Transport of dynamic biochemical signals in steady flow in a shallow Y-shaped microfluidic channel: effect of transverse diffusion and longitudinal dispersion

A microfluidic array enabling generation of identical biochemical stimulating signals to trapped biological cells for single-cell dynamics

Microfluidic-based analyses of single-cell dynamics in response to dynamic biochemical signals are emerging as pivotal approaches for investigating the effects of extracellular microenvironmental biochemical factors on cellular structure, function, and behavior. However, current devices often fail to consistently apply identical dynamic biochemical signals to trapped cells. In this study, we introduce a novel radially distributed single-cell trapping microfluidic array, designed to quantitatively and consistently apply identical biochemical stimulating signals to each trapped cell. Numerical simulations were employed to optimize microchannel geometry, enhancing trapping efficiency while minimizing signal distortion. Experimental validation demonstrated the trapping success rate and the single-cell trapping efficiency exceeding 99% and 85%, respectively. The microarray's capability to deliver identical dynamic biochemical stimulating signals, with various waveforms, to each unit was confirmed through fluorescein transport tests. Furthermore, we examined the intracellular calcium dynamics of U-2 OS human osteosarcoma cells in response to dynamic ATP signals, observing both single-peak calcium responses and calcium oscillations, which were modelled by a second-order system with a natural frequency of 1.6 mHz. Overall, our proposed microfluidic array offers a robust and valuable framework for advancing the understanding of single-cell dynamics.

Clog-free high-throughput microfluidic cell isolation with multifunctional microposts

Microfluidics have been applied to filtration of rare tumor cells from the blood as liquid biopsies. Processing is highly limited by low flow rates and device clogging due to a single function of fluidic paths. A novel method using multifunctional hybrid functional microposts was developed. A swift by-passing route for non-tumor cells was integrated to prevent very common clogging problems. Performance was characterized using microbeads (10 µm) and human cancer cells that were spiked in human blood. Design-I showed a capture efficiency of 96% for microbeads and 87% for cancer cells at 1 ml/min flow rate. An improved Design-II presented a higher capture efficiency of 100% for microbeads and 96% for cancer cells. Our method of utilizing various microfluidic functions of separation, bypass and capture has successfully guaranteed highly efficient separation of rare cells from biological fluids.

A Microfluidic Array Device for Single Cell Capture and Intracellular Ca2+ Response Analysis Induced by Dynamic Biochemical Stimulus

A microfluidic array was constructed for trapping single cell and loading identical dynamic biochemical stimulation for gain a better understanding of Ca2+ signalling in single cells by applying extracellular dynamic biochemical stimulus. This microfluidic array consists of multiple radially aligned flow channels with equal intersection angles, which was designed by a combination of stagnation point flow and physical barrier. Numerical simulation results and trajectory analysis shown the effectiveness of this single cell trapping device. Fluorescent experiment results demonstrated the effects of flow rate and frequency of dynamic stimulus on the profiles of biochemical concentration which exposed on captured cells. In this array chip, the captured single cells in each trapping channels were able to receive identical extracellular dynamic biochemical stimuli which being transmitted from the entrance at the middle of the microfluidic array. Besides, after loading dynamic Adenosine Triphosphate (ATP) stimulation on captured cells by this device, consistent average intracellular Ca2+ dynamics phase and cellular heterogeneity were observed in captured single K562 cells. Furthermore, this device is able to be used for investigating cellular respond in single cells to temporally varying environments by modulating the stimulation signal in terms of concentration, pattern, and duration of exposure.

Modeling of Endothelial Calcium Responses within a Microfluidic Generator of Spatio-Temporal ATP and Shear Stress Signals

Intracellular calcium dynamics play essential roles in the proper functioning of cellular activities. It is a well known important chemosensing and mechanosensing process regulated by the spatio-temporal microenvironment. Nevertheless, how spatio-temporal biochemical and biomechanical stimuli affect calcium dynamics is not fully understood and the underlying regulation mechanism remains missing. Herein, based on a developed microfluidic generator of biochemical and biomechanical signals, we theoretically analyzed the generation of spatio-temporal ATP and shear stress signals within the microfluidic platform and investigated the effect of spatial combination of ATP and shear stress stimuli on the intracellular calcium dynamics. The simulation results demonstrate the capacity and flexibility of the microfluidic system in generating spatio-temporal ATP and shear stress. Along the transverse direction of the microchannel, dynamic ATP signals of distinct amplitudes coupled with identical shear stress are created, which induce the spatio-temporal diversity in calcium responses. Interestingly, to the multiple combinations of stimuli, the intracellular calcium dynamics reveal two main modes: unimodal and oscillatory modes, showing significant dependence on the features of the spatio-temporal ATP and shear stress stimuli. The present study provides essential information for controlling calcium dynamics by regulating spatio-temporal biochemical and biomechanical stimuli, which shows the potential in directing cellular activities and understanding the occurrence and development of disease.

