Measuring Young's Modulus of soft gels in a planar microfluidic device via simple clogging

Measuring the elastic modulus of soft gels usually requires complex micro-pipette aspiration or atomic force microscopy, two complex methods. Here we investigate the deformation of a soft hydrogel particle when it is aspirated into a high aspect ratio slit as a way to measure its Young's modulus. This geometry provides a simple analog to micro-pipette aspiration that can be implemented using microfluidic channels. Using a single layer microfluidic chip with a bypass line microgels are trapped and forced into a narrow constriction. PIV is used to measure the amount of flow passing in the bypass and through-pass channels. The ratio of these flow rates provides a measurement of the resistance of the hydrogel to flow as it is squeezed through the slit. The deformation of the soft particle is also measured, thus providing a relationship between the forcing pressure and deformation for different elastic properties and particle and slit sizes. These measurements are collapsed onto a master curve by comparing with a Herzian contact model for a rectangular hold, which yields a value of the elastic modulus of the particles.