Systematic characterization of effect of flow rates and buffer compositions on double emulsion droplet volumes and stability

Calhoun, Suzanne G.K.; Brower, Kara K.; Suja, Vineeth Chandran; Kim, Gaeun; Wang, Ningning; McCully, Alexandra L.; Kusumaatmaja, Halim; Fuller, Gerald G.; Fordyce, Polly M.

Abstract

Double emulsion droplets (DEs) are water/oil/water droplets that can be sorted via fluorescence-activated cell sorting (FACS), allowing for new opportunities in high-throughput cellular analysis, enzymatic screening, and synthetic biology. These applications require stable, uniform droplets with predictable microreactor volumes. However, predicting DE droplet size, shell thickness, and stability as a function of flow rate has remained challenging for monodisperse single core droplets and those containing biologically-relevant buffers, which influence bulk and interfacial properties. As a result, developing novel DE-based bioassays has typically required extensive initial optimization of flow rates to find conditions that produce stable droplets of the desired size and shell thickness. To address this challenge, we conducted systematic size parameterization quantifying how differences in flow rates and buffer properties (viscosity and interfacial tension at water/oil interfaces) alter droplet size and stability, across 6 inner aqueous buffers used across applications such as cellular lysis, microbial growth, and drug delivery, quantifying the size and shell thickness of >22 000 droplets overall. We restricted our study to stable single core droplets generated in a 2-step dripping–dripping formation regime in a straightforward PDMS device. Using data from 138 unique conditions (flow rates and buffer composition), we also demonstrated that a recent physically-derived size law of Wang et al. can accurately predict double emulsion shell thickness for >95% of observations. Finally, we validated the utility of this size law by using it to accurately predict droplet sizes for a novel bioassay that requires encapsulating growth media for bacteria in droplets. This work has the potential to enable new screening-based biological applications by simplifying novel DE bioassay development.

Citation

Calhoun, S. G., Brower, K. K., Suja, V. C., Kim, G., Wang, N., McCully, A. L., Kusumaatmaja, H., Fuller, G. G., & Fordyce, P. M. (2022). Systematic characterization of effect of flow rates and buffer compositions on double emulsion droplet volumes and stability. Lab on a Chip, 22(12), https://doi.org/10.1039/d2lc00229a

• Journal Article Type: Article
• Acceptance Date: May 3, 2022
• Online Publication Date: May 9, 2022
• Publication Date: 2022
• Deposit Date: Jul 21, 2022
• Publicly Available Date: Jul 21, 2022
• Journal: Lab on a Chip
• Print ISSN: 1473-0197
• Electronic ISSN: 1473-0189
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 22
• Issue: 12
• DOI: https://doi.org/10.1039/d2lc00229a
• Public URL: https://durham-repository.worktribe.com/output/1199714