemotherapeutical agent thermocarriers. The resulting hydrogels enable targeted drug delivery and release by taking advantage of the hyperthermia provided by the magnetic particles. [PERSON] et al. prepared a magnetic crosslinked hydrogel based on chitosan and telechelic difunctional poly(ethylene glycol) loaded with doxorubicin and docetaxel as a dual-drug-loaded system for breast cancer therapy. The formulated system exhibits better performance compared with single drug-loaded hydrogels, and the controlled drug release under an alternating magnetic field was also shown to improve the antitumor efficacy of the chemotherapy [106]. As a different matrix medium, [PERSON] et al. exploited a [PERSON]'s base crosslinked hydrogel with dispersed magnetic gelatine macrocapsules that was also shown to be a promising candidate for drug delivery and soft tissue engineering [102]. Similarly, [PERSON] et al.