Microfluidics test

I've been playing around with a microfluidic channel, to be used with optical tweezers experiments later. There's clear fluid coming in from the left in the wide (ca 30um) channel, and I've colored the fluid from the top red and the fluid coming in from the bottom blue. The top and bottom channels are narrower, ca 10um.

This page should have 3 videos, but I put them on Jumpuct and they have disappeared - sorry!

Here all the channels are on at first, then the red channel is switched on/off two times.
Here's the same thing, but switching the blue channel on/off.
Here the clear channel is switched off, and the main channel fills with red/blue fluid.

It's interesting to follow the laminar flow at these very small Reynolds numbers - the fluids effectively don't mix at all (they do mix by diffusion, but very slowly) and there's a clear boundary between red and blue. At the end the clear channel is switched on again.I'm using pressurized air to drive the fluid flow, similar to a product from French company Fluigent (nice videos here and here). Their product sells for around the price of a small car, so I'm thinking I can come up with a DIY solution for slightly less. Switching is by solenoid valves that switch either high pressure or ambient pressure to the fluid bottles (2ml Eppendorfs). The pressures required are surprisingly small, here I'm using the smallest pressure my regulator will output, 5 psi, but I have a feeling this is too much... so I'll need a pressure regulator with fine control between 0 and 5 psi, any ideas?The other option is using gravity to drive fluid flow, 0.5m H2O is around 5 kPa or 0.7 psi which could be OK. The problem is you then have to switch the fluid lines directly. I tried this with solenoid pinch-valves, and the valves create huge pressure transients when switching off - completely flushing the channel with rapid flow. So the gravity driven solution requires valves that open and close very gently.

One thought on “Microfluidics test”

  1. Hi Anders:

    Don't know if you are still looking for a low pressure regulator, but I had some thoughts. If you need a small finite volume of air (or gas) for an experiment, you could simply use a thin plastic bag large enough to hold the required amount of gas, with a weight on top to set the pressure. If you need more gass than conveniently fits in a bag, add a supply port and a switch and solenoid valve that feeds in more gas when the weight falls too far. Basically a low pressure version of a hydraulic accumulator.

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