PDMS Microfluidic Chip Guide: Handling, Storage, and Troubleshooting

Why PDMS Chips Need Special Care

PDMS (polydimethylsiloxane) is the most common material for research microfluidic chips because it's cheap, transparent, gas-permeable, and easy to mold. But PDMS has quirks that will ruin your experiment if you don't know how to work with it:

• Surface properties change over time — a freshly plasma-bonded chip is hydrophilic, but PDMS recovers its native hydrophobicity within hours to days
• PDMS absorbs small molecules — dyes, drugs, and hydrophobic compounds partition into the bulk material, skewing concentrations
• Bonding can fail — PDMS-glass bonds delaminate if you exceed the pressure limit or expose the chip to certain solvents
• Air bubbles stick — PDMS's hydrophobicity makes bubble removal harder than in glass or plastic chips

This guide gives you the practical knowledge to avoid these pitfalls and get reliable results from PDMS/glass chips.

Unpacking and Initial Inspection

What to check when your chip arrives

1. Visual inspection under ambient light

   • Look for cracks in the glass substrate (disqualifies the chip)
   • Check PDMS layer for tears, especially near inlet/outlet ports
   • Confirm the bond line is uniform (no obvious gaps between PDMS and glass)

2. Hold up to a bright light

   • Channels should appear as clean, uniform lines
   • Look for trapped particles or dust (some particulate is normal; large debris is not)
   • Check for air gaps at the PDMS-glass interface (small bubbles at the periphery are OK; large voids under channels are not)

3. Gently flex the chip

   • The PDMS should NOT peel away from the glass
   • If you see the bond line move or separate, the plasma bond has failed—don't use this chip under pressure

First-use recommendation: If the chip passed inspection, flush all channels with IPA (isopropyl alcohol) using a syringe, then blow dry with clean air or nitrogen. This removes any residual dust from fabrication.

Storage: Keeping Your Chips Ready to Use

Short-term storage (days to weeks)

For chips you plan to use soon:

• Store in the original sealed ESD bag or a clean petri dish
• Keep at room temperature in a drawer (light exposure degrades PDMS over months)
• Do NOT refrigerate — condensation when you bring the chip back to room temperature will coat channels with water droplets

Surface treatment preservation: If your chip was plasma-treated or coated (e.g., with PLL-PEG for anti-fouling), use it within 24 hours. After that, the treatment degrades.

To extend surface treatment life by a few days:

• Immediately after receiving the chip, fill all channels with sterile water or PBS
• Seal inlet/outlet ports with tape or parafilm
• Store submerged in water in a sealed container at 4°C
• This keeps the surface hydrophilic longer, but you still lose ~50% effectiveness after 3 days

Long-term storage (months)

For backup chips or future experiments:

• Keep in the original ESD bag with desiccant pack
• Store in a dark, dry place at room temperature (not in a freezer)
• PDMS shelf life is ~1 year if stored properly; after that, the material becomes stiffer and more prone to cracking

Re-activation before use: After long storage, PDMS surfaces are fully hydrophobic. You'll need to re-treat them (see Pre-Use Preparation below).

Pre-Use Preparation

For water-in-oil droplet generation (hydrophobic channels needed)

Goal: Ensure PDMS channels are hydrophobic so the continuous oil phase wets the walls.

1. Check current hydrophobicity

   • Pipette a small drop of water onto the chip surface
   • If it beads up (contact angle >90°), channels are already hydrophobic—proceed to step 3
   • If it spreads out, you need to restore hydrophobicity (step 2)

2. Restore hydrophobicity (if needed after long storage or previous aqueous use)

   • Method A (fastest): Bake the chip at 80°C for 1 hour. This accelerates PDMS's natural hydrophobic recovery.
   • Method B (if no oven): Let the chip sit at room temperature for 24–48 hours. PDMS will slowly recover hydrophobicity.
   • Method C (chemical): Flow Aquapel (glass treatment solution) through channels, wait 5 min, flush with air. Gives strong, durable hydrophobicity.