Transport of dynamic biochemical signals in a microfluidic single cell trapping channel with varying cross-sections

Dynamic biochemical signal control in vitro is important in the study of cellular responses to dynamic biochemical stimuli in microenvironment in vivo. To this end, we designed a microfluidic single cell trapping channel with varying cross-sections. In this work, we analyzed the transport of dynamic biochemical signals in steady and non-reversing pulsatile flows in such a microchannel. By numerically solving the 2D time-dependent Taylor-Aris dispersion equation, we studied the transport mechanism of different signals with varying parameters. The amplitude spectrum in steady flow shows that the trapping microchannel acts as a low-pass filter due to the longitudinal dispersion. The input signal can be modulated nonlinearly by the pulsatile flow. In addition, the nonlinear modulation effects are affected by the pulsatile flow frequency, the pulsatile flow amplitude and the average flow rate. When the flow frequency is much smaller or larger than that of the biochemical signal, the signal can be transmitted more efficiently. Besides, smaller pulsatile flow amplitude and larger average flow rate can decrease the nonlinear modulation and promote the signal transmission. These results demonstrate that in order to accurately load a desired dynamic biochemical signal to the trapped cell to probe the cellular dynamic response to the dynamic biochemical stimulus, the transport mechanism of the signals in the microchannel should be carefully considered.

A microfluidic device with spatiotemporal wall shear stress and ATP signals to investigate the intracellular calcium dynamics in vascular endothelial cells

Intracellular calcium dynamics plays an important role in the regulation of vascular endothelial cellular functions. In order to probe the intracellular calcium dynamic response under synergistic effect of wall shear stress (WSS) and adenosine triphosphate (ATP) signals, a novel microfluidic device, which provides the adherent vascular endothelial cells (VECs) on the bottom of microchannel with WSS signal alone, ATP signal alone, and different combinations of WSS and ATP signals, is proposed based upon the principles of fluid mechanics and mass transfer. The spatiotemporal profiles of extracellular ATP signals from numerical simulation and experiment studies validate the implementation of our design. The intracellular calcium dynamics of VECs in response to either WSS signal or ATP signal alone, and different combinations of WSS and ATP signals have been investigated. It is found that the synergistic effect of the WSS and ATP signals plays a more significant role in the signal transduction of VECs rather than that from either WSS signal or ATP signal alone. In particular, under the combined stimuli of WSS and ATP signals with different amplitudes and frequencies, the amplitudes and frequencies of the intracellular Ca²⁺ dynamic signals are observed to be closely related to the amplitudes and frequencies of WSS or ATP signals.

A Y-Shaped Microfluidic Device to Study the Combined Effect of Wall Shear Stress and ATP Signals on Intracellular Calcium Dynamics in Vascular Endothelial Cells

The intracellular calcium dynamics in vascular endothelial cells (VECs) in response to wall shear stress (WSS) and/or adenosine triphosphate (ATP) have been commonly regarded as an important factor in regulating VEC function and behavior including proliferation, migration and apoptosis. However, the effects of time-varying ATP signals have been usually neglected in the past investigations in the field of VEC mechanobiology. In order to investigate the combined effects of WSS and dynamic ATP signals on the intracellular calcium dynamic in VECs, a Y-shaped microfluidic device, which can provide the cultured cells on the bottom of its mixing micro-channel with stimuli of WSS signal alone and different combinations of WSS and ATP signals in one single micro-channel, is proposed. Both numerical simulation and experimental studies verify the feasibility of its application. Cellular experimental results also suggest that a combination of WSS and ATP signals rather than a WSS signal alone might play a more significant role in VEC Ca²⁺ signal transduction induced by blood flow.