Fig. 4: Neuronal modulation induced by the ionic droplet device.

a, The triggering strategy used to modulate neuronal activity by generating ionic current from a droplet device. The high-salt and ion-selective droplets together acted as a droplet device, which was attached to droplets that contained neural microtissues or ex vivo mouse brain slices. Droplet no. 1, no. 2 and no. 3 received a cation influx from the left and an anion influx from the right. b, The ionic-current-modulated neuronal activity as reflected by intracellular Fluo-4 fluorescence. c, Output of the droplet device across the low-salt droplets. The voltage readout was conducted in open-circuit mode to ensure that the continuous hydrogel network was the only current path (n = 5). The volume of each droplet was 500 nl. The average voltage during the first 10 min was 120 mV. The corresponding ionic current was about 2.6 µA. d, Frames at various time points showing neurons embedded in droplet no. 1. Neurons were cultured for different periods (day 3 and 17), and reflected a change of neuronal network activities. The high-salt droplets contained 0.5 M CaCl₂. Ionic current flowed from left to right into droplet no. 1. Orange dashed lines mark the modulated area. Scale bars, 150 μm. e, Relative fluorescence intensities at different time points along the white dashed lines indicated in d. The black dot in each plot indicates the centre of fluorescence (weighted-mean distance) at the corresponding time point. a.u., arbitrary units. f, Relative displacement of the centre of fluorescence over 90 s for neuronal networks after different culture periods and in ex vivo brain slices from mice. GABA treatment was used on the day-17 neural tissues to suppress activities of neuronal networks (n = 3; *P < 0.05; **P < 0.01; NS, not significant; unpaired one-tail t-test). Data in f are presented as mean values ± s.d.

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