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Without liquid crystals there would be no life. Even the simplest single-celled
creature has an outer skin whose fabric is liquid crystalline. It is this
skin that forms the membrane separating the inner workings of the cell from
its surroundings. More complex life forms, such as human beings, use liquid
crystalline membranes for a vast variety of biological processes, for example,
transmitting nerve impulses and digesting fats.

You might be surprised to find out that cell membranes are liquid crystals.
In fact, the first recorded observations of the liquid crystalline phase
were of myelin, the material that coats nerve fibres. In 1855, a German
ophthalmologist called C. Mettenheimer was studying myelin under a polarising
microscope, and noted that, although it flowed like a liquid, it was brightly
coloured, or ‘birefringent’ like a crystal when viewed between crossed polarisers
(see ‘The fourth state of matter’, New Scientist, 4 May). It was not, however,
until much later that myelin was identified as a liquid crystalline material.

We now know that the liquid crystal structure of myelin consists of
regularly stacked layers of membranes, with each membrane consisting of
molecules that move around freely within it. In the direction of the stacked
membranes it behaves like a crystal, but in the plane of the membrane it
behaves like a liquid. Without exception, all biological membranes behave
simultaneously like a liquid and a solid, so liquid crystallinity must play
an important part in the function of cells. Over the past 20 years there
has been a surge of interest in biological liquid crystals. This has produced
new and exciting ideas about how liquid…