Ruike Renee Zhao

Dynamically tunable surface textures offer a powerful route to spatiotemporally regulate surface and interfacial properties, enabling emerging applications ranging from adaptive optics to soft robotic manipulation. However, achieving programmable, reversible, and spatiotemporal modulation of surface texture remains a fundamental challenge. Here, we present a photothermal-actuated liquid crystal elastomer bilayer that enables reversible, on-demand spatiotemporal modulation of surface textures through dynamically emerging and propagating wrinkles. Using direct laser writing or projected light fields, programmable and self-erasable wrinkle patterns are generated for dynamic information encoding. This spatiotemporal wrinkling enables object manipulation across diverse geometries, including uphill transport and navigation along predesigned paths. By coupling wrinkle-driven motion with thermally reversible dynamic bonding, the bilayer further enables assembly and disassembly of dynamic polymers, as well as cargo transportation. This work demonstrates spatiotemporally programmable wrinkling as a powerful mechanism for dynamic modulation of surface textures, establishing a versatile platform for multifunctional and reconfigurable smart surfaces. Dynamic control of surface textures is limited by static or coarse-patterned approaches, restricting their application in programmable object manipulation and information encoding. This study achieved reversible, spatiotemporally programmable surface wrinkling on a photothermal liquid crystal elastomer bilayer, enabling precise, on-demand surface patterning, object propulsion, self-erasing information encoding, and reversible assembly processes through localized light stimuli.

Ring origami, consisting of closed-loop rods, can realize diverse shape-morphing behaviors, including 2D-to-1D, 2D-to-2D, and 2D-to-3D transformations, by harnessing snap-buckling instability. To broaden its application potential in areas such as deployable aerospace structures, soft robotics, and reconfigurable metamaterials, a programmable design framework is highly desired. In this work, we develop a unified framework for the forward prediction and inverse design of ring origami by integrating Kirchhoff rod theory with a physics-informed neural network. The framework can identify the stable states of various segmented rings (e.g., square and hexagonal rings) composed of rod segments with prescribed constant or varying natural curvature (i.e., curvature in the stress-free state). By introducing an additional shape-matching loss, the framework can also determine the natural curvature profile of segmented rings required to achieve stable configurations that can be confined within a target spatial domain or conform to a target curved surface. Its generality and robustness are further demonstrated by extending it to 3D rod systems. This work establishes a powerful strategy for the programmable design of elastic rod systems exemplified by ring origami and opens new opportunities for functional applications that demand shape-morphing structures with simple geometries, high packing capability, and prescribed stable configurations.

Modern engineering systems increasingly operate under varying vibrational environments, necessitating structural components capable of adapting their dynamic responses on demand. While springs have long served as the core of vibration control systems, their fixed stiffness fundamentally limits adaptability. Here, we introduce reconfigurable springs based on the structural instability of rod origami (RodOri), constructed from pre-stressed, naturally curved elastic rods. By tailoring the natural curvature and cross-sectional aspect ratio of the constituent rods, both the onset of snap-through buckling and the post-buckling response of individual RodOri springs can be systematically programmed. Leveraging this geometric programmability, we establish a system-level design principle in which multiple RodOri springs of identical length but distinct buckling behaviors are assembled into a multistable metamaterial. Differences in snapping displacements enable stepwise structural reconfiguration via sequential snap-through transitions, while variations in post-snapping stiffness govern the mechanical response of each configuration. This hierarchical tunability enables both broad and fine control of resonance frequencies and dynamic responses across stable states. Numerical simulations and experiments demonstrate on-demand modulation of vibration amplification, isolation, and impact mitigation within a single metamaterial, establishing RodOri springs as reconfigurable, programmable building blocks for adaptive structural and wave dynamics.

