Fig. 3: The homogeneity proving of hydrogel coating spots.

a The real-time image of the droplet mixing process. b Raman spectrum of the representative hydrogel coating spot. Raman mapping of c S=O vibration; d CH3/CH2 vibration; e C=O vibration and f C–H vibration on a representative hydrogel coating spot. g Green and h red fluorescence intensity image of a representative hydrogel coating spot.