Generation of Dynamic Concentration Profile Using A Microfluidic Device Integrating Pneumatic Microvalves

Abstract

Generating and maintaining the concentration dilutions of diffusible molecules in microchannels is critical for high-throughput chemical and biological analysis. Conventional serial network microfluidic technologies can generate high orders of arbitrary concentrations by a predefined microchannel network. However, a previous design requires a large occupancy area and is unable to dynamically generate different profiles in the same chip, limiting its applications. This study developed a microfluidic device enabling dynamic variations of both the concentration in the same channel and the concentration distribution in multiple channels by adjusting the flow resistance using programmable pneumatic microvalves. The key component (the pneumatic microvalve) allowed dynamic adjustment of the concentration profile but occupied a tiny space. Additionally, a Matlab program was developed to calculate the flow rates and flow resistance of various sections of the device, which provided theoretical guidance for dimension design. In silico investigations were conducted to evaluate the microvalve deformation with widths from 100 to 300 µm and membrane thicknesses of 20 and 30 µm under the activation pressures between 0 and 2000 mbar. The flow resistance of the deformed valve was studied both numerically and experimentally and an empirical model for valve flow resistance with the form of Rh=aebP was proposed. Afterward, the fluid flow in the valve region was characterized using Micro PIV to further demonstrate the adjustment mechanism of the flow resistance. Then, the herringbone structures were employed for fast mixing to allow both quick variation of concentration and minor space usage of the channel network. Finally, an empirical formula-supported computational program was developed to provide the activation pressures required for the specific concentration profile. Both linear (Ck = −0.2k + 1) and nonlinear (Ck = (110)k) concentration distribution in four channels were varied using the same device by adjusting microvalves. The device demonstrated the capability to control the concentration profile dynamically in a small space, offering superior application potentials in analytical chemistry, drug screening, and cell biology research.

A tempo-spatial controllable microfluidic shear-stress generator for in-vitro mimicking of the thrombus

“…However, measurement of the deformation is challenging and mainly by either numerical simulation or imaging. For instance, simulation revealed that 2000 mbar was necessary to deflect a 20 μm thick film (with a curing ratio of 10:1) for by 30 μm [ 56 , 57 ]. The confocal microscopy has been employed for a more intuitive visualization of membrane deformation [ 48 ].…”

Actuation for flexible and stretchable microdevices

“…Soft lithography is frequently used to fabricate microdevices such as pneumatic micropumps 51,59–62 and microvalves. 52,57,63,64 This fabrication technique has also been used for hydraulically actuated microdevices. 55 Ni et al 111 reported an electromagnetic actuator with liquid metal embedded in the microfluidic structures.…”

“…Furthermore, the flexible structure not only serves as a valve to fully close a microchannel in microvalves but also acts as a regulator by partially closing the microchannel to tune its fluidic resistance. 64…”

“…PDMS has advantages such as durability, corrosion resistance, biocompatibility, and high optical transparency. 22 In addition, the low shear and Young's modulus, high strains at fracture, and ease of manufacturability enable the utilisation of PDMS in pneumatic 52,57,58,63,64 and hydraulic microactuators. 55 Microdevices such as micropumps and microvalves are generally made of multiple stacked layers, such as the supporting, fluidic, and control layers.…”

Microfluidics for Biomedical Applications

“…Generating the concentration dilutions of diffusible molecules in microfluidic devices is important for high-throughput biochemical analysis. Chen et al [22] reported a microfluidic device integrated with programmable pneumatic microvalves for adjusting both the concentration in a single channel and the concentration distributions in different channels. They systematically studied the performance of the pneumatic microvalves via experiments and numerical simulations.…”