Cell Culture in Microfluidic Droplets

Cell manipulation in droplets has emerged as one of the great successes ofmicrofluidic technologies, with the development of single-cell screening. However, thedroplet format has also served to go beyond single-cell studies, namely by considering theinteractions between different cells or between cells and their physical or chemicalenvironment. These studies pose specific challenges linked to the need for long-term cultureof adherent cells or the diverse types of measurements associated with complex biologicalphenomena. Here we review the emergence of droplet microfluidic methods for culturingcells and studying their interactions. We begin by characterizing the quantitative aspects thatdetermine the ability to encapsulate cells, transport molecules, and provide sufficientnutrients within the droplets. This is followed by an evaluation of the biological constraintssuch as the control of the biochemical environment and promoting the anchorage ofadherent cells. Thisfirst part ends with a description of measurement methods that have been developed. The second part of themanuscript focuses on applications of these technologies for cancer studies, immunology, and stem cells while paying specialattention to the biological relevance of the cellular assays and providing guidelines on improving this relevance.