Experimental study on damage mechanism of blood vessel by cavitation bubbles

Ball motion and bubble ripples in the interaction of cavitation bubble-elastic ball-curved wall

Elastic ball motion and cavitation bubble ripples in cavitation bubble-elastic ball-curved wall interaction was investigated experimentally using single-electrode periodic discharge bubble generation technology and high-speed photography. It was found that the hard ball undergoes a process of "push-pull-push-pull" as the dimensionless bubble-ball distance increases, while the elastic ball undergoes a process of "push-pull" in the same scenario. This is mainly due to the combined effects of the expansion ejection effect, the reverse thrust of liquid jet and the secondary Bjerknes force of cavitation bubble and its rebound bubble, which are strengthened or weakened. The radial vibration of the elastic ball causes a continuous secondary Bjerknes force attraction effect between the ball and the wall, similar to that between an acoustic bubble and a wall. In the interaction of "cavitation bubble-elastic ball-curved wall," there is a state of equilibrium stability where the centerline of the "bubble-ball" coincides with the centerline of the "bubble-wall." Both the ball and the bubble will move towards this equilibrium position. This is a result of the three forces with different starting and ending points-the "bubble-wall" secondary Bjerknes force, the "ball-wall" secondary Bjerknes force, and the "bubble-ball" interaction force-reaching a condition of equilibrium. The evolution of the cavitation bubble is usually dominated by toroidal jets, sometimes forming multi-layered nested toroidal jets (annular cylindrical jet). The surface tension waves of the bubble, the elastic modulus waves and the curvature waves of the elastic ball work together to form cavitation bubble ripples. Under the primary intensification of the bubble's rapid collapse and the secondary intensification of the wall effect, the bubble ripples are reinforced, leading to the formation of multi-layered nested toroidal jets.

Enhancing thrombolysis efficiency using acoustic vortex tweezers and microbubbles: a microscale mechanistic study with experimental validation

Previous research has shown that acoustic vortex tweezers (AVT) combined with microbubbles (MBs) and tissue plasminogen activator (t-PA) can enhance thrombolytic efficiency. However, due to varying evaluation methods, an objective framework for investigating its mechanisms is lacking. This study establishes a standardized thrombolysis evaluation protocol to compare AVT, t-PA, and MBs with mainstream sonothrombolysis and to explore their thrombolytic mechanisms. A miniature ultrasound transducer capable of generating an AVT field was applied to fluorescent fibrin clots. The MB penetration and fibrin structure changes were observed using a high-speed camera and confocal microscopy. The drug permeability, thrombolytic efficiency, fragment size, and quantity were then quantified to assess the efficacy and safety of AVT. The results showed that AVT with MBs produced deeper (up to 30 μm) and wider MBs channels and increased fibrin looseness by 32.6 %, significantly enhancing t-PA penetration and fibrin clot dissolution. Within 30 min, the dissolution area in the AVT + t-PA + MBs group was 43.6 % larger than the t-PA only group, without creating excessive or oversized fragments. These findings confirm the potential of AVT for promoting fibrin disruption and drug penetration. Future validation using ex vivo vascular models and animal studies may position AVT as an important adjunct therapy in clinical thrombolysis.

Laser-induced microbubble as an in vivo valve for optofluidic manipulation in living Mice's microvessels

Optofluidic regulation of blood microflow in vivo represents a significant method for investigating illnesses linked to abnormal changes in blood circulation. Currently, non-invasive strategies are limited to regulation within capillaries of approximately 10 μm in diameter because the adaption to blood pressure levels in the order of several hundred pascals poses a significant challenge in larger microvessels. In this study, using laser-induced microbubble formation within microvessels of the mouse auricle, we regulate blood microflow in small vessels with diameters in the tens of micrometers. By controlling the laser power, we can control the growth and stability of microbubbles in vivo. This controlled approach enables the achievement of prolonged ischemia and subsequent reperfusion of blood flow, and it can also regulate the microbubbles to function as micro-pumps for reverse blood pumping. Furthermore, by controlling the microbubble, narrow microflow channels can be formed between the microbubbles and microvessels for assessing the apparent viscosity of leukocytes, which is 76.9 ± 11.8 Pa·s in the in vivo blood environment. The proposed design of in vivo microbubble valves opens new avenues for constructing real-time blood regulation and exploring cellular mechanics within living organisms.

Dynamics of cavitation bubbles in viscous liquids in a tube during a transient process

We experimentally, numerically, and theoretically investigate the dynamics of cavitation bubbles in viscous liquids in a tube during a transient process. In experiments, cavitation bubbles are generated by a modified tube-arrest setup, and the bubble evolution is captured with high-speed imaging. Numerical simulations using OpenFOAM are employed to validate our quasi-one-dimensional theoretical model, which effectively characterizes the bubble dynamics. We find that cavitation onset is minimally affected by the liquid viscosity. However, once cavitation occurs, various aspects of bubble dynamics, such as the maximum bubble length, bubble lifetime, collapse time, and collapse speed, are closely related to the liquid viscosity. We further establish that normalized bubble dynamics are solely determined by the combination of the Reynolds number and the Euler number. Moreover, we also propose a new dimensionless number, Ca2, to predict the maximum bubble length, a critical factor in determining the occurrence of liquid column separation.

Collapsing behavior of spark-induced cavitation bubble in rigid tube

The phenomenon of cavitation within tubes is a common scenario in the fields of medicine and industry. This paper focuses on the effects of rigid circular tube length, diameter and the distance of bubble - tube port on the behavior of bubble in tube. The low-voltage discharge technique was utilized to induce a cavitation bubble in deionized water. The effects of rigid tube lengths, diameters, and bubble-tube port distances on the morphology of bubbles are observed using high-speed camera. It has been found that as the length of the rigid tube increases, so does the period, and this effect is more pronounced in tubes with smaller diameters. Conversely, the cavitation bubble period decreased and then stabilized as the tube diameter increased, the ratio of tube radius and the bubble radius exceeds 4.8, the period of bubble in tube is similar to that of bubble in free field. Further analysis of the influence of tube characteristics on microjets reveals that a pair of oppositely microjets were formed along the tube axis by the bubble near the midpoint of the tube axis. Moreover, when the non-dimensional tube length η < 3.5, the increase tube diameter results in a decrease microjet velocity. It has also been observed that as the bubble gradually approaches the interior of the tube, the velocity of microjets directed inward decreases. Additionally, the smaller the diameter of the tube, the greater the bubble-tube port distance required for the microjets to reach the same level of velocity as bubble near the center of the tube axis. These findings hold theoretical implications for improvement of targeted drug delivery efficiency in medicine and enhance the operational efficiency of inertial micropumps in industries.