Week 7

Week 7

As we narrowed the critical pressure threshold for the glass VacuStor tube, we noticed a slight complication. Depending on the speed at which we pierced the cap of the tube to transfer the liquid, we got differing amounts of sample transfer. Piercing the tube faster resulted in more sample transfer. We realized that this is due to pressure leak during the puncture, but before the bevel has entered the tube. The sample only begins to be drawn into the tube when the bevel fully enters the tube. However, if the bevel is longer than the cap thickness, there is pressure leakage until the bevel enters wholly into the tube. Because there is such a huge pressure difference between the internal pressure and the external pressure, we have to find a needle that has a bevel shorter than the cap thickness. Thus, we slightly modified the experiment by manufacturing new needles with capillaries that have a shorter bevel.

Modified Needles with Capillary Tubes

We used the same method to make these needles as the previous needles. However, we used 30 Gauge 1/2 inch needles instead of 21 Gauge 1 inch needles. Using the UV epoxy, we attached the capillaries to the needles. This was the result:

Modified Capillary Tube with Needle

This needle has a much shorter bevel as compared to the previous needles we used, and is also much thinner and shorter. The following pics show a comparison of the two needles (the green needle is the old needle):

Comparison of Bevel Length

Comparison of Length of Needle

This should aid in the sample transfer to provide more accurate results. Hence, this week I made these needles, which will be the needles that we will use for the remainder of experimentation.

Week 6

Week 6

As we began collecting data on the leaking rate of the plastic tube as well, we have begun preliminary testing of  the critical pressure. We finished constructing the experimental setup and tried varying internal pressures to see if the setup worked.

Critical Pressure Threshold Experimentation

We finally finished fabricating the experimental setup for the critical pressure testing. This is how the experimental setup looked like:

Experimental Setup for Critical Pressure Experimentation

The protocol simulates how the capillary tube will pierce the tube with reagent in it. First, we will the tube with 'reagent'. In this case, we used water, as shown:

VacuStor Tube with Mock Reagent (Water)

Then, we fit it onto the rubber stopper, which has a half-drilled hole to place the tube in. Then, we attach the vacuum tube to the tube and evacuate the tube at the desired pressure we want. We can evacuate the tube to varying extents to create differing levels of internal vacuum. Finally, we cap the tube, and then remove the tube out of the setup. Then, we fill the capillary with fluid, and then pierce the tube with the capillary. Depending on the pressure, we can get no sample transfer, partial sample transfer, or full sample transfer. Since we wanted to make sure this setup worked, we chose pressures that we knew the outcome would be, and here were the results:

Left tube was tube with high vacuum; Right tube was tube with low vacuum

As you can see, one had no sample transfer, and one did. We weighed the tubes before adding the water, after adding the water, and after the sample transfer, and used the density of liquid in order to determine how much sample transfer there was.

Week 5

Week 5

This week we mainly began building our experimental setups for determining the critical pressure for the tube and for determining the leaking rate for the plastic tube. We had already constructed a setup for the glass tube to figure out the leaking rate, so we created the exact setup for the plastic tube.

Leaking Rate - Plastic Tube

We created the same setup for the leaking rate of the plastic tube as the setup for the glass tube since both are approximately the same size. We sealed the gauge to the tube using a vacuum epoxy and then we evacuated the tube and sealed the tube with a rubber cap through teh use of the setup we developed. Here are both tubes with their respective gauges monitoring the internal pressure:

Leaking Rate gauges attached to both the glass and plastic VacuStor tubes

Top View of both gauges attached to their respective tubes

We will be monitoring both tubes now to determine which of these materials will be most effective in maintaining the vacuum, and thus, having the longest shelf life.

Critical Pressure Experimental Setup

We have started building the critical pressure experimental setup, but were unable to finish it this week. Hopefully, we will be able to finish it next week. However, this is what we have so far:

Central portion of Critical Pressure Experimental Setup

In theory, we will have a similar setup to the leaking rate setup, but the gauge will be on the outer tube instead of the VacuStor tube. This is because we only need to know the pressure inside the VacuStor just before we cap it, after which we will puncture the cap with the capillary tubes we fabricated to see how much liquid the vacuum will draw. Once we find the minimum pressure that can draw enough fluid into the tube, we can use this as our reference for extending the shelf life.

Week 4

Week 4

This week we manufactured the capillary tube with the piercing needle for testing, which will likely happen next week. In addition, the materials we ordered for our experiments arrived, which also means we will likely begin experimentation next week.

Capillary Tube with Piercing Needle Fabrication

In the schematic shown from Week 1, our design requires a piercing needle with a capillary tube. We need the needle to pierce the cap of the VacuStor tube so that the vacuum in the tube is maintained until blood collection. To do this, we took capillary tubes and cut them so that they hold around 100 microliters. Then, we took 21 Gauge 1-inch needles and sawed off the hub where you would put the syringe. We then used an epoxy to stick the capillary tube to the opening of the hub of the needle, and cured the epoxy with the capillary and needle under ultraviolet light.

The result was this:

Capillary Tube with Piercing Needle

We made a few of these to set up for next week's experiments. In addition, the pressure gauges, along with other materials we purchased, have arrived, so we can begin experimentation. We will likely follow a similar experimental setup as the rise time setup, but instead we need to determine a method to have the gauge measure the pressure within the tube, but be able to change the pressure of the tube as well so that we can determine at the lowest pressure difference through which we can still draw fluid through into the tube. We will likely use a three way valve to facilitate this, though a major part of next week will be hashing out how to go about doing this and hopefully running some trials.