Fig. 2: Skin-interfaced microfluidic chronometric sampling by passive valve structures.
From: Skin-interfaced colorimetric microfluidic devices for on-demand sweat analysis
a Schematic illustration of the capillary bursting valve. b Top view of microfluidic channels for chrono-sampling of sweat67. c Schematic illustration of the Tesla valve and (d) its demonstration in the sampling process using methyl red and methylene blue74 (increased pressure inside the upper right return channel due to the air pressure). e Schematic illustration of the hydrophobic valve (HV) and (f) its use in an epidermal microfluidic device with one-opening chambers, along with (g) optical images and numerical simulations of the hydrodynamic flow process into the one-opening chamber with a HV71 (scale bar: 1 mm). h Schematic illustration of the polymer valve and (i) its use in the super absorbent polymer (SAP) system with valve activation before (top) and after (after) sweat collection72. j Microfluidic channel design of the combined use of HV and SAP valves with reservoirs72 (scale bar: 0.5 mm).
