Double network (DN) materials have emerged as a groundbreaking class of tough and resilient soft materials, exhibiting exceptional mechanical properties through the synergistic interactions of two interpenetrating networks with contrasting characteristics. Novel synthesis strategies, including dynamic covalent bonding, supramolecular interactions, and hybrid crosslinking techniques, have further enhanced their toughness, self-healing capability, and functional adaptability. Recent advancements have expanded DN materials beyond traditional hydrogels to include elastomers, nanocomposites, and biomimetic structures, enabling their application in diverse fields such as biomedical engineering, soft robotics, and structural materials[1].
DN materials have recently garnered significant attention as an outstanding platform for polymer mechanochemistry [2]. Their unique architecture—where a highly pre-stretched, brittle first network is embedded within a more flexible second network—enables the efficient transmission of macroscopic stress to individual polymer chains. This localized stress concentration at the molecular level facilitates the activation of mechanophores, triggering force-induced chemical reactions such as bond scission, crosslinking, and fluorescence without causing material failure.
Leveraging this intrinsic mechanochemical responsiveness, we have developed DN-based materials capable of real-time damage sensing, adaptive strengthening, and autonomous repair through mechanoradical polymerization [3,4]. This mechanism also enables DN materials to undergo force-activated morphogenesis and surface patterning [5]. Such force-induced structural growth not only expands the material design possibilities of DN gels and contributes to the development of adaptive and self-growing materials but also holds the potential for application to biomimetic "living materials".