Pull an elastic band apart and the elastic band becomes thinner and thinner until it finally snaps.  Now imagine an elastic band that grows thicker as you stretch it out. This is a property of auxetic materials, such as the auxetic honeycomb, and a group of Cambridge researchers have announced that they have recently discovered this property somewhere surprising: in embryonic stem cells.

A study published in Nature Materials shows that the nuclei of stem cells in mice exhibit this rare auxetic property.  Scientists squeezed stem cells in a micro-channel that is smaller than a strand of hair, and the nucleus of the cell, rather counterintuitively, grew in volume when squeezed.

Dr Kevin Chalut of the Cambridge Stem Cell Institute, who led this investigation into the auxeticity of cellular nuclei, expressed surprise at the results. “This is a pretty bizarre finding and very unexpected. When the stem cell is in the process of transforming into a particular type of cell, its nucleus takes on an auxetic property, allowing it to ‘sponge up’ essential materials from its surrounding. This property […] is highly unusual in the natural world.”

Auxeticity is a material property that occurs very rarely in nature but has been synthetically reproduced in manmade materials.  Bulletproof vests, for example, take advantage of this material property to stop projectiles. Despite the technological advances with auxetic materials, Dr Chalut adds that they “are still rare and there is still much to discover about them in order to manufacture them better. To overcome this, materials scientists can […] learn from nature.”

It seems that, although the stem cells in your body won’t quite stop a bullet, the understanding of their material behaviour may help us to design other more effective bulletproof materials.