a, An illustration of the fibre drawing process. Tungsten and gold-plated tungsten wires were converged into the preform during the draw. b, Cross-sectional image of the preform containing three hollow channels. Scale bar: 3 mm. c, Cross-sectional microscope image of the resulting fibre. Scale bar: 100 μm. d, A photograph of a bundle of fibre produced during the draw. Scale bar: 10 cm. e, An illustration of fibre connectorization, followed by functionalization of the cathode and anode microwires with Pt-Fe3S4 nanocatalysts and Pt layer, respectively. f, A photograph of a fully assembled NO-delivery fibre. Scale bar: 10 mm. g, Infusion of Tyrode’s solution containing 0.1 M NaNO2 and a dye (BlueJuice) into a brain phantom (0.6% agarose gel) through the microfluidic channel. Images were taken at 0, 300 and 600 s after the infusion at a rate of 100 nL/min. Scale bar: 500 μm. h, Chronoamperometry profiles of the NO-delivery fibre in the Tyrode’s solution containing 0.1 M NaNO2.