Bulletproof vests from stem cells?

Known as auxeticity, the property may have application as wide-ranging as soundproofing, super-absorbent sponges and bulletproof vests, said the study.

Until now, auxeticity has only been demonstrated in man-made materials and very rarely in nature, such as some species of sponge.

What is auxeticity?

Most materials when stretched will contract. For example, if one pulls on an elastic band, the elastic itself will get thinner.

The opposite is also true: squeeze a material and it will expand. For example, if one squeezes a tennis ball between both hands, the circumference around the ball gets larger.

However, auxeticity has the opposite effect - squeeze it and it will contract, stretch it and it will expand.

This means that auxetic materials act as excellent shock absorbers or sponges, a fact that is being explored for various uses.

"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," said Kevin Chalut from Stem Cell Institute, University of Cambridge.

The researchers treated the transitioning cell's cytoplasm, the fluid surrounding the nucleus, with a coloured dye and found that when they stretched the nucleus, it absorbed the dye, suggesting that it had expanded to become porous.

Auxetic materials are of great interest to material scientists and engineers and this new discovery may provide clues to different methods of manufacture.

The study appeared in the journal Nature Materials.