title: Simple Multi-level Microchannel Fabrication by Pseudo-Grayscale Backside Diffused Light Lithography.
abstract: Photolithography of multi-level channel features in microfluidics is laborious and/or costly. Grayscale photolithography is mostly used with positive photoresists and conventional front side exposure, but the grayscale masks needed are generally costly and positive photoresists are not commonly used in microfluidic rapid prototyping. Here we introduce a simple and inexpensive alternative that uses pseudo-grayscale (pGS) photomasks in combination with backside diffused light lithography (BDLL) and the commonly used negative photoresist, SU-8. BDLL can produce smooth multi-level channels of gradually changing heights without use of true grayscale masks because of the use of diffused light. Since the exposure is done through a glass slide, the photoresist is cross-linked from the substrate side up enabling well-defined and stable structures to be fabricated from even unspun photoresist layers. In addition to providing unique structures and capabilities, the method is compatible with the "garage microfluidics" concept of creating useful tools at low cost since pGS BDLL can be performed with the use of only hot plates and a UV transilluminator: equipment commonly found in biology labs. Expensive spin coaters or collimated UV aligners are not needed. To demonstrate the applicability of pGS BDLL, a variety of weir-type cell traps were constructed with a single UV exposure to separate cancer cells (MDA-MB-231, 10-15 μm in size) from red blood cells (RBCs, 2-8 μm in size) as well as follicle clusters (40-50 μm in size) from cancer cells (MDA-MB-231, 10-15 μm in size).
authors: Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA ; Reproductive Sciences Program, University of Michigan, Ann Arbor, MI, USA.
authors: David
authors: D
authors: Lai
authors: Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA.
authors: Joseph M
authors: JM
authors: Labuz
authors: Reproductive Sciences Program, University of Michigan, Ann Arbor, MI, USA ; Department of Macromolecular Science and Engineering, University of Michigan, Ann Arbor, MI, USA.
authors: Jiwon
authors: J
authors: Kim
authors: Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA ; Department of Radiology, University of Michigan, Ann Arbor, MI, USA ; Department of Microbiology and Immunology, University of Michigan, Ann Arbor, MI, USA.
authors: Gary D
authors: GD
authors: Luker
authors: Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA ; Reproductive Sciences Program, University of Michigan, Ann Arbor, MI, USA ; Department of Macromolecular Science and Engineering, University of Michigan, Ann Arbor, MI, USA.
authors: Ariella
authors: A
authors: Shikanov
authors: Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA ; Reproductive Sciences Program, University of Michigan, Ann Arbor, MI, USA ; Department of Macromolecular Science and Engineering, University of Michigan, Ann Arbor, MI, USA ; Division of Nano-Bio and Chemical Engineering WCU Project, UNIST, Ulsan, Republic of Korea.
authors: Shuichi
authors: S
authors: Takayama