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<p>Paper-based microfluidics has emerged as a promising platform for point-of-care testing (POCT) owing to its capillary-driven flow, low cost, and portability. Geometric modification is a widely adopted strategy for regulating paper-based capillary flow, yet its underlying flow-control mechanisms remain insufficiently understood, and relevant design optimization relies largely on empirical experience. This study combines dye flow visualization experiments and numerical simulations to systematically investigate the effects of contraction geometric parameters (width, length, inlet angle and outlet angle) on capillary flow behavior in rectangular paper strips. The results demonstrate that contraction geometries effectively modulate the mean front speed, flow rate, and fluid front evolution. As the contraction width increases from 2&#xa0;mm to the uncontracted width of 10&#xa0;mm, the average front speed declines by 38.1%. Increasing the inlet angle shortens the fluid propagation time through the contraction region, whereas a larger outlet angle suppresses axial transport by enhancing transverse fluid redistribution. Moreover, non-uniform propagation of the fluid front is identified as a distinctive flow phenomenon. The results clarify the geometry-dependent capillary flow mechanism and could provide practical guidelines for the structural design and precise flow regulation of high-performance paper-based microfluidic devices.</p>

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Effects of contraction structures on capillary flow characteristics on paper-based microfluidic strips

  • 期刊论文

  • 发表日期：

    2026年7月8日

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  • Feng Shen,
  • Dongwei Li,
  • Jiahui Du,
  • Zhaomiao Liu

摘要

Paper-based microfluidics has emerged as a promising platform for point-of-care testing (POCT) owing to its capillary-driven flow, low cost, and portability. Geometric modification is a widely adopted strategy for regulating paper-based capillary flow, yet its underlying flow-control mechanisms remain insufficiently understood, and relevant design optimization relies largely on empirical experience. This study combines dye flow visualization experiments and numerical simulations to systematically investigate the effects of contraction geometric parameters (width, length, inlet angle and outlet angle) on capillary flow behavior in rectangular paper strips. The results demonstrate that contraction geometries effectively modulate the mean front speed, flow rate, and fluid front evolution. As the contraction width increases from 2 mm to the uncontracted width of 10 mm, the average front speed declines by 38.1%. Increasing the inlet angle shortens the fluid propagation time through the contraction region, whereas a larger outlet angle suppresses axial transport by enhancing transverse fluid redistribution. Moreover, non-uniform propagation of the fluid front is identified as a distinctive flow phenomenon. The results clarify the geometry-dependent capillary flow mechanism and could provide practical guidelines for the structural design and precise flow regulation of high-performance paper-based microfluidic devices.