The connective tissues in our body – such as skin, tendon, or bones – all contain a molecule called collagen. When you cut your skin, it springs open. This shows that the tissues in our body are under pretension. The research presented in this video is interested in the question of whether the interaction of collagen with water causes this tension. The researchers found, as PETER FRATZL explains, that the pretension comes from the contraction of the collagen molecules which is due to a competition for water between collagen and the sugar-rich molecules that surround them. By using synchrotron diffraction, the group managed to show that this leads to a conformational change of this helix; it shortens and creates enormous stresses. These findings are relevant for research in regenerative medicine as well as research into the uses of osmotic pressure for complex movements and force generation more generally.