Dynamic micropipette aspiration rheometry

Abstract

Pipette aspiration is widely used to probe the mechanics of viscoelastic materials such as vesicles, emulsions, and living cells. Here, we implement micropipette aspiration rheometry based on piezoelectric pressure control in a conventional glass-pipette setup. We characterize its dynamic response over a wide range of pressures and frequencies. We describe the aspiration of viscoelastic liquids and solids using theoretical formulations based on modified Kelvin-Voigt models that combine springs and dashpots. The corresponding elastic and dissipative parameters are derived from scaling laws in polymer physics and viscoelasticity. This enables measurement of elastic moduli of gels from 0.1 kPa to 3 MPa and interfacial tensions in aqueous two-phase systems down to 20 μN m−1. Computer control of pressure also allows programming of arbitrary pressure sweeps. Using oscillatory pressures, we also extract frequency-dependent elastic and viscous properties. The piezoelectric control of pressure hence allows dynamic micropipette aspiration rheometry, broadening the applicability of pipette aspiration.