Droplet microfluidics has emerged as a prospering field for lab-on-a-chip devices, where droplets serve as liquid vessels e.g. for biochemical reagents. Key to the fluid processing in droplet format are the controlled droplet handling and movement on the microscale. Hence this paper proposes droplet handling by combining droplet microfluidics with bulk acoustic wave (BAW) acoustophoresis. BAW acoustophoresis has formerly focused on cell and particle handling, whereas here we determine the various abilities of this method for the field of droplet microfluidics. In silicon microdevices, water-in-oil droplets of 200 μm size were generated for a set of unit operations including droplet fusion, focusing, sorting and medium exchange around 0.5-1 MHz acoustic frequency. Compared to existing droplet handling methods, the shown method is simple in fabrication, robust in operation and versatile to meet the needs of various droplet processing microfluidic devices.

TCR aggregation at the point of contact with an APC is thought to play an important role in T cell signal transduction. However, this potentially important phenomenon has never been documented during an immune response in vivo. Here we used immunohistology to show that the TCR on naive Ag-specific CD4 T cells in the lymph nodes of mice injected with Ag redistributed to one side of the cell. In cases where the APC could be identified, the TCR was concentrated on the side of the T cell facing the APC. In those T cells that produced IL-2, the TCR and IL-2 localized to the same side of the cell. In vivo IL-2 production depended on costimulatory signaling through CD28, whereas TCR redistribution did not. These results show that Ag-stimulated CD4 T cells produce IL-2 in a polarized fashion and undergo CD28-independent TCR redistribution in vivo.

Design, fabrication and characterization of thin film piezoelectric devices for bulk acoustic wave acoustophoresis of micrometer-sized particles.

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