LabBot3D-Pi - Getting the air bubbles out of the microfluidics


    For some applications having air bubbles in the lines affect the accuracy of liquid handling. Most liquid handler robotics use Upchurch fitting which reduces the extent of the problem (but does not resolve it since bubbles often do form in lines anyway when not in use). When using luer-lock connections instead, the problem is more prevalent but since its so much more convenient then the Upchurch if the bubbles can be easily removed then why use Upchurch (unless for higher pressure applications maybe but then this extends beyond the scope of common pipetting?). This explains how to remove the air bubbles from the LabBot3D-Pi microfluidics.

    There are 3 areas where air bubbles form that can affect the flow path:
      1. Tubing coming out of the pressure compensation vessel (PCV)
      2. Tubing from the pressure compensation vessel to the 4 way valves (valve input path)
      3. Tubing from syringe to valve and valve output path

Having a stop cock valve in the 1/8 inch diameter PCV tubing makes it convenient to load a syringe for tube priming!


    Shown are 2 stop cock valves for positioned in the 1/8 inch tubing coming out of the PCV before branching out to the 8 valves.
1. Tubing coming out of the PCV
The tubing coming out is 1/8 inch diameter but before the tubing branches to each 4-way servo valve (in this case there are 8 units for 8 pipette modules), the tubing diameter is reduced to 1/16 inch diameters. Pretty large air pockets can form in this larger tubing when the system is not in use over time. Rather then perfusing the air out of the whole microfluidics path, putting two stop cock valves at either end of the 1/8 inch tubing makes it easy to clear. Also for priming the other syringes it is convenient to use one of these valves to draw water.

Valve input tubing path is the line from the PCV after it branches to the 4-way valve the gets drawn into the syringe
    2. Tubing from the pressure compensation vessel to the 4 way valves (valve input path). To perfuse the air out the luer lock connection connecting the valve input tubing to the 4-way servo valve, position the valve so that the flow path to the syringe is shut off. Then fill up a syringe with water and attach that to one of the stop cock values positioned along the 1/8 inch tubing. Then perfuse until the air bubbles are flushed out of the line. In some cases 1 or 2 of the valves may still have air where others are clear, then just put the clean valves into bypass mode the flush out the rest.

    This part is the tubing that directly connects to the motorized syringe but to perfuse this line position the 4-way servo valve to output so that the entire line gets drained
3. Tubing from syringe to valve and valve output path. This part of the line directly attaches to the motorized syringe so if there is air (from the valve input line originally but passing through into parts of the 4-way servo valve or if air forms in the output path) then air will get drawn into the syringe. It is very probably that every line (ie., in the example all 8 lines) need to be drained and in order to do this you need to remove the luer lock connection to each of the motorized syringes (Note: remember to put the 4 way servo valve into the bypass position before doing so). After connecting a water filled syringe, position the servo valve into the output orientation in order to perfuse the whole line.