Biomimetic Tough Gels with Weak Bonds Unravel the Role of Collagen from Fibril to Suprafibrillar Self‐Assembly

Biological tissues rich in type I collagen exhibit specific hierarchical fibrillar structures together with remarkable mechanical toughness. However, the role of collagen alone in their mechanical response at different structural levels is not fully understood. Here, it is proposed to rationalize such challenging interplay from a materials science perspective through the subtle control of this protein self‐assembly in vitro. It is relied on a spray‐processing approach to readily use the collagen phase diagram and set a palette of biomimetic self‐assembled collagen gels in terms of suprafibrillar organization. Their mechanical responses unveil the involvement of mechanisms occurring either at fibrillar or suprafibrillar scales. Noticeably, both modulus at early stage of deformations and tensile toughness probe the suprafibrillar organization, while durability under cyclic loading and stress relaxation reflect mechanisms at the fibril level. By changing the physicochemical environment, the interfibrillar interactions are modified toward more biomimetic mechanical responses. The possibility of making tissue‐like materials with versatile compositions and toughness opens perspectives in tissue engineering. A palette of tough, self‐assembled 3D collagen matrices with tissue‐like microstructure is produced based on a previously described spray‐processing strategy. Their tensile response sheds light on the role of collagen at suprafibrillar scale, while long‐term mechanical properties evidence fibrillar scale phenomena such as self‐stiffening. The possibility of adding other components of the extracellular matrix opens perspectives in tissue engineering.