We ran some experiments in our office on how to cut of the silicone tube affects the droplet size produced. Why is the droplet size important? When dosing, the smaller the droplet size, the more fine the resolution that your dose can be, and the less likely a drop will “hang on” due to surface tension.
We compared a 45deg cut to a 90deg cut by dropping single droplets from a syringe with a pre-cut silicone tube connected. We measured droplet size using a scale with 0.001g resolution.
We found that a 45 degree cut angle but produced droplet sizes of 32.2 mg (std=4.5 mg), and a 90 degree cut produced 49.5 mg (std=5.4 mg).
We’ve sold our vial caps with tubes cut at 90 degrees, but going forward, we’ll be cutting them at 45 deg.
Our pump calibration routine asks you to hold the sink tube above a container and measure the amount of volume that passes. This worked okay, but like above, the relatively large hole in the male luer lock would cause large droplet sizes (see photo below, left). This reduces the resolution of calibration.
We found that an easy solution is to attach the male luer lock to a 1/16" female luer lock (photo right), like the ones provided with the Pioreactor vials. This reduces the size of the droplets to about 33% the original!
We’ll be updating the pump calibration routine to add this change as a step.
We didn’t, but it’s definitely best. However, and this is from personal experience, one gets lazy and end up just leaning the tube on the edge of the container, which can more easily cause spills.
Good point. Is there a way that you can easily run the calibration in cumulative mode - entering the total weight with time rather than incremental weights?
Mmm there’s no current way. I worry that a method like that would make “REDO” actions more difficult. Normally one would tare their scale to reset it to 0g, and then proceed. Am I missing some use case though?
You’re right, we could just tare each time even if the tube was submerged.
The issue I recall having was hanging onto the tube with my left hand, operating the scale with the right, and then having the keyboard over to the left, so I had to keep crossing hands each time & risking knocking a drop between measurements. Now I describe it, it sounds pretty simple so there may have been something else going on…
I thought that being able to just operate the Pioreactor keyboard for everything would have been easier:
Hit enter to start
Type weight and hit enter
Type weight and hit enter
Type weight and hit enter
…
I guess if a redo was required you could hit x and enter then it would ask for the current weight before adding any volume.
Of course I would need to do the x a few times with my current scales which like to turn off after almost no time, but with decent scales I could see this being the most efficient and accurate way to enter a calibration.
