Fig. 2: The preparation process, working principle, performance characterization, and operational performance of the glucose monitoring unit.

a Fabrication process of the glucose concentration-responsive bendable hydrogel microneedle array. b Optical image of the glucose concentration-responsive bendable hydrogel microneedle array. Scale bars, 25 mm. The inset shows an optical image of the microneedles bent at a 90° angle, demonstrating their flexibility. c Mechanical properties of blank PVP/PVA hydrogel microneedles compared with PVP/PVA/9-ANB hydrogel microneedles. d The absorption spectrum and fluorescence emission spectrum of the 9-ANB material. e 3D fluorescence profile of the PVP/PVA/9-ANB hydrogel microneedles. f In vitro characterization results of the glucose concentration-responsive bendable hydrogel microneedle array, including optical (Scale bars, 10 mm) and fluorescence microscopy images (Scale bars, 300 μm, n = 10). g The response of microneedle arrays to glucose and interfering ions. h SEM images of microneedles after dissolving upon insertion into a porcine skin model. Scale bars, 180 μm. i The color change of the microneedle array after absorbing rhodamine B solution. The inset shows an optical image of a 2.25 cm² microneedle array absorbing a Rhodamine B solution