Microfluidic Device Fabrication

From LPDwiki

About this protocol: This assumes the user has created a mold following the steps outlined in Laser Cutting Channel Mold.

Necessary Materials

1. Sylgard 184 Silicone Elastomer Kit

  • Purchased from Dow Corning
  • Includes elastomer base and curing agent

2. One or more 50 mL tubes

  • Purchased from Vet Med Central Services

3. Tube rack and transfer box for transporting between rooms

4. Petri dish containing laser cut silver film for shaping PDMS

5. Aluminum foil (Reynolds Wrap)

  • Can be purchased from VMCS

6. 1 mL bottle filled with tap water

  • Not essential, but will assist in the heating process

7. Razor blades

  • These can be bought from various sources

8. Substrate, usually glass slides or silicon chips

  • Cover glass breaks easily and cannot be used for staining. Thicker microscope slides are recommended.

9. Hole punch, 1.5 mm diameter

Procedure

1. Take PDMS kit, tube(s) and rack in transfer box to room 1246.

2. Turn the scale on and ensure that it reads 0.00 g (tare if needed). Place an uncapped 50 mL tube on the rack. Press the “tare” button and wait until the scale reads 0.00 g.

3. Slowly pour desired amount of elastomer base into tube (generally 20-30 g is sufficient for a 100 mm diameter petri dish).

4. Take note of the displayed mass and tare the scale again.

5. Carefully pour the appropriate amount of curing agent into the tube (1:10 ratio is most common, which would require 1/10th of the mass of elastomer base).

Note: the stir bar may be dirty, so cleaning beforehand with acetone (located in fume hood) is recommended.

6. Use stir bar to mix PDMS mixture. Use a vigorous, swirling motion while vertically moving the bar to evenly mix. This will create many air bubbles. 7. Clean up and move supplies to the desiccator / vacuum chamber.

8. Pour PDMS mixture slowly into petri dish with silver mold.

9. Place a fresh layer of aluminum foil over the bottom of the chamber to prevent PDMS from dripping onto any surfaces.

10. Place dish in chamber (without lid), close the chamber, and turn the vacuum line on to evacuate the chamber. This will remove air bubbles from the mixture. Let sit in evacuated chamber for 1 hour.

11. After turning the vacuum line off and removing the cover, place the lid on the petri dish, turn the hot plate on and set to 80 °C, and place dish on center of hot plate. Place the filled bottle on top of the petri dish. Let sit for at least 2 hours.

12. After removing bottle and dish from hot plate, ensure that the PDMS has set by probing with tweezers. If any PDMS sticks to the tweezers, place dish and bottle back onto hot plate for additional time.

13. Carefully peel PDMS from petri dish using metal spatula. Keep petri dish for future use. The PDMS can be stored in a separate petri dish.

14. Cut PDMS around channel impression with razor blade so that it will fit onto substrate. Leave sufficient area to ensure strong enough bonding.

15. Using 1.5 mm hole punch, carefully push perpendicular to PDMS surface where holes are needed. Ensure that hole breaches other side of PDMS.

16. If PDMS is dusty, wash with 70% ethanol solution, dry with nitrogen gas, and use small strips of tape to remove particles from surface. Repeat for substrate if needed.

17. Cover the plasma cleaner’s removable glass slide with a large Kimwipe and place PDMS and substrate onto slide and into the plasma cleaner. The PDMS should be facing upside-down in order to treat the underside.

18. Place the seal over the opening of the plasma cleaner, ensure that the knob is loosened by several turns, and turn pump on. Air rushing into the chamber should be heard. Tighten the knob fully and slowly to evacuate the chamber. Let evacuate for 1 minute at least.

19. Turn plasma switch on while power knob is set to “off”. After evacuating is finished, turn knob to high power and loosen seal knob slightly, until a deep purple color can be seen in the chamber. Time for 15-20 seconds.

20. Turn power knob to off position, turn plasma off, and turn pump off (in order). Loosen seal knob until air stops rushing into chamber, then remove cover.

21. Quickly place PDMS on substrate, making sure to align if necessary. Bonding should take a matter of seconds.

22. After ensuring that PDMS has bonded, place device in vacuum chamber and evacuate for 30 minutes to prevent bubble formation in channel.

The device can then be stored or used immediately. See Microfluidic Cell Culture protocol.