Fig. 1. Schematic diagram of the process for the fabrication of the NC-LM circuit using the evaporation-induced transfer printing technology: (a) Printing liquid metal circuit on a PVC substrate. (b) Pouring the nanocellulose solution onto the PVC substrate, (c) Evaporation and film-formation. (d) Peeling the NC-LM circuit off the sacrificial substrate, (e) NC-LM circuit with EGaIn ink embedded in the nanocellulose membrane. (f) Mounting the components.

Fig. 2. Samples of the NC-LM circuit fabricated using the evaporation-induced transfer printing technology: (a) A large-area NC-LM circuit, (b) NC-LM interdigital electrodes, (c) Flexible NC-LM RFID antennas, (d) A NC-LM circuit attached to the non-flat object, (e) NC-LM samples for printing character and pattern, (f) SEM image of a liquid metal line embedded in the nanocellulose membrane, (g) SEM image of the cross-section of a liquid metal line embedded in the nanocellulose membrane, (h) Thickness of the liquid metal lines with different widths. The inset is a schematic diagram of thickness measurement, (i) Comparison between designed width and actual width of liquid metal lines after transfer printing. The inset shows the measured liquid metal lines with different width.

Fig. 3. Electrical and optical properties of the NC-LM pattern: (a) Resistances of liquid metal lines with different width, (b) Resistance changes of the NC-LM lines after bending with different angles, (c) Resistance changes with time for different NC-LM lines.

Fig. 4. Samples of the NC-LM circuit and its application in the double-layer circuit fabrication: (a) Flexible NC-LM circuits connected with LEDs, (b) LC-NM circuit rolled around the wrist as a wristband, (c) A tiny NC-LM circuit stuck to the fingernail compliantly, (d) Schematic diagram of the double-layer NC-LM circuit, (e) Practical pictures of a 2 × 2 LED array circuit, (f) Performance of the LED array circuit.

Fig. 5. Mechanism of the evaporation-induced transfer printing technology for the fabrication of NC-LM pattern: (a) Measurement of the contact angle of liquid metal on the nanocellulose membrane, (b) Schematic diagram of the formation process of the nanocellulose membrane with liquid metal embedded in it, (c) Peeling off the nanocellulose membrane.

Fig. 6. Degradation and reuse process of the NC-LM circuit: (a) Immersing the NC-LM circuit in the surface dish filled with deionized water, (b) Fragmentized circuit after 24 h later, (c) Liquid metal lines pattern becoming blurry after soaking for another 24 h, (d) Ultrasonic treatment to accelerate the degradation rate, (e) The mixture of uniform nanocellulose solution and liquid metal ink, (f) Separating the nanocellulose solution and the liquid metal ink through centrifugal treatment, (g) Re-spreading nanocellulose solution on the liquid mental circuits, (h) Recycled circuit with the same morphology as the original one.