Enhanced single-cell printing by acoustophoretic cell focusing

Abstract

Recent years have witnessed a strong trend towards analysis of single-cells. To access and handle single-cells, many new tools are needed and have partly been developed. Here, we present an improved version of a single-cell printer which is able to deliver individual single cells and beads encapsulated in free-flying picoliter droplets at a single-bead efficiency of 96% and with a throughput of more than 10 beads per minute. By integration of acoustophoretic focusing, the cells could be focused in x and y direction. This way, the cells were lined-up in front of a 40 μm nozzle, where they were analyzed individually by an optical system prior to printing. In agreement with acoustic simulations, the focusing of 10 μm beads and Raji cells has been achieved with an efficiency of 99% (beads) and 86% (Raji cells) to a 40 μm wide center region in the 1 mm wide microfluidic channel. This enabled improved optical analysis and reduced bead losses. The loss of beads that ended up in the waste (because printing them as single beads arrangements could not be ensured) was reduced from 52% ± 6% to 28% ± 1%. The piezoelectric transducer employed for cell focusing could be positioned on an outer part of the device, which proves the acoustophoretic focusing to be versatile and adaptable.

The Poisson distribution and beyond: methods for microfluidic droplet production and single cell encapsulation

“…This differs from the case demonstrated a decade ago, where optical trapping was used to guide an individual cell to the fluid-fluid interface, a methodology that is not inherently suited to even moderate-throughput applications. 188,190 Fig. In an example of single-cell printing, Schoendube et al used a set of electrodes to detect the local electrical impedance change induced by the presence of a cell in a continuous flow, ejecting a single cell when it arrived at the dispensing port.…”

Microfluidic techniques for high throughput single cell analysis

“…Potential applications include controlled cell growth in 3D biomaterial niches[66], stem cell trophic factor therapeutics[67], tissue engineering[68], and in vitro screening[69]. Three dimensional tissue bioprinting[70] and related techniques adapted from inkjet printing may incorporate these capabilities for cell and biomaterial patterning[71]. …”

Microfluidic droplet handling by bulk acoustic wave (BAW) acoustophoresis

“…As described in literature, 40,41 frequency modulation around the estimated acoustophoretic resonance frequency can be employed to result in a more robust device operation. This piezoelectric block was glued on the bottom of the device with conductive epoxy (Epo-Tek H20E).…”