Biomicroparticles such as proteins, bacterium, and cells are known to be viscoelastic, which significantly affects their performance in microfluidic applications. However, the exact effects and the quantitative study of cellular viscoelastic creep within different applications remain unclear. In this study, the cellular-deforming evolution within a filter unit was studied using a multiphysics numerical model. A general cellular creep deformation process of viscoelastic particle trapping in pores was revealed. Two featured variables, namely, the maximum surface displacement and the volumetric strain, were identified and determined to quantitatively describe the evolution. The effects of flow conditions and physical characteristics of the microparticles were studied. Furthermore, a Giardia concentration experiment was conducted using an integrated hydraulic filtration system with a porous membrane. The experimental results agreed well with the numerical analysis, indicating that, compared to pure elastic particles, it is more difficult to release cellular material matters including cells, chemical synthetic particles, and microbes from trapping due to their time-accumulated creep deformation.

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Microfluidic technologies have been developed for decades, especially in bio-chemical research and applications. Among them, sheath flow is one of the most well-known techniques used for focusing microparticles into extremely narrow widths. With varying Reynolds numbers, sheath flow displays different behaviors, including diffusion, stable thread, and turbulence. In this study, a previously unknown phenomenon, namely, stable expansion, is originally reported in a 200 × 70 μm microchannel with a Reynolds number ranging from ∼10 to ∼110. This stable expansion of focusing width differs from all the reported phenomena in the literature and is experimentally explored in this study. First, the phenomenon is introduced, identified, and comprehensively described using different experimental samples and methods. Subsequently, an image processing algorithm of post-analysis is proposed and calibrated by the theoretical results of stable thread. Based on the calibrated standard protocol, the effects of flow rates and a hysteresis phenomenon due to variation in the flow rate are revealed and studied. In addition, the effects of fluid viscosity are investigated by introducing a mixture of deionized (DI) water and glycerin. It is found that, in this 200 × 70  μm2 (weight × height) microchannel made of PDMS, the stable expansion phenomenon will occur when the Reynolds number exceeds 10, and the expanded width will increase with total flow rate. Moreover, it is found that the expanded width in a flow rate reducing route is displayed to be wider than that in an increasing route. On the other hand, a high viscosity contrast (>40) between the middle sample and sheath flows can eliminate the focusing width expansion. The results indicate that this originally revealed phenomenon is experimentally repeatable and worth further studying to help researchers better understand the mechanism of microfluidics.