Spinning elastic beads: a route for simultaneous measurements of the shear modulus and the interfacial energy of soft materials.

Large deformations of soft elastic beads spinning at high angular velocity in a denser background fluid are investigated theoretically, numerically, and experimentally using millimeter-size polyacrylamide hydrogel particles introduced in a spinning drop tensiometer. We determine the equilibrium shapes of the beads from the competition between the centrifugal force and the restoring elastic and surface forces. Considering the beads as neo-Hookean up to large deformations, we show that their elastic modulus and interfacial energy constant can be simultaneously deduced from their equilibrium shape. Also, our results provide further support to the scenario in which interfacial energy and interfacial tension coincide for amorphous polymer gels.

Spinning Drop Dynamics in Miscible and Immiscible Environments.

We report on the extensional dynamics of spinning drops in miscible and immiscible background fluids following a rotational speed jump. Two radically different behaviors are observed. Drops in immiscible environments relax exponentially to their equilibrium shape, with a relaxation time that does not depend on the centrifugal force. We find an excellent quantitative agreement with the relaxation time predicted for quasi-spherical drops by Stone and Bush (Q. Appl. Math. 1996, 54, 551), while other models proposed in the literature fail to capture our data. By contrast, drops immersed in a miscible background fluid do not relax to a steady shape: they elongate indefinitely, their length following a power-law l(t)∼t2/5 in very good agreement with the dynamics predicted by Lister and Stone (J. Fluid Mech. 1996, 317, 275) for inviscid drops. Our results strongly suggest that low compositional gradients in miscible fluids do not give rise to an effective interfacial tension measurable by spinning drop tensiometry.

Postprocedural management of patients after transcatheter aortic valve implantation procedure with self-expanding bioprosthesis.

BACKGROUND: Transcatheter aortic valve implantation (TAVI) carries higher risk of post-procedural adverse events than conventional percutaneous cardiovascular interventions. We report our experience about postoperative management protocol adopted in our Division. METHODS: One hundred and ten patients underwent TAVI and 108 were transferred to the cardiac intensive care unit (CICU) after procedure. During the first 48 hours, vital parameters were monitored continuously. Close attention was given to rhythm and atrio-ventricular conduction disturbances, systemic blood pressure, fluid balance and vascular accesses. RESULTS: The most common complications were renal impairment (21.3%), femoral artery pseudo-aneurysms (FAP) (11%), new complete atrioventricular block (20.3 %), cerebral vascular accident (4.5%) and cardiac perforation due to temporary pacemaker lead (1.8%). Ultrasound-guided compression repair was considered the first line treatment for FAP, but in 6 cases surgical treatment was immediately performed due to the rapid expansion of FAP. Complete atrio-ventricular block occurred in 22 patients (20.3 %) within the first 24 hours after TAVI and a permanent pacemaker was implanted in 21 patients (19.1%). Acute kidney injury occurred in 18 patients (35%) with pre-procedural chronic renal failure and in 5 patients (9%) without preoperative renal dysfunction. CONCLUSIONS: After TAVI, cardiovascular complications are common and therefore accurate standardized management of patients in CICU during the first 48 hours is mandatory to early detect and manage complications and to decrease the rate of adverse events and the length of in-hospital stay. © 2010 Wiley-Liss, Inc.