We present a library of resin formulations for projection micro-stereolithography (PµSL) consisting of 4-hydroxybutyl acrylate (HBA), poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) and poly(ethylene glycol) diacrylate (PEGDA), diluted with aqueous solutions of the photoinitiator lithium phenyl(2,4,6-trimethylbenzoyl)phosphinate (LAP) and the photoabsorber tartrazine. By varying the concentration and molecular weight of PEGMEMA and PEGDA, the swelling ratios of as-PµSL-printed hydrogel microstructures in water are well tunable with a reversible volume increase ranging from 13% to 86%. Furthermore, we illustrate the influence of exposure time per 3D-printed layer on the swelling ratio of the hydrogels, as well as the swelling time. The minimum feature size of rectangular void structures achieved with an exemplary resin from our material library is approx. 71 μm, while rectangular microchannels at the surface of a PµSLprinted hydrogel made from the same photopolymer formulation exhibit cross-sectional dimensions designed at 54 μm x 50 μm. Based on this initial characterization, microfluidic devices are fabricated to elucidate dimensional changes of microchannels under different swelling conditions (e.g., free swelling and confined swelling inside a chamber or microfluidic device). In addition, we PµSL-print microscopic parts with tailored geometries (cylindrical, pyramidal) that are capable of completely closing microfluidic chambers made from commercially available Perfactory R11 resin in a time-dependent fashion. Our resin library provides 3D-printed hydrogels with micron-scale feature size combined with tunable water uptake, rendering them suitable for designing functional microfluidic units such as membranes, valves and pumps.
Chemically resistant polymer materials are of great interest due to their versatile implementation in a broad range of applications, including the design of robust microfluidic devices. While flow cells, conventionally fabricated by using poly(dimethylsiloxane) (PDMS), are hardly resistant toward organic solvents, fluorinated materials are chemically inert. However, focusing on the latest developments in microfluidic device design via high-resolution additive manufacturing, e.g., based on micro-stereolithography (μSL), only a few resin formulations have been demonstrated suitable for 3D printing chemically resistant polymer objects. Here, we introduce a homemade resin formulation based on 1H,1H,6H,6H-Perfluoro-1,6-hexyl diacrylate (PFHDA) for high-resolution 3D printing utilizing μSL. By investigating the optical dose, the wettability, the resistance toward organic solvents, and the minimal resolution achievable, we fabricate inner structures down to 200 μm. Finally, water-in-oil (W/O) emulsions are generated in a 3D-printed droplet maker with planar microchannel geometry made from the PFHDA-based resin yielding droplets with an average diameter of 271 μm ± 26 μm. The presented material is resistant against commonly used organic solvents including THF, DMF and toluene with a swelling below 1.5% and shows no solvent-induced damage to the micro-printed structure, which makes the PFHDA-based resin a promising base material for several potential applications such as organic synthesis in microreactors.
Here, we demonstrate the additive manufacturing of two key microvalve designs, namely Nordin’s and Quake’s microvalves, based on a formulation consisting of tri(propylene glycol) diacrylate (TPGDA) as a base material, diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO) as a photoinitiator and Sudan1 as the UV-absorber via micro-stereolithography (μSL). Mechanical measurements of test prints show an average Young’s modulus of 15.7 MPa, which is eight times lower compared to several previous studies on 3D-printed microvalves and micropumps based on poly(ethylene glycol diacrylate) 255 (PEGDA-252). We use a high-resolution Cerafab7500 printer (Lithoz GmbH, Vienna) with a minimal lateral resolution of 10.3 μm to print membrane valves with voxel dimensions down to 60μm. Particularly, we study the effect of different comonomers added to the photopolymer formulation – neopentyl glycol propoxylate (1 PO/OH) diacrylate (NPGPDA), 1,6- hexanediol diacrylate (HDDA) and 2-phenoxyethyl acrylate (POEA) – on the layer thickness, which is identified to be a crucial parameter. 3D-printed valves are tested regarding maximum operating pressure withstanding pressures of up to 5 bar. We show that TPGDA-based resins combine high flexibility, mechanical stability, and sufficient resolution for the future design of flow control units in microfluidics.
Conference Committee Involvement (5)
Microfluidics, BioMEMS, and Medical Microsystems XXIII
25 January 2025 | San Francisco, California, United States
Microfluidics, BioMEMS, and Medical Microsystems XXII
28 January 2024 | San Francisco, California, United States
Microfluidics, BioMEMS, and Medical Microsystems XXI
29 January 2023 | San Francisco, California, United States
Microfluidics, BioMEMS, and Medical Microsystems XX
22 January 2022 | San Francisco, California, United States
Microfluidics, BioMEMS, and Medical Microsystems XIX
6 March 2021 | Online Only, California, United States
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