Rapid Prototyping of Organ-on-a-Chip Devices Using Maskless Photolithography

Abstract

Organ-on-a-chip (OoC) and microfluidic devices are conventionally produced using microfabrication procedures that require cleanrooms, silicon wafers, and photomasks. The prototyping stage often requires multiple iterations of design steps. A simplified prototyping process could therefore offer major advantages. Here, we describe a rapid and cleanroom-free microfabrication method using maskless photolithography. The approach utilizes a commercial digital micromirror device (DMD)-based setup using 375 nm UV light for backside exposure of an epoxy-based negative photoresist (SU-8) on glass coverslips. We show that microstructures of various geometries and dimensions, microgrooves, and microchannels of different heights can be fabricated. New SU-8 molds and soft lithography-based polydimethylsiloxane (PDMS) chips can thus be produced within hours. We further show that backside UV exposure and grayscale photolithography allow structures of different heights or structures with height gradients to be developed using a single-step fabrication process. Using this approach: (1) digital photomasks can be designed, projected, and quickly adjusted if needed; and (2) SU-8 molds can be fabricated without cleanroom availability, which in turn (3) reduces microfabrication time and costs and (4) expedites prototyping of new OoC devices.

Microfluidic Organ-on-A-chip: A Guide to Biomaterial Choice and Fabrication

“…The first one, which is also named optical lithography or UV lithography, is a method that utilizes light, mostly UV light with a wavelength of 250–435 nm, to transfer three-dimensional designs from a template onto a thin photo-sensitive (photoresist) film attached over a silicon substrate [ 112 , 164 ]. When exposed to light, the photo resistant parts change their chemical structure and become solidified at the end of the process.…”

“…For example, the equipment for this technique is exorbitant, and it requires a cleanroom for the photolithographic machine to operate [ 111 ]. Recently, to eliminate those disadvantages, Kasi et al (2022) used a simplified process called maskless photolithography [ 112 ]. The novel approach developed a more time- and cost-effective and cleanroom-free fabrication using 375 nm UV light for a negative photoresist (SU-8) mould.…”

“…The authors reported that grayscale photolithography could produce microstructures with different widths and heights in a single-step operation. They concluded that the findings would promote the manufacture of variable OoAC platforms in the future [ 112 ].…”

Homebrew Photolithography for the Rapid and Low-Cost, “Do It Yourself” Prototyping of Microfluidic Devices

“…Any damage or changes to designs would require having to pay again and repeat the process for every minute modification to the design, which is incompatible with the design, build, and test engineering principle of exploratory development and negates any ability to rapidly prototype. In light of this constraint, various alternative methods have been investigated, including the use of 35 mm photographic negatives as photomasks, and even maskless photolithography, including the use of standard inkjet printers both to produce a photomask by printing negative designs onto transparency film and more direct methods of inkjet print-patterning onto surfaces using a variety of inks. Inkjet printers can produce linewidths down to 50 μm …”

Rapid Prototyping of High-resolution Large Format Microfluidic Device Through Maskless Image Guided In-situ Photopolymerization

“…On one side, some techniques focused on using hot embossing 4 , micro-milling 5 , micro-injection molding 6 , etc. to fabricate devices out of an alternative thermoplastic material such as thermoplastic materials such as polymethyl methacrylate (PMMA) 7 , cyclic olefin copolymer (COC) 8 or polycarbonate (PC) 9 while others focused on replacing the conventional mold making process still keeping the PDMS as the base material for replication such as wax-printing 10 , laser-jet printing 11 , 3D printing 12,13 , tonerprinting 14 , femtosecond laser 15 , two photon polymerization (2PP) 16 , digital micromirror devices (DMD) 17,18 , direct laser writing (DLW) 19,20 , electron-beam lithography (EBL) 21,22 , ion-beam etching (IBE) 23,24 , etc. Moreover, most of them fail to bridge the balance between the minimum feature size and cost.…”