Making vial caps w/ laser cutter and pipette tip

Here’s how I make vial caps using a laser cutter, pipette tips, tubing, and luer adapters.

You’ll need:
2 Female Luer Lock w/ 1/16" barb, polypropylene
1 Extended length pipette tip (same as used for sampling)
1 10-32 Thread to 1/16" barb, polypropylene
some 1/8" opaque polypropylene sheeting
some ID 1/16" OD 1/8" silicone tubing
1 40mL borosilicate vial & cap

Sharp razor (I get out a new one each time I make caps)
10-32 UNF tap-drill bit
Primer (Loctite 7701 or similar for polypropylene)
Glue (Permabond 820)

First, I cut out round caps on the laser cutter, to make a round cap 0.8125" in diameter, with three holes, one 0.125" in diameter, and two 0.1625" in diameter. The small hole will hold our influx straw, made from flexible tubing, and the larger holes fit the extended length pipet tips, used as the efflux straw in this design.
Next, I use the tapping drill bit to add threading to the pipette tip. The threading will engage on the part of the tip below where the pipettor normally sits, as shown below.
Next, cut the pipette tip just below this ridge, so that the threading comes right to the top. This may take a bit of force, so use a sharp razor to reduce effort and improve safety. Try to keep this cut straight, as it will make it easier to seal the connection.
Apply primer to the threading on the bard adapter, then a small dab of glue, as shown.
Screw the barb adapter into the pipette. The glue will seal any gaps in the threading, or at the seam between the tip and the barb adapter. Do the same primer/glue procedure for the tip and press into place in one of the holes on the cap.
Next, cut the influx straw ~1-1.5" in length and the efflux adapter ~0.25-0.5" in length and add the luer lock adapters. I like to use the color of tubing that matches the type of line it gets attached to.
To determine the length to cut your efflux straw, add water up to your desired culture volume (in this case 25mL).
Once you’ve determined the length from the top of the vial to the water level, you can cut the tip accordingly. Since the length from the bottom of the white cap to the bottom of the tip is the important measurement, not the overall tip length, I prefer to wait until this stage to cut the tips.
Feed the cap through the green screw cap, and you’re good to go!
Test your cap by using a peristaltic pump or syringe to suck up through the efflux line. If there are bubbles forming, you did not make a good seal, and the cap should not be used, as it could lead to overflow from poor efflux flow.

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A couple of notes:
I usually just leave the sampling port open during experiments, but you can cover it with a sterile breathable film if you want. Even with the port open, I don’t observe high rates of contamination.

You can also make caps much more easily by using the 1/8" silicone tubing for both influx and efflux. Just laser-cut caps to have two holes of this diameter, leaving just one large hole for sampling. You can cut the efflux tubing to set your desired volume, but since it is bendable, this is hard to control from vial to vial. This might not be so bad for turbidostat, but will definitely affect chemostat flow rates, and so I don’t recommend for that application.

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Added tutorial using nylon caps and PEEK tubing.