Skin-interfaced colorimetric microfluidic devices for on-demand sweat analysis

As sweat biomarker levels are continuously changing over metabolism and daily activities, pathological and physiological processes can be dynamically analyzed by wearable devices. The colorimetric skin-interfaced microfluidic devices that do not have external circuit modules exhibit enhanced deformability with a small footprint. However, it is difficult to achieve sampling over time and self-feedback for closed-loop systems. This review summarizes recent advances in microfluidic valves for biofluid management and chrono-sampling, as well as active triggers in microfluidics self-feedback. After enumerating the current limitations in temporal resolution and reliability, we further point out a few potential feasible strategies for future developments.