Massimiliano M. Villone

Dynamics of prolate spheroidal elastic particles in confined shear flow

We investigate through numerical simulations the dynamics of a neo-Hookean elastic prolate spheroid suspended in a Newtonian fluid under shear flow. Both initial orientations of the particle within and outside the shear plane and both unbounded and confined flow geometries are considered. In unbounded flow, when the particle starts on the shear plane, two stable regimes of motion are found, i.e., trembling, where the particle shape periodically elongates and compresses in the shear plane and the angle between its major semiaxis and the flow direction oscillates around a positive mean value, and tumbling, where the particle shape periodically changes and its major axis performs complete revolutions around the vorticity axis. When the particle is initially oriented out of the shear plane, more complex dynamics arise. Geometric confinement of the particle between the moving walls also influences its deformation and regime of motion. In addition, when the particle is initially located in an asymmetric position with respect to the moving walls, particle lateral migration is detected. The effects on the particle dynamics of the geometric and physical parameters that rule the system are investigated.

Numerical simulations of linear viscoelasticity of monodisperse emulsions of Newtonian drops in a Newtonian fluid from dilute to concentrated regime

The bulk viscoelastic properties of monodisperse emulsions of Newtonian drops in a Newtonian matrix subjected to small amplitude oscillatory shear (SAOS) flow are investigated by means of arbitrary Lagrangian Eulerian finite element method 3D numerical simulations. Volume fractions of the suspended phase from the dilute to the concentrated regime (up to 30 %), and a range of several orders of magnitude of the drops-to-matrix viscosity ratio and of the frequency of the oscillatory flow are examined; the eventual presence of slip between the two fluids is also considered. The computational results are compared with theory, yielding a quantitative agreement with Oldroyd (Proc R Soc Lond A 218:122–132, 1953) predictions in a wide range of values of the considered parameters, even well beyond the dilute regime, and also in the cases with slip.

Elasticity in Bubble Rupture

When a Newtonian bubble ruptures, the film retraction dynamics is controlled by the interplay of surface, inertial, and viscous forces. In case a viscoelastic liquid is considered, the scenario is enriched by the appearance of a new significant contribution, namely, the elastic force. In this paper, we investigate experimentally the retraction of viscoelastic bubbles inflated at different blowing rates, showing that the amount of elastic energy stored by the liquid film enclosing the bubble depends on the inflation history and in turn affects the velocity of film retraction when the bubble is punctured. Several viscoelastic liquids are considered. We also perform direct numerical simulations to support the experimental findings. Finally, we develop a simple heuristic model able to interpret the physical mechanism underlying the process.

Recent Advancements and Perspective About Digital Holography: A Super-Tool in Biomedical and Bioengineering Fields

Digital holographic microscopy (DHM) has become a technique utilized widely for sample inspection, having many applications in different fields of science and technology. The capability for recovering the complex amplitude distribution scattered by the sample permits numerical refocus after acquisition and quantitative phase imaging. These are two of the features that make DHM a very versatile microscopy technique. The standard DHM system is based on a Mach–Zehnder interferometer that can be configured for operating in transmission or reflection modes, working in either the in-line or off-axis architecture. With the benefit of such special characteristics, DHM is used in basic research as much in the industry. Here we review some of the recent advancements for the label-free inspection of biological samples and the study of thin films.

Tomographic flow cytometry of circulating human breast adenocarcinoma cells

We demonstrate the non-invasive investigation of circulating human breast adenocarcinoma cells in microfluidic environment by implementing the full-angle tomographic phase microscopy (TPM). The proposed approach lies in a completely passive optical system, i.e. avoiding mechanical scanning or multi-direction probing of the sample and exploiting the engineered rolling of cells while they are flowing along a microfluidic channel.

Particle manipulation through polymer solutions in microfluidic processes

Manipulation of particles suspended in fluids flowing in microfluidic channels is required in a variety of biological, diagnostic and therapeutic applications. For instance, alignment of particles into a tight stream is a necessary step prior to counting, detecting, and sorting. Generally, this task is accomplished by using a Newtonian fluid as suspending medium and by properly fabricating a complex device aimed to displace particle trajectories. In the last years, however, the use of polymeric liquids in microfluidic processes has received a growing interest. Indeed, the addition of a small amount of polymer in a Newtonian suspension flowing in a channel promotes “internal” forces that can be exploited to manipulate the trajectories of suspended particles in simple devices. In this work, we show the possibility to align particles in simple square-shaped microfluidic channels by exploiting viscoelastic forces in flowing suspending liquids. Experiments have been performed to investigate the effect of the channel length, flow rate, confinement ratio (i.e., the ratio between the particle and channel size) and fluid rheology on the particle alignment. Finally, we present experimental results where particle alignment induced by fluid viscoelasticity is combined with magnetophoresis to deflect magnetic beads in a H-shaped channel. High-efficiency separation of magnetic and non-magnetic beads is demonstrated.Manipulation of particles suspended in fluids flowing in microfluidic channels is required in a variety of biological, diagnostic and therapeutic applications. For instance, alignment of particles into a tight stream is a necessary step prior to counting, detecting, and sorting. Generally, this task is accomplished by using a Newtonian fluid as suspending medium and by properly fabricating a complex device aimed to displace particle trajectories. In the last years, however, the use of polymeric liquids in microfluidic processes has received a growing interest. Indeed, the addition of a small amount of polymer in a Newtonian suspension flowing in a channel promotes “internal” forces that can be exploited to manipulate the trajectories of suspended particles in simple devices. In this work, we show the possibility to align particles in simple square-shaped microfluidic channels by exploiting viscoelastic forces in flowing suspending liquids. Experiments have been performed to investigate the effect of the c...