Zhaomiao Liu

Platelet-rich plasma (PRP) has broad therapeutic potential, yet current separation methods remain challenged by the trade-off between platelet (PLT) concentration, purity, and activation status. Here, we develop a microfluidic strategy for PRP separation by integrating lateral migration regulation with gravitational settling of blood cells. We demonstrate that microchannel architecture modifies the secondary-flow structure within the settling chamber, thereby regulating the lateral migration of blood cells. Compared with a discrete settling chamber, a continuous settling chamber provides a longer settling path, facilitating PLT enrichment and blood cell separation. Simulations of the microchannel structural unit demonstrated preferential settling of WBCs and RBCs, while PLTs remained largely suspended. Across the tested operating conditions, the PRP chip achieved a maximum PLT enrichment ratio of 4.6 and a maximum purity of 94%. Compared with conventional centrifugation, PRP produced by the chip exhibited lower platelet activation, as evidenced by a lower CD62P-positive platelet fraction and lower platelet-activating factor concentrations. Comprehensive evaluation of PLT activation and PRP composition identified a Reynolds number range of 50−100 as optimal for the PRP chip.

High-precision size sorting of liquid-metal microspheres is of great significance for flexible electronics, biomedicine, and microfluidics. Traveling surface acoustic waves (TSAWs) enable non-contact manipulation under continuous-flow conditions; however, the acoustic response of liquid-metal microspheres, which combine high density and extremely low compressibility, remains unclear, and the competition between acoustic radiation force and acoustic streaming is difficult to decouple. Solid Ga microspheres were used as the primary objects, with polystyrene (PS) and fused silica microspheres as references, while liquid eutectic gallium–indium droplets were limited to dispersion-medium screening and liquid-droplet-model validation. Electro-acoustic-fluid multiphysics simulations and experimental observations were combined to investigate the swirling, patterning, and migration modes of microspheres of different materials and sizes in TSAW fields. The results showed that, in the small-particle-size range, the migration boundary of solid Ga microspheres shifted overall toward smaller sizes. Low-ka analysis and PS-baseline parameter scans showed that the small-size acoustic-radiation-force response was highly sensitive to bulk compressibility. Further analysis showed that Ga microsphere trajectories exhibited an alternating step-like pattern of steep-rise and plateau segments, caused by alternating strengthening and weakening of the acoustic radiation force along the propagation direction due to near-wall diffraction; when a microsphere entered a low-force region, the driving force dropped abruptly, and the lateral motion temporarily slowed. These results provide mechanistic insight into acoustofluidic manipulation of materials with complex properties and quantitative parameters for precise size sorting of liquid-metal microspheres.

The excellent electrical and thermal conductivity of eutectic gallium–indium (EGaIn) particles makes them attractive materials for flexible and wearable electronics. However, conventional synthesis methods inevitably produce particles with a broad size distribution. Therefore, efficient size-based sorting is required for practical applications. In this study, the effects of acoustic field parameters and inlet flow velocity ratios on the sorting of EGaIn particles driven by surface acoustic waves are investigated. It is found that increasing the inclination angle of the acoustic field induces a transition in particle motion from a continuous mode to an intermittent mode. The influence of acoustic pressure on particle sorting is found to depend strongly on particle diameter. As the acoustic pressure increases, the motion of 10 and 15 μm particles transitions from an intermittent to a continuous mode, accompanied by an increase in lateral deflection that reaches a maximum and then saturates. By contrast, 20 μm particles remain in the continuous motion mode, with their lateral deflection remaining at its maximum value over the entire range of acoustic pressures considered. Numerical simulations show that, at an acoustic pressure of 0.2 MPa and an inclination angle of 2°, particles of different diameters can be separated by tuning the inlet flow velocity ratio. For particle sorting at high concentrations, dynamic adjustment of parameters such as flow velocity, inclination angle, acoustic frequency, and acoustic pressure is required to maintain a high recovery rate.

Precise control of cell lateral positions in microchannels is critical for high-accuracy cell isolation, with such positioning primarily governed by lateral migration. Among the various factors influencing lateral migration, interphase forces play a key but underexplored role. In this study, a simulation model was developed to resolve the evolution of interphase interaction during cell-cell collisions. Using this model, we systematically analyze cell migration under the combined influence of lateral lift forces and interphase force. The results show that under low Reynolds number (Re) conditions, lateral lift forces dominate, and cells gradually reach equilibrium positions through repeated collision and separation. As Re increases, however, collisions occur with greater relative velocity, generating stronger interphase forces that drive rapid separation and induce transient but pronounced shifts in lateral cell position, typically persisting for only a few milliseconds, with peak displacements of about 25% of the equilibrium position. Experimental validation of the simulation results is achieved through microcapillary flow tests with blood cells and particles, supporting the simulation model's predictive accuracy. Notably, we observe the formation of transient secondary rings under high Re conditions, which are attributed to interphase interactions. This study delivers mechanistic insights into intercellular dynamics in confined microflows and establishes a rigorous modeling framework for the design of high-throughput, high-purity cell isolation systems.

This study utilizes numerical methods to systematically investigate the effect of viscosity ratio on the formation dynamics and size modulation of microdroplets within cross-shaped microchannels with a contraction structure. It demonstrates that varying the viscosity ratio between the dispersed and continuous phases gives rise to three droplet formation modes: dripping, transition, and jetting. In contrast to standard cross-junction microchannels, the contraction geometry significantly enhances local shear stress and pressure differentials, resulting in a non-monotonic dependence of droplet size on viscosity ratio—exhibiting an initial decrease followed by a subsequent increase. Specifically, in the dripping mode, a higher dispersed phase viscosity reduces internal vorticity and deformation resistance, increases pressure-driven forces beyond the interfacial tension, and thereby accelerates droplet breakup to yield smaller droplets. Conversely, in the jetting mode, the high viscosity of the dispersed phase impedes deformation, elongates the breakup cycle, and ultimately increases droplet size. The flow field analysis reveals the underlying force competition mechanism that dynamically governs the droplet breakup process across regimes. Additionally, theoretical scaling relations are proposed for predicting droplet size, which is derived from the capillary number and viscosity ratio, and validated against simulation data.