Reconfigurable mechanical systems enable precise programmable control over structural properties, expanding opportunities in architected materials, adaptive devices, and multifunctional structures. Here, we introduce elastic rod origami (RodOri), a platform that exploits remarkably simple elements-prestressed, naturally curved rods-into a system with an extraordinary degree of multistability and configurational richness. For example, a single six-rod RodOri unit can easily access 11 distinct configurations, far exceeding the reconfigurability of conventional origami or general mechanical reconfigurable systems. Individual rods, constrained under clamped boundary conditions, undergo transitions between discrete morphologies whose strain energy and stiffness are precisely prescribed by their natural curvature. Assembling these rods into modular multirod architectures yields metamaterials with numerous stable configurations that can be selectively and reversibly programmed. This configurational diversity enables tunable static stiffness and nonlinear force response, thus enabling tunable dynamic behaviors such as vibration filtering, wave propagation switching, and mode conversion within a single, easily manufactured platform. By leveraging curvature-induced mechanical instability, RodOri unlocks highly programmable static and dynamic mechanical behavior, offering tailorable design strategies for reconfigurable structures, soft robotics, medical devices, and adaptive materials.

Dynamically tunable surface textures offer a powerful route to spatiotemporally regulate surface and interfacial properties, enabling emerging applications ranging from adaptive optics to soft robotic manipulation. However, achieving programmable, reversible, and spatiotemporal modulation of surface texture remains a fundamental challenge. Here, we present a photothermal-actuated liquid crystal elastomer bilayer that enables reversible, on-demand spatiotemporal modulation of surface textures through dynamically emerging and propagating wrinkles. Using direct laser writing or projected light fields, programmable and self-erasable wrinkle patterns are generated for dynamic information encoding. This spatiotemporal wrinkling enables object manipulation across diverse geometries, including uphill transport and navigation along predesigned paths. By coupling wrinkle-driven motion with thermally reversible dynamic bonding, the bilayer further enables assembly and disassembly of dynamic polymers, as well as cargo transportation. This work demonstrates spatiotemporally programmable wrinkling as a powerful mechanism for dynamic modulation of surface textures, establishing a versatile platform for multifunctional and reconfigurable smart surfaces.

Dynamically tunable surface textures offer a powerful route to spatiotemporally regulate surface and interfacial properties, enabling emerging applications ranging from adaptive optics to soft robotic manipulation. However, achieving programmable, reversible, and spatiotemporal modulation of surface texture remains a fundamental challenge. Here, we present a photothermal-actuated liquid crystal elastomer bilayer that enables reversible, on-demand spatiotemporal modulation of surface textures through dynamically emerging and propagating wrinkles. Using direct laser writing or projected light fields, programmable and self-erasable wrinkle patterns are generated for dynamic information encoding. This spatiotemporal wrinkling enables object manipulation across diverse geometries, including uphill transport and navigation along predesigned paths. By coupling wrinkle-driven motion with thermally reversible dynamic bonding, the bilayer further enables assembly and disassembly of dynamic polymers, as well as cargo transportation. This work demonstrates spatiotemporally programmable wrinkling as a powerful mechanism for dynamic modulation of surface textures, establishing a versatile platform for multifunctional and reconfigurable smart surfaces.

Vascular diseases such as atherosclerosis, thrombosis, and aneurysms can lead to life-threatening medical events. Conventional catheter- or guidewire-based interventional devices often struggle to navigate through highly tortuous vasculature. The recently developed multifunctional magnetic milli-spinner offers a promising wireless solution by integrating a central through-hole and side slits into a cylindrical body with helical fins, enabling rapid and stable navigation for clot debulking, targeted drug delivery, and aneurysm treatment. Here, we combine computational fluid dynamics simulations with experimental validation to optimize the milli-spinner's structural design for high-velocity propulsion and high-efficiency clot debulking in tubular flow environments. By systematically investigating the effects of through-hole radius, fin number, fin helical angle, and slit dimension on propulsion performance, the optimized milli-spinner achieves swimming velocities of 55 cm/s (175 body lengths per second) in saline water and 44 cm/s (140 body lengths per second) in a fluid with viscosity (3.5 mPa.s) comparable to that of arterial blood at high shear rates, far exceeding existing untethered magnetic robots in tubular environments (less than 80 body lengths per second). This exceptional velocity enables stable upstream operation against strong physiological flows representative of major arteries and veins, establishing the milli-spinner as a robust untethered navigation platform for operation in high-flow, tortuous vasculature.

