Cavitation Pressure Limit of Water Confined in Bio-Mimetic Water-Responsive Structures

Water-responsive (WR) materials that actuate in response to changing relative humidity (RH) have demonstrated potential for various engineering applications, including soft robotics, energy harvesting, and smart textile. Despite the growing interest in exploring natural WR materials, the fundamental mechanisms of their WR actuation, including the interaction between water and material’s supramolecular network, are still unclear due to natural materials’ inherent complexity. Inspired by peptidoglycan, the most WR material up-to-date, we developed biomimetic, minimalistic nanofabricated structures with characteristic pore sizes ranging from 10 nm to 50 nm. Using these nanofabricated structures, we found that water confined in materials with high WR performance has an anomalously high resistance against cavitation under changing relative humidity. For example, when humidity decreases from 90% to 25%, the rigid nanofabricated structures with 20 nm confinement shrink by 2.2 nm, and surprisingly, the most negative pressure of its confined water reaches ~17 MPa. Our observation indicates that natural materials’ WR deformation could be benefit from nanoconfined water’s enhanced cavitation limit, suggesting general design criteria for structures that mimic natural materials’ significant WR behaviors.