One-Step Approach to Fabricating Polydimethylsiloxane Microfluidic Channels of Different Geometric Sections by Sequential Wet Etching Processes

Summary

Several methods are available for the fabrication of channels of non-rectangular sections embedded in polydimethylsiloxane microfluidic devices. Most of them involve multistep manufacturing and extensive alignment. In this paper, a one-step approach is reported for fabricating microfluidic channels of different geometric cross sections by polydimethylsiloxane sequential wet etching.

Abstract

Polydimethylsiloxane (PDMS) materials are substantially exploited to fabricate microfluidic devices by using soft lithography replica molding techniques. Customized channel layout designs are necessary for specific functions and integrated performance of microfluidic devices in numerous biomedical and chemical applications (e.g., cell culture, biosensing, chemical synthesis, and liquid handling). Owing to the nature of molding approaches using silicon wafers with photoresist layers patterned by photolithography as master molds, the microfluidic channels commonly have regular cross sections of rectangular shapes with identical heights. Typically, channels with multiple heights or different geometric sections are designed to possess particular functions and to perform in various microfluidic applications (e.g., hydrophoresis is used for sorting particles and in continuous flows for separating blood cells^6,7,8,9). Therefore, a great deal of effort has been made in constructing channels with various sections through multiple-step approaches like photolithography using several photoresist layers and assembly of different PDMS thin sheets. Nevertheless, such multiple-step approaches usually involve tedious procedures and extensive instrumentation. Furthermore, the fabricated devices may not perform consistently and the resulted experimental data may be unpredictable. Here, a one-step approach is developed for the straightforward fabrication of microfluidic channels with different geometric cross sections through PDMS sequential wet etching processes, that introduces etchant into channels of planned single-layer layouts embedded in PDMS materials. Compared to the existing methods for manufacturing PDMS microfluidic channels with different geometries, the developed one-step approach can significantly simplify the process to fabricate channels with non-rectangular sections or various heights. Consequently, the technique is a way of constructing complex microfluidic channels, which provides a fabrication solution for the advancement of innovative microfluidic systems.

Introduction

Microfluidic techniques have drawn attention over the past decades because of their intrinsic advantages for a variety of biomedical and chemical research and applications. Several material usage options for constructing microfluidic chips are available nowadays, such as polymers, ceramics, and silicon materials. To the best of our knowledge, among the microfluidic materials, PDMS is the most common one due to its appropriate material properties for various microfluidics research and applications, including its optical and biological compatibilities with particles, fluids, and extremely small living organisms^1,2

Protocol

1. Fabrication of Microfluidic Devices with Single-Layer Channel Layouts

NOTE: In this paper, the soft lithography method³ is adopted for fabricating microfluidic devices made of PDMS materials, to demonstrate how to manufacture channels with various sections.

1. Creation of master molds for a PDMS layer with designed topology features
   1. Design channel layouts on a PDMS layer for a single etching process or etching in sequence.
   2. Sketch the inverted topology features of the designed PDMS layer using a computer-aided drawing program.
   3. Deliver the sketch file to a ....

Results

Recently, a large number of studies have been made on the fabrication of microfluidic devices with channels of different sections by lithography replica molding^13,14,15 and PDMS etching techniques^{17,18,19,20,21,}

Discussion

Over the past decades, microfluidics has offered promising means by which experimental platforms for chemical and biomedical research can be constructed systematically^1,2,3,4,5. The platforms have also presented their capabilities of investigating several cellular functions in vivo under physiological microenvironment conditions via in vitro .......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
1-Methyl-2-Pyrrolidinone	Tedia, Fairfield, OH	ME-1962	NMP
10 ml Syringe	Becton-Dickinson, Franklin Lakes, NJ	302151
150 mm Petri dish	Dogger Science	DP-43151
1H,1H,2H,2H- Perfluorooctyltrichlorosilane	Alfa Aesar, Ward Hill, MA	L16606	97 % silane
4'' Silicon Dummy Wafer	Wollemi Technical, Taoyuan, Taiwan	-
Acetone	ECHO Chemical, Miaoli, Taiwan	AH3102-000000-72EC
AG Double Expose Mask Aligner	M&R Nano Technology, Taoyuan, Taiwan	AG500-4D-D-V-S-H
Biopsy Punch	Miltex, Plainsboro, NJ	33-31
Blunt Needle	Jensen Global, Santa Barbara, CA	Gauge 16
Buffered Oxide Etch	ECHO Chemical, Miaoli, Taiwan	PH3101-000000-72EC
Desicattor	A-VAC Industries, Anaheim, CA	35.10001.01
Fluorescein Sodium Salt Water	Sigma-Aldrich Co., St Louis, MO	F6300
ImageJ	National Institutes of Health, Bethesda, MD	Ver. 1.51	Imaging Processing Program
Inverted Fluorescence Microscope	Leica Microsystems, Wetzlar, Germany	DMI 6000 B
Isopropyl Alcohol (IPA)	ECHO Chemical, Miaoli, Taiwan	CMOS112-00000-72EC
Leica Application Suite	Leica Microsystems GmbH	LAS X
MATLAB	MathWorks, Natick, MA	R2015b	Programming for MR evaluation
Mechanical Convention Oven	ThermoFisher Scientific,Waltham, MA	Lindberg Blue M MO1450C
Plasma Tretment System	Nordson MARCH, Concord CA	PX-250	Oxygen plasma surface treatment
Polydimehtylsiloxane (PDMS)	Dow Corning, Midland, MI	SYLGARD 184
Polyethylene Tubing	Becton-Dickinson and Company, Sparks, MD	427446	PE 205, 10'
Spin Coater	ELS Technology, Hsinchu, Taiwan	ELS 306MA
Negative Tone Photoresist	MicroChem, Westborough, MA	SU-8 2050
Negative Tone Photoresist Developer	MicroChem, Westborough, MA	Y020100	SU-8 Developer
Surgical Blade	Feather, Osaka, Japan	5005093	PDMS cutting
Syringe Pump	Chemyx, Houston, TX	Fusion 400
Tetra-n-butylammonium Fluoride (TBAF)	Alfa Aesar, Ward Hill, MA	A10588