It 'clear that to have a few materials, in practice two, proteins and cellulose,
is unsettling for the engineer. Until now, materials science has always changed
materials such as heat treatment by heating and cooling that is more or less
quickly, or by inserting other elements or compounds, and then modified chemically.
Nature does not behave this way, even obsessively repeats the same structure
phone, change to micro-variations or approximations.
This allows the nature to provide materials of unusual properties, such materials can be auxetici, which is to increase its own section (widen) when subjected to stretch (ie pulled).
seems a curiosity, but the fact that the skin of some reptiles, such as salamanders, both auxetica allows abrupt movements and sudden without giving a crash. And the fact that the skin of snakes is auxetica is due to their characteristic properties (and a bit 'scary actually) such as macrophages (swallow big mouthfuls very suddenly opened his mouth ...).
From a structural standpoint, there is a material auxetico to be specific, but (potentially)
all cellular materials can be auxetici, just do not have the hexagonal cells, such as those left in the figure, or other more complex shapes, for example tetradecagonali (14 sides) but the shape that you see in the picture right, "bow tie".
E 'this is just the beginning of the story, because the applications of the materials are only hypothetical for now auxetici engineering, of course we will turn to nature to have some other ideas.
