On-chip pressure measurements and channel deformation after oil absorption

Liam Hunter,Julia Gala De Pablo,Jung-Uk Shim,Ashley C Stammers,Neil H Thomson,Stephen D Evans

doi:10.1007/s42452-020-03288-8

Liam Hunter, Julia Gala De Pablo + Show 4 more

Open Access

https://doi.org/10.1007/s42452-020-03288-8

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Abstract

Microfluidic channels moulded from the soft polymer poly(dimethylsiloxane) (PDMS) are widely used as a platform for mimicking biological environments, and can be used for the simulation of fluid filled structures such as blood and lung vessels. The control of pressure and flow rate within these structures is vital to mimic physiological conditions. The flexibility of PDMS leads to pressure-induced deformation under flow, leading to variable flow profiles along a device. Here, we investigate the change in Young’s modulus of microfluidic channels due to infiltration of mineral oil, a PDMS permeable fluid, and how this affects the resulting pressure profile using a novel pressure measurement method. We found a 53% decrease in Young’s modulus of PDMS due to mineral oil absorption over the course of 3 h accounted for lower internal pressure and larger channel deformation compared to fresh PDMS at a given flow rate. Confocal fluorescence microscopy used to image channel profiles before and after the introduction of mineral oil showed a change in pressure-induced deformation after infiltration of the oil. Atomic force microscopy (AFM) nanoindentation was used to measure Young’s modulus of PDMS before (2.80 pm 0.03 MPa) and after (1.32 pm 0.04 MPa) mineral oil absorption. Raman spectroscopy showed the infiltration of mineral oil into PDMS from channel walls and revealed the diffusion coefficient of mineral oil in PDMS.

Highlights

Microfluidic devices fabricated from polymers like poly(dimethylsiloxane) (PDMS) are used in a large variety of studies due to their low cost, ease of fabrication, transparency and biocompatibility [1,2,3]
We report the change Young’s modulus of PDMS microchannels through absorption of mineral oil and these changes in local mechanical properties causing the internal pressure and the channel profile to differ from that of a liquid that is impermeable in PDMS
The internal pressure of the microchannels increased as a function of flow rate with maximum pressures measured, at the point closest to the inlet of149 ± 8 kPa and 278 ± 9 kPa for flow rates of 600 μl/h and 1800 μl/h, respectively

Summary

Introduction

Microfluidic devices fabricated from polymers like poly(dimethylsiloxane) (PDMS) are used in a large variety of studies due to their low cost, ease of fabrication, transparency and biocompatibility [1,2,3]. Due to the soft nature of the polymers used, channels can be deformed under flow as a result of internal pressure build-up within the system [4,5,6,7,8]. While this is of use for systems such as valve structures [3], in others the change in geometry and associated pressure drops may become problematic when scaling devices. Data collection and analysis for confocal and pressure measurements were performed by Liam Hunter.

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