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Palestrante: Assoc. Prof. Eitan Kimmel

Biomedical Engineering, do Technion, Haifa, Israel


Data: 26/07/2011 (3a. feira)

Horário: 14:00h

Local: CT, SALA G-205




Ultrasound, is a mechanical, pressure wave that is used in medicine for imaging mostly and also as a therapeutic tool, at this stage besides physiotherapy of sore muscles and joints, the use is mostly experimental. It was shown in the lab that even without heating the exposed cells and tissue ultrasound increases rate of transport of drugs into the cells and through the tissue, that nerve cells can be stimulated to deliver electric signals, and that new blood vessels were formed, broken bones were recovered more rapidly and many other reports on cell functioning changes under ultrasound.  For decades it is a common knowledge that the ultrasonic pressure pulse does not have any direct effect on cells and tissues. It needs a mediator. Only when tiny gas bubbles are formed, what is known as cavitation, that a physical explanation can be provided. Once a bubble is formed near a cell liquid jets will hit the cell or tiny but powerful explosions and shock waves will affect the cell and change its functioning. Cells are known to be very sensitive to forces that act on them. However, how to explain the many cases that ultrasound affects cells even without any trace of cavitation being present. Lately, after some 15 years of attempts to solve this mystery, our group came up with a novel model that says that ultrasound induces a very unique form of cavitation inside the cell - or more precisely - inside the bilayer membranes that encloses the cell, the nucleus and many organelles in the cell. While ultrasound is working the membrane inflates and deflates periodically as the two lipid leaflets that form the bilayer membrane are pulled apart, deform, stretch, and then pushed back towards each other. This occur more in cells that are not closed to free surfaces as in blood vessels or lung airways. The level of stretching and deformation depends on the pressure amplitude and frequency and can range between tiny stretching of protein molecules that are embedded in the membrane under low ultrasound intensity to rupture of cells in high ultrasound intensity. Ultrasound is a very promising technology in the sense that it is non invasive and can be targeted. Now we say that we can control the forces it applies on the membranes and thereby on the cells. Selective and targeted cell stimulation by ultrasound could pave the way for many applications, from neuron stimulation (hearing prosthesis) and pain suppression, to tissue engineering and stem cell controlled differentiation, to opening of the blood brain barrier to drug delivery.  


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