Oct 12, 2021

Public workspaceMicrofluidics 4: PDMS Chip Soft Lithography V.4

DOI
dx.doi.org/10.17504/protocols.io.byy2pxye
  • Serhat Sevli1,
  • C. Yunus Sahan1
  • 1Nehir Biyoteknoloji Ltd. www.nehirbt.com
  • NehirBT
    Tech. support email: bilgi@nehirbt.com.tr
Serhat S
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DOI: dx.doi.org/10.17504/protocols.io.byy2pxye
Protocol Citation: Serhat Sevli, C. Yunus Sahan 2021. Microfluidics 4: PDMS Chip Soft Lithography. protocols.io https://dx.doi.org/10.17504/protocols.io.byy2pxyeVersion created by Serhat S
License: This is an open access protocol distributed under the terms of the Creative Commons Attribution License,  which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited
Protocol status: Working
We use this protocol and it’s working
Created: October 12, 2021
Last Modified: October 12, 2021
Protocol Integer ID: 54010
Keywords: microfluidics, pdms
Abstract
Microfluidics materials are of various types and application-specific. PDMS is one of the most preferred and cost-effective solutions for research and low-volume manufacturing. After having the mold, PDMS replicas are generated by a technique called soft-lithography. This protocol describes the preparation of PDMS microchannels using SU8 molds, 3D Printed resin molds, and/or metal molds by the soft lithography technique, SLA printing, or CNC machining.
Materials
PDMS material; Dow Corning, Sylgard 184

Safety warnings
* All the related steps must be done in a clean room classD (minimum).
* Please learn well about the hazards of Sylgard 184 chemicals.
Before start
This protocol is also called "soft lithography" in the literature the reference protocol is taken from the manual of Sylgard 184 silicone elastomer, Dow-Corning.
Mixing Components of PDMS
Mixing Components of PDMS
10m
10m
1.0.1. PDMS constituents are mixed in 10:1; Sylgard184 monomer : Hardening agent

Equipment
Centrifuge
NAME
Sigma
BRAND
s
SKU

Equipment
Vacuum
NAME
Vacuum Chamber with Vaccum Pump
BRAND
V
SKU

Equipment
Weighing machine
NAME
BEL Engineering
BRAND
LW423i - IT1502888
SKU

Safety information
This step is performed inside class2 laminar flow hood cabinet

1m
1.1.1. Switch on weighing machine power.

1.1.2. Place an empty 50 mL tube on the weighing machine and tare the balance.

1.1.3. Pour the Sylgard184 monomer inside a 50mL tube and make it 10gr or multiples of it.

1.1.4. Pour the Hardening Agent on Sylgard184 monomer and make the weight added 1.0 gr of the first one. So the final weight ratio for both will be 10:1.

1m
1.2.1. Components are mixed well in a tube or beaker using a glass stick.

1.2.2. The time duration required to perform the physical mixing of the Sylgard184 components must be minimum 3 minutes for 50mL tube and it can be prolonged until being sure about complete mixing.

1.2.3. Hard mixing of ingredients causes air bubbles inside which may disappear as late as an hour.
3m
1.3.1. In order to remove air bubbles quickly there are two main options;

1.3.2. The mixture is centrifuged at 500g for 5 minute.

1.3.3. The mixture is exposed to a vacuum inside the chamber.
5m
PDMS on mold
PDMS on mold
3h 36m
3h 36m
2.0.1. Pour the mixture into the mold.

Equipment
Hot Plate
NAME
Electromag
BRAND
LB.EM.M4060
SKU

Equipment
Heater Oven
NAME
Heater Oven
BRAND
30-100C
SKU

1m
2.1.1. Pour the mixture into the molds which could be the SU8 mold, 3D printed mold, or metal mold, those are put inside a petri plate and leave it for around 30 minutes at room temperature.

2.1.2. Leaving for 30 minutes at RT is necessary when air bubbles are showed up during the pouring.

2.1.3. When there are air bubbles remaining in the material, place the PDMS poured mold inside vacuum chamber for degassing for 5 minutes.
35m
2.2.1. Heating of the PDMS in the mold has alternative options.

2.2.2. If the mold is SU8 on a Silicon wafer then, PDMS is heated at 65°C for 2-3 hours on a heater plate device.

2.2.3. If the mold is 3D printed resin or metal then, PDMS is heated at 85°C for 3 hours inside a heated oven.

Safety information
The bottom of the heater plater or heater oven must be even for not to cause defects of uneven thickness on PDMS.

3h
Stock of PDMS
Stock of PDMS
1w
1w
3.0.1. The excess of mixed PDMS (but not heated) can be stored in a refrigerator (+4°C) for up to one week.
3.0.2. Just take from the refrigerator and pour on a new mold and incubate.

Safety information
A longer duration for storage is not suggested since PDMS can polymerase longer even at lower temperatures.

1w
Demolding of Cured PDMS
Demolding of Cured PDMS
11m
11m
4.0.1. After completion of the curing time of PDMS on mold, the PDMS gel is removed carefully away from the mold.

4.0.2. Being gentle is important at this step not to form defects on the PDMS layer.

4.0.3. The PDMS layer is put inside a clean petri dish or clean plastic surface.
Safety information
This step is performed inside the class2 laminar flow hood cabinet.

10m
4.1.1. Visual check of PDMS layer is performed under a digital microscope, and these parameters are checked mainly;

- Debris (Trace), air bubbles (active areas), Stains-Voids, Scratch marks, Broken PDMS, Uneven PDMS, Wrong Orientation (PDMS)
1m