Freeze drying blood!

So we have ways of protecting proteins, enzymes, and bacteria - but what about something infinitely more complicated - human blood!
10 June 2014

Interview with 

Krishnaa Mahbubani, University of Cambridge


So we have ways of protecting, proteins, enzymes, and bacteria - but what about something infinitely more complicated - human cells, and particularly blood!

Krishnaa Mahbubani from the University of Cambridge spoke to Chris Smith about how she's started to try and unpick this new challenge.

Chris - Why do you want to freeze dry blood? We've got blood banks that they're pretty accessible. Why do you need to freeze dry this stuff?

Krishnaa -  Say for example, you're in the frontline of a war zone. You've just gotten shot in the leg and no medic is going to be able to get to you for a little while. What do you do then? Your chances of survival are suddenly dropping dramatically. Now, if you could imagine that within your pack, in your rucksack, you had with you - a bag of your own blood powdered and dried down so it would store for quite a decent amount of time and a bag of saline to make sure that you always had something sterile to mix with it. One of your buddies on the force has come on over very quickly, very valiantly to come rescue you, mix these two together and set you up an IV. All of a sudden, your rates of survival have increased dramatically. So, that's partly some of the motivation behind why I want to do this. It's also an ability to create a supply chain for red blood cells. Now, while we do have blood banks, we can only store our blood for up to 42 days before we have to pretty much chuck it out.

Chris - So, if you could in some way freeze dry the blood, preserve it in a dried format, A) it would take up less space, but it could potentially be stored indefinitely or at least for a much longer period of time so our blood crisis would be solved.

Krishnaa - Yeah, absolutely. I mean, this comes into account when we've got big national or international events that take place where we suddenly got an influx of people coming into the country. When we had the Olympics here for example, when Brazil is about to have the World Cup, they're going to have a mass influx of people in there which means they're suddenly going to have to be stockpiling blood products to make sure that they have enough, should there be an emergency scenario.

Chris - Why can't we do this at the moment for blood? You can do it for bacteria. Why can't you do it for human blood?

Krishnaa - Blood is a mammalian cell. It's slightly different from bacteria in the sense that they're less hardy. Now bacterial cells have a cell wall around them which are quite robust. I always like to say that you can pretty much chuck your bacteria at the wall and it's still going to survive up there. You put any other mammalian cell or any softer cell up against a wall and it's just going to pop and rupture. And that's the problem with red blood cells.

They're very sensitive materials. They have to be able to be flexible enough to go through the smallest of your capillaries in order to allow you to get that transfer of oxygen and carbon dioxide in and out of your system. But also the fact that their entire nature is a transfer of gases which means that membrane on the outside of them that holds them all together has got to be thin enough and simple enough for these gases to just diffuse in and out of very quickly. Otherwise, we'd be struggling to breathe on a regular basis.

Chris - So, that makes them very vulnerable. So, you've got a challenge of overcoming that vulnerability. So, how are you doing it?

Krishnaa - So, we're using a slightly more conservative method in which we dry the cell. So, with the bacteria that we did before, I was saying we use vacuum drying where we effectively mix it up with a surfactant and just put it under pressure and boil the water off. Now, what we have to do is freeze the blood down first and then gradually pull it under vacuum and use that to remove the water. So, we're actually subliming the water out. We're taking it from the ice phase, straight into the vapour phase. We're not actually putting it under a liquid phase at all.

Chris - So, you're putting a chemical in, which will get inside the cells and stabilise everything.

Krishnaa - Well, we're not really putting a chemical in because we have to remember that at some point, we're going to be putting these cells back into another human being. So, we're trying to make use of items and components that are quite natural and very easy for us to break down. So, I'm using natural sugars as the chemical component to protect our cells from freezing.

Chris - Those will therefore protect the cells so that they can then tolerate being frozen.

Krishnaa - Yes.

Chris - And then once they're frozen, you put the whole thing under a vacuum or a low pressure and that causes the water molecules to just - for want of a better phrase - evaporate off.

Krishnaa - Absolutely. So, what you're doing is basically changing what would be the boiling point of water by putting it under a vacuum. So where normally water would boil off at a hundred degrees, we're dropping it down so it would boil off as low as negative 30 degrees.

Chris - Right and do the cells actually survive this treatment?

Krishnaa - At the moment, very few of them.

Chris - Okay, how many?

Krishnaa -  Currently only about 2 to 3% of my cells survive every one I do.

Chris - Do you know why they don't survive? Is it just that you need more of these sugars and things to stabilise them better?

Krishnaa - Yes. Well, there's a variety of reasons that might be causing them to die. The freezing process itself is quite a stressful scenario. Imagine what it feels like to your fingers and hands when you've kind of rummaged around in the freezer. You feel like your fingers are very numb and you sometimes have these things where you feel like you've actually worn the surface of your skin off with freezer burn. This is what's happening, when you freeze things, water expands as it freezes and what's happening is that these cells are then expanding because they're mostly made of water. And that's causing the cells to rupture as well. So, the freezing process could be part of the problem. The reason we load them with sugar is to actually try and stop the ice crystals from forming in the wrong parts of the cells, causing them to lyse as well.

Chris - And how long do you think it'll be before we actually have an answer to this?

Krishnaa - I want it to be in the next few years really, but I really have no idea.


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