Vascular diseases such as atherosclerosis, thrombosis, and aneurysms can lead to life-threatening medical events. Conventional catheter- or guidewire-based endovascular diagnostic and therapeutic devices often struggle to navigate through highly tortuous vascular pathways. The recently developed multifunctional magnetic milli-spinner offers a promising wireless solution by integrating a central through-hole and side slits into a cylindrical body with helical fins, enabling rapid and stable navigation in complex vascular environments for clot debulking, targeted drug delivery, and aneurysm treatment. Here, we combine computational fluid dynamics simulations with experimental validation to optimize the milli-spinner's structural design for high-speed untethered navigation and high-efficiency clot debulking in tubular flow environments. By systematically examining the effects of through-hole radius, fin number, fin helical angle, and slit dimension on propulsion performance, the optimized magnetic milli-spinner achieves a swimming speed of 55 cm/s (~175 body lengths per second), far exceeding existing untethered magnetic robots in tubular environments (< 80 body lengths per second). This exceptional speed enables stable upstream operation against strong physiological flows representative of major arteries and veins, establishing the magnetic milli-spinner as a robust untethered navigation platform for operation in high-flow, tortuous vasculature, with potential applications in robotic mechanical thrombectomy, embolectomy, and targeted drug delivery.

Certain cephalopods can dynamically camouflage by altering both skin texture and color to match their surroundings. Inspired by this capability, we present a cholesteric liquid crystal elastomer-liquid crystal elastomer (CLCE-LCE) bilayer capable of simultaneous, reversible modulation of surface texture and structural color through programmable wrinkling. By tuning the bilayer's fabrication parameters, on-demand wrinkle morphologies and color combinations are achieved. Spatially selective ultraviolet (UV) curing allows localized surface textures, while chemical patterning of the CLCE layer enables region-specific color responses, expanding the design space for multifunctional, spatially encoded optical materials. The CLCE-LCE bilayer enables dynamic thermal regulation by tuning light absorption through synergistically modulating surface morphology and color. Notably, this system achieves strain-dependent multistate encoding via multistep selective UV curing, revealing distinct visual content under different applied strains. This work establishes a versatile platform that merges surface instabilities with tunable structural coloration, advancing intelligent materials with programmable, strain-responsive surface and optical properties.

Ring origami, consisting of closed-loop rods, is a class of shape-morphing structures that undergo shape transformation through folding enabled by snap-buckling instabilities, referred to as snap-folding instabilities. Previous studies have shown that 2D ring origami composed of rod segments with in-plane natural curvature (i.e., the stress-free curved state lies in the plane of the planar ring) can achieve diverse and intriguing 2D-to-2D shape transformations. Here, we propose a 2D-to-3D shape transformation strategy for ring origami by introducing out-of-plane natural curvature (i.e., the stress-free curved state lies in a plane perpendicular to the planar ring) into the rod segments. Due to natural curvature-induced out-of-plane bending moments, a 2D elastic ring spontaneously snaps out-of-plane and reaches equilibrium in a 3D configuration. These snapping-induced out-of-plane shape transitions not only enable self-guided, spontaneous shape morphing, but also allow the construction of complex structures from simple geometries, making them promising for the design of functional deployable and foldable structures. By combining a multi-segment Kirchhoff rod model with finite element simulations and experiments, we systematically investigate the 3D equilibrium states and transition behavior of these systems. Using square and hexagonal rings as representative examples, we demonstrate that by rationally designing the out-of-plane natural curvature of rod segments, 2D rings can exhibit a range of functional behaviors, including spontaneous 2D-to-3D shape transformation (e.g., planar square to sphere) via snap-folding, multistability with various 3D configurations, and monostability with a compact zero-energy 3D configuration.

