Sara Thorslund

On-chip fluorescence-activated cell sorting by an integrated miniaturized ultrasonic transducer.

An acoustic microfluidic system for miniaturized fluorescence-activated cell sorting (microFACS) is presented. By excitation of a miniaturized piezoelectric transducer at 10 MHz in the microfluidic channel bottom, an acoustic standing wave is formed in the channel. The acoustic radiation force acting on a density interface causes fluidic movement, and the particles or cells on either side of the fluid interface are displaced in a direction perpendicular to the standing wave direction. The small size of the transducer enables individual manipulation of cells passing the transducer surface. At constant transducer activation the system was shown to accomplish up to 700 microm sideways displacement of 10 microm beads in a 1 mm wide channel. This is much larger than if utilizing the acoustic radiation force acting directly on particles, where the limitation in maximum displacement is between a node and an antinode which at 10 MHz is 35 microm. In the automatic sorting setup, the system was demonstrated to successfully sort single cells of E-GFP expressing beta-cells.

A fluidic device to study directional angiogenesis in complex tissue and organ culture models

Many signals that induce angiogenesis have been identified; however, it is still not clear how these signals interact to shape the vascular system. We have developed a fluidic device for generation of molecular gradients in 3-dimensional cultures of complex tissues and organs in order to create an assay for precise induction and guidance of growing blood vessels. The device features a centrally placed culture chamber, flanked by channels attached to a perfusion system used to generate gradients. A separate network of vacuum channels permits reversible attachment of the device to a flat surface. We show that the fluidic device can be used to create growth factor gradients that induce directional angiogenesis in embryonic mouse kidneys and in clusters of differentiating stem cells. These results demonstrate that the device can be used to accurately manipulate complex morphogenetic processes with a high degree of experimental control.

Instant oxidation of closed microchannels

A new method for instant oxidation of closed, bonded microchannels is presented and evaluated. By placing the tip-formed electrode of a corona plasma equipment in the reservoir of a PDMS microstructure, the plasma spark can spread into the microchannel and oxidize the inner PDMS channel walls. By applying this process, the non-specific adsorption of hydrophobic affinity analytes is markedly decreased, here evaluated with the fluorescent dye Rhodamine B and standard protein BSA. The results show that the surface adsorption in plasma-treated channels is reduced significantly, e.g. the amount of BSA adsorbed at 35 mm distance from the reservoir is only 35% of the amount of BSA adsorbed in non-treated channels. The surface shows very low adsorption during the first 200 min after oxidation, and has recovered (90%) its hydrophobicity first after 24 h. This method of instant surface oxidation has in our group been widely used to simplify microfluidic studies of microstructure prototypes, since the need of other more complicated surface modifications to lower analyte adsorption is eliminated.