Figure 2.

On‐skin investigation of the hydrogel performance toward continuous sweat extraction. A) Schematic depicting how the performance of a hydrogel toward sweat withdrawal is examined on the fingertip. Using various hydrogels in the patch, the transport of red dye (model biomarker) is tracked on the paper fluidic channel using image analysis. B) Schematic depicting how the hydrogel swelling is related to the intensity of the sampled dye on the paper channel. C) Plot showing the swelling rate of five different hydrogels on the fingertip under i combination of osmotic and natural perspiration, and ii natural perspiration. D) Plot with the measured dye flow rate as obtained using five different hydrogels on the fingertip under i combination of osmotic and natural perspiration, and using ii natural perspiration alone. E) Optical images of the dye‐stained paper channels for the two best performing hydrogels on fingertip for 2 h. Scale 2 mm. f Plot showing the i hydrogel swelling rate and the ii dye flow rate for pure PAAm (orange) and PVA‐PAAm (purple) hydrogels on the forearm. The bar plots represent mean ± standard deviation (S.D.), and all error bars denote S.D. from n = 4 trials.