Electrical, optical, and thermal characteristics of 3D-POPs. a) Current and optical intensity of μ-ILEDs as a function of supplied voltage. b) Normalized light intensity of μ-ILEDs for 3D-POPs bent at 90° with a radius of curvature ranging from 2 to 10 mm. c) Temperature change in brain tissue during the μ-ILED operation at different pulse frequencies (5, 10, 20, and 40 Hz; 10 ms pulse width), measured using an infrared camera after insertion of a μ-ILED into brain tissue at a depth of 1 mm. d) Normalized optical intensity of 3D-POPs as a function of time in saline water (0.9%) at physiological and extreme temperatures (37, 60, and 90 °C).