Dispersion of Dynamic Biochemical Signals in Steady Flow in a Shallow Y-type Microfluidic Channel

This paper presents an analysis of dispersion of dynamic biochemical signals in steady flow in a shallow Y-type microfluidic channel. A method is presented to control the flow widths of two steady flows in the Y-type microchannel from two inlets.The transfer function for the Y-type microchannel is given by solving the governing equation for the Taylor-Aris dispersion in the microchannel. The amplitude-frequency and phase-frequency relations are provided which show that a shallow Y-type microchannel acts as a low-pass filter. The transports of different dynamic biochemical signals are investigated. In comparison with a fully mixing microfluidic channel, the magnitudes of the dynamic signals at the outlets in a Y-type microchannel are much smaller than those in a fully mixing microchannel, which demonstrates that the amplitude attenuation in a Y-type microchannel is larger than that of a fully mixing microchannel due to the transverse molecular diffusion. In order to control the desired signal in a microchannel, the solution of the inverse problem for the channel is also presented.

急性有氧自行车运动对动脉血流电导率和电阻抗的影响

血流动力学参数不仅在运动调控动脉结构和功能的过程中扮演重要的角色,而且是评估心血管功能的重要生理指标。血流电阻抗监测技术因为便携、可穿戴和微型化等优点,便于运动过程中血流动力学参数的在线监测。然而,由于运动前后血流电导率、电阻抗和血流动力学参数之间的定量关系仍未完全阐明,阻碍了这一技术在血流动力学监测中的广泛应用。该文采用运动干预实验、数值模拟及统计学相关性分析方法,研究了运动前后血流动力学参数的变化规律及其与血流电导率和电阻抗之间的定量关系。结果显示,急性有氧自行车运动对颈总动脉血压、管径、轴心流速和电阻抗影响显著,对电导率影响较小;电导率波形主要受轴心流速波形影响,与轴心流速成线性关系,而电阻抗波形主要受动脉半径波形影响,与动脉半径平方的倒数成线性关系。该文的研究结果为进一步开发基于血流动力学参数监测评估心血管功能的可穿戴医疗设备提供了一定的理论基础。

SYNERGY OF WALL SHEAR STRESS AND CIRCUMFERENTIAL STRESS IN STRAIGHT ARTERIES

The Wall Shear Stress （WSS） generated by blood flow and Circumferential Stress （CS） driven by blood pressure have been thought to play an important role in blood flow-dependent phenomena such as angiogenesis, vascular remodeling, and atherosgenesis. The WSS and CS in straight arteries were calculated by measuring the blood pressure, center-line velocity, wall thickness, and radius of vessels. The WSS and CS in the time domain were then decomposed into the amplitude and phase in the frequency domain. The CS amplitude to the WSS amplitude ratio （referred as stress ampli tude ratio, Zs ） and the phase difference between the CS and the WSS （referred as stress phase difference, SPA） in the fre quency domain were calculated to characterize the synergy of the CS and WSS. Numerical results demonstrated that the CS is not in phase with the WSS, a time delay in the time domain or a stress phase difference in the frequency domain between the WSS and the CS exists. Theoretical analysis demonstrated that the Zs and SPA are primarily determined by the local fac tors （blood viscosity, local inertial effects, local geometry, loeal elasticity） and the input impedance of whole downstream arterial beds. Because the arterial input impedance has been shown to reflect the physiological and pathological states of whole downstream arterial beds, the stress amplitude ratio Zs and stress phase difference SPA would be thought to be the appropriate indices to reflect the effects of states of whole downstream arterial beds on the local blood flow dependent phenomena such as angiogenesis, vascular remodeling, and atherosgenesis.

ANALYSIS OF PULSATILE FLOW IN THE PARALLEL-PLATE FLOW CHAMBER WITH SPATIAL SHEAR STRESS GRADIENT

The Parallel-Plate Flow Chamber （PPFC）, of which the height is far smaller than its own length and width, is one of the main apparatus for the in-vitro study of the mechanical behavior of cultured vascular Endothelical Cells （ECs） exposed to fluid shear stress. The steady flow in different kinds of PPFC has been extensively investigated, whereas, the pulsatile flow in the PPFC has received little attention. In consideration of the characteristics of geometrical size and pulsatile flow in the PPFC, the 3-D pulsatile flow was decomposed into a 2-D pulsatile flow in the vertical plane, and an incompressible plane potential flow in the horizontal plane. A simple method was then proposed to analyze the pulsatile flow in the PPFC with spatial shear stress gradient. On the basis of the method, the pulsatile fluid shear stresses in several reported PPFCs with spatial shear stress gradients were calculated. The results were theoretically meaningful for applying the PPFCs in-vitro, to simulate the pulsatile fluid shear stress environment, to which cultured ECs were exposed.

微通道中细胞划痕尺寸的定量控制

细胞划痕尺寸的定量控制是探究细胞迁移过程的先决条件。该文基于微流控技术,设计了一种利用胰蛋白酶消化法制造细胞划痕的微流控芯片,提出了基于流量控制定量调控细胞划痕尺寸的方法,并通过数值仿真、荧光素可视化实验以及细胞实验对该方法进行了分析和验证。荧光粉实验与数值仿真结果表明,荧光粉溶液宽度,等效于划痕宽度,与荧光粉溶液流量比成正比例线性关系。在总流量一定情况下(Q0=100μl/min),增加荧光粉溶液流量(Q2=50μl/min)可减小分子横向扩散的影响,维持主通道内划痕宽度的一致性。内皮细胞划痕实验结果有效证明了基于流量控制胰蛋白酶消化产生细胞划痕方法的可行性,且与数值仿真和荧光粉可视化实验结果吻合良好。该文设计的微流控芯片及细胞划痕尺寸定量控制方法为研究细胞迁移和开展内皮细胞划痕愈合实验提供了有效的实验平台。