Synergy of Smart Materials and Structures Toward Intelligent Metamaterials

Abstract

Metamaterials are artificially engineered systems in which the geometry and arrangement of designed unit cells give rise to effective properties that are not available in natural materials. Intelligent metamaterials extend this concept by integrating stimulus-responsive materials with programmable architectures, thereby creating functional matter that blurs the conventional boundary between materials and structures and enables dynamic, adaptive, and reconfigurable functionalities. These systems can respond to diverse stimuli such as thermal, electrical, optical, magnetic, and mechanical inputs, and convert them into tunable shape change, adaptive mechanical/optical responses, and other reconfigurable functionalities [1-5]. Through this synergy, they acquire lifelike and emergent behaviors, making them attractive platforms for next-generation applications in soft robotics, bioengineering, information encryption, and mechanical computation. Yet, without this integration, both components face intrinsic limitations. Standalone smart materials are typically constrained by specific modes, directionalities, and spatial complexities, restricting their use in multifunctional devices. Many promising material behaviors remain underutilized due to challenges in harnessing and controlling their properties at the system level. Likewise, mechanical structures alone are limited by their static configuration, which severely curtails their functional versatility. To overcome these challenges, a promising approach lies in the synergistic integration of smart materials with structural designs. Coupling programmable geometries with responsive materials not only surmounts the intrinsic limitations of each component but also unlocks emergent functionalities unattainable by either alone. Examples of these novel capabilities include programmable shape morphing, adaptive mechanical properties, and multimodal responses, all arising naturally from this codesign paradigm. This perspective elucidates this transformative paradigm by focusing on the integration of smart materials and structural architectures as a platform for intelligent metamaterials. We systematically review representative classes of smart materials and structural design and then highlight the fundamental principles underpinning material–structure coupling and discuss how structural design facilitates the full realization of material functionalities. Finally, we examine emerging applications and identify key challenges and future directions essential for developing the next generation of architected intelligent metamaterials. Figure 1 illustrates the core concept: the nexus of material properties, structural design, and emergent functionalities, where reconfigurability and dynamic operation arise from seamless integration, opening avenues to intelligent, reprogrammable metamaterials with profound technological impact. Synergistic integration of smart materials and structural design, highlighting how their coupling provides the foundation for intelligent metamaterials. One of the defining features of smart materials is their ability to actively respond to environmental stimuli. These responses originate from intrinsic molecular architectures, phase transitions, or energy conversion mechanisms [6], as illustrated in Figure 2A. Thermal responsiveness represents the most fundamental and widely applied category. Phase transitions provide the driving force: shape-memory polymers (SMPs) [7] and shape-memory alloys (SMAs) [8] recover their programmed configuration upon heating through reversible thermal transitions (glass transition or melting of crystalline domains) and reversible martensite–austenite transformation, which release the stored elastic strain energy and drive macroscopic shape recovery accordingly, whereas liquid-crystalline elastomers (LCEs) [9] actuate through the reorientation of mesogenic units, which directly drives macroscopic deformation. Electrical responsiveness can be classified into direct and indirect mechanisms. Direct response arises from electrochemical reactions, or piezoelectric conversion, where electrical input is translated into mechanical deformation or sensing output [10, 11]. Indirect responses are mediated by joule heating: composites, for example, incorporating carbon nanotubes, silver nanowires, or conductive polymers generate localized heating that triggers thermal deformation [12]. Optical responsiveness mostly originates from either photothermal conversion or photochemical reactions. In the former, absorbed light is transformed into heat that drives thermal actuation, whereas in the latter, molecular transformations, such as azobenzene cis-trans isomerization, induce reversible deformation or stiffness modulation [13, 14]. Representative (A) smart materials with diverse active mechanisms and (B) typical structural designs with various deformation modes. Reproduced with permission from Ref. [6]. Copyright 2024, Science China Press, and Oxford University Press. Besides these common actuation mechanisms, magnetic responsiveness offers an additional pathway for remote, wireless, and rapid control. Polymers embedded with magnetic particles or nanomaterials can undergo orientation, deformation, or stiffness modulation under external magnetic fields, enabling noncontact actuation and programmability [15]. Meanwhile, fluidic and chemical responsiveness arises from interactions with liquid environments: swelling or contracting hydrogels [16], ionic polymers, or pH-sensitive systems undergo reversible volume expansion, contraction, or surface reconstruction, which are particularly valuable in biomedical and soft-robotic applications. Finally, the integration of multiple responsive units—thermal, electrical, optical, magnetic, and fluidic—offers a pathway toward higher-order intelligence. Modular coupling of these mechanisms enables synergistic functions such as self-sensing, adaptive morphing, and multifunctional actuation, thereby greatly expanding the design space of smart material systems. Meanwhile, structural design serves as the cornerstone in the development of metamaterials. Over the years, numerous fundamental strategies have emerged: kirigami structures that exploit rotational motion of patterned cuts [17]; origami configurations in which