Abstract Navigating the complex and high‐flow environment of human vasculature remains a major challenge for conventional endovascular tools and externally actuated tethered systems. While catheter‐based approaches are the clinical standard, their limited steerability and force transmission hinder access to tortuous or distal vessels, especially in the brain. Untethered robotic systems have emerged as a promising alternative for enhanced flexibility and reachability. However, most designs struggle against the high, pulsatile blood flow in human arteries. Here, the study presents a magnetically actuated milli‐spinner robot that overcomes existing limitations in navigating complex and high‐flow vasculature. Capable of swimming at 23 cm·s −1 (73 body lengths per second), the milli‐spinner enables rapid, stable navigation through complex vasculature. This performance is driven by its hollow cylindrical structure with integrated helical fins and slits, which together generate a spinning‐induced flow field that enhances propulsion efficiency and allows the robot to maintain stability and control even in dynamic, pulsatile blood flow environments. In addition to its navigation capabilities, the milli‐spinner enables multifunctional treatment, including localized suction and shear for efficient clot removal, targeted drug delivery, and in situ embolization for aneurysm treatment. These features establish the milli‐spinner as a versatile and powerful platform for next‐generation, untethered endovascular interventions.

Kidney stones can cause severe pain and complications like chronic kidney disease. Although retrograde intrarenal surgery with laser lithotripsy is effective, current retrieval methods are inefficient, typically capturing only 1–3 fragments per ureteroscope pass and requiring many passes for full clearance. A novel spinner device that enables ultra‐efficient fragment removal through spinning‐induced localized suction is introduced. It generates spiral and circulating flows to capture fragments from over 20 mm away, eliminating the need to chase them. Optimized via computational fluid dynamics and validated in vitro and ex vivo, the spinner retrieves ≈60 small (0.5–2 mm) or ≈15 larger (2–3 mm) fragments per pass. It demonstrates nearly 100% capture of 60 fragments in bench tests and removes 45 fragments in 4 s in a porcine kidney model. This technology markedly improves procedural efficiency by reducing operative time, increasing stone‐free rates, and minimizing the number of ureteroscope passes.

Insulin pumps typically use piston-based mechanisms with bulky transmission components to convert rotary motion into the piston's forward motion. These mechanical transmission systems and insulin reservoirs occupy more than one-third of pumps' volume, significantly limiting miniaturization and making pumps cumbersome for daily use. Herein, a compact, magnetically actuated insulin pump is developed that is less than one-quarter the size of piston-based pumps. Instead of bulky mechanical components, the pump uses a magnetic soft actuator to directly compress the insulin chamber, controlled by a precisely tuned electromagnetic field. This innovative design eliminates the need for large transmission systems, enabling a notably smaller form factor. In addition, the fine-tunable magnetic actuation enables a 0.01 μL delivery resolution, significantly surpassing the 0.25 μL resolution of piston-based pumps. This high-resolution mechanism facilitates further miniaturization by allowing the use of high-concentration insulins, thereby reducing the reservoir size. By varying the magnetic field's waveform, amplitude, and duration, the pump's performance can be further enhanced. The reported magnetic insulin pump exhibits superior repeatability and accuracy across single-pulse, basal, and bolus modes compared to commercial insulin pumps. This miniaturized, high-resolution magnetic insulin pump is anticipated to substantially benefit people with diabetes by improving portability, precision, and cost efficiency.

Abstract Mechanical instabilities, phenomena in which solids and structures lose stability under external stimuli, were traditionally regarded as failure mechanisms but have recently been harnessed to design various functional structures and systems. Over the past century, significant progress has been made in both understanding the fundamental mechanisms behind mechanical instabilities and leveraging them for innovative functional applications. In this review, we classify mechanical instabilities into five categories based on their underlying failure mechanisms: buckling instability, snap-buckling instability, surface instability, buckling-driven delamination, and dynamic instability. First, a brief historical overview of research in this field is presented. Then, for each category of mechanical instabilities, we systematically introduce the underlying mechanisms and associated functional applications, with a particular focus on three fundamental aspects: the conditions under which instability is triggered, the evolution of the system after the onset of instability, and the strategies for exploiting these instabilities in functional design. Finally, we discuss several promising directions for future research. We expect that this review can help readers have a deeper understanding of mechanical instabilities and thereby inspire their broader application in advanced materials and structural systems.

