Dispersed Nanodroplets Research Articles

Spatiotemporal Distribution of Nanodroplet Vaporization in a Proton Beam Using Real-Time Ultrasound Imaging for Range Verification.

The potential of proton therapy to improve the conformity of the delivered dose to the tumor volume is currently limited by range uncertainties. Injectable superheated nanodroplets have recently been proposed for ultrasound-based in vivo range verification, as these vaporize into echogenic microbubbles on proton irradiation. In previous studies, offline ultrasound images of phantoms with dispersed nanodroplets were acquired after irradiation, relating the induced vaporization profiles to the proton range. However, the aforementioned method did not enable the counting of individual vaporization events, and offline imaging cannot provide real-time feedback. In this study, we overcame these limitations using high-frame-rate ultrasound imaging with a linear array during proton irradiation of phantoms with dispersed perfluorobutane nanodroplets at 37°C and 50°C. Differential image analysis of subsequent frames allowed us to count individual vaporization events and to localize them with a resolution beyond the ultrasound diffraction limit, enabling spatial and temporal quantification of the interaction between ionizing radiation and nanodroplets. Vaporization maps were found to accurately correlate with the stopping distribution of protons (at 50°C) or secondary particles (at both temperatures). Furthermore, a linear relationship between the vaporization count and the number of incoming protons was observed. These results indicate the potential of real-time high-frame-rate contrast-enhanced ultrasound imaging for proton range verification and dosimetry.

Microfluidic preparation of various perfluorocarbon nanodroplets: Characterization and determination of acoustic droplet vaporization (ADV) threshold.

Over the last two decades, liquid perfluorocarbon nanodroplets (PFC-NDs), also known as Phase Change Contrast Agents (PCCAs), that are capable of vaporizing into gaseous echogenic microbubbles via an external stimulus, have gained much attention for diagnostic and therapeutic applications. In the present work, a microfluidic platform is evaluated for the preparation of various size-controlled nanodroplets. Here, two major lines of investigations were carried out. The first was to define the microfluidic device settings for the preparation of nanodroplets depending on the nature of the encapsulating shell such as lipids, fluorinated surfactants and PLGA biopolymers as well as the liquid perfluorocarbon core (perfluoropentane, perfluorohexane). Specifically, the effect of the microfluidic system parameters, such as total flow rate and flow rate ratio on PFC-NDs attributes including size and uniformity was assessed. Secondly, a custom-made set-up, based on echogenicity signals from produced bubbles, was designed and successfully applied to determine the Acoustic Droplet Vaporization (ADV) threshold of PFC-NDs. Finally, the influence of various formulation parameters on the vaporization outcome was investigated depending on the PFC type and the encapsulating shell composition (soft versus hard shells). This study indicates the usefulness of this novel formulation platform enabling the rapid design and optimization of narrowly dispersed nanodroplets at a reliable yield and ultimately accelerate nanomedicines development.

Manipulation of Nanodroplets via a Nonuniform Focused Acoustic Vortex

Techniques for the manipulation of nanodroplets are central to many miniaturized systems in chemical and biological research and applications. In this study, we demonstrate that the dispersed nanodroplets composed of perfluorocarbon can be manipulated to form a micron-sized elliptical aggregation via a nonuniform focused acoustic vortex, and the aggregation location can be further flexibly regulated. In addition, it is unveiled theoretically and experimentally that the fundamental mechanism for the elliptical aggregation is the nonuniform distribution of the pressure, which makes the acoustic radiation forces acting on the dispersed nanodroplets converge at a certain point. Moreover, the required acoustic droplet vaporization threshold for the nanodroplets is significantly lowered, while the generated microbubbles remain similar in size after aggregation. The findings of this study provide an alternative field of opportunities for targeted drug delivery and imaging using nanodroplet emulsions.

Nanostructured phase-changeable heat transfer fluids

AbstractCooling is one of the most important technique challenges faced by a range of diverse industries and military needs. There is an urgent need for the innovative heat transfer fluids with improved thermal properties over the currently available. This review paper discusses the concept of using phase-changeable nanoparticles to increase the effective heat capacity and the heat transfer rate of the fluid. A large amount of heat can be absorbed or released when these nanoparticles undergo phase transition from solid to liquid or liquid to gas or vice versa and, thus, enhancing the heat transfer rate. Two types of phase-change fluids are introduced: one contains liquid nanodroplets that will evaporate at elevated temperatures or solidifies at reduced temperatures, called “nanoemulsion fluids”; the other is suspensions of solid-liquid metallic phase-change nanoparticles. The material synthesis and property characterizations of these phase-changeable fluids are two main aspects of this paper. The explosive vaporization of the dispersed nanodroplets would significantly improve the heat transfer in the nanoemulsion fluid. The solid-liquid metallic phase-change nanoparticles will increase the effective heat capacity and thermal conductivity of the base fluids simultaneously. This paper also identifies the several critical issues in the phase-changeable fluids to be solved in the future.