crease-induced stiffness reduction enables programmable 3D folding [18]; post-buckling 3D architectures assembled through mechanically guided deformation [19-21]; interlocking or Lego-like assemblies formed by geometric fitting; torsional configurations generated under twisting loads; and horseshoe-shaped unit cells derived from cantilever bending (Figure 2B). Based on these strategies, metamaterials with unique mechanical behaviors, such as auxetic response [22], zero stiffness [23], J-shaped stress-strain profile [24], and high specific stiffness [25], can further be enhanced by lattice arrangements and hierarchical combinations of unit cells. Beyond these, more complex systems have been created, such as compression-torsion couplings [26], multistable [27] and snap-through architectures [28], and path-dependent design [29]. To fully exploit the potential of structural design, researchers increasingly pursue two complementary design dimensions. The first focuses on geometric nonlinearity amplification, where origami, kirigami, and bimetallic structures can achieve large deformations under minimal actuation, enabling programmable morphing and multistability for deployable devices and bioinspired actuators. The second emphasizes coupled optimization of topology and deformation mechanisms. For example, auxetic systems can reversibly switch between positive and negative Poisson's ratios through localized rotations or tensile mechanisms, and when integrated with responsive materials, they combine high compliance with enhanced energy absorption. Unlike conventional functional materials, which are constrained by intrinsic composition, metamaterials derive their properties from structural freedom, offering virtually unlimited opportunities to tailor deformation modes and mechanical responses. The integration of smart materials with architected structures opens broad opportunities for advancing intelligent metamaterials toward revolutionary functionalities. However, a fundamental challenge lies in the mismatch between the microscale actuation mechanisms of smart materials and the macroscale deformations required by structural architecture. Bridging this disparity to fully leverage the strengths of both components and unlock unprecedented performance remains highly attractive but nontrivial. In this section, we review two representative approaches and discuss key considerations spanning material fabrication, structural design, and coupling strategies. These insights lay the foundation for the development of the next generation of intelligent metamaterials. A widely used strategy for fabricating intelligent metamaterials from smart materials relies on direct incorporation via additive manufacturing (i.e., 3D printing), molding, or subtractive manufacturing [30], offering important pathways to achieve material-structure synergy. When coupled with architected deformation modes, the inherent responsiveness of smart materials to external cues such as temperature, magnetic fields, light, pH, or ion concentration enables direct actuation for programmable structural reconfigurations and motions at the system level [31]. For example, LCEs provide a representative example, where actuation strain and elastic modulus can be tuned by the transition temperature across different thermal states [32] (Figure 3A). Triangular lattice metamaterials composed of LCEs with distinct transition temperatures and moduli allow complex patterns that switch at programmed temperatures. By encoding different LCE types in each lattice strut, spatially differentiated actuation can be achieved, enabling local thermal reconfigurations that generate reversible global shape transformations. Besides, embedding magnetic components introduces an additional degree of actuation freedom. For instance, magnetic sheets folded into origami-based configurations form programmable magnetic origami metamaterials. Under applied magnetic fields, these architectures exhibit multimodal behaviors, such as directed deformation, rolling, contraction, and crawling, highlighting the versatility of integrating magnetic actuation with origami mechanics [33] (Figure 3B). In addition, integrating smart materials responsive to solvents, pH, or ion concentration further broadens the design space [40]. A notable case involves lattice structures composed of microscale liquid-crystalline polymer (LCP) plates [34] (Figure 3C). Exposure to acetone softens the LCP, lowering its modulus so that capillary forces dominate: plates are pulled together, eliminating original nodes and generating new ones, thus reconfiguring the lattice. Upon solvent evaporation, the LCP plates stiffen, locking in the new geometries. Re-exposure to dichloromethane (DCM) induces swelling, and ethanol enables gradual and controllable recovery, thereby restoring the original configuration. This system demonstrates how solvent–structure interactions, coupled with the tunable stiffness, can enable reversible and reprogrammable lattice transformation. Two strategies for synergizing smart materials with designed structures. (A–D) Intelligent metamaterials directly composed of response materials. (A) Lattice metastructure composed of printable LCE exhibiting tunable actuation strain and elastic modulus. Reproduced with permission from Ref. [32]. Copyright 2024, Wiley. (B) Origami metamaterials actuated by magnetic fields, enabling multimodal motion. Reproduced with permission from Ref. [33]. Copyright 2022, Springer Nature Ltd. (C) Micro-lattice with tunable cell topology induced by capillary force. Reproduced with permission from Ref. [34]. Copyright 2021, Springer Nature Ltd. (D) 3D concatenated metamaterials demonstrating reversible and precise deformation driven by electrostatic force. Reproduced with permission from Ref. [35]. Copyright 2025, AAAS. (E–H) Smart-substrate enabled intelligent metamaterials. (E) Kirigami-designed structures exhibiting reconfigurable deformation when stretched by an LCE substrate. Reproduced with permission from Ref. [36]. Copyright 2021, Wiley. (F) Micro-metamaterials embedded in hydrogel, enabling intelligent information decryption via thermally induced deformation. Reproduced with permission from Ref. [37]. Copyright 2023, Springer Nature Ltd. (G) Electrochemical-driven, microscopically configurable origami metamaterial with crease designs for morphing. Reproduced with permission from