Bistable magnetic valves for selective sweat sampling in wearable microfluidics

Selective sweat sampling with high spatial and temporal resolution remains a key challenge in wearable microfluidic systems for biochemical monitoring. Here, we present a skin-conformal microfluidic platform that enables targeted, chamber-specific sweat collection by integrating bistable, magneto-active elastomeric valves. Each valve is toggled between open and closed states using a simple external magnetic field, requiring no continuous power. The bistable design provides mechanical memory, maintaining valve states without sustained actuation, and thus allows highly energy-efficient fluid control. By embedding magnetic particles in a shell structure with geometric bistability, we achieve reliable magnetic actuation and characterize the critical pressures associated with valve switching under varying magnetic flux densities. These results demonstrate the feasibility of using the system for practical, localized sweat collection and suggest its utility in wearable sensing applications that require spatially discrete and contamination-free sampling.