Application note: cell encapsulation in small double emulsions

Microfluidic droplet generation is a powerful technique for encapsulating biological molecules or cells within precisely controlled nL- to pL-volumes. Microfluidic droplets have been used for a wide variety of applications, including directed evolution of enzymes and proteins, digital PCR, large-scale gene assembly, cell culture, and, recently, single-cell genomic, epigenomic, and transcriptomic analyses.

The need for cell encapsulation methods and sorting devices that are safer, more effective, and simpler to use than current technologies has grown due to the exponential growth of novel techniques of cell analysis.

To perform cell encapsulation, double emulsions are ideally generated because, unlike single emulsions, they provide aqueous compartments as well as an aqueous carrier fluid, which makes the emulsion compatible with most flow cytometry and cell sorting systems.

For successful sorting, DE droplets must be significantly smaller (< 60 µm in diameter) than commercial cell sorters nozzles (typically 70–130 μm in diameter) while simultaneously large enough to encapsulate variants of interest within the inner core volume. Therefore, the possibility of developing a cell encapsulation method in double emulsions small enough to be compatible with commercial cell sorters would be a major breakthrough in the field of biomedical research.

Typically, double emulsions are produced in batches by a two-step emulsification process, resulting in a highly polydisperse population with low encapsulation efficiency. Therefore, droplet generation using microfluidics is an alternative, as it offers maximum control over droplet generation.

With the RayDrop platform, we demonstrate an easy-to-use and robust cell encapsulation method for encapsulating large, complex cells within highly monodisperse DE droplets small enough (∼ 25µm to 60µm) for high-throughput cell screening/sorting. We demonstrate the capabilities of this method by encapsulating Human Adult Peripheral Blood Mononuclear Cells (PBMC) in highly monodisperse double emulsions of 50µm in size.

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