Air-displacement micropipette design ideas

Hi all!

I would like to start an open discussion on what might be important for the design of open hardware micro-pipettes.

Sharing ideas, insight, possible challenges, or links to existing projects could be good places to start.

Pipettes have been around for a long time, so maybe looking for expired patents could also be interesting. Help with this type of search would also be super valuable.

We want help to design an electronic pipette set, which doesn’t have to be perfect at first. The idea is that it works well enough, and that it can be eventually improved to pass quality standards.

Some hopefully ice-breaking bullet-points:

  1. Piston and seal: choice for a suitable piston material / manufacturing process and air-tight seal (for example a rectified linear rod and a chemically resistant o-ring).
  2. Actuation and transmission: choosing between DC/stepper motors + threaded rods, piezo-based actuation, or others; planning movements for different pipetting modes, and fluids of different charachteristics (surface tension, volatility, viscosity, etc.).
  3. Pipette tip, shaft, and body: geometry and mechanical stability for tip placement, choice of chemically resistant materials, keeping air cushion volume low, etc.
  4. :world_map: Sourcing parts and manufacturing: choose widely available parts and keep it at lower-costs.

This post for help is associated to a project supported by GOSH’s CDP :gosh: :partying_face:, so there will be funds for parts and work-hours eventually, in case someone is interested.


Just in case, I’ve continued discussing this on the project’s GitLab: Micropipettes (#80) · Issues · pipettin-bot / Pipetting Bot · GitLab

I have been thinking about this. If you stretched a rubber tube, does the volume in it increase or decrease? I tried a crude test. The answer is, the volume increases by maybe 50uL for 15cm of stretch (just eyeballing the bulge of the meniscus) of a latex rubber tube 3mm ID 5mm OD.

I don’t have access to pipette tips, nor a ug scale, to test repeatability, durability, and linearity.

The advantage of using this principle in a pipette is that it is small enough to gang multiple units and actuate them all in parallel. The mechanical gain seems very favourable. Silicone tubing is cheap and available in many sizes.

Looks like a good idea!

15 cm displacement for 50 uL is great… it could be possible to pipette 0.5 uL just by adding a scale to it :0

What about using a regular speaker? I liked about it the idea of a “stretchy” diaphragm, and regulating volume with the permanent magnet-electromagnet pair in the speaker. It adds electronics though.

Also I have no idea if the materials on a speaker are chemically resistant; but silicone would surely work.

Did the stretching require much force?

I like these stretchy mechanisms specially for low-volume micropipettes (2-5 uL), because the thinner shaft is harder to machine precisely.

Perhaps a 6 mm stretch of the tube could work great for a 2 uL pipette (15 cm * 2uL/50uL = 6 cm).

I’ll try to reproduce adding the p200 tip.

Thanks Harold!

Now I want a cup of tea. :tea:

I hadn’t thought of using regular loudspeakers, but you may want to look into voice coil actuators. These are precise enough that they are used for hard drive RW heads.

I’m not sure what shafts you mean, but maybe you can use dowel pins. These can be had with diameter tolerances of 10um or less, as standard parts.

The rubber tube I used was a slingshot replacement, so it was designed to be stiff. In practice, you would use silicone rather than latex rubber (more stable), you would specify thin not thick wall tubing, and there could be a compensating spring to enable cheap (not powerful) stepper motors to be used to actuate it.

After the main payload has been dispensed, the last bit could be
spat out of the pipette tip by squeezing or rolling the now-flaccid tube, like dispensing toothpaste.

Looking forward to your results!

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