Exerting pulling forces in fluids by directional disassembly of microcrystalline fibres.

Biomolecular polymerization motors are biochemical systems that use supramolecular (de-)polymerization to convert chemical potential into useful mechanical work. With the intent to explore new chemomechanical transduction strategies, here we show a synthetic molecular system that can generate forces via the controlled disassembly of self-organized molecules in a crystal lattice, as they are freely suspended in a fluid. An amphiphilic monomer self-assembles into rigid, high-aspect-ratio microcrystalline fibres. The assembly process is regulated by a coumarin-based pH switching motif. The microfibre crystal morphology determines the monomer reactivity at the interface, resulting in anisotropic etching. This effect exerts a directional pulling force on microscopic beads adsorbed on the crystal surface through weak multivalent interactions. We use optical-tweezers-based force spectroscopy to extract mechanistic insights into this process, quantifying a stall force of 2.3 pN (±0.1 pN) exerted by the ratcheting mechanism produced by the disassembly of the microfibres.