*2.2.3 Damage volume*

The capacity of a self-healing system to address damage volume plays a vital role in determining its ability to improve material reliability and lifespan. This capability relies on factors such as loading conditions, geometry, and polymer properties, and it can vary depending on the specific self-healing approach employed. Intrinsic selfhealing systems are particularly effective for handling small damage volumes because they require the damaged surfaces to be in close proximity for re-bonding to occur. Wu et al. [43] employed epoxidized soybean oil (ESO) and natural glycyrrhizic acid to fabricate bio-based recyclable vitrimers that possess outstanding mechanical properties and thermal stability. Notably, crack widths measuring 100 microns gradually vanished within a span of 60 mins, highlighting the material's potential for recycling and chemical degradation. Microcapsule-based systems repair small to moderate damage volumes at limited microcapsule volume fractions. Microvessel-based systems offer the advantage of addressing a broader range of damage volumes since the healing agent can be replenished as required. In another study, it was observed that the microcrack located within the interface region possesses the ability for triple healing, showcasing its most remarkable self-healing performance at an impressive efficiency of 90.60% [44]. This noteworthy achievement was accomplished by developing an innovative interfacial self-healing system that utilizes carbon fiber and epoxy composites, anchored in the principles of the Diels-Alder reaction. Through the strategic integration of post-synthetic modified (PSM) metal-organic frameworks, these frameworks not only undergo in-situ grafting onto the carbon fiber (CF) surface but also serve as nanofillers, contributing to the dispersion of epoxy resin and enabling the fabrication of PSM/epoxy nanocomposites.
