人工细胞质流动的受限热粘性流理论模型
Theoretical model of confined thermoviscous flows for artificial cytoplasmic streaming
AI总结：
本文提出了一个完全解析的理论模型，描述了二维受限空间中由激光诱导的热粘性流和示踪剂输运，揭示了瞬时流动源于热膨胀而净位移与热点振幅呈二次方关系，与实验结果高度吻合，为设计新实验研究细胞内物理输运的生理作用提供了理论基础。
摘要：
细胞生物学中的近期实验探究了人工诱导的细胞内流动对细胞和生物体时空组织的影响。在这些实验中，通过激光聚焦的红外光进行温和的动态加热，导致细胞内部细胞质的长程热粘性流动，该方法在细胞生物学中被推广为FLUCS（聚焦光诱导的细胞质流动）。在此，我们提出了一个完全解析的理论模型，描述了二维受限空间中由激光在所有长度尺度上诱导的流体流动和示踪剂输运。聚焦光引起微小的局部温度变化，进而导致流体密度和粘度的局部微小变化。我们解析求解了具有任意时间依赖振幅的热点沿扫描路径平移引起的瞬时流场。我们表明，主导阶的瞬时流动纯粹源于热膨胀。它与温度扰动的幅度成正比，其远场行为通常由源流或汇流主导，且与热点振幅的变化率成正比。相比之下，且与实验测量结果一致，由于热点完整扫描引起的示踪剂净位移与热点振幅呈二次方关系，因为这是热膨胀与热粘度变化相互作用的结果。示踪剂在单次扫描中相应的平均速度在远场表现为流体动力学源偶极子，其方向取决于热膨胀和热粘度变化的相对重要性。我们的定量结果与近期实验结果高度吻合，并将有助于设计新的受控实验，以确立细胞内物理输运过程的生理作用。
英文摘要：
Recent experiments in cell biology have probed the impact of artificially-induced intracellular flows in the spatiotemporal organisation of cells and organisms. In these experiments, mild dynamical heating via focused infrared light from a laser leads to long-range, thermoviscous flows of the cytoplasm inside a cell, a method popularised in cell biology as FLUCS (focused-light-induced cytoplasmic streaming). Here, we present a fully analytical, theoretical model describing the fluid flow and transport of tracers induced by the laser at all length scales in two-dimensional confinement. The focused light causes a small, local temperature change, which in turn results in a small change in the density and viscosity of the fluid locally. We analytically solve for the instantaneous flow field due to the translation of a heat spot of arbitrary time-dependent amplitude along a scan path. We show that the leading-order instantaneous flow results purely from thermal expansion. It is proportional to the magnitude of the temperature perturbation, with far-field behaviour typically dominated by a source or sink flow and proportional to the rate of change of the heat-spot amplitude. In contrast, and in agreement with experimental measurements, the net displacement of a tracer due to a full scan of the heat spot is quadratic in the heat-spot amplitude, as it results from the interplay of thermal expansion and thermal viscosity changes. The corresponding average velocity of tracers over a scan is a hydrodynamic source dipole in the far field, with direction dependent on the relative importance of thermal expansion and thermal viscosity changes. Our quantitative findings show excellent agreement with recent experimental results and will enable the design of new controlled experiments to establish the physiological role of physical transport processes inside cells.
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