The characterisation of physical properties in biologically relevant processes and the development of novel microfluidic devices for this purpose are experiencing a great resurgence at present. In many of measurements of this type where a probe in a fluid is used, the strong influence of the boundaries of the volume used is a serious problem. In these geometries the proximity of a probe to a wall can severely influence the measurement. However, although much knowledge has been gained about flat walls, to date, the effect of non-planar surfaces at microscopic scale on rotational motion of micro-objects has not been studied. Here we present for the first time both experimental measurements and numerical computations which aim to study the drag torque on optically trapped rotating particles moving near 3D-printed conical and cylindrical walls on-chip. These results are essential for quantifying how curved walls can effect the torque on particles, and thus enable accurate hydrodynamic simulations at the micron-scale. This opens the potential for new sensing approaches under more complex conditions, allowing both dynamic and microrheological studies of biological systems and lab-on-chip devices.

中文翻译：

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复杂表面对使用光镊的生物微流变学测量的影响

目前，生物学相关过程中物理性质的表征以及为此目的开发的新型微流控设备正在经历复兴。在许多此类使用流体中探针的测量中，所用体积边界的强烈影响是一个严重的问题。在这些几何形状中，探头与墙壁的接近度可能会严重影响测量。然而，尽管已经获得了大量有关平坦壁的知识，但是迄今为止，尚未研究微观尺度上的非平面表面对微物体旋转运动的影响。在这里，我们首次展示了实验测量和数值计算，旨在研究在芯片上3D打印的圆锥形和圆柱形壁附近移动的光学捕获的旋转粒子上的阻力。这些结果对于量化弧形壁如何影响颗粒上的扭矩，从而实现微米级的精确流体动力学仿真至关重要。这为在更复杂条件下的新传感方法打开了可能性，从而允许对生物系统和芯片实验室设备进行动态和微观流变学研究。