**8. Conclusive remarks**

*Functional Materials*

**Table 4.**

and magnetic fillers are added [29]. In addition to plasticizer such as zinc stearate

5 Chitosan polyurethane networks Photoinduced reaction [79] Coating

Photoinduced healing is currently demanding because of rapid, eco-friendly concept of healing of polymer matrix composites. It is induced by the application of a strong light irradiation. To damage healing, the foreign healing inserts, catalyst, or additional heat is neither required to comply with the healing process. Such system

The objective of self-healing phenomenon is focused to respond upon fracture based on quasi-static performance. In the future, self-healing materials can be used in various applications including nuclear reactors, marine structures, and various cutting tools. Self-healing aircrafts or spacecraft is currently desired in references of micrometeoroids and orbital debris protection, low-temperature repairs for aerostructures, and re-healable fuel tanks. Cost-efficient healable wind power blades and wire insulation materials are also desirable based upon self-healing materials. Durable targets for military personnels and training are also part of self-healing

Self-healing systems represent a wide interdisciplinary area and are performed

by different techniques. Understanding the basic mechanism and principle of damage healing is also still a challenge for science community. Healing chemistries

ionic domain, the matrix properties are intact [75].

**S.N. Healing system Healing mechanism** 

1 1,1,1-tris(cinnamoyloxy-methyl) ethane (TCE) monomer

> (3-mercaptopropionate) and triethylene glycol divinyl ether

> acrylate)s/SCS-cyclometalated

4 Epoxy/SiO2 microcapsule UV-triggered

6 Epoxy/nano-TiO2 Photoabsorbing

2 Pentaerythritol tetra

system

*Photoinduced damage-healing system.*

3 Pyridine-capped poly(methyl

dipalladium

**(photoinduced)**

Reversible cleavage of allyl sulfide linkage

Light-induced cis-trans isomerization

polymerization

microcapsules

**Ref. Remarks**

[76] Hemolytic photolysis

[77] Molecular switching

[78] Aerospace coatings

[80] Protection coatings

applications

of cinnamoyl groups

[2 + 2] Cycloaddition [40] Cycloaddition

**5. Photochemically induced healing chemistry**

based on photochemical reactions is developed (**Table 4**).

ionomers which protect against ballistic penetrations.

**7. Current scenario, challenges, and future perspective**

**6. Significance of healing functionality**

**34**

Conclusively, the self-healing techniques explore the possibility of damage detection and subsequent damage management in materials. Some technological restrictions and possible solutions are also explored. Self-healing techniques intimate damages at the early stage and recovered mechanical properties at some extent which reduces the probability of replacement and loss of structures. Currently, we are still waiting for fully self-healing systems that can show both stimuli responsiveness and healing characteristics.