3. Pre-condition channels with continuous phase

   • Flow your oil + surfactant mixture through all channels at a moderate rate (e.g., 50 µL/min) for 5–10 minutes
   • This coats the walls with surfactant and displaces any residual water
   • Critical: Do NOT introduce the dispersed (aqueous) phase until channels are fully oil-wet

For aqueous-only applications (hydrophilic channels needed)

Goal: Make PDMS channels hydrophilic so aqueous solutions wet the walls and flow easily.

1. Plasma treatment (best option, if you have a plasma cleaner)

   • Oxygen plasma at low power (10–30 W) for 30–60 seconds
   • Makes PDMS surface hydrophilic for 1–4 hours (temporary)
   • Use the chip immediately after treatment

2. Chemical coating (for longer-lasting hydrophilicity)

   • After plasma treatment, immediately flow a blocking solution through channels:
     • PLL-PEG (poly-L-lysine-polyethylene glycol): 0.1 mg/mL in PBS, incubate 30 min
     • BSA (bovine serum albumin): 1% in PBS, incubate 10 min
   • Flush with PBS, then proceed with experiment
   • Coating lasts days to weeks depending on flow conditions

3. Solvent pre-wet (quick field fix if no plasma cleaner available)

   • Flow 100% ethanol through channels
   • Flush with water
   • Water will now wet the channels (temporarily—lasts ~30 minutes)

Connecting Tubing: Preventing Leaks

Port connection methods

Most PDMS chips have punched holes (0.75–1.5 mm diameter) as inlet/outlet ports. Common connection types:

1. Luer fittings (easiest, most reliable)

• Use blunt luer-lock needles (18–23 gauge)
• Insert straight into the port with gentle pressure
• PDMS self-seals around the needle—no glue needed
• Max safe pressure: ~1.5 bar for a well-inserted needle

2. PTFE tubing direct insertion

• Use tubing with OD = port diameter (e.g., 1/16" OD tubing for 1.5 mm port)
• Cut tubing end cleanly (not at an angle)
• Insert 2–3 mm into the port
• If loose, add a drop of UV-cure adhesive around the interface

3. Flangeless fittings

• Thread a fitting onto PTFE tubing, insert tubing into chip
• Tighten fitting to compress a ferrule against the chip surface
• Good for high-pressure applications (up to 3 bar)

Leak prevention tips

• Never over-insert: Pushing tubing too deep can puncture through the PDMS into the channel, creating an irreversible leak path
• Bevel check: If using needles, ensure the bevel faces up (away from the glass substrate)
• First use under low pressure: When connecting a new chip, ramp flow rate slowly and watch for leaks before going to your target flow rate
• Have spares: Keep extra tubing/fittings on hand—damaged ports are hard to salvage

Removing Air Bubbles

Air bubbles are the #1 frustration with PDMS chips. Here's how to deal with them:

Prevention (best approach)

1. De-gas all fluids before use

   • Place syringes or vials in a vacuum chamber for 5–10 minutes
   • Bubbles in the fluid will expand and escape
   • Particularly important for aqueous solutions (water dissolves a lot of air)

2. Pre-fill channels with ethanol (for aqueous experiments)

   • Ethanol has lower surface tension than water and wets PDMS better
   • Fill channels with ethanol using a syringe
   • Switch to your aqueous solution—it will displace ethanol without trapping air

3. Start at low flow rates

   • Ramp up flow gradually (e.g., 5 → 10 → 20 µL/min)
   • Gives small bubbles time to dissolve or exit before they grow

Removal (when bubbles are already in the chip)

Method 1: Increased pressure

• Temporarily increase flow rate 3–5×
• Higher shear often dislodges stuck bubbles
• Once clear, return to target flow rate

