Stabilization of Gas Bubbles Released from Water-Soluble Carbohydrates Using Amphiphilic Compounds: Preparation of Formulations and Acoustic Monitoring of Bubble Lifetime
The ultrasound contrast agents Echovist® and Levovist® (Bayer AG, Schering AG, Germany) are based on the release of gas bubbles from milled α-d-galactose. In diagnostic ultrasound, for this class of contrast agents, there is a need for prolonged contrast duration. To investigate if new carbohydrate compositions could prolong the lifetime of the gas bubbles, α-d-galactose was mixed with other carbohydrates or amphiphiles with varying log P. Acoustic attenuation vs. time (390 s) area under the curve (A390) and bubble half-time (t½) were used as measures of prolonged lifetime of gas bubbles. The products, to which 0.1% of a lipophilic carboxylic acid (5β-cholanic acid, behenic acid, and melissic acid) has been added, showed more than 5, 7 and 11 times enhancement of A390, respectively, compared with the reference compound 2 (RC2) corresponding to the commercial product Levovist®. The half-time t ½ of the same compounds was prolonged more than 6 times compared with RC2. A partial least square (PLS) statistical analysis confirmed that, for additives, high log P carboxylic acids lead to the highest A390. The present results bear a promise of products with a more persistent in vivo ultrasound contrast effect than the commercially available agents.
Nanobubbles in water - how to identify them and why they are stable
Gas bubbles smaller than 1 micrometer in water, commonly referred to as nanobubbles, is a growing field of research and innovation. Applications range from medical imaging and drug delivery to mining industry and environmental remediation. There are many possibilities but important questions remain – how is it possible for small gas bubbles to be stable against dissolution and how can they be detected and differentiated from solid particles and oil droplets ? In this work we demonstrate that several common nanobubble generation methods can generate contamination particles which can be mistaken for bubbles and that with sufficient cleanliness, neither particles, droplets or bubbles are generated. Theories on nanobubble stability that does not include impurities can thus be dismissed. (Paper 1). Lipid stabilization and the dynamic equilibrium model based on hydrophobic dirt particles appear to be the only valid models for nanobubble stability at present. We furthermore demonstrate Holographic Nanoparticle Tracking Analysis (H-NTA) as a powerful new method to detect and differentiate between nanobubbles and nanoparticles in the same solution (Paper 2). As H-NTA determines the refractive index of tracked objects, bubbles will differ very significantly from solid particles or oil droplets. The refractive index of a bubble also indicates the amount of adsorbed material as well as possible clustering of multiple bubbles. The method also powerfully enables detection of different particle populationsclose in size and refractive index in a dispersion. The size range is 0.3-0.4 mm to 1.5 mm.
Numerical Simulation of Thermal Sensitivity for Explosives
In order to compare the thermal sensitivity of several typical explosives, this article solved numerically one-dimensional transient heat conduction equation including thermal decomposition for explosives with finite difference method. The explicit difference equations under different boundary conditions were established, and the corresponding stability criterion was derived. The ignition times for typical explosives were calculated, which was used to evaluate thermal sensitivity of explosives.