Dynamics of vesicle suspension in shear flow between walls by digital holographic microscopy with a spatially reduced coherent source

Abstract

Digital Holographic Microscopy (DHM) is a powerful tool that strongly increases the field of investigation of classical microscopy. It allows to be used as phase contrast microscopy with the additional information of the z position over a whole experimental volume by acquiring a single frame. The use of a spatially reduced coherent source strongly reduces the coherent noise.Vesicles are close lipid membranes enclosing a sugar-water solution. Those biomimetic deformable objects are good mechanical models of living cells such as Red Blood Cells. We investigate the dynamics of a vesicle suspension in shear flow between walls (with a gap of about 200 µm). When vesicles are placed in a shear flow, they undergo a lift force that pushes them away from the wall until they reach the centre of the channel where the effects of both walls are compensated. On the other hand, hydrodynamical interactions between vesicles and segregation effects tend to push small vesicles away from the centre of the channel. The final distribution is thus a compromise between both effects that structures the distribution and has strong impact on rheology.DHM with reduced coherence and specific related algorithms (phase compensation, best focus plane determination, segmentation, …) provide a full description of each object in the experimental volume as a function of their size and shape. Results are provided and illustrate the quantification of the lift force and the hydrodynamical interactions (shear induced diffusion).

Heterodyne Near Field Speckles: from laser light to X-rays

“…In this regard, applications to digital holographic microscopy are worth mentioning, where partially coherent illumination effectively suppresses the coherent speckled noise inherent in laser sources, as well as multiple reflection fringes [143][144][145][146][147][148][149][150][151][152]. This is definitely an asset for applications such as improved three-dimensional imaging [143], pattern recognition [144], three-dimensional particle flow analysis [146], characterization of deformable objects [147] and studies of vesicle suspensions in shear flow [150], to name a few. Digital holographic microscopy with partially coherent illumination has been originally demonstrated with filtered white LEDs [143].…”