Use of semi-permeable capsules in multi-step processing of single cells

Soumya Sarathi Ganguly, Indian Institute of Technology, Kharagpur

Droplet microfluidic technologies can be used to isolate and process millions of single cells, but it fails to include molecular biology and cell-based phenotypic assays. Here, we can use a semi-permeable hydrogel capsule based on a microfluidic-based technique to simultaneously isolate and process millions of cells. The hydrogel capsules can retain biomolecules, such as the genome while allowing passive diffusion of small molecules like protein in the surrounding buffer. This surrounding buffer can be changed without the use of sophisticated pieces of equipment. This can be used to perform each step of a multi-step process independently from the preceding step, as the molecule or the microorganism is embedded in the hydrogel mesh. The hydrogel particles are made up of an aqueous two-phase system (ATPS) composed of dextran and acrylate-modified PEG. This study compared the efficiency of genome amplification of both gram-positive and gram-negative organisms. The results say that efficiency is higher in capsuled-based systems. 

These semi-permeable-based systems help keep the capsules intact during harsh laboratory procedures rather than leading to disintegration and thus are well-suited for single-cell assays. Sequential and incompatible reactions were performed, to signify the use of these gel-based systems in biology, on gram-positive and gram-negative bacterial cells. The results showed a high yield of amplified genomes in the capsule-based system due to the efficient exchange of reagents across the semi-permeable shells. In another experiment, it is showed that these capsules can be expanded to isogenic microcolonies, as the physiological activity is well maintained inside the capsules by the bacteria cells. This is done by harvesting and characterizing encapsulated cells, by their biological and phenotypic features, using fluorescence-based readouts. These capsule-based systems also have some limitations, as they don’t retain the small molecules like proteins or enzymes; thus this creates a problem while screening of secreted proteins. By changing the pore size of the semi-permeable capsules by varying the concentration of acrylate-modified PEG, this limitation can be resolved. Though more efforts are required for preparing the right blend of the composition of the semi-permeable capsules. And the diameter of the capsule is limited to 25-60 µg range by using the PEGDA polymer blend.

The advantages of these semi-permeable capsules are huge in front of the limitations, and these systems greatly benefit the application in biology, in various multi-step single-cell processes.

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Reference: Leonaviciene G, Leonavicius K, Meskys R, Mazutis L. Multi-step processing of single cells using semi-permeable capsules. Lab on a Chip. 2020;. https://pubs.rsc.org/en/content/articlelanding/2020/LC/D0LC00660B#!divAbstract 

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