Dhiman Chatterjee

Characterization of ultrasound contrast microbubbles using in vitro experiments and viscous and viscoelastic interface models for encapsulation

Zero-thickness interface models are developed to describe the encapsulation of microbubble contrast agents. Two different rheological models of the interface, Newtonian (viscous) and viscoelastic, with rheological parameters such as surface tension, surface dilatational viscosity, and surface dilatational elasticity are presented to characterize the encapsulation. The models are applied to characterize a widely used microbubble based ultrasound contrast agent. Attenuation of ultrasound passing through a solution of contrast agent is measured. The model parameters for the contrast agent are determined by matching the linearized model dynamics with measured attenuation data. The models are investigated for its ability to match with other experiments. Specifically, model predictions are compared with scattered fundamental and subharmonic responses. Experiments and model prediction results are discussed along with those obtained using an existing model [Church, J. Acoust. Soc. Am. 97, 1510 (1995) and Hoff et al., J. Acoust. Soc. Am. 107, 2272 (2000)] of contrast agents.

Ultrasound-mediated destruction of contrast microbubbles used for medical imaging and drug delivery

Micron-size bubbles encapsulated by a stabilizing layer of surface-active materials are used in medical ultrasound imaging and drug delivery. Their destruction stimulated by ultrasound in vivo plays a critical role in both applications. We investigate the destruction process of microbubbles in a commercially available contrast agent by measuring the attenuation of ultrasound through it. The measurement is performed with single-cycle bursts from an unfocused transducer (with a center frequency of 5MHz) for varying pressure amplitudes at 50-, 100-, and 200-Hz pulse repetition frequencies (PRF) with duty cycles 0.001%, 0.002%, and 0.004%, respectively. At low excitation, the attenuation is found to increase with time. With increased excitation level, the attenuation level decreases with time, indicating destruction of microbubbles. There is a critical pressure amplitude (∼1.2MPa) for all three PRFs, below which there is no significant bubble destruction. Above the critical pressure amplitudes the rate of des...

Physics of the Interaction of Ultrasonic Excitation With Nucleate Boiling

Physics of ultrasound-assisted augmentation of saturated nucleate boiling through the interaction of multiphase fluid flow is revealed in the present work. Different regimes of influence of ultrasound, ranging from augmentation to deterioration and even no effect, as reported in literature in a contradictory fashion, have been observed. However unlike the previous studies, here it has been clearly demonstrated that this apparent anomaly lies in the different natures of interactions between the influencing parameters like heat flux, ultrasonic frequency, and pressure amplitude. The present results clearly bring out an interactive effect of these operating parameters with surface parameter like surface roughness. A mechanistic model unifying all these parameters has been presented to explain quantitatively the physics of the interaction. The model-based predictions match experimental results quite well suggesting the validity of the hypothesis on liquid–vapor-surface interaction through the process of nucleation and its site density, on which the model is built, and thus revealing the underlying physics.

An efficient numerical method for predicting the performance of valveless micropump

Numerical characterization of valveless micropumps involves fluid–structure interaction (FSI) between a membrane and the working fluid. FSI being computationally difficult, efforts have been mainly restricted to analyzing a given micropump performance. Designing an optimum micropump involves understanding the role of different geometric parameters and this forms the focus of the present work. It is shown that membrane displacement information extracted from a two-way coupled FSI simulation at a given frequency can be reliably used to carry out fluid flow simulations over a wide range of geometrical and operating parameters. The maximum variation between this approach and FSI is within 4% while there is a drastic reduction in computational time and resource. A micropump structure suitable for MEMS technology is considered in this work. An optimum micropump geometry, having a pump chamber height of 50 μm, diffuser length of 280 μm, throat width of 100 μm and separation distance between nozzle and diffuser openings of 2.5 mm, is recommended. The numerical prediction of flowrate at 200 Hz (68 μl min−1) for this pyramidal valveless micropump matches well with the experimental data (60 μl min−1) of the micropump fabricated using MEMS-based silicon micromachining. Thus an efficient numerical method to design valveless micropumps is proposed and validated through rigorous characterization.

Erosion Characteristics of Nanoparticle-Reinforced Polyurethane Coatings on Stainless Steel Substrate

Hydropower generation from the Himalayan rivers in India faces challenge in the form of silt-laden water which can erode the turbine blades and reduce turbine life. To address this issue, polyurethane coatings reinforced with boron carbide (B4C) or silicon carbide (SiC) nanoparticles on 16Cr-5Ni martensitic stainless steel substrate were used in the present investigation to improve erosion wear resistance in silt erosion conditions. Slurry erosive wear tests were carried out based on ASTM G-73 protocol at various test conditions of impact velocity, impingement angle, and erodent particle size as well as slurry concentrations as determined by the implementation of Taguchi design of experiments. Analysis of variance studies of erosion rate indicated that nanoparticle content in PU material is the single most important parameter, and interaction of impact velocity and impingement angle was also proved to be significant. The coatings with B4C nanoparticles had higher wear resistances than those with SiC nanoparticles due to higher hardness of the former. An interesting finding from the results is that there is an optimum amount of nanoparticles at which mass removal is the minimum. This observation has been explained in terms of surface characteristics of coatings as brought out by a combination of measurements including SEM images as well as roughness measurement.

