fig2

Figure 2. Invasive microneedle electrodes. (A) SEM image of the polyimide microneedle array electrode and its sample diagram^[24]. Reprinted with permission. Copyright 2022, Springer Nature. (B) SEM image of the Miura-ori structured electrode (illustration inside is an enlarged SEM image of a single microneedle) and its sample diagram^[25]. Reprinted with permission. Copyright 2021, Springer Nature. (C) Size and shape drawing of the hook electrode and its sample diagram^[26]. Reprinted with permission. Copyright 2020, Elsevier. (D) SEM image of the barbed electrode and its physical picture^[27]. Reprinted with permission. Copyright 2022, American Chemical Society. SEM: Scanning Electron Microscope.