Capillarity-driven dynamics of water–alcohol mixtures in nanofluidic channels

We investigated the spontaneous capillarity-driven filling of nanofluidic channels with a thickness of 6 and 16 nm using mixtures of ethanol and water of variable composition. To improve the visibility of the fluid, we embedded metal mirrors into the top and bottom walls of the channels that act as a Fabry–Pérot interferometer. The motion of propagating liquid–air menisci was monitored for various concentrations in transmission with an optical microscope. In spite of the visible effects of surface roughness and different affinity of water and ethanol to the channel walls, the dynamics followed the classical t 1/2—dependence according to Lucas and Washburn. While the prefactor of this algebraic relation falls short of the expectations based on bulk properties by 10–30%, the relative variation between mixtures of different composition follows the expectations based on the bulk surface tension and viscosity, implying that—despite the small width of the channels and the large surface-to-volume ratio—specific adsorption or chemical selectivity effects are not relevant. We briefly discuss the impact of surface roughness on our experimental results

Subharmonic Venture

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Corrigendum to "In vivo characterization of ultrasound contrast agents: microbubble spectroscopy in a chicken embryo" (Ultrasound Med Biol 2012;38:1608-1617)

The authors regret that there was a mistake in reporting the mol% of the microbubble coating composition used. For all experiments, the unit in mg/mL was utilized, and the conversion mistake occurred only when converting to mol% to define the ratio between the coating formulation components. The correct molecular weight of PEG-40 stearate is 2046.54 g/mol (Shen et al. 2008; Kilic and Bolukcu 2018), not 328.53 g/mol. On page 1610, the sentence should read “The coating was composed of DSPC (84.8 mol%; P6517, Sigma-Aldrich, Zwijndrecht, The Netherlands); PEG-40 stearate (8.2 mol%; P3440, Sigma-Aldrich); DSPE-PEG(2000) (5.9 mol%; 880125P, Avanti Polar Lipids, Alabaster, AL, USA); and DSPE-PEG(2000)-biotin (1.1 mol%; 880129C, Avanti Polar Lipids).” This correction does not change the conclusions published in this work. The authors apologize for any inconvenience caused

Characterizing the subharmonic response of phospholipid-coated microbubbles for carotid imaging

The subharmonic vibration of BR14 (Bracco Research S.A., Geneva, Switzerland) contrast agent microbubbles is investigated within the preferable frequency range for carotid ultrasound imaging (8–12 MHz). The response of the bubbles was recorded optically with an ultra-fast recording camera (Brandaris 128) at three acoustic pressures (50, 100 and 120 kPa). The vibration of the microbubbles was measured as a function of the excitation frequency and its frequency content was determined. Among 390 recordings, 40% showed subharmonic oscillations. It was observed that for smaller microbubbles (diameter < 3 μm) the frequency of the maximum subharmonic response increases for increasing pressures (shell hardening) opposite to what has been reported for larger microbubbles (3 μm < diameter < 15 μm). These findings are well predicted by the model proposed by Marmottant et al. (2005) after including the dilatational shell viscosity of the microbubbles measured by Van der Meer et al. (2007), which indicates a marked shear-thinning behavior of the phospholipid shel

Optical characterization of individual liposome-loaded microbubbles

Newly developed liposome-loaded (LPS) microbubbles are characterized by comparing their oscillating response with standard phospholipid-coated (bare) microbubbles using the ultra-high speed imaging (Brandaris 128) camera. A study of the shell properties indicate nearly the same shell elasticity and a higher shell viscosity for LPS bubbles than for bare bubbles. A frequency and pressure-dependent bubble acoustical behavior study shows a higher threshold for the initiation of bubble vibrations for LPS bubbles. In addition, an “expansion-only” behavior was observed for up to 69% of the investigated LPS bubbles which mostly occurred at lower acoustic pressures (≤30 kPa). Liposome attachment stability were studied using fluorescence imaging. The internal relationship among morphological structure, shell properties and ultrasonic behavior of LPS bubbles by optical characterization facilitate preclinical study and clinical application of LPS bubbles in ultrasound triggered drug delivery system.Newly developed liposome-loaded (LPS) microbubbles are characterized by comparing their oscillating response with standard phospholipid-coated (bare) microbubbles using the ultra-high speed imaging (Brandaris 128) camera. A study of the shell properties indicate nearly the same shell elasticity and a higher shell viscosity for LPS bubbles than for bare bubbles. A frequency and pressure-dependent bubble acoustical behavior study shows a higher threshold for the initiation of bubble vibrations for LPS bubbles. In addition, an “expansion-only” behavior was observed for up to 69% of the investigated LPS bubbles which mostly occurred at lower acoustic pressures (≤30 kPa). Liposome attachment stability were studied using fluorescence imaging. The internal relationship among morphological structure, shell properties and ultrasonic behavior of LPS bubbles by optical characterization facilitate preclinical study and clinical application of LPS bubbles in ultrasound triggered drug delivery system

Characterization of Definity™ Ultrasound Contrast Agent at Frequency Range of 5–15 MHz

The status of vasa vasorum, which can be imaged using ultrasound contrast agents, is an indication for the progression of atherosclerosis. The preferred ultrasound frequency for this purpose is between 5 and 15 MHz. Therefore, it is essential to have knowledge about the acoustic properties of microbubbles such as elasticity and viscosity to be able to implement the current models for lipid encapsulated microbubbles developed for frequencies used in precordial imaging. In this study, the shell parameters, stiffness Sp and friction Sf, of Definity™ microbubbles have been calculated at frequency range of 5–15 MHz by comparing the theoretical modeling of acoustic bubble response and experimental measurements. Derived parameters are in good agreement with previous estimations on SonoVue™ and Sonazoid™ contrast agent. However, the value of Sf is higher than previously estimated for Definity™ between 12–28 MHz

Dynamic manipulation of the subharmonic scattering of phospholipid-coated microbubbles \ud

In this paper, the influence of a dynamic variation in the ambient pressure on the subharmonic response of phospholipid-coated microbubbles was investigated. The ambient pressure in water was modulated by a 2.5 kHz acoustic wave with a peak amplitude of 15 kPa. We investigated the fundamental and subharmonic emissions at two driving frequencies: 5 and 10 MHz. The modulation of the bubble radius induced by the dynamic variation in the liquid ambient pressure subsequently causes modulations of the scattered acoustic pressure at the fundamental and subharmonic frequencies (half the fundamental frequency). As a first result, we measured that the variation in the ambient pressure of 15 kPa can modulate the subharmonic amplitude up to 10 dB as compared to the static atmospheric pressure condition. As a second result, we noticed that the relative subharmonic amplitude modulation as a function of the LF acoustic pressure was symmetrical for the 5 MHz driving frequency but asymmetric for 10 MHz. In the latter case, the subharmonic amplitude was more enhanced for an ambient overpressure than reduced for an ambient depression of the same amplitude likely due to the buckling of the lipid shell. However, the fundamental amplitude was symmetrically modulated during bubble compression and expansion. Moreover, subharmonic and fundamental amplitude modulations were found to be either in phase or out of phase with the low-frequency acoustic pressure. Numerical simulations showed that this behavior can be obtained depending on the bubbles' diameter. The highest subharmonic amplitude was measured when microbubbles were insonified at 10 MHz. This fact together with the asymmetry observed in the subharmonic modulation suggests that smaller bubbles with a buckling shell are excited at 10 MHz compared to 5 MHz. These results present new potentials for in vitro characterization of contrast agent microbubbles and possibly a new imaging modalit