Bistable magnetic valves for selective sweat sampling in wearable microfluidics
with Chaemin Kim, Chanyong Shin, Jonghyun Ha and Jungil Choi
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.
Related Publication:
Chaemin Kim, Chanyong Shin, Anna Lee*, Jonghyun Ha*, Jungil Choi*, "Bistable magnetic valves for selective sweat sampling in wearable microfluidics," Lab on a Chip, published online. [pdf]
Stretchable Anisotropic Conductive Film with Position-Registered Conductive Microparticles Used for Strain-Insensitive Ionic Interfacing in Stretchable Ionic Sensors
with Doowon Park, Hyunsu Kwak, Seonghyeon Kim, Hyeongseok Choi, Ighyun Lim, Mingyu Kwak, Iksoo Kim, Hyeji Park,Inyong Eom,Jungwoon Lee,Ikbum Park and Unyong Jeong*
Numerous approaches are explored to achieve precise position registry of microparticles (MPs) with minimal defects; however, MP assembly in a periodic pattern or an arbitrary manner has been a challenging issue over the past several decades. Utilizing the position-registered conductive MPs, polymer composites of the MPs are used as anisotropic conductive film (ACF) and soft interfacing. One of the remaining challenges is maintaining the MP positions while producing or utilizing the ACF. This study proposes a simple strategy to produce a stretchable ACF (S-ACF) by mechanical rubbing, without disturbing the MP positions during the production and use. A practical means of precise MP positioning on a ultraviolet (UV)-patternable soft template is investigated first. This study investigates, through both experiment and finite element method calculation, the relationship between local adhesion of the template and mechanical rubbing variables (pressure, rubbing velocity, and MP size). Based on this exploration, a fast and simple method to fabricate large-area S-ACF is presented. This study demonstrates that the S-ACF can be used for electronic interfacing in stretchable devices and for ionic interfacing to remove the effect of external mechanical force in ionic sensors.
Related Publication:
Doowon Park, Hyunsu Kwak, Seonghyeon Kim, Hyeongseok Choi, Ighyun Lim, Mingyu Kwak, Iksoo Kim, Heyji Park, In-Yong Eom, Jung-Woon Lee, Ikbum Park*, Anna Lee*, and Unyong Jeong*, "Stretchable anisotropic conductive film with position-registered conductive microparticles used for strain-insensitive ionic interfacing in stretchable ionic sensors," Advanced Functional Materials 34 (49), 2408902 (2024). [pdf]
