Extremely bending-resistant and compression-insensitive flexible circuits enabled by real-time crack healing via spontaneous interfacial wetting

Flexible circuits that allow stable electrical conductance and signal transmission under deformation are highly required for flexible electronics. However, bending-induced fatigue cracks in solid conductive materials can significantly reduce the stability of flexible circuits. Although liquid metal (LM) is a promising candidate for bending-resistant circuits, LM circuits are prone to being squeezed and susceptible to compression. Here, an extremely bending-resistant and compression-insensitive flexible circuit was achieved by the complementary effects of the fluidity of the upper LM and the good conductivity and rigidity of a thick bottom copper (Cu) layer. The fluidic LM can heal Cu cracks in real-time by spontaneous interfacial wetting to enhance the bending durability, whereas the solid Cu layer can maintain conductivity under compression to enhance the compression insensitivity. Compared with a conventional Cu circuit, such a flexible circuit achieves a 120-fold improvement in folding lifespan, while its resistance fluctuation under compression is only 0.05% of that of the counterpart LM circuit. Meanwhile, the bottom Cu pattern exactly facilitates the high-resolution selective printing of LM by reactive wetting. As a demonstration, a flexible signal acquisition system constructed with this circuit can continuously capture pulse signals during bending and remain functional after 10 000 bending cycles. The simultaneously enhanced bending stability and compression insensitivity greatly increase the applicability and reliability of flexible circuits under various deformation conditions.