Method 2: Isopropyl alcohol (IPA) flush

• Stop flow, disconnect tubing
• Flush channel with IPA using a syringe (IPA wets PDMS well and displaces air easily)
• Flush with water to remove IPA
• Reconnect and resume experiment

Method 3: Vacuum degassing in situ

• Some chips can be placed in a vacuum chamber while filled with liquid
• PDMS is gas-permeable—bubbles will diffuse out through the walls over 10–30 minutes
• Warning: Only works for bubbles <100 µm; large bubbles may expand and damage channels

Method 4: Tap and wait

• Gently tap the chip on the bench (like flicking a syringe)
• Let it sit for 5 minutes
• PDMS's gas permeability means bubbles slowly shrink as air diffuses out
• Not fast, but works for stubborn small bubbles

Common Problems and How to Fix Them

Problem: Chip is leaking at the PDMS-glass interface

Symptoms: Liquid seeps out from the bond line, not from ports or tubing connections.

Causes:

• Plasma bond has failed (incomplete bonding during fabrication, or bond degraded over time)
• Pressure exceeds the bond strength (PDMS-glass bonds typically fail at 2–4 bar)

Fixes:

• Immediate: Reduce flow rate to drop pressure below the leak threshold
• Short-term: Apply gentle, even pressure across the top of the chip (e.g., place a weight on top). This can temporarily reseal a weak bond.
• Long-term: This chip is compromised. Use it only for low-pressure experiments (<1 bar), or discard it.

Prevention: Always ramp pressure slowly on a new chip to find its limit before running critical experiments.

Problem: Liquid doesn't flow / channels are blocked

Symptoms: Pump is running but no flow visible in channels, or pressure alarm on pump.

Causes:

• Large particle or debris blocking a channel
• PDMS has swollen and collapsed the channel (happens with strong organic solvents)
• Tubing kinked or not fully inserted

Fixes:

• Check tubing first: Disconnect and inspect for kinks or blockages
• Backflush: Reverse flow direction at high rate (e.g., 200 µL/min) for 10 seconds
• Solvent flush: If blocked by particulate, flush with IPA or acetone (brief exposure OK)
• If channel collapsed: No fix—PDMS absorbed a solvent it shouldn't have. Use glass/polymer chips for that solvent next time.

Problem: Droplets aren't forming / flow is unstable

For droplet generation chips:

Symptoms: Jetting (continuous stream instead of droplets), or irregular droplet sizes.

Causes:

• Surfactant hasn't coated the channel walls yet
• Air bubble near the junction
• Flow rates not in the right regime

Fixes:

• Pre-wet channels: Flow oil + surfactant for 5–10 minutes before introducing aqueous phase
• Check for bubbles: A bubble near the T-junction or orifice will destabilize breakup
• Adjust flow rates: Refer to the droplet microfluidics guide for your geometry's operating window

Problem: PDMS surface is contaminated / channels look cloudy

Symptoms: Channels appear hazy, or you see a film on the surface.

Causes:

• Absorption of hydrophobic compounds (dyes, drugs) into PDMS
• Protein or salt crystallization on channel walls

Fixes:

• For absorbed compounds: Soak chip in IPA for 1 hour, then bake at 80°C for 2 hours. This extracts absorbed molecules and regenerates PDMS.
• For protein fouling: Flow 1% SDS (sodium dodecyl sulfate) solution through channels for 10 minutes, then rinse thoroughly with water. SDS solubilizes proteins.
• For salt crystals: Flush with distilled water (not PBS or buffer).

Prevention: Use lower concentrations of dyes/drugs, or coat channels with PEG to reduce absorption.

How Long Does a PDMS Chip Last?

Lifetime depends on use:

• Single-use (common): Many researchers use a chip once and discard it, especially for cell work or when working with precious samples (avoids cross-contamination risk).

