Humidity responsive tripeptide crystals

Water-responsive materials undergo reversible shape changes upon varying humidity levels. These mechanically tough, yet flexible structures can exert significant forces and hold promise as efficient actuators for energy harvesting, adaptive materials, and soft robotics. Using nanoporous tripeptide crystals, we demonstrate that energy transfer during evaporation-induced actuation results from strengthening of water H-bonding that drives the contraction of the pores. The seamless integration of mobile and structurally bound water inside these pores with a supramolecular network which contains readily deformable aromatic domains, translates dehydration-induced mechanical stresses through the crystal lattice, suggesting a general mechanism of efficient water-responsive actuation. The observed strengthening of water bonding complements accepted understanding of capillary force induced reversible contraction for this class of materials. These minimalistic peptide crystals are much simpler in composition compared to natural water-responsive materials, and the insights provided here can be applied more generally for the design of high-energy molecular actuators.