Lei Wu

Reprogrammable materials enable post‐fabrication tuning of mechanical properties, yet existing concepts are largely confined to uniaxial responses. Engineering materials, on the other hand, are routinely subjected to loading in multiple directions, yet their mechanical responses along these directions cannot be tuned in situ. Here, we introduce a class of chiral metamaterials built from isochoric rotationally bistable units that unlock reprogrammable behavior across multiaxial loading states. Integrating theory, simulations, and experiments, we demonstrate that the bistable units can reversibly switch between open and closed states under clockwise or counterclockwise torque, enabling isochoric switching between soft and stiff responses without geometric reconfiguration of the surrounding architecture. Upon selective activation of given bistable cores, the metamaterial exhibits reprogrammable snap‐through instabilities that alter in situ global buckling modes and energy dissipation pathways. Under multiaxial loading, a set of volume‐dominated properties, including effective bulk modulus and volumetric instability, can be reprogrammed, enabling erasable and rewritable two‐dimensional snapping sequences that encode complex mechanical memory within the material. Beyond property tuning, the work suggests a scalable, reprogrammable framework that can be extended to Cosserat media to achieve multiaxial multifunctionality in soft robotics, fluidic devices, and mechanically intelligent systems.

Shape memory behavior in engineered systems is traditionally achieved through material-level phase transformations or polymer network rearrangements. While effective, these approaches tightly couple functionality to chemistry, limiting scalability, material choice, and manufacturing flexibility. An alternative paradigm is to embed recoverability within structural architecture itself, decoupling actuation from intrinsic material phase changes. We present a feather-inspired phase-transforming cellular material–spring system (F-PXCM) that achieves shape recovery through structural interactions rather than active phases. PXCMs, designed with bistable sinusoidal geometries, mimic the hydration-induced softening of the feather matrix, while temperature-invariant springs replicate keratinous fibers. Finite element simulations show that thermal softening of PXCMs, combined with spring restitution, enables complete recovery, while additive-manufactured prototypes confirm the computational results. Exploratory microscale fabrication with two-photon polymerization highlights key challenges and pathways forward.

To compare the in-vitro retentive forces of Novaloc-TiN and Locator attachment systems for two-implant overdentures before and after insertion-removal and compressive cyclic loading, representing up to 12 months of wear. Insertion-removal and compression-cycles of two-implant Novaloc (Novaloc® TiN, Straumann) and Locator (Locator®, Straumann) overdenture attachments embedded into 3D-printed acrylic blocks were performed (n=10 each). For compressive cycling, a force approximating 66.7-N was applied at the center of the blocks using a Bose ElectroForce Fatigue Testing machine over a sum of 300,000 cycles per sample. The retentive force was recorded at baseline and after certain insertion-removal (23, 270, 540, and 1080) and compression-cycles (5k, 25k, 75k, 150k, and 300k). Deformation and crystallization were assessed using micro-computed tomography and differential scanning calorimetry coupled with thermal gravimetric analysis. Compressive cycling of two-implant overdenture yielded a greater retentive force for Locator attachments relative to Novaloc-TiN attachments at simulated mastication equivalent to one-week, one, three, six and 12-months of wear. However, Locator attachments displayed fluctuating retentive forces throughout the 300,000-cycle duration. Retention forces for Novaloc system had no significant differences between baseline and the following 300,000 cycles, indicating consistent retention throughout the cycling duration. Similarly, insertion-removal cycles resulted in retention loss for Locator, whereas Novaloc showed more consistency. Novaloc-TiN system offers superior durability following compressive and insertion-removal cycling. This indicates more longevity for retentive forces relative to Locator attachment system, despite the lower overall retentive forces of Novaloc attachments.

Bistability enables a physical system to reversibly transition between two stable states via snapping instability, and is broadly classified as either global–facilitating macroscopic shape morphing of a structure–or local, which enables internal geometric reconfiguration within a metamaterial. In existing metamaterials and structures, each form of bistability is implemented independently from the other, failing to capitalize on the benefits that their interaction can offer. In this work, locally bistable metamaterials are integrated into a globally bistable structure, enabling reprogrammable global bistability. By selectively transitioning local unit cells of the metamaterial into a self‐contact state, a specific combination of soft hinges is encoded into the global structure. The encoded hinges can significantly alter the global kinematics of the structure, allowing reprogrammable triggering force, snapping trajectory, and energy barrier. Distinct combinations of local hinges are shown to enable a metamaterial arch to deliver multi‐target actuation, a linkage to switch seamlessly between multistable, bistable, and monostable states, and a dome to transform into various curved shapes. The local‐to‐global interplay unveiled in this work can be leveraged to design multi‐modal jumping/leaping robots and space structures capable of dynamically adjusting their actuation and morphing modes by simply flipping the local states of their unit cells.

A closed surface is generally more resistant to deformation and shape changes than an open surface. An empty closed box, for example, is stiffer and more stable than when it is open. The presence of an opening makes it less constrained, more deformable, and easier to morph, as demonstrated by several studies on open-surface morphing across patterns, materials, and scales. Here, we present a platform to morph closed surfaces with bistability that harnesses a balanced integration of origami and kirigami principles. By harmonizing panel rotation around creases nearly tangent to the closed surface and panel rotation around hinges nearly perpendicular to the closed surface, we show that origami-kirigami assemblages can shape-morph between a cube and a sphere, scale between spheres of dissimilar size, and change topology between a sphere and a torus, with programmed bistability. The framework offers a promising strategy for designing bistable reconfigurable structures and metamaterials with enclosed configurations.

Existing mechanical metamaterials are typically designed to either withstand loads as a stiff structure, shape morph as a floppy mechanism, or trap energy as a multistable matter, distinct behaviours that correspond to three primary classes of macroscopic solids. Their stiffness and stability are sealed permanently into their architecture, mostly remaining immutable post-fabrication due to the invariance of zero modes. Here, we introduce an all-in-one reprogrammable class of Kagome metamaterials that enable the in-situ reprogramming of zero modes to access the apparently conflicting properties of all classes. Through the selective activation of metahinges via self-contact, their architecture can be switched to acquire on-demand rigidity, floppiness, or global multistability, bridging the seemingly uncrossable gap between structures, mechanisms, and multistable matters. We showcase the versatile generalizations of the metahinge and remarkable reprogrammability of zero modes for a range of properties including stiffness, mechanical signal guiding, buckling modes, phonon spectra, and auxeticity, opening a plethora of opportunities for all-in-one materials and devices.

Power‐free shape retention enables soft pneumatic robots to reduce energy cost and avoid unexpected collapse due to burst or puncture. Existing strategies for pneumatic actuation cannot attain motion locking for trajectories combining extension and bending, one of the most common modes of operation. Here, a design paradigm is introduced for soft pneumatic actuators to enable zero‐power locking for shape retention in both extension and bending. The underpinning mechanism is the integration of a pneumatic transmitter and a multistable guider, which are programmed to interact for balanced load transfer, flexural and extension steering, and progressive snapping leading to state locking. Through theory, simulations, and experiments on proof‐of‐concept actuators, the existence of four distinct regimes of deformation is unveiled, where the constituents first interact during inflation to attain locking in extension and bending, and then cooperate under vacuum to enable fully reversible functionality. Finally, the design paradigm is demonstrated to realize a soft robotic arm capable to lock at desired curvature states at zero‐power, and a gripper that safely operates with puncture resistance to grasp and hold objects of various shapes and consistency. The study promises further development for zero‐power soft robots endowed with multiple deformation modes, sequential deployment, and tunable multistability.