Dynamic Organic–Inorganic Interpenetrating Nanonetwork for Stiff and Durable Flexible Material

The longstanding trade-off between stiffness and durable flexibility has limited the performance envelope of structural materials, constraining their application in demanding engineering fields. Here, we reveal an alternative organic-inorganic hybrid architecture to integrate these contradictory properties. Inspired by interpenetrating polymer networks, we interpenetrate an inorganic nanonetwork into the organic network via polymerization of inorganic ionic oligomers. In this way, an organic-inorganic (bacterial cellulose-calcium phosphate) interpenetrating nanonetwork was constructed, and notably, a dynamically reversible inter-network bonding was discovered under external force. This dynamic organic-inorganic interpenetrating nanonetwork (DIN) leads to a composite material with both high stiffness and high energy dissipation ability during deformation, exhibiting metal-like bending rigidity while sustaining 20 000 bending cycles without fatigue fracture. This demonstrates a resolution to stiffness and durable flexibility integration in structural materials. Moreover, the DIN structure exhibits resistance to harsh environments, including extreme temperatures (-196°C to 200°C) and high humidity (90% RH). Combined with its lightweight, electromagnetic transparency, and naturally derived components, DIN-based composites represent promising candidates for next-generation stiff yet durable flexible protective structural materials. This work extends the polymer-inspired approach to synthesize non-classical inorganic structures, while broadening the understanding of organic-inorganic composite architectures in integrating distinct material properties.