Reconfigurable polarizers overcome problems associated with linear polarization communication systems and are adaptable to complex requirements. Electronically reconfigurable polarizers are restricted by design complexity and scalability. In contrast, mechanical polarizers avoid these problems by reconfiguring the global layout and utilizing simpler electromagnetic designs. In this paper, we demonstrate the use of a magnetically actuated, reconfigurable shape morphing structure to convert linear polarization into either right-handed circular polarization (RHCP) or left-handed circular polarization (LHCP). The PCB design complements the geometry of the tunable shape morphing structure to selectively produce RHCP and LHCP. The polarizer operates in C-band with a fractional bandwidth of 10.5 % and exhibits reflection loss of less than 1 dB as well as an axial ratio less than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{3 ~ d B}$</tex> for RHCP and LHCP.

Abstract Active metamaterials exhibit unique and tunable functionalities by altering their shape and material properties in response to external stimuli. While this enables the creation of material systems that can respond to dynamically changing environments, it also necessitates the development of innovative computational strategies for active metamaterial design. Recent advancements in computational algorithms, such as physics-based optimization techniques and artificial intelligence, have offered new opportunities and attracted significant interest in the field. In this perspective, we examine how these advancements are shaping the development of metamaterial systems. First, we discuss the different levels of complexity for metamaterial design, categorized by the material system (passive versus active) and design approach (forward prediction versus inverse design). We then provide an overview of recent efforts aimed at overcoming the challenges presented by design problems of increasing difficulty. Finally, current limitations and possible future directions for the field are discussed, emphasizing the importance of active property tuning and multifunctionality. This article is expected to provide a comprehensive overview of the current computational landscape, offer insights into emerging strategies for active metamaterial design, and guide future research toward more programmable, multifunctional material systems.

Blood clots, consisting of red blood cells (RBCs) entrapped within a fibrin network, can cause life-threatening conditions such as stroke and heart attack. The recently developed milli-spinner thrombectomy device presents a promising mechanical approach to removing clots by substantially modifying the microstructure of the blood clot, resulting in up to 95% volume reduction through combined compressive and shear forces. To better understand the mechanism and optimize this approach, it is important to quantitatively understand of how compression and shear loadings alter the clot structure. In this study, we combine in vitro experiments with dissipative particle dynamics (DPD) simulations to investigate the effectiveness of clot debulking under integrated compression and shear. Controlled experiments quantify clot volume changes, while simulations offer microscopic insight into fibrin network densification and RBC release. This integrated approach enables a systematic evaluation of mechanical response and microstructure change of different clot types, providing fundamental knowledge to guide the rational design of next-generation mechanical thrombectomy technologies.

The development of amphibious soft robots with multimodal locomotion is of great importance for next-generation intelligent and adaptive devices. Here, we report an untethered amphibious soft robot with diverse locomotion modes driven by high-frequency alternating magnetic fields. The robot is a layered strip composed of liquid crystal elastomer and liquid metal. It can crawl, flip, move upward to water surfaces, swim and steer on water, and transition seamlessly between terrestrial and aquatic environments. This amphibious multimodal locomotion is enabled by two distinct untethered actuation mechanisms under high-frequency alternating magnetic fields: i) thermally driven reversible bending deformation facilitated by ultrafast and programmable induction heating to achieve crawling, flipping, and surfacing motions; and ii) Lorentz force to power on-water swimming. Steerable crawling and swimming are achieved by spatially controlling the alternating magnetic fields. With these capabilities, multimodal amphibious locomotion of the soft robot over a hybrid terrestrial-aquatic environment is further demonstrated for targeted cargo transportation. We anticipate the reported amphibious soft robot with integrated actuation mechanisms and environmental adaptivity will facilitate a broad spectrum of applications, such as environmental monitoring, underwater exploration, and biomedical interventions.

