Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session M09: Bubbles: Cavitation and Biomedical Acoustics |
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Chair: Kausik Sarkar, George Washington University Room: Georgia World Congress Center B214 |
Tuesday, November 20, 2018 8:00AM - 8:13AM |
M09.00001: Simulation of the collapse of a vapor bubble near or attached to a rigid surface Kevin Schmidmayer, Timothy E Colonius Several applications require a detailed understanding of cavitation and bubble dynamics in and near soft materials, such as biological tissues, polymeric coatings or biofouling. Few preliminary studies highlight the dependence of the bubble dynamics on the material properties and point to the need to develop a comprehensive multiscale theory capable of accounting for physical phenomena not present in traditional hydrodynamic cavitation. However, before modeling viscoelastic effects that would allow to extend our understanding of cavitation in and near soft materials, we focus on developing accurate algorithms for bubble dynamics in water near rigid surfaces. For that purpose, two-dimensional-axi-symmetric numerical simulations of vapor-bubble collapses are performed for microbubbles near or attached to a rigid surface and different initial pressure ratio between the ambient and the vapor bubble. A mechanical-equilibrium multiphase model and an interface-capturing scheme along with an adaptive mesh refinement algorithm are used. Spatially and temporally resolved field data are shown and compared with experimental data. |
Tuesday, November 20, 2018 8:13AM - 8:26AM |
M09.00002: Modeling and validation of ultrasound-generated cavitation bubble dynamics Lauren Mancia, Jonathan Sukovich, Chad Wilson, Zhen Xu, Eric Johnsen Cavitation plays an important role in a variety of ultrasound procedures. |
Tuesday, November 20, 2018 8:26AM - 8:39AM |
M09.00003: Ultrasound-induced nonlinear oscillation of a spherical bubble in gels of different gelatin concentrations Yushi Yamakawa, Kazuya Murakami, Eric Johnsen, Keita Ando The viscoelasticity of soft tissue surrounding bubbles play an important role in bubble dynamics in the context of medical applications. In this study, we experimentally observe the (finite-amplitude) nonlinear oscillations of a spherical gas bubble in gels under 28-kHz ultrasound irradiation; we treat the gelatin concentration, the equilibrium bubble radius, and the pressure amplitude of the ultrasound as experimental parameters. A spherical bubble is generated by focusing a laser pulse into an air-supersaturated gel; the nucleated bubble shows gradual growth due to mass influx of the dissolved gas. 28-kHz ultrasound with varying its pressure amplitude is irradiated toward the bubble and resonant curves regarding the bubble oscillation amplitude as a function of the equilibrium radius are constructed. The viscosity and rigidity of the gel can be estimated from a comparison between the linearized Rayleigh--Plesset theory and the experimental result for small-amplitude oscillations. In the presentation, we will present the experimental results for finite-amplitude oscillations and compare them to the extended Rayleigh--Plesset calculations that account for nonlinear elasticity and dissipative effects that result from viscosity, compressibility, and heat and mass transfer. |
Tuesday, November 20, 2018 8:39AM - 8:52AM |
M09.00004: Non-spherical oscillations drive the ultrasound-mediated release from targeted microbubbles Guillaume Lajoinie, Ying Luan, Erik Gelderblom, Benjamin Dollet, Frits Mastik, Heleen Dewitte, Ine Lentacker, Nico de Jong, Michel Versluis Ultrasound-driven microbubbles are attractive for a variety of applications in medicine, including real-time organ perfusion imaging and targeted molecular imaging. Bubbles decorated with a functional payload become convenient transport vehicles and offer highly localized release. How to efficiently release and transport these nanomedicines to the target site remains unclear owing to the microscopic length scales and nanoseconds timescales of the process. Here, we show theoretically how non-spherical bubble oscillations lead first to local oversaturation, thereby inducing payload release, and then to microstreaming generation that initiates transport. Experimental validation is achieved through ultra-high-speed imaging in an unconventional side-view at tens of nanoseconds timescales combined with high-speed fluorescence imaging to track the release of the payload. Transport distance and intrinsic bubble behavior are quantified and agree well with the model. |
Tuesday, November 20, 2018 8:52AM - 9:05AM |
M09.00005: Simulation of cell membrane poration by single bubble acoustic cavitation Jan Felix Heyse, Sanjeeb T Bose, Gianluca Iaccarino Microbubble cavitation resulting from therapeutic ultrasound can create temporary perforations in cell membranes (referred to as sonoporation), allowing for enhanced intracellular uptake of therapeutic agents. The poration of the cell membrane then allows targeted drug delivery, and if reduced dosages can be used it could reduce side effects from drug regimens, e.g. reduce chemotoxicity effects in cancer therapies. The present investigation aims to simulate the micro-jetting observed from the insonation of a single microbubble experiencing inertial cavitation near a cell membrane, replicating the results observed in the experiment of Zhou et al. (2012). Comparisons of the microbubble dynamics to the high speed imaging of the experiment will be made. Estimates of the membrane perforation from the surface pressure loading will be made.
