| In cellular microenvironment, in addition to time-varying fluid shear stress induced by moving microfluid flow, there are various biochemical substances of which the concentration is changing with time, i.e., dynamic biochemical signals. The biological processes and behaviors of cells are regulated by these dynamic biomechanical and biochemical signals. To date, microfluidic technology has been becoming an important experimental platform for constructing cellular microenrivonment in vitro and investigating the interactions between cells and their microenvironments. While in most of previous investigations cells are exposed to biochemical environment with constant concentration, and also only to single static biomechanical and/or biochemical signal, the effect of microchannel transmission characteristic on biochemical signal transportation is neglected as well, it results in the failure to the accuracy control of cellular dynamic microenvironment in vitro.Based upon the principle of fluid mechanics and the technique of microfluidic chip, a Y-shaped microfluidic shear device controlled by inlet flow rates for rapid switching of two dynamic biochemical signals is designed in this research. The device can be used to accurately load fluid shear stress and switch biochemical stimuli between two types of biochemical substances on cells in vitro for cell biology analysis. By treating the mixing channel of the Y-shaped microfluidic shear device as a signal transmission system, and by taking into consideration the effects of the velocity profiles of steady flow or non-reversing oscillatory flow, Taylor-Aris dispersion, transverse molecular diffusion, and the geometrical size of the microchannel, etc, the transmission characteristics of the mixing microchannel of Y-shaped microfluidic shear device and transportation of dynamic biochemical signals in it are systematically studied.In steady flow circumstance, by the method of separation of variables, the governing equation for time-dependent Taylor-Aris dispersion and molecular diffusion is analytically solved. The analytical expressions for the transfer function and the cutoff frequency of the mixing channel are presented. The numerical results show that the mixing channel acts as a low-pass filter. The cutoff frequency is the function of the channel heightH, the fluid viscosityμ, the diffusivity D, the longitudinal coordinate z and the shear stress τw. In non-reversing oscillatory flow, the effects of the oscillatory flow frequency, the oscillatory flow amplitude, the mean flow rate and the transmission distance on transportation of dynamic biochemical signals are investigated by numerical simulations. The simulation results show that oscillatory flow has obvious nonlinear modulation effect on biochemical signals transportation when the oscillation frequency is close to the signal frequency. Increasing the oscillation amplitude amplifies nonlinear distortion degree of biochemical signals. The results of perturbation analysis show that nonlinear modulation effect of oscillatory flow is the primary cause for the difference of biochemical signal transportation between in non-reversing oscillatory flow and in steady flow.This work helps to understand the transportation of dynamic biochemical signals in the dynamic microenvironment, and also provides some theoretical evidences for optimizing the associated microchannel transmission system in the construction of dynamic microenvironment in vitro by microfluidics technology. |
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