Home Blood Fractionation
Although at first glance blood looks like a single substance, you have probably learnt that it is composed of many different things. This article shows how you can separate out the two main parts using cardboard and string (and sticky tape) - which in medical terms is called blood fractionation. This is based on the work of Manu Prakash and his team at Stanford, and is best explained by the video below.
If you have more time then you can watch Manu's slightly longer Ted talk, and/or read the scientific paper - Paperfuge: An ultra-low cost, hand-powered centrifuge inspired by the mechanics of a whirligig toy. An important part of science is reproducibility, so why not test it for yourself?
Separating blood into different parts can be useful in medical diagnosis (as described in the video above). It is also reguarly used to make donated blood more useful - with the different parts more useful to different types of patients. In healthy blood the percentage of red blood cells (Erythrocytes) in the whole blood sample varies depending on age, gender, etc; but should be between 38% and 54% for adults. Don't panic if your results come out differently during this experiment - remember that you are not a medical lab.
The core components of the paperfuge (paper/card, string, some-sort of handles) are very easy to come-by. However, if you want to try it yourself then you will need some items that aren't found in the average home. The items are relatively inexpensive (in my case £10 total); but you will likely have to buy them in packs that contain a lot more than you need.
- Lancet: You have plenty of blood in you in order to do the experiment; but your body tries its hardest not to let any out. A blood lancet will allow you to extract some safely - so long as you follow the instructions and keep the area clean. They are intended to draw a small amount of blood from a finger, for such things as testing glucose levels.
- Capillary tubes: These are tiny glass tubes, which when placed in contact with a liquid appear to suck it up - through capillary action. You can also tilt the tube so that gravity pulls down the tube's contents, drawing more liquid in.
The process of filling a capillary tube is shown in the video below. Make sure that you have everything set-up and ready to go before drawing any blood.
Simplifying the Design
The paperfuge shown above includes several design features that are tailored to a lab environment. Straws to hold the capillary tubes and a cover disc that attaches with velcro, both provide added safety and allow easy, repeated use. Eventually I settled on a simplified design with the compromise of only expecting to use it a few times, and with less safety (I was only dealing with my own blood).
I used a single disc of cardboard so that I could pause the spinning and check the progress of the separation, and just used a strip of sticky tape to secure the capillary tube. There is a chance that the capillary tube could become a projectile. It never happened to me, even after lengthy spinning; but there's always the risk that an unusual combination of factors could result in an accident. It is always a good idea to wear eye protection.
I also chose to 'heat-seal' the capillary tubes instead of using epoxy. You just heat one end of the tube with a cigarette lighter until it seals completely. Heat the opposite end that you drew the blood through, and make sure that the sample itself is not heated - otherwise it boils and explodes out through the opening. You can tilt the tube to move the sample closer to the end before sealing; but it isn't really necessary.
Sealing with epoxy seems easier; but the only time that I was sprayed with blood was when I used epoxy, and didn't wait long enough for it to dry. Time also seems to be a critical factor when you do this at home - see Results below - so waiting 30 minutes for it to fully set can be a problem.
First you should build and practice with you paperfuge - just getting a nice, steady rythm. You should also practice drawing water into the capillary tubes and sealing them (you likely ended up buying 50-100 of them, so there's plenty to spare). The actual process should be very straight-forward; but I still ended up having to draw blood from every finger except the little ones; and some multiple times. Hopefully you can learn from my mistakes.
When you're ready, the process to follow is:
- Prime the paperfuge so that the string is already twisted.
- Use a lancet to prick a finger of your choice.
- Use a capillary tube to collect some blood. Filling about a third of the tube is plenty.
- Use a cigarette lighter to seal one end of the capillary tube - be careful, it will be very hot.
- Wait a few seconds for the capillary tube to cool.
- Tape the capillary tube onto the card disk - sealed end facing away from centre.
- Spin the paperfuge for approximately 2 minutes.
I initially misread the published paper and through that samples should be spun for 15 minutes. If you actually check the paper you will see that after 1.5 minutes the sample should be pretty much separated, and there probably won't be a noticeable change once you go past 2 minutes. A 15 minute spin can separate something called the buffy coat; but only with a special float inside the capillary tube.
The first results (after spinning for around 20 minutes) were promising - shown below. You can clearly see a separation of plasma and red blood cells - particularly near the bottom. However, a number of air bubbles were introduced during collection that seemed to cause problems. There was some transfer of fluids around the air bubble; but you can see it isn't quite what we were expecting.
Subsequent attempts actually led to worse results. The sample shown below was actually spun for 40 minutes. This was of course a waste of time, since there wasn't going to be any real change once it passed the two minute mark. There is some indication of separation - there is clearly some plasma at the top, and the red is darker towards the bottom (more concentrated red blood cells). However, there is still a larger area in the middle that seems unseparated.
After some frustration it seems that time is a factor. Firstly the longer you spend drawing blood, the thicker the blood seems to be. With the initial blood that's added, if you tilt the tube the blood moves quickly; after a while the thicker blood that is added is taken up less easily and prevents any movement when tilted. Also, having the blood sit in the tube seems to affect separation. The obvious answer seems to be that some clotting is taking place. The paper mentions using purchased blood samples, which possibly contain an anti-coagulant.
I got the best results by sampling a smaller amount of blood - the initial free-flowing part - and then sealing and spinning the sample in as short a time as possible. A good result is shown below:
Looking at the plasma-blood cell boundary using the DIY microscope (from another article) shows an interesting transition; but I'm not really sure what is going on.
The paperfuge is a very elegant design, and can achieve the desired result even if operated by a complete novice. Just be sure to take your sample and spin in a fairly short time period. Don't rush and make mistakes - seconds don't matter, but minutes do.