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Two-dimensional shape-morphing networks are common in biological systems and have garnered attention due to their nontrivial physical properties that emanate from their cellular nature. Here, we present the fabrication and characterization of inhomogeneous shape-morphing networks composed of thermoresponsive microfibers. By strategically positioning fibers with varying responses, we construct networks that exhibit directional actuation. The individual segments within the network display either a linear extension or buckling upon swelling, depending on their radius and length, and the transition between these morphing behaviors resembles Landau's second-order phase transition. The microscale variations in morphing behaviors are translated into observable macroscopic effects, wherein regions undergoing linear expansion retain their shape upon swelling, whereas buckled regions demonstrate negative compressibility and shrink. Manipulating the macroscale morphing by adjusting the properties of the fibrous microsegments offers a means to modulate and program morphing with mesoscale precision and unlocks novel opportunities for developing programmable microscale soft robotics and actuators.

Shape-morphing networks of mesoscale filaments are a common hierarchical feature in biology and hold significant potential for a range of technological applications, from micro-muscles to shape-morphing optical devices. Here, we demonstrate both experimentally and computationally that the shape-morphing of highly-ordered 2D networks constructed of thermoresponsive mesoscale polymeric fibers strongly depends on the physical attributes of the single fiber, in particular on its diameter, as well as on the network's density. We show that based on these parameters, such fiber-networks exhibit one of two thermally driven morphing behaviors: (i) the fibers stay straight, and the network preserves its ordered morphology, exhibiting a bulk-like behavior; or (ii) the fibers buckle and the network becomes messy and highly disordered. Notably, in both cases, the networks display memory and regain their original ordered morphology upon shrinking. This hierarchical principle, demonstrated here on a range of networks, offers a new way for controlling the shape morphing of materials with mesoscale resolutions and elucidates that minute changes in the mesoscale structural attributes can translate to a dramatic change in the morphing behaviors at the macroscale., Comment: 19 PAGES, 4 FIGURES