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Tuesday, November 20, 2018 9:05AM - 9:18AM |
M09.00006: Acoustic microstreaming due to a pulsating free or coated bubble near a wall: velocity, vorticity shear stress and closed streamlines Kausik Sarkar, Nima Mobadersany Acoustic microstreaming due to an oscillating microbubble, either coated or free, is analytically investigated. We use the classical 1958 perturbative analysis of Nyborg clarifying its underlying assumptions. The detailed flow field is obtained and the closed streamlines due to the ring vortex are plotted in both Eulerian and Lagrangian descriptions. Analytical expressions are found for the ring vortex showing that its length depends only on the separation of the microbubble from the wall and the dependence is linear. The circulation as a scalar measure of the vortex is computed quantitatively identifying its spatial location using a d2 method of vortex identification. The functional dependence of circulation on bubble separation and coating parameters was shown to be similar to that of the shear stress. The dependence of shear stress on coating parameters are explained using the underlying bubble dynamics such as its resonance. |
Tuesday, November 20, 2018 9:18AM - 9:31AM |
M09.00007: Driven bubble dynamics with coupled vaporization and non-Newtonian relaxation time scales Arpit Tiwari, Ratnesh Shukla, Jonathan Ben Freund In cavitation-based therapeutic applications, the rheological and thermodynamic properties of the surrounding generalized Newtonian fluid play a crucial role. The effects of these properties are, however, often studied in isolation. We study the influence of the interaction of non-Newtonian viscous behavior with phase transition on spherically symmetric cavitation dynamics. The overlap of time scales associated with these phenomena leads to interesting effects on bubble dynamics. In particular, during collapse in a Carreau shear thinning fluid, we report lower first minimum radii (Rmin) for a range of values of relaxation time constant (λ) compared with that obtained using the minimum viscosity value (λ approaches infinity) of the Carreau model. Rmin versus λ profile attains a minimum value in this range, where we obtain significant (up to orders of magnitude depending upon shear thinning and phase transition parameters) reduction in Rmin. |
Tuesday, November 20, 2018 9:31AM - 9:44AM |
M09.00008: Model for an encapsulated microbubble using transient network theory Bashir M. Alnajar, Fathia Arifi, Michael L. Calvisi Encapsulated microbubbles (EMBs) are widely used to enhance contrast in ultrasound sonography and are finding increasing use in biomedical therapies such as drug/gene delivery and tissue ablation. EMBs consist of a gas core surrounded by a shell made of protein, polymer, or lipid. We present a novel model for an EMB based on a statistically-based continuum theory for the encapsulating material using transient networks. The use of transient network theory provides a general framework that allows a variety of viscoelastic shell materials to be simulated, including a purely elastic solid or a viscous fluid. The model permits local stress in the shell to be calculated, and can be readily extended to modeling nonspherical EMB deformations. The model accurately reproduces the experimentally-measured radial response of an ultrasonically-driven, spherical, lipid-coated microbubble, and provides a better fit than that given by common spherical EMB models by Marmottant et al., Chatterjee and Sarkar, and Hoff. Extensions of the model to nonspherical EMB oscillations are discussed. |
Tuesday, November 20, 2018 9:44AM - 9:57AM |
M09.00009: Surface instability of a bubble during inertial collapse in soft matter Kazuya Murakami, Jonathan Sukovich, Zhen Xu, Eric Johnsen The shape of a bubble during its collapse is an important factor to predict tissue damage in therapeutic ultrasound and other medical applications. For this reason, we investigate the surface instability of a bubble during violent, inertial collapse in soft matter induced by an ultrasound pulse. The time history of mean bubble radius is obtained by the Rayleigh-Plesset type equation, where compressibility, heat diffusion and mass diffusion are taken into account to precisely predict the nonlinear bubble dynamics. In addition, we solve an equation for non-spherical mode amplitudes via one-way coupling of the mean bubble radius and determine the non-spherical bubble shape. Our analysis is compared to the experiments, in which we observe that the ultrasound pulse induces surface instability of a bubble in an agarose gel and the bubble splits into many fragments after collapsing. Finally, the viscoelastic effects of surrounding soft matter on the surface instability are quantitatively examined. |
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