Week 1
This week I had developed some background for my project, which is to develop a device with an integrated vacutainer for blood collection. The vacutainer, known as a Vacustor, is like a miniature version of the commercially available vacutainer. The Vacustor is supposedly designed to store around 20 microliters of blood and have a shelf life of around a year. However, before divulging into how we will go about doing this, I want to share some background regarding the concept of vaccutainers. In addition, I have provided a schematic of the device we are attempting to fabricate.
Figure 1: Schematic of Concept Device
Background:
The introduction of evacuated blood collection systems have provided greater safety, while offering ease-of-use, speed, and accuracy in blood-to-additive ratios. Advancements in blood collection has accumulated in the current commercially available vacutainer. Vacutainers rely on a capillary tube so that the vacuum within the cylindrical chamber is maintained. That way, liquid can be inserted into the chamber without disrupting the established vacuum. However, investigations into different factors that influence the performance of evacuated tube performance, including factors such as tube
material, additive stability, and environmental
conditions impact the expiration
dates of certain tubes. We need to consider these factors when developing our tube as well. In addition, we need to consider permeability and evaporation of liquid from tube, which is a major issue considering the small sample volume.
This week we considered the ends of the tube and its effects on the capillary action of the tube. We tested an angled cut versus a straight cut on how much liquid could be dispensed solely by gravity. We want to reduce the dead volume of liquid (liquid stuck in the tube), especially since when the tube is integrated, it will not be easily accessible. Using a liquid that mimics blood, we tested the capillary of the tube and how easily the blood would flow vertically, and how much liquid would come out of the tube without agitation. This was done by using the mass of the tube with the liquid before and after dispense, and using a density approximation of 1 g/mL to determine the volume of liquid dispensed. The data showed that straight cut is more consistent in dispensing around 30 microliters of liquid as compared to the angled cut.
Next week, we hope to test the evaporative behavior of the liquid in the tube and assemble the valves we will be using in our device.
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ReplyDeleteWhen you mention blood-to-additive ratios, do you mean stuff that is added to the blood, or dissolved particles in the blood that you are measuring?
ReplyDeleteBlood-to-additive ratio refers to the stuff that is added to the blood, such as anticoagulants (EDTA, citrate, etc). The reason why evacuated tubes have improved speed and accuracy in maintaining the blood-to-additive ratio is because the evacuated tube draws a predetermined amount of blood based on the pressure difference of the vacuum in the tube and the blood volume. Hence, when manufacturing the tube, you can topically apply these additives or disperse it along the inner wall. Since the volume is predetermined and consistent, it is easier to maintain the amount of additive necessary depending on the circumstance.
DeleteHopefully this clarifies it!