(A) (i) Photograph of a stretchable MEA device on a PDMS substrate with 3D electrodes composed of Pt-coated Au-TiO2 nanowires. Scale bar, 1mm. (Reproduced with permission from Advanced Materials (2018) 30, 1706520. Copyright 2018 Advanced Materials) (Tybrandt et al., 2018) (ii) Ultraflexible probes for electrical recording and imaging during brain implantation. Inset shows OM image of the probes with microelectrodes. Inset scale bar, 100 mm. (Reproduced with permission from Science Advances (2017) 3, e1601966. Copyright 2017 Science Advances) (Luan et al., 2017) (iii) Schematic illustration of neuron-like electronics for three-dimensional in vivo mapping and electrophysiology studies. (Reproduced with permission from Nature Materials (2019) 18, 510–517. Copyright 2019 Nature Materials) (Yang et al., 2019). (B) (i) Flexible MEAs with PEDOT:PSS 3D wrinkle microstructures. Inset shows magnified OM images of the wrinkles. (Top right) Inset scale bar, 100mm. (Bottom right) Inset scale bar, 10mm. (ii) Photograph of the MEA connected to a rodent brain for in vivo optical stimulation. Inset shows attachment of the MEA to the rodent brain. (iii) Schematic illustration of the electrode position (black line; dashed) with four channels across the somatomotor and somatosensory cortices of the brain. (iv) ECoG signals recorded by the 3D MEA before and after light stimulation. (Reproduced with permission from Bionsensors and Bioelectronics (2019) 135, 181–191. Copyright 2019 Bionsensors and Bioelectronics) (Ji et al., 2019). (C) (i) Optical microscope (OM) image of the nanostructured ultraflexible MEAs. (ii) Magnified image of the linear electrode arrays. (iii) Close-up images of the microelectrode arrays. Scale bar, 10 mm. (Top right) SEM image of the 3D electrode structure. Inset scale bar, 2 mm. (Bottom right) Schematic illustration of the electrode nanostructure. (iv) Photographic image of the implanted MEA for intracortical recordings. (Reproduced with permission from Advanced Science (2018) 5, 1700625. Copyright 2018 Advanced Science) (Wei et al., 2018).