Amphiphilic behavior of two phosphonium based ionic liquids

Solution and surface chemical behavior of two phosphonium based ionic liquids triisobutyl (methyl) phosphonium tosylate (IL-1) and trihexyl (tetradecyl) phosphonium bis 2,4,4-(trimethylpentyl)phosphinate (IL-2) have been studied. The polar IL-1 is surface active and water soluble, whereas the weakly polar IL-2 is more surface active with very low aqueous solubility. IL-1 does not form micelles but affects the micellization properties of ionic, nonionic, and zwitterionic surfactants more strongly than conventional electrolytes. IL-2 itself forms micelles and mixed micelles with Triton X-100 (TX-100) in aqueous solution. It also forms Langmuir monolayers of liquid expanded type, at the air/water interface. IL-1 can replace water in forming microemulsions with the oil isopropylmyristate (IPM), stabilized by IL-2 (surfactant)+isopropanol (IP as a co-surfactant) like the IL-1/IPM/(IL-2+IP) system. It produces a large monophasic zone in the pseudoternary phase diagram. The thermodynamics of formation of the microemulsions of IL-1 in oil (IPM) have been examined. The dimensions and the polydispersity of the dispersed nano-droplets in the microemulsions have been determined by DLS. The thermal stability of the microemulsion forming systems has also been studied. ILs studied against Sarcoma-180 cell lines have evidenced proficient anti-cancer activity of IL-1 and moderate activity of IL-2.

Dynamics of percolation and energetics of clustering of water/AOT/isooctane microemulsions in the presence of propylene glycol and its oligomers

The temperature-induced percolation of water/AOT/isooctane microemulsion systems has been studied at different concentrations of AOT in the presence of varying concentrations of mono-, di-, and tri-propylene glycols employing conductometric technique. Volume-induced percolation of these microemulsion systems as a function of temperature has also been studied using the same method. The volume-induced percolation data has been analyzed to find the threshold percolation volume fraction. The performance of the scaling equation for volume-induced percolation was tested. The results from temperature-induced percolations have been analyzed to quantify the threshold percolation temperature, performance of the scaling equation, the activation energy for the percolation process, and the thermodynamic parameters of clustering of the dispersed nanodroplets. A simple structural model has been applied in the calculation of the various parameters, i.e. aggregation number ( n), core radius ( r n ), surface number density of the surfactant molecules at the interface ( α s), and the number of droplets per unit volume. The structural parameters were rationalized in terms of the percolation temperatures for the microemulsion systems under investigation.

Physiochemical properties of water/AOT/isooctane microemulsion system in the presence of pyrrolidine derivatives and polyvinyl pyrrolidone polymers

The temperature induced percolation process of w/o microemulsion of water/AOT/isooctane system at W = [H 2O]/[AOT] = 25 in the presence of various additives, was investigated by conductivity measurements. The additives include N-methyl pyrrolidone, 2-pyrrolidone, pyrrolidine and polyvinyl pyrrolidone polymers of varying molecular masses. The results were analysed by employing a Sigmoidol-Boltzmann equation (SBE) to obtain the percolation temperatures ( θ t) and other related parameters (In σ i and ln σ f). The data were also analysed to quantify the percolation temperature, scaling equation parameters (n, ln P) and the activation energy of percolation (Ep). Thermodynamic analysis of the energetics of percolation revealed that the clustering process of the dispersed nanodroplets in the presence of additives is enthalpically driven.

Physicochemical Studies on Microemulsions. 8. The Effects of Aromatic Methoxy Hydrotropes on Droplet Clustering and Understanding of the Dynamics of Conductance Percolation in Water/Oil Microemulsion Systems

The temperature-induced dynamic percolation of water/oil (w/o) microemulsions (water/AOT/heptane, water/AOT/octane, and water/AOT/decane) has been studied in the presence of hydrotropes (2-methoxy phenol, 4-methoxy phenol, 5-methoxy resorcinol, and 3-methoxy catechol). The results have been analyzed (1) to estimate the threshold percolation temperature, (2) to test the performance of the scaling equation, (3) to obtain the activation energy for the percolation process, and (4) to assess the thermodynamics of clustering of the dispersed nanodroplets. The influence of substitution of the methoxy group (at different positions of the phenolic moieties) on the process has been compared with their nonmethoxy analogues and analyzed in favor of “fusion−(mass transfer)−fission” mechanism of dynamic percolation. The assessment of role of the hydrophobic chain length of the hydrocarbon oil on the process of percolation has also been attempted.

Physicochemical Studies on Microemulsions. 7. Dynamics of Percolation and Energetics of Clustering in Water/AOT/Isooctane and Water/AOT/Decane w/o Microemulsions in Presence of Hydrotopes (Sodium Salicylate, α-Naphthol, β-Naphthol, Resorcinol, Catechol, Hydroquinone, Pyrogallol and Urea) and Bile Salt (Sodium Cholate)

The temperature induced percolation of w/o microemulsions (water/AOT/isooctane and water/AOT/decane) has been studied at different [water]/[AOT] mole ratios (ω), and in the presence of hydrotopes (sodium salicylate, α-naphthol, β-naphthol, resorcinol, catechol, hydroquinone, pyrogallol, urea) and the bile salt sodium cholate. The results have been analyzed to quantify the threshold percolation temperature, performance of the Scaling equation, the activation energy for the percolation process, and the thermodynamics of the clustering of the dispersed nanodroplets. The influence of temperature and additives on the droplet dimension, the polydispersity, and the diffusion coefficient has been also investigated by the DLS studies. An attempt has been made to correlate the results with the differential activities of the hydrotopes. A possible mechanism of the varied activities of the hydrotopes is proposed.