Bioinspired interface-engineered flexible islands: a mechanical interlocking approach to achieve a highly flexible-to-stretchable platform
The integration of rigid and flexible substrates into stretchable electronics is fundamentally limited by elastic modulus mismatch, which induces interfacial failure under mechanical strain. Conventional approaches, including serpentine and kirigami geometries and rigid island methods, have not fully resolved strain mismatch, scalability, or long-term stability. Inspired by the root-soil interlocking mechanism in nature, Park et al. developed a bioinspired interfacial engineered flexible island (BIEFI) that employs polyimide (PI) primary and secondary roots embedded in Ecoflex to create a mechanically interlocked interface. The primary roots distribute stress and delay interfacial failure, while secondary roots grasp the elastomer and suppress failure through flexible interlocking until a deformation threshold is reached. Optimization of primary root number (N), secondary root number (Rn), and root width (K) reveals that increasing N enhances stretchability. This platform enables reliable performance under diverse deformation modes, including stretching and twisting, and demonstrates application in a smart resistance band for workout monitoring. The BIEFI approach offers a scalable, stable solution for flexible-to-stretchable electronics, addressing critical challenges in wearable devices, displays, and energy harvesting.