Clever micro-dosing design (untested!)

Hardware, PWM, and Optics
1

Here’s a simple idea for micro-dosing (sub 0.05ml dosing) without any pumps. I don’t know if it works or how accurate it is - we don’t have the R&D time atm to test it.

The idea is to use a pressurized liquid line into the Pioreactor with a normally-closed pinch-valve controlling the dosing. When you want to dose, the pinch valve opens (or pulses¹, not sure which is more accurate for microdoses) and the flow enters.

  • Pressure is introduced into the headspace of the media bottle via compressed air or air pump. A dip line is in the liquid, comes out the cap, and feeds into the Pioreactor.
  • The pinch valve can be controlled from the Pioreactor’s PWM output.
regulated air/N2
       |
   [regulator]
       |
       v
   (gas in)
   ____|____
  |         | <- sealed bottle 
  |  GAS    |
  |---------|
  | LIQUID  |
  |____ ____|
       |
   dip tube (liquid out)
       |
   [pinch valve]
       |
   to Pioreactor

¹ You can take advantage of the PWM here: set a moderately low hz in the PWM, and change DC% to modulate flow. (The alternative is to pulse in Python, which will be much slower and less accurate)

2

Is the recommended pinch valve still the one from Takasago Fluidics, or have you identified other pinch valves that can work?

The Harris Lab at Brown University has an open-source stepper motor based design for a pinch valve, but we haven’t tried it yet:

3

We tried the Takasago pinch valve years ago, and it worked back then, so I would give it a looser recommendation now. There’s probably more affordable or open source versions using off-the-shelf solenoids, too.

4

Might be better off using a syringe pump for this application? This one works well: GitHub - pachterlab/poseidon: poseidon system - open source syringe pumps and microscope for laboratories · GitHub

1 Like