Combining Hydrophilic and Hydrophobic Materials in 3D Printing for Fabricating Microfluidic Devices with Spatial Wettability

Abstract

The fabrication of microfluidic flow cells via projection micro‐stereolithography (PμSL) has excited researchers in recent years. However, due to the inherent process properties of most commercial PμSL, microfluidic devices are fabricated in a monolithic fashion with uniform material properties across a flow cell. Yet, the large surface‐to‐volume ratio in microfluidics demands to tailor microchannel surface properties—particularly in planar microchannel arrangements—with spatial control and micron‐scale resolution to form a desired flow profile, e.g., emulsion droplets. Here, the fabrication of planar microfluidic devices by PμSLbased 3D printing with spatial control over surface properties is presented. For that, homemade photopolymer formulations being either hydrophilic or hydrophobic are designed. Adding acrylic acid to a resin containing poly(ethylene glycol) diacrylate lowers the contact angle down to 0° against water creating a superhydrophilic surface. By utilizing 1H,1H,2H,2H‐perfluorodecyl acrylate, a photopolymer formulation allowing for 3D‐printing a hydrophobic microchannel surface with a contact angle >120° against water is obtained. Combining these two materials, microfluidic flow cells with spatially defined wettability are 3D‐printed for emulsion formation. Finally, the resin vat of the commercial PμSL printer is switched during the printing process for fabricating multimaterial geometries, as exemplarily applied for realizing a hydrophobic‐hydrophilic‐hydrophobic device for forming O/W/O double emulsions.

A novel biomedical compatibilizer (polyvinyl alcohol‐allyl polyethylene glycol graft copolymer) for polyvinyl alcohol/polyethylene oxide composite system

“…The results of the lyophilicity of PVA‐g‐APEG/PVA/PEO nanofiber dressings for different liquids are shown in Figure 9a. The surface contact angles of nanofiber dressings to three different liquids are far less than 90°, indicating that nanofiber dressings have excellent lyophilicity and can maintain good affinity when in contact with damaged wounds 59 . Figure 9b shows the results of the liquid absorption rate and liquid absorptivity of the nanofiber dressings.…”

“…The surface contact angles of nanofiber dressings to three different liquids are far less than 90 , indicating that nanofiber dressings have excellent lyophilicity and can maintain good affinity when in contact with damaged wounds. 59 Figure 9b shows the results of the liquid absorption rate and liquid absorptivity of the nanofiber dressings. It can be seen that the nanofiber dressings have a faster liquid absorption rate and larger liquid absorptivity for different liquids, and the maximum liquid absorption amount can reach 214.53%.…”

Fundamentals and utilization of solid/ liquid phase boundary interactions on functional surfaces

“…As miniaturisation is ganining ground in nanotechnology, analytics (Lab-on-a-chip or LOC) [283], emulsification [284] or demulsification [280][281][282], flow chemistry [285] and other applications, the implementation of manipulating extremely small liquid volumes becomes more and more important.…”

“…especially PDMS [288], polyacrilates [284] and cellulose [290,291]. It is a common practice to hydrophilize the inherently hydrophobic silicone surfaces via oxidative treatment, however, these surfaces slowly transform back to hydrophobic overtime as the diffusion of lower molecular weight silicone species towards the interface proceeds [288].…”

Super‐Hydrophilic Zwitterionic Polymer Surface Modification Facilitates Liquid Transportation of Microfluidic Sweat Sensors

“…[32,33] However, traditional elastomers often suffer from inherent limitations due to their hydrophobic nature, which leads to poor wettability of the microfluidic devices and results in insufficient sweat transportation of the sensors. Common strategies to improve the wettability of PDMS-based microfluidic devices include 1) mixing hydrophilic polymers such as 2-[methoxy (polyethyleneoxy) propyl] heptamethyltrisiloxane with PDMS during the fabrication of the microfluidic devices, [34][35][36] 2) in situ coating of hydrophilic polymers on the microfluidic devices, [37][38][39] and 3) creating surface microstructures in non-wetting substrates within the channels. [40][41][42][43] However, all these approaches face different problems.…”