Fluorous-phase iron oxide nanoparticles as enhancers of acoustic droplet vaporization of perfluorocarbons with supra-physiologic boiling point
Alexander VezeridisCaroline de Gracia LuxSarah A. BarnhillSejung KimZhe WuSungho JinJacques LuxNathan C. GianneschiRobert F. Mattrey
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Vaporization
Thermogravimetric analysis
Iron oxide nanoparticles
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Journal of the Chemical Society Faraday Transactions 1 Physical Chemistry in Condensed Phases (1979)
The size and aggregation number of reversed micelles formed by the system aerosol-OT + H2O + organic solvent have been determined by viscosity and dynamic light scattering methods. For the viscosity method, a procedure for deriving values of the aggregation number from particles of variable density is described. Measurements were made in cyclohexane, toluene and chlorobenzene. The dynamic light scattering method, based on photon correlation spectroscopy, yields single exponential correlation functions from which values of the translational diffusion coefficient and the micelle radius can be derived. The droplet size was found to depend primarily on the ratio of surfactant to water concentrations, but was essentially independent of solvent and concentration at a fixed surfactant to water concentration ratio. Satisfactory agreement was obtained among the two methods discussed in this paper and one (sedimentation ultracentrifugation) described previously.
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Abstract Dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) are widely used to determine the size of biological nanoparticles in liquid. In both cases, one first measures the nanoparticle diffusion coefficient and then converts it to the nanoparticle radius via the Stokes-Einstein relation. This relation is based on the no-slip boundary condition. Now, there is evidence that this condition can be violated in biologically relevant cases (e.g., for vesicles) and that in such situations the partial-slip boundary condition is more suitable. I show (i) how the latter condition can be employed in the context of DLS and NTA and (ii) that the use of the former condition may result in underestimation of the nanoparticle radius by about 10 nm compared with the nominal one.
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We investigate micellar aggregates of amphiphilic block terpolymers, polybutadiene-block-poly(2-vinyl pyridine)-block-poly(methacrylic acid) (PB800P2VP190PMAA550) and their quaternized analogues polybutadiene-block-poly(N-methyl-2-vinylpyridinium)-block-poly(methacrylic acid) (PB800P2VPq190PMAA550) in aqueous solution using light scattering (DLS, SLS) and cryogenic transmission electron microscopy (cryo-TEM). At high pH, PB800P2VP190PMAA550 forms core--shell--corona micelles with a hydrodynamic radius Rh approximately 100 nm and a continuous shell of P2VP. However, at pH 4 partial intramicellar interpolyelectrolyte complex (im-IPEC) formation between P2VP and PMAA results in a patchy, collapsed shell. This is far more pronounced for the quaternized analogue, PB800P2VPq190PMAA550, which forms aggregates of similar size, also exhibiting a noncontinuous, patchy shell. Here, these im-IPECs of the positively charged P2VPq and the partially negatively charged PMAA are present over the whole investigated pH range (4-10). We further demonstrate that size and charge of the corona can be tuned through the block terpolymer composition, in particular, the ratio between P2VPq and PMAA. These micelles are dynamic and able to react to changes in pH or salinity in terms of corona diameter and aggregation number.
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INTRODUCTION Gas-filled microbubbles were originally developed as an intravascular contrast agent to enhance backscattering in ultrasound imaging. Microbubbles possess the ability to be an MR susceptibility contrast agent due to the induction of large local magnetic susceptibility differences by the gas-liquid interface. Feasibility of microbubbles as an MR pressure sensor, based on the susceptibility change caused by pressure-induced microbubble size change, has been explored through theoretical and phantom studies. Gas-filled microbubbles have also been shown as an MR susceptibility contrast agent in vivo. However, microbubble susceptibility effect is relatively weak when compared with other intravascular MR susceptibility contrast agents. By optimizing the microbubble size distribution and choice of shell coating material and core gas, it is possible to substantially enhance the microbubble susceptibility effects and reduce the dosage requirement for MR applications. In this study, we aim to demonstrate that microbubble susceptibility effects can be improved by embedding and entrapping iron oxide nanoparticles. METHODS Synthesis of iron oxide nanoparticles embedded albumin-coated microbubbles: Iron oxide nanoparticles embedded albumin-coated microbubbles (AMB) were produced by an adapted sonication method. Briefly, 18 mg of monocrystalline iron oxide nanoparticles (MION; MGH) was added into a 5% solution of bovine serum albumin (10857, USB Corporation). The mixture was preheated to about 70C and sonicated under aseptic conditions using an ultrasound frequency of 20 kHz. Synthesis of iron oxide nanoparticles entrapped polymeric microbubbles: Iron oxide nanoparticles entrapped polymeric microbubbles (polymeric MB) were produced by an adapted double emulsion method. Briefly, 0.5g poly(D,L-lactide-co-glycolic acid 50:50, PLGA; Sigma) was dissolved in 10 mL of ethyl acetate (Sigma). 