PicoShells: Hollow Hydrogel Microparticles for High-Throughput Screening of Clonal Libraries.

Microfluidics enables the creation of monodisperse, micron-scale aqueous droplets, or other compartments. These droplets serve as picolitre-volume reaction chambers which can be utilized for various chemical assays or reactions. Here we describe the use of a microfluidic droplet generator to encapsulate single cells within hollow hydrogel microparticles called PicoShells. The PicoShell fabrication utilizes a mild pH-based crosslinking modality of an aqueous two-phase prepolymer system, avoiding the cell death and unwanted genomic modifications that accompany more typical, ultraviolet light crosslinking techniques. The cells are grown inside of these PicoShells into monoclonal colonies in any number of environments, including scaled production environments using commercially relevant incubation methods. Colonies can be phenotypically analyzed and/or sorted using standard, high-throughput laboratory techniques, namely, fluorescence-activated cell sorting (FACS). Cell viability is maintained throughout particle fabrication and analysis, and cells exhibiting a desired phenotype can be selected and released for re-culturing and downstream analysis. Large-scale cytometry runs are of particular use when measuring the protein expression of heterogeneous cells in response to environmental stimuli, notably to identify targets early in the drug discovery process. The sorted cells can also be encapsulated multiple times to direct the evolution of a cell line to a desired phenotype.