Ref. [38]. Copyright 2025, Springer Nature Ltd. (H) Nanomagnetic encoding of morphing 3D architected structure. Reproduced with permission from Ref. [39]. Copyright 2019, Springer Nature Ltd. Notably, interfacial forces such as electrostatics can dominate as structural dimensions shrink. Acrylic polymers fabricated into 3D annular concatenated metamaterials via two-photon lithography and coated with copper [35] (Figure 3D) expand upon electrostatic charging in a Van de Graaff generator. As electrostatic repulsion between interlocked rings overcomes gravity, the initially collapsed structure deploys outward; once discharged, it rapidly returns to its original state. This reversible transition illustrates how electrostatic interactions can be harnessed for microscale structural reconfiguration. Together, these examples demonstrate that integration of smart material responsiveness with architected deformation modes—whether thermal, magnetic, chemical, or electrostatic—enables sophisticated, reversible, and multimodal transformations. Moreover, when the characteristic dimensions are at the microscale, forces such as capillarity and electrostatics become increasingly influential, and when combined with smart materials that mitigate stiffness or gravity constraints, they provide powerful mechanisms for reversible and precise structural reprogramming. A complementary strategy employs smart materials as active platforms to drive otherwise passive, architected structures, enabling them to morph into specific shapes on demand [42]. In this scheme, the intrinsic responsiveness of the material couples with predesigned structures, allowing both global and local control of deformation [43]. Global control relies on uniform actuation of the smart material—often serving as an active substrate—where tailored structural patterns translate large-scale deformations into functional morphologies [44]. For instance, uniaxially aligned LCEs deform upon heating, stretching microscale kirigami structures to achieve reconfigurable patterns that switch between distinct configurations, enabling information display and encryption [36] (Figure 3E). Similarly, microscale metastructures embedded into thermal-responsive hydrogels can yield broad configuration programmability: different sinusoidal morphologies can be generated as a result of the site-specific variations in the induced structural deformation, which encode and decode complex images upon heating and cooling, such as high-resolution paintings [37] (Figure 3F). Besides, localized manipulation provides more precise control by selectively actuating specific points or regions of a structure [42]. In monostable systems, introducing pneumatic actuation creates competition between pneumatic forces and elastic restoring forces, giving rise to tunable dynamic behaviors. For example, the inflation of soft pneumatic actuators induces bending in a monostable structure, where stored elastic energy is rapidly released through snap-through behavior, followed by snap-back upon the application of negative pressure [45]. Beyond pneumatics, diverse localized actuation methods have been demonstrated, including electronically driven actuation [38] (Figure 3G), magnetic encoding [39, 46, 47, 41] (Figure 3H), and electric heating [48, These strategies enable site-specific of smart materials, including LCEs and thereby offering tunable responses otherwise structures. By coupling the responsiveness of smart materials with engineered structures, devices can exhibit and emergent behaviors that materials structures achieve alone. One is the of and where geometric design material responses into Figure illustrates a energy that the to motion each the from to under then as and to generate electrical Similarly, designs such as or geometries can to motion. Figure demonstrates a on a that thermal generating that and drives of an embedded Besides, strategies provide toward behaviors. For example, a fabricated into a structure with (Figure can into by shape as swelling of the in the the to the into Representative intelligent devices enabled by the of architectures and tailored smart materials. (A) Reproduced with permission from Ref. Copyright Wiley. (B) Reproduced with permission from Ref. Copyright Springer Nature Ltd. (C) Reproduced with permission from Ref. Copyright 2023, Springer Nature Ltd. (D) intelligence. Reproduced with permission from Ref. Copyright 2024, AAAS. can also arise from and reconfigurable systems, where interactions such as and allow and adaptive multiple For instance, Figure illustrates with unit a of multistable interlocking features that form between units, enabling Upon thermal the on the reconfigurable and a which the and a of the metamaterials. these to to materials and architected structures from smart materials, smart to actuate otherwise architectures, and driven by smart materials. 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Representative examples include soft actuators (Figure and soft which diverse modes but remain due to on or programmed external in of intelligent metamaterials across representative (A) soft actuators. Reproduced with permission from Ref. Copyright 2025, AAAS. (B) motion of or structures under Reproduced with permission from Ref. Copyright 2024, Springer Nature Ltd. (C) LCE lattice for Reproduced with permission from Ref. Copyright 2021, Wiley. (D) metamaterial composed of materials and a structure. Reproduced with permission from Ref. Copyright 2022, Wiley. (E) display and encryption enabled by materials combined with structures. Reproduced with permission from Ref. Copyright 2023, Wiley. (F) information and encryption of structures driven by Reproduced with permission from Ref. Copyright 2023, Springer Nature Ltd. (G) magnetic metamaterial with Reproduced with permission from Ref. Copyright 2021, Springer Nature Ltd. (H) metamaterials composed of soft conductive materials and kirigami structures. Reproduced with permission from Ref. Copyright 2022, Springer Nature Ltd. demonstrate that coupling structural designs with zero elastic energy modes and induced strain enables under A between structural and strain by surface the LCE to across or fluidic under the (Figure Similarly, achieve motion by and between and external under designs on energy inputs, the potential of soft toward more and systems. 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