Collagen-inspired self-assembly of twisted filaments

There have been dramatic developments in our ability to functionalize submicron scale objects with molecules enabling specific interactions between building blocks, opening up an enormous design space for solutions of particular engineering problems. Here, we explore the physics of collagen self-assembly in order to deduce design rules for the self-assembly of twisted filaments. Despite the well-known structure of collagen, identifying which aspects of its design are required for reproducing collagen-like features in synthetic analogues is unknown. Using computer simulations, we propose a scheme mediated by specific interactions to self-assemble collagen-like triple helices. The assembly nucleates chiral defects, in which two of the filaments switch orientations. Such defects can be eliminated with a modest energetic bias, or nucleated by introducing mechanical weak spots. By inducing spatial variation of the enthalpy of helix formation, we can localize another type of defect where the helix becomes locally unbound. Local unbinding slows assembly, evoking kinetic pathologies previously ascribed to mutations in the primary collagen amino acid sequence. In analogy to collagen, controlled formation of defects could enable hierarchical self-assembly of bundles of twisted filaments.