Genetically encodable gas-filled particles, known as gas vesicles (GVs), have shown promise as a biomolecular contrast agent for ultrasound imaging and have the potential to be used as cavitation nuclei for ultrasound therapy. In this study, we used passive acoustic mapping techniques to characterize GV-seeded cavitation, utilizing 0.5 and 1.6 MHz ultrasound insonation over peak rarefactional pressures ranging from 100 to 2200 kPa. We found that GVs produce cavitation for the duration of the first applied pulse, up to at least 5000 cycles, but that bubble activity diminishes rapidly over subsequent pulses. At 0.5 MHz, the frequency content of cavitation emissions was predominantly broadband in nature, while at 1.6 MHz, narrowband content at harmonics of the main excitation frequency dominated. Simulations and high-speed camera imaging suggest that the received cavitation emissions come not from individual GVs but instead from the coalescence of GV-released gas into larger bubbles during the applied ultrasound pulse. These results will aid the future development of GVs as cavitation nuclei in ultrasound therapy.
We present simulation results for the Donnan equilibrium between a homogeneous bulk reservoir and inhomogeneous confining geometries with varying number of restricted dimensions, d c. Planar slits (d c = 1), cylindrical pores (d c = 2), and spherical cavities (d c = 3) are considered. The walls have a negative surface charge density. Because different dielectric constants are used in the reservoir and confined system, we used the Donnan grand canonical Monte Carlo method [Boda and Gillespie, J. Mol. Liq. 391, 123372 (2023)] to simulate the equilibrium. The systems with larger confining dimensionality produce greater adsorption of counterions (cations) into the confinements, so cation selectivity increases with increasing dimensionality. The systems with smaller dielectric constants produce more effective coion (anion) exclusion, so cation selectivity increases with decreasing dielectric constant. The combined effect of a more confining space and solvation penalty produces even more efficient anion exclusion and cation selectivity than each separately.
Diffusive adsorption/association is a fundamental step in almost all chemical reactions in diluted solutions, such as organic synthesis, polymerization, self-assembly, biomolecular interactions, electrode dynamics, catalysis, chromatography, air and water environmental dynamics, and social and market dynamics. However, predicting the rate of such a reaction is challenging using the equations established over 100 years ago. Several orders of magnitude differences between the theoretical predictions and experimental measurements for various systems, from self-assembled monolayers to protein-protein aggregations, make such calculations meaningless in many situations. I believe the major problem is that the time-dependent evolution curve of Fick's gradient is an ideal assumption in most cases, and its slope is significantly overestimated. This paper digs into Fick's gradient problem for 3D cases and provides a solution using the single-molecule diffusion probability density function discretely.
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