• Light reuse (5–10 runs): If you're running the same experiment repeatedly with the same reagents, a chip can be reused after cleaning:

  • Flush with IPA
  • Flush with water
  • Dry with nitrogen
  • Store in a sealed container
  • Surface properties degrade slightly with each use

• Heavy reuse (weeks): For continuous perfusion or long-term culture experiments, a chip can stay in use as long as:

  • No leaks develop
  • Channels remain clear (no fouling or swelling)
  • Flow characteristics don't change

End-of-life signs:

• Bond delamination (visible gap forming at PDMS-glass interface)
• Permanent channel blockage or deformation
• Surface so fouled that cleaning doesn't restore performance

Cleaning and Reuse

Standard cleaning protocol (between identical experiments):

1. Flush channels with IPA at high flow rate (100 µL/min) for 5 minutes
2. Flush with DI water for 5 minutes
3. Blow dry with clean air or nitrogen
4. Inspect channels under microscope for residue
5. Store in a sealed container

Deep cleaning (for heavily fouled chips):

1. Soak entire chip in 1% SDS solution for 1 hour
2. Rinse with copious DI water
3. Soak in IPA for 30 minutes
4. Bake at 80°C for 1 hour to fully dry and regenerate PDMS
5. Re-treat surface (plasma or chemical) before next use

DO NOT:

• Autoclave PDMS chips (distorts channels)
• Use strong bases (>pH 12) for extended periods (attacks PDMS)
• Use chlorinated solvents (dichloromethane, chloroform) unless you want to dissolve the chip

PDMS + Biological Samples: Special Considerations

For cell culture in PDMS chips

PDMS absorbs small molecules, including:

• Growth factors
• Signaling molecules
• Drug candidates

This can skew your results. Mitigation strategies:

1. Pre-saturate the chip: Before introducing cells, flow cell culture medium through channels for 12–24 hours. This saturates PDMS's absorption capacity for common medium components.

2. Use high concentrations: If testing a drug, start with 2–10× the concentration you'd use in a well plate. PDMS will absorb some, bringing effective concentration down to your target.

3. Surface coating: Coat channels with Pluronic F-127 (0.5% in PBS, 1 hour) or PLL-PEG before introducing cells. These coatings block PDMS absorption and reduce non-specific cell adhesion.

Gas exchange through PDMS

PDMS is gas-permeable—O₂ and CO₂ diffuse through it freely. This is:

• Good for cell culture (cells get oxygen from the environment even in static channels)
• Bad for anaerobic experiments (oxygen will leak in)

If you need anaerobic conditions, place the entire chip in an anaerobic chamber or use glass/silicon chips instead.

Safety Notes

• PDMS is inert and non-toxic once cured. Uncured PDMS (liquid) can irritate skin—commercial chips are fully cured.
• Wear gloves when handling chips to avoid transferring oils from your hands to the chip surface
• Dispose of chips as regular lab plastic waste (unless contaminated with biohazards)

When to Choose PDMS vs. Other Materials

PDMS is best when you need:

• Low cost
• Optical transparency (for imaging)
• Gas permeability (for cell culture)
• Rapid prototyping (easy to mold)

Avoid PDMS when:

• Working with strong organic solvents (use glass or COC chips)
• Absorption of small molecules is unacceptable (use glass or thermoplastic)
• Need very high pressure (>5 bar) (use glass or silicon)
• Long-term stability (months of continuous use) is required (use glass)

LabCore PDMS Chips: What You Get

All LabCore PDMS/glass chips ship:

• Pre-bonded with oxygen plasma (no bonding needed)
• Particle-free (cleanroom fabrication)
• With tubing kits (PTFE tubing + fittings for immediate use)
• Tested for leaks (every chip pressure-tested before shipping)

Shelf life: 12 months from ship date if stored properly (sealed, room temp, dark).

Browse PDMS chip options:

• Droplet generation chips
• T-junction droplet chips
• Herringbone mixers
• Standard PDMS chips

All chips are RUO (research use only)—not for clinical diagnostics.