This macroscopic understanding of mechanical stresses and strains within the fracture zone will be complemented by an analysis of the regain of tissue pre-tensioning carried out by Zaslansky and Fratzl. They will unravel the principles of regaining pre-tension in healing bone using X-ray diffraction, in situ collagen visualisation and nanoCT strategies. Zaslansky and Fratzl explore the hypothesis that cells orchestrate and use large polymer molecules (e.g. collagen, glycosaminoglycan) to induce and develop an internal stress state in the extracellular matrix around them. Stress is also generated by adjusting the osmotic gradients through the localised control of the molecular composition of the extracellular matrix, as well as by modulation of the pH and salt concentrations. Specifically in bone, collagen may operate under tension. Zaslansky and Fratzl will study collagen contraction and internal stresses in collagen-rich tissues in archetypical situations of regeneration.