An Easy Method for Pressure Measurement in Microchannels Using Trapped Air Compression in a One-End-Sealed Capillary

Abstract

Pressure is one basic parameter involved in microfluidic systems. In this study, we developed an easy capillary-based method for measuring fluid pressure at one or multiple locations in a microchannel. The principal component is a commonly used capillary (inner diameter of 400 μm and 95 mm in length), with one end sealed and calibrated scales on it. By reading the height (h) of an air-liquid interface, the pressure can be measured directly from a table, which is calculated using the ideal gas law. Many factors that affect the relationship between the trapped air volume and applied pressure (papplied) have been investigated in detail, including the surface tension, liquid gravity, air solubility in water, temperature variation, and capillary diameters. Based on the evaluation of the experimental and simulation results of the pressure, combined with theoretical analysis, a resolution of about 1 kPa within a full-scale range of 101.6–178 kPa was obtained. A pressure drop (Δp) as low as 0.25 kPa was obtained in an operating range from 0.5 kPa to 12 kPa. Compared with other novel, microstructure-based methods, this method does not require microfabrication and additional equipment. Finally, we use this method to reasonably analyze the nonlinearity of the flow–pressure drop relationship caused by channel deformation. In the future, this one-end-sealed capillary could be used for pressure measurement as easily as a clinical thermometer in various microfluidic applications.

Overcoming technological barriers in microfluidics: Leakage testing

“…Pressure decay testing to identify leaks typically requires placing pressure sensors at the inlet and/or outlet of the microchannel ( Casanova-Moreno et al, 2017 ). A reproducible method to characterize microfluidic channel deformations and liquid leaks can be achieved by positioning a sealed capillary tube with a calibrated scale at the channel outlet ( Shen et al, 2020 ). The resolution of the measurement can be improved by simply decreasing the capillary diameter, further resolving the scale, or by complementing the visualization technique with optical detection of the fluid meniscus.…”

Sequential quantification of blood and diluent using red cell sedimentation-based separation and pressure-induced work in a microfluidic channel

“…In this study, the blood and diluent were quantied from a mechanical point of view by using the interface (b) in the coowing channel instead of blood image intensity or air-liquid interface to estimate junction pressure. 16,[50][51][52][53][54][55] Based on the temporal variations of b, the junction pressure of blood was estimated between t 3 and t 4 . In addition, the junction pressure of the diluent was calculated between t 5 and t 6 .…”

High‐Gain Microfluidic Amplifiers: The Bridge between Microfluidic Controllers and Fluidic Soft Actuators

“…The ranges of values noted here and in the remainder of this section will be used to define the ranges of our targets for the metrics mentioned; despite quoted data for these measurements being sparse in the literature, we found that a common command input for soft actuators is 103.4 kPa [22][23][24][25][26][27][28] while microfluidic output signals vary from 3.4 to 34.5 kPa due to the large resistances of the narrow channels which cause a large pressure drop limiting the output pressure at flow rates relevant to typical soft fluidic actuators. [29] Therefore, a gain range that guarantees that all microfluidic output signal magnitudes can be amplified to drive the largest soft robotic loads is 3-30.…”