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Clotted fat in the blood can be separated with ultrasound

September 23, 2002

An entirely new method for purifying blood has been developed at the Lund Institute of Technology, LTH, in Sweden. The blood is led out in hair-thin channels and is processed with ultrasound. A company in the neighboring research village IDEON is now perfecting the first medical application: a treatment to separate out clotted fat so-called fat embolin blood. But the method is a general one and can be applied to other medical treatments.

Heart surgery can be troubled by certain intellectual disturbances: such as memory, learning, and counting in the head function less well than before the operation. These problems often disappear after a few weeks or a couple of months, but up to 30 percent of patients are permanently affected.

"The cause of the phenomenon is a bone of contention," says Associate Professor Henrik Jönsson at the Thorax Clinic in Lund.

In connection with heart surgery, bleeding causes blood to gather in the heart and lungs. This blood is usually suctioned up and returned to the patient. This is a natural process considering the shortage of donated blood and the risk that is always involved in transfusing blood from people other than the patient.

"In the early 1990s Dixon Moody discovered that patients who have had heart surgery have fat emboli in the brain. Research up to 1998 then showed that this clotted fat comes from the area operated on. I personally met Dixon Moody and asked him how many fat clots there are in the brain after heart surgery. His answer was: 'About three million!'"

Henrik Jönsson has conducted research in the same field and started to wonder whether it would be possible to purify the blood with the help of ultrasound. He contacted the Department of Electrical Measurements at LTH, a pioneer in the use of ultrasound for medical purposes. Different components in the blood reflect ultrasound in different ways, a phenomenon called acoustic impedance. Henrik Jönsson's idea was that if blood were exposed to a standing acoustical wave, the blood cells would gather at the nodes (where the waves intersect each other) and the fat in the opposite positions, at the antinodes.

The blood is pumped into a chamber. Ultrasound can then be directed in such a way that the fat is pressed against the sides of the chamber. The blood is driven forward through the chamber, but the fat is forced out in side-channels. This worked in principle, but in practice the process was disturbed by vortexes that built up in the side-channels. At this juncture, Professor Thomas Laurell at Electronic Measurements suggested that the process should be scaled down to the micro format.

"We etched the channels in silicon chips. In this way we avoided the vortexes," says Thomas Laurell. On the other hand, the flow is tiny. A single channel lets through only 0.3 ml/hr. But that problem is easily solved by simultaneously pumping the blood through several parallel channels on the chip. At present we have achieved a flow of 60 ml/hr with one chip. The objective is to deploy a few chips to attain a rate of one liter per hour. The method will then be practicable. The degree of purification is also high: at least 95% of the fat emboli are removed in the process.

Two years ago Henrik Jönsson established the Ideon company Erysave AB, where Thomas Laurell is now an associate. They are developing a silicon rack containing many parallel channels that are nine by nine centimeters in full scale. In industrial production, however, silicon would be too expensive as a material base, and Erysave is working on a disposable component of form-sprayed plastic. They are applying the same technique as is used for impressing CDs.

Vetenskapsrådet (The Swedish Research Council)