Autonomous wearable sensing enabled by capillary microfluidics: a review.

Abstract

Capillary microfluidic wearables have emerged as a versatile class of autonomous biosensing platforms for continuous, non-invasive monitoring of biofluids such as sweat, saliva, tears, and interstitial fluid. This review critically examines recent advances in skin-conformal device architectures that enable passive, power-free fluid sampling and integration with biochemical sensing modalities. Systems are classified by fluid handling strategy chrono-sampling <i>versus</i> continuous flow and sensing mode on-body <i>versus</i> off-body analysis. Key design principles including the use of burst valves, evaporative reservoirs, multilayer channel networks, and hydrogel-assisted interfaces are discussed in the context of minimizing evaporation, backflow, and biofouling. Advances in electrochemical and optical biosensing for real-time quantification of physiologically relevant analytes such as cortisol, glucose, lactate, pH, and electrolytes are evaluated alongside emerging trends in multiplexing and closed-loop therapeutic integration. Finally, the review highlights translational challenges in clinical validation, biocompatibility, and manufacturing scalability, outlining a roadmap for future development of lab-on-skin diagnostics and personalized health monitoring.