Stop-flow Lithography to Continuously Fabricate Microlens Structures Utilizing an Adjustable Three-Dimensional Mask

Abstract

Stop-flow lithography (SFL) is a microfluidic-based particle synthesis method, in which photolithography with a two dimensional (2D) photomask is performed in situ within a microfluidic environment to fabricate multifunctional microstructures. Here, we modified the SFL technique by utilizing an adjustable electrostatic-force-modulated 3D (EFM-3D) mask to continuously fabricate microlens structures for high-throughput production. The adjustable EFM-3D mask contains a layer filled with a UV-absorbing liquid and transparent elastomer structures in the shape of microlenses between two conductive glass substrates. An acrylate oligomer stream is photopolymerized via the microscope projection photolithography, where the EFM-3D mask was set at the field-stop plane of the microscope, thus forming the microlens structures. The produced microlens structures flow downstream without adhesion to the polydimethysiloxane (PDMS) microchannel surfaces due to the existence of an oxygen-aided inhibition layer. Microlens structures with variations in curvature and aperture can be produced by changing objective magnifications, controlling the morphology of the EFM-3D mask through electrostatic force, and varying the concentration of UV-light absorption dyes. We have successfully demonstrated to produce microlens structures with an aperture ranging from 50 μm to 2 mm and the smallest focus spot size of 0.59 μm. Our proposed method allows one to fabricate microlens structures in a fast, simple and high-throughput mode for application in micro-optical systems. OPEN ACCESSMicromachines 2014, 5 668

Stop-Flow Lithography for the Continuous Production of Degradable Hydrogel Achiral Crescent Microswimmers

“…Note that the oxygen that penetrated the microfluidic chip inhibited the cross-linking polymerization reactions; as a result, a 2–3 μm thick lubricating layer was formed around the microchannel, where no crosslinking occurred. This layer is known as an oxygen inhibition layer ( Figure 1 B) [ 24 ]. The oxygen inhibition layer allowed the solidified hydrogel crescent microswimmers to be easily flushed out by pressure-driven flow without sticking to the surface of the microchannel.…”

Hydrogel microparticles for biosensing

“…A recent paper reported the use of temperature-responsive poly(N-isopropylacrylamide) particles in conjunction with an electrochemical luminescence amplification method [129]. Hydrogel microlenses were fabricated from poly(N-isopropylacrylamide-co-acrylic acid (pNIPAAM) for label-free sensing using differential interference constrast imaging [130], and microlens particles were produced using stop-flow lithography [131]. Combined with detection techniques and biomolecule immobilization strategies, these novel chemistries could open new avenues for target detection on gel particle arrays.…”

Flow lithography for structured microparticles: fundamentals, methods and applications

“…Structured microparticles with customizable shapes, sizes, and chemistries (chemical and material compositions) 1 have demonstrated value across multiple fields including diagnostics, 23 drug/cargo delivery microrobots, [4][5][6][7] tissue engineering, [8][9][10] multiplexed assays, 11,12 self-assembly, [13][14][15] photonics, 16 optics, 17,18 and pharmaceuticals. 19 Particularly for numerous biomedical applications, these structured microparticles provide solid surfaces for barcoded or shapecoded molecular assays, 20,21 act as scaffolds to promote cell growth and infiltration for tissue regeneration, 22,23 enable uniform compartmentalization for high-throughput single-cell analysis, 24 serve as carriers for adhesive cell lines in imagingbased cytometry studies, 25 etc.…”