Chemical Technology July 2015

NANOTECHNOLOGY

huge immune response. And kill you. So you really do want the right blood for you. All-in-all, there are 342 different blood-group antigens, of which 160 are defined as ‘high prevalence’. If you’re lucky, you’re in that group and you’ll be able to get a transfusion in an emergency. If you’re not … let’s just say, you don’t want to be in that group. There are, for example, only 43 people in the world with Rhesus null blood. They have no Rhesus antigens. This makes their blood heart-breakingly precious since they can donate to anyone who falls into the rare Rhesus blood type groups. Donated blood is, literally, a life-saver. And, once donated, it lasts only 42 days. Given this, and the difficulty of safely storing and distributing blood to those in need, it is no surprise that the pharmaceuticals industry has been looking for suitable alternatives. Artificial blood The requirements for any artificial oxygen-carrying blood are many and various. Firstly, it must be compatible with all

blood-types, ensuring it can be used by anyone. It must be able to transport oxygen at least as efficiently as does blood; and that is both in terms of its capacity to absorb oxygen, and to release it once it gets to its destination. It must last about 120 days once it is transfused to ensure that its rate of decay matches your body’s rate of production (otherwise it’s like having a continuous bleed and requires a just as continuous top-up). And, if that isn’t enough, it must have similar properties to blood since your body control systems are designed to deal with specific homeostatic pressures and flow-rates. Blood doesn’t only carry oxygen. It acts to clot at sites of injury to aid healing. It regulates body temperature and pH, as well as delivering antibodies and white blood cells to infection. There are currently two main approaches to developing artificial blood. The first is to use haemoglobin (Hb), the molecule in blood which does the job in the first place. Given that red blood can only be stored for 42 days, a vast amount of blood is discarded. One can have a shortage

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Chemical Technology • July 2015