Temperature-Driven Topological Transformations in Prestressed Cellular Metamaterials

Stimuli-responsive materials are able to alter their physicochemical properties, e.g., shape, color, or stiffness, upon exposure to an external trigger, e.g., heat, light, or humidity, exhibiting environmental adaptability. Their capacity to undergo shape reconfiguration, pattern transformation, and property modulation enables multifunctionality. In this work, two strategies are harnessed, i.e., prestressed assembly and temperature-dependent stiffness reversal, to introduce a class of temperature-responsive metamaterials capable of undergoing topological transformations, endowing them with smart functionality. Through a combination of mechanics theory, numerical simulations, and thermomechanical experiments, the physical mechanisms underlying the temperature-triggered topological transformations leading to pattern switches are first elucidated, and then the insights are leveraged to demonstrate tunable bandgaps and robotic capturers. These findings reveal the attainment of giant negative and positive values of coefficient of thermal expansion, accompanied by isotropic expansion and shrinkage under thermal actuation within a fairly rapid timeframe, below 6 s. The strategy here presented is versatile as it relies on a pair of off-the-shelf 3D printable materials, can be up- and down-scaled, and can also be realized through other physical stimuli, e.g., light and moisture, paving the way for use in multifunctional applications, including stimulus-triggered morphing devices, autonomous sensors and actuators, and reconfigurable soft robots.