Water-regulated viscosity-plasticity phase transitions in a peptide self-assembled muscle-like hydrogel

The self-assembly of small molecules through non-covalent interactions is an emerging and promising strategy for building dynamic, stable, and large-scale structures. One remaining challenge is making the non-covalent interactions occur in the ideal positions to generate strength comparable to that of covalent bonds. This work shows that small molecule YAWF can self-assemble into a liquid-crystal hydrogel (LCH), the mechanical properties of which could be controlled by water. LCH can be used to construct stable solid threads with a length of over 1 meter by applying an external force on 2 µL of gel solution followed by water-regulated crystallization. These solid threads can support 250 times their weight. Cryogenic electron microscopy (Cryo-EM) analysis unravels the three-dimensional structure of the liquid-crystal fiber (elongated helix with C2 symmetry) at an atomic resolution. The multiscale mechanics of this material depend on the specificity of the molecular structure, and the water-controlled hierarchical and sophisticated self-assembly. Assembly of small molecules offers possibilities in the preparation of materials, but obtaining desirable mechanical strength can be challenging. Here, the authors report the assembly of a tetrapeptide to form a liquid crystal hydrogel, able to support significant weight.