1 mL of MION solution (1.164mg/mL) was added to the polymer solution and probe sonicated for 30 s. The W/O emulsion was then poured into a 5% poly(vinyl alcohol) (PVA; Sigma) solution and homogenized for 5 min. The double (W/O)/W emulsion was then poured into a 2% isopropyl alcohol (Sigma) and stirred at room temperature for 1 hour. The capsules were collected by centrifugation, washed once with deionized water, centrifuged at 15°C for 5 min. at 3000g and the supernatant discarded. The capsules were then washed three times with hexane (Sigma). The capsules were frozen in a -80°C freezer and lyophilized using a freeze dryer to fully dry the capsules and sublime the encapsulated water. MRI and Data Analysis: All MRI experiments were performed on a 7 T Bruker MRI scanner. Microbubble phantom study was performed with 38-mm quadrature resonator for RF transmission and receiving. AMB were diluted from a well-mixed microbubble suspension to 4% volume fraction with the addition of saline, while polymeric MB were prepared by adding saline of 2 mL to 50 mg of the lyophilized powder. The microbubbles were then placed in separate 2-mL cylindrical phantom tubes. Each phantom tube was slowly warmed to room temperature and gently mixed for 2 min outside the magnet prior to MR measurements. To ensure uniform suspension of microbubbles, the phantom was then continuously stirred by rotation inside the magnet. It was then arrested in horizontal position immediately before the start of MR acquisition sequence. Apparent transverse relaxation rate enhancement (ΔR2 ) was measured by acquiring multi-echo gradient-echo (GE) signals continuously without phase encoding for 2 min from an axial 1-mm slice at middle of the phantom. The measurement was repeated six times for each microbubble phantom. The parameters were TR = 1000 ms, TE = 3.5, 7, 10.5, 14, 17.5, 21, 24.5, 28 ms, flip angle = 30o and NEX = 1. Phantom R2 * values were computed by monoexponential fitting of the peak magnitudes of the multi-echo GE signals using a software toolkit developed in MATLAB (MathWorks). Initially, there was a uniform suspension of microbubbles. As GE signals were acquired, microbubbles started to migrate upward; therefore, in the final state the microbubbles aggregated in the upper part of the tube. Microbubble induced ∆R2 * was then calculated as the difference between R2 * in the initial state and that in the final state. To demonstrate that MION were embedded and entrapped, R2 * was measured before and after cavitation, which was performed by applying ultrasound of frequency 40 kHz. R2 * maps of the suspending solutions were acquired before and after cavitation with multiple gradient echo sequences. In vivo Demonstration: Normal SD rats (~200-250 g) were injected intravenously with 0.2 mL of microbubble suspension (~4% volume fraction; N = 1 for AMB with MION and N = 1 for polymeric MB with MION) at a rate of 1.2 mL/min to avoid possible microbubble destruction due to high pressure and shear stress under femoral vein catheterization. Dynamic susceptibility weighted liver MRI was performed with respiratory-gated single-shot GE-EPI sequence under inhaled isoflurane anaesthesia using TR ≈ 1000 ms, TE = 10 ms, FA = 90o, FOV = 50 mm × 50 mm, slice thickness = 2 mm, acquisition matrix = 64 × 64, and NEX = 1. RESULTS AND DISCUSSIONS Values of R2 * were plotted against time in Figure 1 for different microbubbles. As GE signals were acquired, microbubbles started to migrate upward; therefore, in the final state values of R2 * were due to the suspending solution. The different amounts of free MION in the suspended solution accounted for the difference in the R2 * of the suspending solution. Microbubble induced ∆R2 * of different microbubbles were depicted in Figure 2. The MION embedded and entrapped would enhance the susceptibility effect and increased the values of ∆R2 *
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To evaluate Taylor dispersion analysis (TDA) as a novel method for determination of hydrodynamic radius of therapeutic peptides and proteins in non-stressed and stressed formulations and to compare it with dynamic light scattering (DLS). The hydrodynamic radius of oxytocin, bovine serum albumin, various monoclonal antibodies (type IgG) and etanercept at concentrations between 0.05 and 50 mg/ml was determined by TDA and DLS. IgGs and etanercept were stressed (elevated temperatures) and analyzed by TDA, DLS and HP-SEC. TDA and DLS were comparable in sizing non-stressed peptides and proteins in a concentration range of about 0.5 to 50 mg/ml. TDA performed well even at lower concentrations, where DLS tends to provide theoretically high values of the Z-average radius. However, because of differences in the detection physics, DLS was more weighted towards the detection of aggregates in stressed formulations than TDA. Advantageously, TDA was also able to size the small peptide oxytocin, which was not feasible by DLS. TDA allows the accurate determination of the hydrodynamic radius of peptides and proteins over a wide concentration range, with little interference from excipients present in the sample. It is marginally less sensitive than DLS in detecting size increase for stressed protein samples.
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