Preventing wobbling of the glass vial for better OD measurements


I wanted to write a post on simple tricks to improve the OD reading. This mainly involves holding the vial into place with a 3D printed part. I will first walk you guys through what we’ve done in the past.

First Trial - NBT Paper

The OD reading gets disrupted if there is any shaking/perturbation of the glass vial. For our Nature Biotechnology publication, we used small felt pads that we stuck into the inner wall of the aluminum tube to hold the vials in place. These would work well at first but then they would start getting worn out, making the tube very difficult to take out after several cycles of use.

Second Solution - Custom eVOLVER Caps

We started making custom nylon eVOLVER caps that had was made to fit better with the aluminum tube. This was aimed to avoid using the felt pads. The issue with these caps is that there was still wobbling in the bottom of the aluminum tube. This would cause a disruption in OD readings.

Best Solution - 3D printed Aligner

The updated recommended solution is a new 3D printed part that goes in between the glass vial and the aluminum tube to keep it from moving. This part can easily be printed via FDM printing (typically ABS or PLA). The solution involves a part you can clip onto the tube (after autoclaving). FDM plastics are not autoclavable, so please do not try.

Here is the part (black piece):

Insert into the aluminum sleeve and rotate the tube to tighten the hold inside the Smart Sleeve.

Want to 3D print your own?

STL and Solidworks files for tube aligner can be found on Github

Place the part in this orientation, without supports. The part prints best with a raft at the bottom.

1 Like

When you say the " The OD reading gets disrupted if there is any shaking/perturbation of the glass vial."

  • how big of a disruption is this - is it like a massive spike in the OD readings? Or just small baseline noise?
    For example, would this OD reading have benefitted from a vial aligner? We only used the vial cap here.

I don’t think this particular set of OD readings would have benefitted necessarily, but keep in mind that if a perturbation happens mid-experiment (especially likely if you are modulating the spin for some reason) it may throw off readings for the entire duration.

My current understanding is that the jostling is more of a problem becuase it creates more opportunities for the stir bar to generate friction with the glass and start hopping, which can REALLY effect measurements for obvious reasons.

If you do 3D print these is that I would recommend trying slightly flexible material. We have these printed onto brittle materials and they work, but two broke (good thing we got 18!) one in the process of detaching the adhesive layer from the printout and the other when removing it from the vial.

Thanks. Do you find that you can’t screw the vial cap down all the way when using the vial aligner?

I did try putting a couple into sleeves along with a nylon cap and I don’t remember it being an issue. When you put it into the sleeve I found you kind of set it down into the sleeve and then press the extended arm in and the vial slides in. In a few cases, I also really have to push it to get it to go in. Also, for the full set that I actually did a turbidostat run with, I used different chemglass manufactured caps we have.