Multi-step Variable Height Photolithography for Valved Multilayer Microfluidic Devices

Kara Brower; Adam K. White; Polly M. Fordyce

doi:10.3791/55276

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Method Article

Multi-step Variable Height Photolithography for Valved Multilayer Microfluidic Devices

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DOI:

10.3791/55276

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January 27th, 2017

Kara Brower^*¹^,²^,⁴ , Adam K. White^*¹^,² , Polly M. Fordyce¹^,²^,³^,⁴

¹Department of Bioengineering, Stanford University, ²Microfluidic Foundry, Stanford University, ³Department of Genetics, Stanford University, ⁴Chem-H Institute, Stanford University

^* These authors contributed equally

Summary

Multilayer microfluidic devices often involve the fabrication of master molds with complex geometries for functionality. This article presents a complete protocol for multi-step photolithography with valves and variable height features tunable to any application. As a demonstration, we fabricate a microfluidic droplet generator capable of producing hydrogel beads.

Abstract

Microfluidic systems have enabled powerful new approaches to high-throughput biochemical and biological analysis. However, there remains a barrier to entry for non-specialists who would benefit greatly from the ability to develop their own microfluidic devices to address research questions. Particularly lacking has been the open dissemination of protocols related to photolithography, a key step in the development of a replica mold for the manufacture of polydimethylsiloxane (PDMS) devices. While the fabrication of single height silicon masters has been explored extensively in literature, fabrication steps for more complicated photolithography features necessary for many interesting device functionalities (such as feature rounding to make valve structures, multi-height single-mold patterning, or high aspect ratio definition) are often not explicitly outlined.

Here, we provide a complete protocol for making multilayer microfluidic devices with valves and complex multi-height geometries, tunable for any application. These fabrication procedures are presented in the context of a microfluidic hydrogel bead synthesizer and demonstrate the production of droplets containing polyethylene glycol (PEG diacrylate) and a photoinitiator that can be polymerized into solid beads. This protocol and accompanying discussion provide a foundation of design principles and fabrication methods that enables development of a wide variety of microfluidic devices. The details included here should allow non-specialists to design and fabricate novel devices, thereby bringing a host of recently developed technologies to their most exciting applications in biological laboratories.

Introduction

For the past 15 years, microfluidics as a field has undergone rapid growth, with an explosion of new technologies enabling the manipulation of fluids at the micrometer scale¹. Microfluidic systems are attractive platforms for wet laboratory functionality because the small volumes have the potential to realize increased speed and sensitivity while at the same time dramatically increasing throughput and reducing cost by leveraging economies of scale²^,³. Multilayer microfluidic systems have made particularly significant impacts in high-throughput biochemical analysis applications such as s....