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Ultrasonic particle switching cleans blood
sound. “I introduced beads into this microchannel to see if it had agitation or not,” he says, “and to my frustration, I saw particles being lined up in the center at certain frequencies.” He realized that he had set up a standing acoustic wave in the system. “I wanted to generate tur-
COURTESY OF THOMAS LAURELL
taminated medium flows through the two side inlets, and clean medium flows through the center one. Thus, the acoustic forces drive the blood cells into the clean When you think of medical ultrasound, solution. cleaning blood is probably not the first application that springs to mind. But it The key to the acoustic technique is didn’t take long for Thomas Laurell and sending an ultrasound signal that matchcolleagues at Lund University es the mechanical resonance of (Sweden) to realize that the two the width of the channel. This belonged together. They have desets up a standing wave across veloped a microfluidic device that the channel. Generally, the recombines an ultrasonic standing searchers found that they got wave with the laminar flow propbetter separation with smaller erties of a microfluidic channel to channels. “As you go down in separate fat particles from blood— size, the force on the particles a critical part of blood recovery goes up because the resonant during surgery. frequency of the device goes A thoracic surgeon suggested up,” says Laurell. the possibility of finding a better If the dimensions are too way to wash blood. Right now, small, though, the blood cells the blood is centrifuged to collect clog the channels. The researchthe erythrocytes, which are reiners have settled on widths of troduced into the body. It is an 300–350 µm and a depth of imperfect process that leaves fat 125 µm. The flow rate is 8– Depiction of a three-pronged outlet with fat particles exiting particles behind, and when they 10 mL/min, but the channels through the side channels and blood cells collecting in the reach a patient’s brain, they can can be multiplexed. The recenter channel. clog capillaries and cause permasearchers have already fabricated bulence, and I got very nice linear flow nent cognitive decline. an 8 8 channel device. rates instead, so I sort of put that experiLaurell suggested that the surgeon Laurell and colleagues report rement on the shelf.” team up with some medical ultrasound moval of >95% of the fat particles and researchers at Lund University, which >95% collection of the red blood cells Laurell realized that this was exactly has a 50-year history in this area. Later, when the initial fat concentration was what the erythrocyte project needed. he heard about some problems they
