Intrinsic healing mechanism

Self-healing or restoration of lost functionalities without external help is a dream come true with self-healing polymers (Ai ssa et a/., 2012). Healing mechanisms can be extrinsic (the healing compound is isolated from the polymer matrix in capsules, fibers or nanocarriers) or intrinsic (the polymer chains temporarily increase mobility and flow to the damaged area) (Billiet et al, 2013) and are responsible for restoration of properties such as structural integrity (White et fll, 2001), surface aesthetics (Yao et a/., 2011), electrical conductivity (Tee et fl/., 2012), hydrophobicity and hydrophilicity (Ionov and Synytska, 2012), mechanical properties (Jones et al, 2013), etc. 

Intrinsic healing systems based on supramolecular chemistry also have their value for interfacial bonding restoration despite most of the supramolecular material displaying only moderate mechanical properties. The ureidopyrimidinone unit based materials as described by van Gemert et al. (2012) are not only able to show impressive abilities of recovery for surfaces of coatings but can also be considered for use in mend-able adhesive applications. Moreover, it should be noted that almost all approaches related to healing functionalities of composites discussed later, can be considered as systems healing the interfaces between dissimilar materials. 

The above-mentioned properties of metallopolymers are the basic requirements for the generation of self-healing behavior. As a consequence, it is possible to generate a reversible system and to introduce self-healing mechanisms, which is the principle of intrinsic self-healing systems [78-81]. 

Spider silks deserve additional commentary. Again, this example shows as that Nature never gives up to complexity, as if complexity were an intrinsic part of natural materials, and this is so even in these apparently simple materials that Nature has designed just to reach a given mechanical performance. Spider silks show a highly efficient self-healing behavior that is now under intense scrutiny due to its evident technological potential [25]. 

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