Development of human-motion-activated microfluidic pump for next-generation wearable biomedical systems

Soft, skin-conformal microfluidic systems that provide reliable, repeatable, and directional fluid transport under natural body motion are essential for next-generation wearable biomedical applications; however, their broader use remains limited by fluid actuation strategies that require bulky external pumps or rigid actuation hardware. This thesis develops a power-free, strain-driven microfluidic platform that converts human motion into controlled fluid transport using monolithic soft architectures whose fluidic response is programmed through geometry and corresponding morphing mechanics. The work introduces out-of-surface microchannels (OSMiCs) that reshape the strain–fluidic response of elastomeric microchannels: unlike planar channels that expand under tension, OSMiCs can undergo negative volumetric strain under tensile loading, generating positive internal pressure and driving forward fluid displacement under skin-relevant strain. The coupled wrinkling, buckling, and shell-morphing dynamics of OSMiCs are investigated experimentally and computationally, revealing snap-through and snap-back transitions between stable states that govern reversible versus irreversible fluid displacement depending on channel architecture. By tailoring channel parameters, OSMiCs are shown to provide asymmetric pressure generation during loading and release, with measured pressures on the order of 10 kPa (including ~10 kPa forward and ~−14 kPa during release at 20% uniaxial strain). To enable repeatable net transport under cyclic motion, the thesis then introduces OSMiPump, a soft, monolithic micropump that integrates OSMiCs with self-actuated morphing valves (OSMiValves). Here, cyclic tensile strain drives volume reduction in the pumping region while valve snap-through/snap-back modulates hydraulic resistance to suppress backflow during release, converting cycling strain application into accumulated unidirectional transport. Fluid–structure interaction modeling and nonlinear shell deformation analysis validate the operating mechanism, and experiments demonstrate predictable performance across valve geometries, strain levels and profiles, fluid viscosities, and inlet/outlet resistance configurations. For the experimental characterization of both OSMiC and OSMiPump, reproducibility was evaluated using at least three independently fabricated chips for each specific condition, while repeatability was assessed through at least three repeated measurements. It is found that, at 20% strain, OSMiPump achieves average flow rates up to ~0.16 μL/s under low-resistance conditions and maintains ~0.02 μL/s under high-resistance conditions, reaching peak pressures of ~11 kPa and sustaining ~0.6 kPa on average. Over 100 actuation cycles, OSMiPump maintained repeatable net forward pumping, as demonstrated by continued cumulative liquid displacement throughout cyclic operation. Wearable demonstrations confirm direct actuation by body motion and support both on-body delivery and removal, including integration into different form factors such as silicone socks and skin-mounted Tegaderm films. Together, these results show that natural body motion can be used to drive repeatable, directional pumping in a soft, battery-free microfluidic system.