Analyzing the impact of pulsatile flow on drug release from a single strut of a drug-eluting stent.

In this study, in-vitro experiments were performed to investigate the drug release from a single strut of a drug-eluting stent with respect to the systolic-diastolic flow and the continuous flow. Regarding, a test bench comprising a single strut and agarose gel as an arterial wall model was designed. The model chosen represents a large-scaled strut of a stent, to limit the effect of the geometrical shape of the stents on the drug release results. The comparison is carried out between two continuous flow rates and a systolic-diastolic flow pattern varying between these two flow rates, with a frequency of 70 beats per minute. The stent model is a polylactic-co-glycolic acid film (50:50) loaded with 10 % diclofenac sodium. A compartment of agarose gel (1 %) and a phosphate-buffered saline solution at 37 °C are employed to mimic the arterial wall and the blood, respectively. Our results show the importance of flow type on the drug release from the stent and distribution of drug in the hydrogel, such that the pulsatility promotes an increase in the quantity of drug absorbed into the hydrogel.

Highly-repeatable generation of very small nanoparticles by pulsed-laser ablation in liquids of a high-speed rotating target.

By irradiating a cylindrical silver target rotated at a high-speed within the range 300-2400 rpm (lateral speed 0.16-1.25 m s-1) in pure water, we prepare ligand-free Ag nanoparticles (NPs) with a size of 4 ± 2 nm which are likely to be primary particles. Usually, the generation of NPs showing such a small size requires either a laser post-treatment and/or chemical additives. As the rotation rate of the target is increased, calculated 3D flow patterns revealed different hydrodynamic regimes which clearly influence the ablation rate and repeatability of the process as well as the colloidal properties. In addition to revealing the importance of fluid dynamics in pulsed-laser ablations in liquids, this study provides a way for producing in one step pure NPs with sizes below 5 nm which are suitable for applications in catalysis.

New procedure to measure simultaneously the surface tension and contact angle.

This paper proposes a new procedure to simultaneously measure the static contact angle and the surface tension of a liquid using a spherical geometry. Unlike the other existing methods, the knowledge of one of both previous parameters and the displacement of the sphere are not mandatory. The technique is based on the measurement of two simple physical quantities: the height of the meniscus formed on a sphere at the very contact with a liquid bath and the resulting vertical force exerted on this object at equilibrium. The meniscus height, whose exact value requires the numerical resolution of the Laplace equation, is often estimated with an approximate 2D model, valid only for very large spheres compared to the capillary length. We develop instead another simplified solution of the Young-Laplace equation based on the work of Ferguson for the meniscus on a cylinder and adapted for the spherical shape. This alternative model, which is less restrictive in terms of the sphere size, is successfully compared to numerical solutions of the complete Young-Laplace equation. It appears to be accurate for sphere radii larger than only two capillary lengths. Finally the feasibility of the method is experimentally tested and validated for three common liquids and two "small" steel spheres.

Levitating spherical particle in a slightly tapered tube at low Reynolds numbers: application to the low-flow rate rotameters.

In this study, a theoretical framework is developed to predict the equilibrium conditions of a non-neutrally buoyant sphere placed in a vertical conical tube as encountered in liquid rotameters. The analysis presented herein is applicable for a sphere heavier than the surrounding fluid, situated on the axis of a slightly tapered tube. The sphere is subject to the laminar flow conditions with the Reynolds numbers ranging between the Stokes type regimes up to values corresponding to slightly inertial regimes. In this work, we assume that the aperture angle of the tube is small and that the drag force is mainly due to the dissipation located in the gap between the tube and the sphere. Under these conditions, it is possible to consider the tube as locally cylindrical and we can use the results previously obtained for the correction factor of the Stokes force on a sphere subject to a Poiseuille flow in a tube of constant cross-section. We obtain an equation relating the flow rate to the vertical position of the sphere in the tube and the validity of this analysis is demonstrated by applying it to a commercially available rotameter. The present study provides a simple but sound theoretical method to calibrate such flowmeters.