Extended Data Fig. 7: Structures and in vitro electrochemical properties of WRAP electrodes.

a, Optical microscope images show Au lost its continuity on IC/PEO thin film which isotropically swelled. b-d, Optical microscope (b) and SEM images (c, d) show Au on WRAP-400% films became a continuous mesh of wrinkled micron-sized ribbons because WRAP film contracted along the drawing direction and expanded in the transverse direction. e, Resistance of PC-WRAP-Au slightly increased from about 11 Ω to 13 Ω when undergo strain of 40%, indicating that PC-WRAP-Au film is stretchable. f, Longitudinal sectional SEM image shows spin-coated SEBS penetrated the porous WRAP film to form a seamless mechanical interlocking. g, Optical microscope image show after contraction, wrinkles formed on the SEBS layer of PC-WRAP-SEBS. h, EIS spectra show impedance of WRAP electrode is lower than that of Au-elastomer electrode at low frequency (<4 kHz). Solid plots: impedance; hollow plots: phase angle. i-j, Voltage transients of WRAP electrode (i) and Au-elastomer electrode (j). The pulse currents are 600 μA and 350 μA respectively when the E_mc of WRAP electrode and Au-elastomer electrode of the same size are close to −0.6 V. k, Impedance of WRAP-electrode array at 1 kHz remain at about 600 Ω over 5000 cycles of cyclic stretching to 40% strain. l, Impedance of WRAP-electrode array soaked in PBS solution for 2 weeks at 37 °C did not show any obvious changes. m, Accelerated aging test where WRAP electrode is immersed in PBS at 60 °C shows the impedance at 1 kHz more than doubled after 4 days (equivalent to soaking at 37 °C for 20 days). Electrode area exposed to PBS in h-m is around 2.6 mm². Scale bar: 20 µm (a,b,d); 100 µm (c,g); 5 µm(f); 500 nm (d, inset). All experiments in a-d, f-g were repeated thrice with similar results.