Glucose-responsive microneedle patch for insulin delivery. (a) Microneedles loaded with hypoxia-sensitive vesicles: (i) schematic illustrations of responsive insulin release from the microneedles; (ii) fluorescence microscopy image of microneedles carrying vesicles. Insulin is labelled with FITC. Both scale bars are 200 μ
m. Reproduced with permission from Ref. [20
], copyright 2015, PNAS. (b) Microneedles with a glucose-responsive matrix: (i) mechanisms of responsive insulin release from the microneedles; (ii) the application and effects of the microneedles on a diabetic pig; (iii) digital photo of the microneedle patch; (iv) SEM image; (v) fluorescence microscopy image. The scale bars are 500 μ
m. Reproduced with permission from Ref. [53
], copyright 2020, Springer Nature.