Design and Development of a Piezoelectrically Actuated Micropump for Drug Delivery Application

Micropumps form the heart of several microfluidic systems like micro total analysis system (µTAS) and drug delivery devices, which have resulted from the advancement of silicon micromachining technology. Among the different available types of micropumps, valveless micropumps are better suited for biological applications as they do not have flow-rectifying valves and are less prone to clogging and wear. However, their main drawback is low thermodynamic efficiency. This can be improved if we have a better understanding of the effects of geometry on the performance. This forms one of the objectives of this work. This chapter describes the activity on the design and development of valveless micropumps. A numerical parametric study of the performance of valveless micropumps has been carried out and is presented to bring out the effects of different geometrical parameters. Based on these design approaches, silicon-based micropumps are fabricated and characterized. The performance of one of these micropumps is compared with designed value in this work.

Development of flow in a square mini-channel: Effect of flow oscillation

In this research paper, we present a numerical prediction of steady and fully oscillatory flows in a square mini-channel connected between two plenums. Flow separation occurs at the contraction of the plenum into the channel which causes an asymmetry in the development of flow in the entrance region. The entrance length and recirculation length are found, for both steady and fully oscillatory flows. It is shown that the maximum entrance length decreases with an increase in the oscillating frequency while the maximum recirculation length and recirculation area increase with an increase in oscillating frequency. The phase of a velocity signal is shown to be a strong function of its location. The phase difference between the velocities with respect to the different points along the centerline and those at the middle of the channel show a significant dependence on the driving frequency. There is a significant variation in the phase angles of the velocity signals computed between a point near the wall and that at the centerline. This phase difference decreases along the channel length and does not change beyond the entrance length. This feature can then be used to determine the maximum entrance length, which is otherwise problematic to ascertain in the case of fully oscillatory flows. The entrance length, thus obtained, is compared with that obtained from the velocity profile consideration and shows good similarity. The phase difference between pressure and velocity is also brought out in this work.In this research paper, we present a numerical prediction of steady and fully oscillatory flows in a square mini-channel connected between two plenums. Flow separation occurs at the contraction of the plenum into the channel which causes an asymmetry in the development of flow in the entrance region. The entrance length and recirculation length are found, for both steady and fully oscillatory flows. It is shown that the maximum entrance length decreases with an increase in the oscillating frequency while the maximum recirculation length and recirculation area increase with an increase in oscillating frequency. The phase of a velocity signal is shown to be a strong function of its location. The phase difference between the velocities with respect to the different points along the centerline and those at the middle of the channel show a significant dependence on the driving frequency. There is a significant variation in the phase angles of the velocity signals computed between a point near the wall and that...

Flow and Thermal Transport Studies in Microchannel Flows using Lattice Boltzmann Method

The present study numerically investigates the hydrodynamic and thermal characteristics of single phase pressure driven flow for a single square microchannels using Lattice Boltzmann method (LBM). Two dimensional and nine directional model (D 2 Q 9 ) in Lattice Boltzmann method is used to simulate the flow and water is considered as the working fluid. Uniform temperature is assumed at the channel walls and the fluid temperature is taken to be lower than that of the wall. Hydrodynamic and thermal entrance lengths are determined using Lattice Boltzmann method for different Reynolds numbers (5, 10, 50 and 100). The results obtained are compared with the available experimental μ-PIV studies and thermal studies in literature and found to be consistent.

Modeling and Characterization of Encapsulated Microbubbles for Ultrasound Imaging and Drug Delivery

Intravenously injected encapsulated microbubbles improve the contrast of an ultrasound image. Their destruction is used in measuring blood flow, stimulating arteriogenesis, and drug delivery. We measure attenuation and scattering of ultrasound through solution of commercial contrast agents such as Optison (GE Health Care, Princeton, NJ) and Definity (Bristol Meyer‐Squibb Imaging, North Ballerina, MA). We have developed an interfacial rheology model for the encapsulation of such microbubbles. By matching with experimental data, we obtain the characteristic rheological parameters. We compare model predictions with other experiments. We also investigate microbubble destruction under acoustic excitation by measuring time‐varying attenuation data. Three regions of acoustic pressure amplitudes are found: at low pressure, there is no destruction; at slightly higher pressure bubbles are destroyed, and the rate of destruction depends on a combination of PRF and amplitude. At a still higher pressure amplitude, the ...

Destruction of contrast microbubbles used for ultrasound imaging and drug delivery

Microbubble contrast agent destruction by ultrasound pulse is useful in real‐time blood‐flow velocity measurement, stimulating arteriogenesis, or targeted drug delivery. We investigated in vitro destruction of contrast agent Definity (Bristol Meyer‐Squibb Imaging, North Billerica, MA) by measuring attenuation of ultrasound through it. The measurement is performed with single‐cycle bursts for varying pressure amplitudes at 50‐, 100‐, and 200‐Hz pulse repetition frequencies (PRF). At low excitation levels, the attenuation increases with time, indicating an increase in bubble size due to ingress of dissolved air from the surrounding liquid. With increased excitation levels, the attenuation level decreases with time, indicating destruction of microbubbles. A critical pressure amplitude (1.2 MPa) was found for all three PRFs, below which there is no significant bubble destruction. Above the critical excitation level, the rate of destruction depends on excitation levels. But, at high pressure amplitudes destruc...