Peter Favreau | Searcharxiv

arXiv2020

The motion of long levitating drops in tubes in an anti-Bretherton configuration

In his seminal paper, Bretherton [J. Fluid Mech., 10:166 (1961)] studied the motion of long bubbles in capillary tubes, a situation encountered in many two-phase flow systems. Here, we unveil experimentally and numerically the negative configuration, wherein a long liquid drop formed by the rupture of a liquid plug is stably transported in a capillary tube and surrounded by a flow-induced air cushion. After a careful theoretical and numerical analysis of the drop formation process, we show that the shape of the drop and lubricating air film is reminiscent of Bretherthon's calculation and can be inferred from an adapted analytical theory. This work opens tremendous perspectives for drop fast transport in microfluidic systems without walls contamination and friction.

physics.flu-dyn↗

arXiv2020

Cell selective manipulation with single beam acoustical tweezers

Acoustical tweezers open major prospects in microbiology for cells and microorganisms contactless manipulation, organization and mechanical properties testing since they are biocompatible, label-free and can exert forces several orders of magnitude larger than their optical counterpart at equivalent wave power. Yet, these tremendous perspectives have so far been hindered by the absence of selectivity of existing acoustical tweezers -- i.e., the ability to select and move objects individually -- and/or their limited resolution restricting their use to large particle manipulation only. Here, we report precise selective contactless manipulation and positioning of human cells in a standard microscopy environment, without altering their viability. Trapping forces of up to $\sim$ 200 pN are reported with less than 2 mW of driving power. The unprecedented selectivity, miniaturization and trapping force are achieved by combining holography with active materials and fabrication techniques derived from the semi-conductor industry to synthesize specific wavefields (called focused acoustical vortices) designed to produce stiff localized traps. We anticipate this work to be a starting point toward widespread applications of acoustical tweezers in fields as diverse as tissue engineering, cell mechano-transduction analysis, neural network study or mobile microorganisms imaging, for which precise manipulation and/or controlled application of stresses is mandatory.

physics.bio-ph↗