Kidney stones can cause severe pain and complications such as chronic kidney disease or kidney failure. Retrograde intrarenal surgery (RIRS), which uses laser lithotripsy to fragment stones for removal via a ureteroscope, is widely adopted due to its safety and effectiveness. However, conventional fragment removal methods using basketing and vacuum-assisted aspiration are inefficient, as they can capture only 1 to 3 fragments (1--3\,mm in size) per pass, often requiring dozens to hundreds of ureteroscope passes during a single procedure to completely remove the fragments. These limitations lead to prolonged procedures and residual fragments that contribute to high recurrence rates. To address these limitations, we present a novel spinner device that enables ultra-efficient fragment removal through spinning-induced localized suction. The spinner generates a three-dimensional spiral and circulating flow field that dislodges and draws fragments into its cavity even from distances over 20\,mm, eliminating the need to chase fragments. It can capture over 60 fragments (0.5--2\,mm) or over 15 larger fragments (2--3\,mm) in a single pass, significantly improving removal efficiency. In this work, the spinner design is optimized via computational fluid dynamics to maximize suction performance. \textit{In vitro} testing demonstrates near 100\% capture rates for up to 60 fragments in a single operation and superior large-distance capture efficacy compared to vacuum-assisted methods. \textit{Ex vivo} testing of the integrated spinner-ureteroscope system in a porcine kidney confirmed its high performance by capturing 45 fragments in just 4 seconds during a single pass and achieving complete fragment clearance within a few passes.

The buckling behavior of cylindrical shells has gained significant interest over the past century due to its rich nonlinear behavior and broad engineering applications. While the buckling of cylindrical shells under a single load (e.g., compression or torsion) has been extensively studied, the buckling behavior under combined torsional and axial loads remains largely unexplored. In this paper, based on a combination of experiments, theoretical modeling, and finite element simulations, we systematically investigate the buckling and post-buckling behavior of cylindrical shells under combined torsional and axial loads. Three different types of combined loads are considered: compression with pre-torsion, torsion with pre-tension, and torsion with pre-compression. The theoretical model is established within the framework of the Donnell shell theory and solved using the Galerkin method, through which the critical buckling load, critical circumferential wavenumber, buckling pattern, and post-buckling equilibrium path of clamped-clamped thin cylindrical shells under various types of loads can be determined. The theoretical predictions agree well with finite element simulations and qualitatively capture the various buckling phenomena observed in the experiments. It is found that cylindrical shells exhibit quite different post-buckling behavior under combined loads compared to under a single compressive or torsional load. For instance, when a clamped-clamped thin cylindrical shell is subjected to pure torsion or torsion with a relatively small pre-compression, it consistently shows a diagonal-shaped pattern during deformation. However, with a relatively large pre-compression, the shell transitions from a diagonal-shaped pattern to a twisted diamond-shaped pattern.

The buckling behavior of cylindrical shells has gained significant interest over the past century due to its rich nonlinear behavior and broad engineering applications. While the buckling of cylindrical shells under a single load (e.g., compression or torsion) has been extensively studied, the buckling behavior under combined torsional and axial loads remains largely unexplored. In this paper, based on a combination of experiments, theoretical modeling, and finite element simulations, we systematically investigate the buckling and post-buckling behavior of cylindrical shells under combined torsional and axial loads. Three different types of combined loads are considered: compression with pre-torsion, torsion with pre-tension, and torsion with pre-compression. The theoretical model is established within the framework of the Donnell shell theory and solved using the Galerkin method, through which the critical buckling load, critical circumferential wavenumber, buckling pattern, and post-buckling equilibrium path of clamped-clamped thin cylindrical shells under various types of loads can be determined. The theoretical predictions agree well with finite element simulations and qualitatively capture the various buckling phenomena observed in the experiments. It is found that cylindrical shells exhibit quite different post-buckling behavior under combined loads compared to under a single compressive or torsional load. For instance, when a clamped-clamped thin cylindrical shell is subjected to pure torsion or torsion with a relatively small pre-compression, it consistently shows a diagonal-shaped pattern during deformation. However, with a relatively large pre-compression, the shell transitions from a diagonal-shaped pattern to a twisted diamond-shaped pattern.

