Abstract
Photo-mediated ultrasound therapy (PUT) is a novel technique using combined laser and ultrasound to generate enhanced cavitation activity inside blood vessels. The stresses produced by oscillating bubbles during PUT are believed to be responsible for the induced bio-effects in blood vessels. However, the magnitudes of these stresses are unclear. In this study, a two-dimensional axisymmetric finite element method-based numerical model was developed to investigate the oscillating bubble-produced shear and circumferential stresses during PUT. The results showed that increased stresses on the vessel wall were produced during PUT as compared with ultrasound-alone. For a 50-nm radius bubble in a 50-μm radius blood vessel, the produced circumferential and shear stresses were in the range of 100 kPa–400 kPa and 10 Pa–100 Pa, respectively, during PUT with the ultrasound frequency of 1 MHz, ultrasound amplitude of 1400 kPa–1550 kPa, and laser fluence of 20 mJ/cm2, whereas the circumferential and shear stresses produced with ultrasound-alone were less than 2 kPa and 1 Pa, respectively, using the same ultrasound parameters. In addition, the produced stresses increased when the ultrasound pressure and laser fluence were increased but decreased when the ultrasound frequency and vessel size were increased. For bubbles with a radius larger than 100 nm, however, the stresses produced during PUT were similar to those produced during ultrasound-alone, indicating the effect of the laser was only significant for small bubbles.
Highlights
Cavitation may significantly impact the function of a blood vessel
The oscillation of the 2 μm bubble at an ultrasound amplitude of 261.5 kPa at 1 MHz is shown in Fig. 2(a), which is identical to the bubble oscillation in the original paper.[36]
The vessel displacement, circumferential stress, and shear stress obtained in our model matched very well with those in the Hosseinkhah model, as shown in Figs. 2(b) and 3
Summary
In the 1980s, several studies found that the vapor cavity inside blood vessels was responsible for vascular injuries during shock wave lithotripsy treatment.[1,2] Since many studies have shown possible use of microbubbles in the presence of ultrasound for therapeutic applications Many of these investigations are based on the use of ultrasound activated microbubbles for drug and gene delivery in vivo[3,4,5,6,7,8] and in vitro.[4,9,10,11] Other potential applications include temporary blood–brain barrier opening[12,13] and lysis of blood clots and cell membrane.[14,15,16,17] Inertial and non-inertial cavitation inside microvessels can generate significant shear and circumferential stresses through liquid jets and microstreaming, which will lead to various biological responses in blood vessels.[18–25]. Other studies have shown that the changes in circumferential stress were related to parameters such as the vessel diameter, initial bubble size, ultrasound frequency, and amplitude.[12,28,29]
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