Experimental Resonances in Viscoelastic Microfluidics

Abstract

Pulsatile flows of viscoelastic fluids are very important for lab-on-a-chip devices, because most biofluids have viscoelastic character and respond distinctively to different periodic forcing. They are also very important for organ-on-a-chip devices, where the natural mechanical conditions of cells are emulated. The resonance frequency of a fluid refers to a particular pulsatile periodicity of the pressure gradient that maximizes the amplitude of flow velocity. For viscoelastic fluids, this one has been measured experimentally only at macroscales, since fine tuning of rheological properties and system size is needed to observe it at microscales. We study the dynamics of a pulsatile (zero-mean flow) fluid slug formed by a viscoelastic fluid bounded by two air-fluid interfaces, in a microchannel of polymethyl methacrylate. We drive the fluid slug by a single-mode periodic pressure drop, imposed by a piezoactuator. We use three biocompatible polymer solutions of polyethylene oxide as model viscoelastic fluids, and find resonances. We propose a model accounting for surface tension and fluid viscoelasticity that has an excellent agreement with our experimental findings. It also provides an alternative way of measuring relaxation times. We validate the method with parameters reported in the literature for two of the solutions, and estimate the relaxation time for the third one.

Numerical Study of the Time–Periodic Electroosmotic Flow of Viscoelastic Fluid through a Short Constriction Microchannel

“…Moreover, in the study of Collepardo and Poire [68], the resonance frequency of Maxwell fluid was found to shift with the change in obstructions. In the experimental study of Pamela et al [69], the resonance frequency of viscoelastic fluids was dependent on the magnitude of the pressure drop. Therefore, the characteristic frequency for the viscoelastic EOF is expected to shift with the changes in the fluid properties and the flow geometry.…”

“…[66]. Although limited studies have been performed for the electroosmotic flow, the resonance frequency of the viscoelastic flow has been studied in pressure-driven flow both analytically and experimentally [67][68][69], where the resonance frequency was defined as the frequency under which the flow showed the highest dynamic permeability based on observation. However, due to the complexity of viscoelastic fluids, and the mostly used confined flow condition, no general method for the direct prediction of the resonance frequency of the viscoelastic flow has been proposed.…”

Hemodynamics Challenges for the Navigation of Medical Microbots for the Treatment of CVDs

“…They typically control the time-varying pressure gradient [ 69 ] or flow rate [ 70 ] and analyze the velocity profiles as a function of the pulsation phase and the pressure/flow profiles. With the advent of microfluidics, the number of experimental studies considering pulsating flows of viscoelastic flows has rocketed, due to the increasing number of applications that use this type of motion, such as chemical synthesis inside microfluidic channels, liquid–liquid extraction, mixing by oscillatory cross flow, cooling of microelectronic circuits by micro-oscillating heat pipes, inertial focusing of particles of a few microns, DNA elongation studies, or studies of the oscillatory movement of liquid plugs displaced by air in microchannels as model pulmonary flows [ 71 ]. It is also at the microscale where the elastic forces are enhanced due to the small scale [ 72 ].…”

Pulsatile parallel flow of air and a viscoelastic fluid with multiple characteristic times. An application to mucus in the trachea and the frequency of cough

“…For single fluids, resonances have been reported experimentally at macroscales almost two decades ago [29,30]. Recently, the zero-mean flow, pulsatile dynamics of a fluid slug, consisting of a Newtonian [31] or a viscoelastic [32] fluid and two air-fluid interfaces, driven by a periodic pressure gradient in a rectangular microchannel, has been studied theoretically and validated experimentally. The dynamic permeability of both systems presents resonances, due to the presence of elastic elements.…”