Rapid preparation of highly reliable PDMS double emulsion microfluidic devices

Abstract

This article presents a simple and highly reliable method for preparing PDMS microfluidic double emulsion devices that employs a single-step oxidative plasma treatment to both pattern the wettability of microchannels and to bond the chips. As a key component of our strategy we use epoxy glue to define the required hydrophobic zones and then remove this after plasma treatment, but prior to bonding. This novel approach achieves surface modification and device sealing in a single process, which reduces chip preparation times to minutes and eliminates the need for unreliable coating processes. The second key element of our procedure is the maintenance of the patterned surfaces, where we demonstrate that immediate filling of the prepared device with water or the use of solventextracted PDMS vastly extends the operational lifetimes of the chips. The reliability of this technique is confirmed by generating water-in-oil-in-water (W/O/W) double emulsion droplets with controlled core/shell structures and volumes, while its versatility is demonstrated by simply using a different placement of the epoxy glue on the same chip design to create oil-in-water-in-oil (O/W/O) double emulsion droplets. Both W/O/W and O/W/O double emulsion droplets can therefore be created from the same soft-lithography mould. This simple method overcomes one of the key problems limiting the wider use of double emulsions lack of reliability while its speed and simplicity will facilitate the high-throughput production of monodisperse double emulsions. Our method is demonstrated to produce double emulsion down to 55 µm in diameter and could be readily extended to produce microfluidic chips with more complex hydrophilic and hydrophobic patterns.

Marker patterning: a spatially resolved method for tuning the wettability of PDMS

“…As expected the droplets size can be tuned by varying the ow rates: keeping the oil and the external water phase ow rates constant, the higher the internal water phase ow rate, the higher the internal water droplet diameter, in agreement with what is reported in the literature. 15,21,22 Accordingly, for given external and internal water phases ow rate, an increase of the oil phase ow rate leads to a decrease of the internal water droplet size.…”

“…In another paper, Li et al 15 developed a simple method to pattern the PDMS surface by masking the areas to be kept hydrophobic with epoxy glue during the plasma treatment. This method can be used in many geometries.…”

An ultrahigh‐throughput screening platform based on flow cytometric droplet sorting for mining novel enzymes from metagenomic libraries

“…Although the hydrophilicity of plasma‐treated PDMS decreased over time during storage, its contact angle was still 60° (similar to native glass) even when exposed to air at room temperature for 4 h. Moreover, Li et al . (2016) reported that plasma‐treated PDMS hydrophilicity could be stabilized by submersion in water, with a 33.9° contact angle after 72 h. Therefore, during double emulsion droplet generation, we expect the plasma‐treated PDMS device to maintain high hydrophilicity for more than 4 h. Next, we bonded the plasma‐treated PDMS slide with microfluidic channel features to a glass slide, obtaining a sealed hydrophilic microfluidic device. Employing this device, we observed continuous and stable double emulsion droplet generation lasting for at least 10 h (data not shown).…”

Polylactic acid, a sustainable, biocompatible, transparent substrate material for Organ-On-Chip, and Microfluidic applications

“…While some of these issues have been overcome with time-consuming protocols (e.g. soxhlet extraction in ethanol, or other organic solvent, to remove uncrosslinked oligomers [5]), PDMS moulding still remains a difficult process to fully automate [6] significantly slowing down the translation from the research to the mass market production.…”