Left: exploded-view layout of injectable semiconductor device for integrated stimulation/sensing/actuation, highlighting distinct layers for electrophysiological measurement (1), optical measurement (2), optical stimulation (3, micro-ILED array), and temperature sensing (4), all bonded to a releasable base for injection with a microneedle. Top right: injection and release of the microneedle. After insertion (left), artificial cerebrospinal fluid dissolves an external silk-based adhesive (middle) and the microneedle can be removed (right), leaving the active device in the brain. Bottom right: SEM of an injectable micro-LED array, 8.5 μm thick; flexible and rigid forms shown. Adapted with permission from Kim et al., 2013.