Colloidal Gas Aphrons (CGA), consist of gas bubbles with diameters ranging from 10 to 100 micron, surrounded by a thin aqueous surfactant film. This fluid combines certain surfactants and polymers to create the systems of Microbubbles. The function of surfactant in CGAs is to produce the surface tension to contain the aphrons. Also, a biopolymer needs to be considered in the formulation as a viscosifier as well as a stabilizer. The aphron-laden fluid appears to be particularly well suited for drilling through depleted zones. The unique feature of aphron based fluids is to form a solid free, tough, and elastic internal bridge in pore networks or fractures to minimize deep invasion using air Microbubbles. This microenvironment seal readily cleans up with reservoir flow back as production is initiated, thereby reducing cost associated with stimulation processes. This paper presents a comprehensive, comparative study of rheological behavior and filtration properties of CGA based drilling fluids with various concentrations of polymer and surfactant. Laboratory evaluations showed that the CGA based fluid is one of the ideal engineering materials which can control and kill the loss circulation, save cost and increase productivity in which rheological characteristics and filtration properties of them are greatly influenced by the level of polymer and surfactant concentration.

Background: Microbubbles are widely used in diagnostic ultrasound applications as contrast agents. Recently, many studies have shown that Microbubbles have good potential for the use in therapeutic applications such as drug and gene delivery and opening of blood-brain barrier locally and transiently. When Microbubbles are located inside an elastic microvessel and activated by ultrasound, they oscillate and induce mechanical stresses on the vessel wall. However, the mechanical stresses have beneficial therapeutic effects, they may induce vessel damage if they are too high. Microstreaming-induced shear stress is one of the most important wall stresses. Objective: The overall aim of this study is to simulate the interaction between confined bubble inside an elastic microvessel and ultrasound field and investigate the effective parameters on microstreaming-induced shear stress. Material and Methods: In this Simulation study, we conducted a 2D finite element simulation to study confined Microbubble dynamics, also we investigated both acoustical and bubble material parameters on Microbubble oscillation and wall stress. Results: Based on our results, for acoustic parameters in the range of therapeutic applications, the maximum shear stress was lower than 4 kPa. Shear stress was approximately independent from shell viscosity whereas it decreased by increasing the shell stiffness. Moreover, shear stress showed an increasing trend with acoustic pressure. Conclusion: Beside the acoustical parameters, bubble properties have important effects on bubble behavior so that the softer and larger bubbles are more appropriate for therapeutic application as they can decrease the required frequency and acoustic pressure while inducing the same biological effects.

Microbubbles have been presumed as gaseous emboli, which originate during mechanical heart valve closure, but are not seen in bioprosthetic valves. In this report, we presented a cluster of Microbubbles mimicking mobile thrombus in a patient with mechanical mitral valve prosthesis. A 30-year-old female with a history of implanted mechanical valve at the mitral position underwent a routine examination. She was asymptomatic and her physical examination was unremarkable. Transthoracic echocardiography showed a mobile thrombus-like mass on the ventricular side of the prosthetic mitral valve moving into the left ventricular outflow tract. However, close examination of images indicated that the mass was in fact intense Microbubbles mimicking thrombus. Intense mobile Microbubbles can be misdiagnosed as a mobile thrombus. We recommend and underscore the importance of detailed echocardiographic examination in case of mobile mass to avoid misdiagnosis in patients with mechanical heart valves.

During the ultrasound imaging process, the ultrasound contrast agents (UCAs) are beating near the blood vessel wall. Therefore, the purpose of the present simulation study is to investigate the effect of the presence of an elastic wall on the radial and frequency acoustic response of a UCA Microbubble oscillating in a nonlinear regime. For this reason, the numerical simulation of the dynamic behavior of a coated Microbubble was performed using coding in MATLAB and a Rayleigh-Plesset equation modified by Doinikov. To study the nonlinear bubble oscillations, its compression-only behavior and the sub-harmonic nonlinear component are taken from a nonlinear shell model presented by Marmottant et al. Initially, coated bubble oscillations in two linear and nonlinear regimes were investigated for two types of shell models, and it was observed that presence of the elastic wall affects the bubble's compression-only behavior. Finally, due to the importance of the subharmonic component in the nonlinear oscillation of the coated bubble, the threshold of the appearance of subharmonic components for a coated bubble near an elastic wall was investigated using the Fast Fourier Transform (FFT) and compared with the oscillation in the infinite fluid.

High-intensity focused ultrasound is a non-invasive method and provides many therapeutic applications for physicians. One of the ways to increase the efficiency of High-intensity focused ultrasound is using a Levovist contrast agent, which consists of Microbubbles. In the present study, we calculate the pressure field due to the High-intensity focused ultrasound using the Helmholtz equation for linear ultrasonic wave propagation. Using the Keller-Miksis equation, we calculate the thermal effects caused by Microbubble injection after determining the acoustic pressure. The Pennes bioheat transfer equation is used for studying the tissue temperature distribution. The simulation results show that in the presence of a Microbubble under the influence of a High-intensity focused ultrasound pressure field, increasing the applied frequency and power increases the value of heat sources caused by the Microbubble oscillation. An increase in the temperature of biological tissue can be observed after the injection of Microbubbles. Within the pressure range of 2.54 MPa, the tissue temperature at the focal point, for the case where the Microbubble with the initial radius of 50 μm is injected, increases by 8.28 ℃. Meanwhile, if a Microbubble with an initial radius of 50 micrometers is injected, there is a further increase in the tissue temperature by 57.72%. In the absence of Microbubbles, the corresponding temperature rise is only 5.42 ℃ for the same operating conditions. Finally, the Arrhenius model shows that the Microbubbles with different initial radii increase the ablated tissue volume by about 38%.

Cavitation is a process that involves the generation, transport (along with the liquid), and collapse of bubbles upon impact with internal walls. The primary objective of this study is to examine the movement of generated Microbubbles and estimate the frequency of bubble impacts on the walls of pipes with varying degrees of surface clogging and pipes with bends, considering different inlet flow rates. This analysis aims to evaluate the vulnerability to damage due to bubble impacts in each of these geometries. The simulation results for clogged pipes indicate that the higher the degree of clogging, the greater the likelihood of Microbubble impacts on the clogged area and their subsequent collapse, which significantly increases the potential for pipe wall damage. Additionally, for pipes with high clogging percentages (above 36%) , the likelihood of wall damage dramatically increases with higher fluid inlet velocities. Conversely, in pipes with low clogging percentages (below 36%) , lower fluid inlet velocities increase the likelihood of Microbubble impacts on the clogged walls, thereby also increasing the potential for pipe damage.