Delivery of antibacterial nanoparticles into dentinal tubules using high-intensity focused ultrasound.

INTRODUCTION: High-intensity focused ultrasound (HIFU) produces collapsing cavitation bubbles. This study aims to investigate the efficacy of collapsing cavitation bubbles to deliver antibacterial nanoparticles into dentinal tubules to improve root canal disinfection. METHODS: In stage 1, experiments were performed to characterize the efficacy of collapsing cavitation bubbles to deliver the miniature plaster beads into a tubular channel model. In stage 2, experiments were conducted on root-dentin blocks to test the efficacy of HIFU applied at 27 kHz for 2 minutes to deliver antibacterial nanoparticles into dentinal tubules. After the stage 2 experiment, the samples were sectioned and analyzed using field-emission scanning electron microscopy and energy dispersive X-ray analysis. RESULTS: The stage 1 experiment showed that collapsing cavitation bubbles using HIFU delivered plaster beads along the entire length of the tubular channel. It was observed from the stage 2 experiments that the diffusion of fluids alone was not able to deliver antibacterial nanoparticles into dentinal tubules. The collapsing cavitation bubbles treatment using HIFU resulted in significant penetration up to 1,000 microm of antibacterial nanoparticles into the dentinal tubules. The statistical analysis showed a highly significant difference in the depth of penetration of antibacterial nanoparticles between the two groups (<0.005). CONCLUSION: The cavitation bubbles produced using HIFU can be used as a potential method to deliver antibacterial nanoparticles into the dentinal tubules to enhance root canal disinfection.

Interaction of microbubbles with high intensity pulsed ultrasound.

High intensity pulsed ultrasound, interacting with microbubble contrast agents, is potentially useful for drug delivery, cancer treatment, and tissue ablation, among other applications. To establish the fundamental understanding on the interaction of a microbubble (in an infinite volume of water) with an ultrasound pressure field, a numerical study is performed using the boundary element method. The response of the bubble, in terms of its shape at different times, the maximum bubble radius obtained, the oscillation time, the jet velocity, and its translational movement, is studied. The effect of ultrasound intensity and initial bubble size is examined as well. One important outcome is the determination of the conditions under which a clear jet will be formed in a microbubble in its interaction with a specific sound wave. The high speed jet is crucial for the aforementioned intended applications.

Interaction of lithotripter shockwaves with single inertial cavitation bubbles.

The dynamic interaction of a shockwave (modelled as a pressure pulse) with an initially spherically oscillating bubble is investigated. Upon the shockwave impact, the bubble deforms non-spherically and the flow field surrounding the bubble is determined with potential flow theory using the boundary-element method (BEM). The primary advantage of this method is its computational efficiency. The simulation process is repeated until the two opposite sides of the bubble surface collide with each other (i.e. the formation of a jet along the shockwave propagation direction). The collapse time of the bubble, its shape and the velocity of the jet are calculated. Moreover, the impact pressure is estimated based on water-hammer pressure theory. The Kelvin impulse, kinetic energy and bubble displacement (all at the moment of jet impact) are also determined. Overall, the simulated results compare favourably with experimental observations of lithotripter shockwave interaction with single bubbles (using laser-induced bubbles at various oscillation stages). The simulations confirm the experimental observation that the most intense collapse, with the highest jet velocity and impact pressure, occurs for bubbles with intermediate size during the contraction phase when the collapse time of the bubble is approximately equal to the compressive pulse duration of the shock wave. Under this condition, the maximum amount of energy of the incident shockwave is transferred to the collapsing bubble. Further, the effect of the bubble contents (ideal gas with different initial pressures) and the initial conditions of the bubble (initially oscillating vs. non-oscillating) on the dynamics of the shockwave-bubble interaction are discussed.

Numerical analysis of a gas bubble near bio-materials in an ultrasound field.

Ultrasonic cavitation bubble phenomena play a key role in numerous medical procedures such as ultrasound-assisted lipoplasty, phacoemulsification, lithotripsy, brain tumor surgery, muscle and bone therapies and intraocular or transdermal drug delivery. This study investigates numerically the interaction of a bubble with a bio-material (fat, skin, cornea, brain, muscle, cartilage or bone) involved in the treatments mentioned when subjected to an ultrasound field. A range of frequencies is used to study the bubble behavior in terms of its growth and collapse shapes, and the maximum jet velocity attained. Simulation results show complex dynamic behaviors of the bubble. In several cases a jet is formed directed away from the bio-material while in others, toward it. In certain cases, the bubble eventually breaks into two, with or without the formation of opposite penetrating jets. Very high maximum velocities of jets directing away or toward the bio-materials can be observed in some cases (700 to 900 ms(-1)).