The conformal integration of electronic systems with irregular, soft objects is essential for many emerging technologies. We report the design of van der Waals thin films consisting of staggered two-dimensional nanosheets with bond-free van der Waals interfaces. The films feature sliding and rotation degrees of freedom among the staggered nanosheets to ensure mechanical stretchability and malleability, as well as a percolating network of nanochannels to endow permeability and breathability. With an excellent mechanical match to soft biological tissues, the freestanding films can naturally adapt to local surface topographies and seamlessly merge with living organisms with highly conformal interfaces, rendering living organisms with electronic functions, including leaf-gate and skin-gate transistors. On-skin transistors allow high-fidelity monitoring and local amplification of skin potentials and electrophysiological signals.
Rigid materials become more flexible when cast as thin sheets, but they will still bump and buckle when subjected to in-plane rotation or twisting motions and thus cannot conformally cover a curved and mobile surface. Yan et al . formed roughly 10-nanometer-thick freestanding sheets by spin coating films containing flakes of semiconducting materials. The flakes attract each other through bond-free van der Waals interfaces to enable mechanical stretchability and malleability as well as permeability and breathability. These properties make them suitable for bioelectronic membranes that can monitor and amplify a range of electrophysiological signals, including demonstrations of electrocardiography and electroencephalography. —MSL
Freestanding nanosheet films show interlayer sliding and rotation and can conformally stretch and adapt to soft tissues.