NDLI: Low Intensity Therapeutic Ultrasound Effect on Nano-Particle Motion in a Viscous Medium

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Mizrahi, Natalya Weihs, Daphne Kimmel, Eitan
Copyright Year	2008
Abstract	While low intensity therapeutic ultrasound irradiation (LITUS) has been shown to have biological effects on tissue and cells, the physical mechanism leading to those effects has yet to be characterized. As a model system to study effects of LITUS on intracellular organelles, we monitor the dynamics of nanoparticles suspended in a viscoelastic medium, before and during LITUS treatment. Particle motion dynamics can indicate: i) forces acting on similarly-sized intracellular organelles; ii) streaming flow induced in cells and in cavities in contact with cells; and iii) instantaneous (under LITUS) changes in the mechanical properties of viscoelastic media in general and cells in particular. Forces and flow can result in shear stresses that act on the cell membrane of, e.g., endothelial cells in blood vessels and may cause biophysical responses. Particle motion in a high-viscosity, viscoelastic model solution, methyl cellulose, was used as an indicator for sample response under LITUS. The ultrasound-induced motion of nano-particles was quantified by real-time particle-tracking microrheology methods. Particle motion without LITUS irradiation demonstrated diffusive-like behavior with no underlying convection. In contrast, during LITUS irradiation convective motion with a particle-velocity profile parabolic in time was observed. Particles were accelerated after initiation of LITUS irradiation, then a transient phase of constant velocity was observed, and finally the speed was reduced. Altogether the results of the study indicate that LITUS may apply considerable direct forces on suspended particles, a model system for cellular organelles. More studying will help elucidate the mechanisms of LITUS effects. Extending this approach to cells in vitro and evaluating their response can promote the use of ultrasound as a therapeutic tool for delicate manipulation of cells in vivo in a controlled, targeted, and non-invasive way. At the same time, one can define the safety limits and optimal range for therapeutic and diagnostic ultrasound by indicating the threshold for irreversible intracellular changes.
Sponsorship	International
Starting Page	63
Ending Page	67
Page Count	5
File Format	PDF
ISBN	9780791848364
DOI	10.1115/ESDA2008-59245
e-ISBN	0791838277
Volume Number	Volume 2: Automotive Systems; Bioengineering and Biomedical Technology; Computational Mechanics; Controls; Dynamical Systems
Conference Proceedings	ASME 2008 9th Biennial Conference on Engineering Systems Design and Analysis
Language	English
Publisher Date	2008-07-07
Publisher Place	Haifa, Israel
Access Restriction	Subscribed
Subject Keyword	Viscosity Biological tissues Ultrasonic effects Irradiation (radiation exposure) Blood vessels Mechanical properties Cell membranes Flow (dynamics) Convection Endothelial cells Transients (dynamics) Nanoparticles Cavities Dynamics (mechanics) Particulate matter Shear stress Safety Ultrasound
Content Type	Text
Resource Type	Article

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