Cavitation Threshold of Microbubbles in Gel Tunnels by Focused Ultrasound

Abstract

The investigation of inertial cavitation in micro-tunnels has significant implications for the development of therapeutic applications of ultrasound such as ultrasound-mediated drug and gene delivery. The threshold for inertial cavitation was investigated using a passive cavitation detector with a center frequency of 1 MHz. Micro-tunnels of various diameters (90 to 800 μm) embedded in gel were fabricated and injected with a solution of Optison™ contrast agent of concentrations 1.2% and 0.2% diluted in water. An ultrasound pulse of duration 500 ms and center frequency 1.736 MHz was used to insonate the microbubbles. The acoustic pressure was increased at one second intervals until broadband noise emission was detected. The pressure threshold at which broadband noise emission was observed was found to be dependent on the diameter of the micro-tunnels, with an average increase of 1.2 to 1.5 between the smallest and the largest tunnels, depending on the microbubble concentration. The evaluation of inertial cavitation in gel tunnels rather than tubes provides a novel opportunity to investigate microbubble collapse in a situation that simulates in vivo blood vessels better than tubes with solid walls do.

A bibliometric analysis of micro/nano-bubble related research: current trends, present application, and future prospects

“…In addition, ''Cavitation'' (139; 2.9 %) in author keywords steadily ranked in the top 11 during all four 6-year periods, which illustrates that ultrasound-induced microbubble cavitation has been an on-going concern (Doida et al 1998;Postema et al 2004;Zhang et al 2013). Moreover, the investigation of inertial cavitation in micro-tunnels has significant implications for the development of therapeutic ultrasound applications such as ultrasound-mediated drug and gene delivery (Sassaroli and Hynynen 2007). Figure 8 shows that the relationship among ''Microbubble'', ''Blood-Brain Barrier'', and ''Focused Ultrasound'' was close, which the new technique of focused ultrasound with microbubble has widely applied across bloodbrain barriers for drug delivery (McDannold et al 2012;Ting et al 2012;Meairs 2013).…”

“…The other technique of induced air flotation (Li and Tsuge 2006) for microbubble generation was always considered as an alternative to the dissolved air flotation in dealing with wastewater queries. Furthermore, the micro/nano-bubbles could also be generated under some specific phenomenon with or without other auxiliary technologies (Sassaroli and Hynynen 2007;Neethirajan et al 2011). Insonated by specific ultrasound pulse, the cavitation phenomenon (Sassaroli and Hynynen 2007) could be used to produce the microbubbles, which also offer a novel chance to study the microbubble collapse.…”

“…Furthermore, the micro/nano-bubbles could also be generated under some specific phenomenon with or without other auxiliary technologies (Sassaroli and Hynynen 2007;Neethirajan et al 2011). Insonated by specific ultrasound pulse, the cavitation phenomenon (Sassaroli and Hynynen 2007) could be used to produce the microbubbles, which also offer a novel chance to study the microbubble collapse. In comparison to ultrasonication technique, the microfluidics approach (Neethirajan et al 2011) performed an opposite extreme and capacitated the generation of microbubbles with high uniformity which can be readily controlled by the liquid flow rate, the physichemical properties of the fluids, and the microfluidic devices (Lee et al 2015).…”

The collapse of single bubbles and approximation of the far-field acoustic emissions for cavitation induced by shock wave lithotripsy

“…Whilst in vivo cavitation can differ greatly from that in water if, for example, the bubble is confined within a blood vessel (Leighton, White & Marsden 1995a, b;Zhong et al 2001;Cui et al 2006;Gao, Hu & Hu 2007;Sassaroli & Hynynen 2007;Freund 2008), the cavitation simulated for this model resembles more that undertaken in the urine collection system, where cavitation is known to occur more readily during SWL than it does in the parenchyma (Bailey et al 2005). However, the subsequent propagation of the acoustic wave occurs through a variety of other tissue types that can differ significantly from water in the extent to which they tend to promote nonlinear propagation (through B/A) and the extent to which the waves (and particularly any higher harmonics) are suppressed through frequency-dependent absorption.…”

Tiny Bubbles and Endocytosis?

“…2 In the article by Meijering et al in this issue of Circulation Research, this process of low energy permeabilization is called, somewhat confusingly, UMTD (for ultrasound and microbubble-targeted delivery). In addition to the direct relationship with the applied acoustic pressure, other variables that influence whether microbubbles will stably oscillate or cavitate include size, density, 3 and composition. 4 Considerable effort has been expended to optimize microbubble composition, ultrasound parameters, and experimental methods to enhance the transfer of genes or drugs into cells.…”