Table 6.
Second generation self-healing systems
| Trigger mechanism | Autonomous healing? | Healing mechanism | References |
|---|---|---|---|
| Hydrogen bonding | Yes | Quadruple hydrogen bonds dimerized with 2-ureido-4-pyrimidone derivatives | 62 |
| Hydrogen bonding | Yes | Multiple hydrogen bonds formed between amidoethyl imidazolidone, di(amido ethyl) urea, and diamido tetraethyl triurea | 86 |
| Metal-ligand coordination | Yes | Bifunctional palladium or platinum coordinating with pyridine in hydrogel matrix | 77 |
| Heating | No | PPE repair achieved through oxygen and a copper catalyst resulting in polymerization | 16 |
| Steam | No | Polymerization of the PC backbone catalyzed by weak alkali | 16,139 |
| UV light | No | Recombination of free radicals to form PU crosslinks | 80 |
| Heat | Yes | Heat from projectile puncture repairs thin films of EMAA, ethylene-octene, and PB-g-PMA-co-PAN | 74 |
| Heat | No | Thermally reversible Diels-Alder cycloaddition of multi-furan and multi-maleimide | 78,79 |
| Heat | No | Thermoreversibility via denaturing double-stranded DNA crosslinks | 69,87 |
| Competitive binding | No | Competitive binding of a removal strand with DNA crosslink results in dissolution of DNA crosslinks | 69,87 |
| Electric field | No | Enhanced hydrogen bonding under positive electric field | 140 |