Abstract Active metamaterials are a type of metamaterial with tunable properties enabled by structural reconfigurations. Existing active metamaterials often achieve only a limited number of structural reconfigurations upon the application of an external load across the entire structure. Here, a selective actuation strategy is proposed for inhomogeneous deformations of magneto‐mechanical metamaterials, which allows for the integration of multiple elastic wave‐tuning functionalities into a single metamaterial design. Central to this actuation strategy is that a magnetic field is applied to specific unit cells instead of the entire metamaterial, and the unit cell can transform between two geometrically distinct shapes, which exhibit very different mechanical responses to elastic wave excitations. The numerical simulations and experiments demonstrate that the tunable response of the unit cell, coupled with inhomogeneous deformation achieved through selective actuation, unlocks multifunctional capabilities of magneto‐mechanical metamaterials such as tunable elastic wave transmittance, elastic waveguide, and vibration isolation. The proposed selective actuation strategy offers a simple but effective way to control the tunable properties and thus enhances the programmability of magneto‐mechanical metamaterials, which also expands the application space of magneto‐mechanical metamaterials in elastic wave manipulation.

Vascular diseases such as thrombosis, atherosclerosis, and aneurysm, which can lead to blockage of blood flow or blood vessel rupture, are common and life-threatening. Conventional minimally invasive treatments utilize catheters, or long tubes, to guide small devices or therapeutic agents to targeted regions for intervention. Unfortunately, catheters suffer from difficult and unreliable navigation in narrow, winding vessels such as those found in the brain. Magnetically actuated untethered robots, which have been extensively explored as an alternative, are promising for navigation in complex vasculatures and vascular disease treatments. Most current robots, however, cannot swim against high flows or are inadequate in treating certain conditions. Here, we introduce a multifunctional and magnetically actuated milli-spinner robot for rapid navigation and performance of various treatments in complicated vasculatures. The milli-spinner, with a unique hollow structure including helical fins and slits for propulsion, generates a distinct flow field upon spinning. The milli-spinner is the fastest-ever untethered magnetic robot for movement in tubular environments, easily achieving speeds of 23 cm/s, demonstrating promise as an untethered medical device for effective navigation in blood vessels and robotic treatment of numerous vascular diseases.

Active metamaterials are a type of metamaterial with tunable properties enabled by structural reconfigurations. Existing active metamaterials often achieve only a limited number of structural reconfigurations upon the application of an external load across the entire structure. Here, we propose a selective actuation strategy for inhomogeneous deformations of magneto-mechanical metamaterials, which allows for the integration of multiple elastic wave tuning functionalities into a single metamaterial design. Central to this actuation strategy is that a magnetic field is applied to specific unit cells instead of the entire metamaterial, and the unit cell can transform between two geometrically distinct shapes, which exhibit very different mechanical responses to elastic wave excitations. Our numerical simulations and experiments demonstrate that the tunable response of the unit cell, coupled with inhomogeneous deformation achieved through selective actuation, unlocks multifunctional capabilities of magneto-mechanical metamaterials such as tunable elastic wave transmittance, elastic waveguide, and vibration isolation. The proposed selective actuation strategy offers a simple but effective way to control the tunable properties and thus enhances the programmability of magneto-mechanical metamaterials, which also expands the application space of magneto-mechanical metamaterials in elastic wave manipulation.

Additive manufacturing (AM or 3D printing) has advanced significantly over the past decade and has seen a proliferation of new materials, new methods, and new applications. As AM is fundamentally a material processing technology, its advance closely relates to materials. This special issue consists of 32 articles from renowned groups worldwide, presenting their perspective and recent advancements in AM. The articles cover a wide range of topics, which reflect the diversity and breadth of the AM field. The collections in this special issue have attracted seven review articles that cover different aspects of the AM field. Zhu et al. (adma.202314204) discussed the recent progress in multi-material and multi-scale AM. Chen et al. (adma.202307686) also explored multimaterial 3D/4D printing for tissue engineering applications. Wan et al. (adma.202312263) reviewed the latest achievements in 4D printing across diverse fields, including biomedical engineering, electronics, robotics, and photonics. Machine learning has immersed into different fields, including AM. Ng et al. (adma.202310006) discussed the challenges and opportunities of integrating machine learning with AM, including quality control, process optimization, design optimization, microstructure analysis, and material formulation, etc. Laser is one of the most commonly used energy sources for AM. Park et al. (adma.202307586) discussed the principle, material selection, and applications of laser-based AM. The progress of AM also significantly advances other fields, such as soft robotics. Xin et al. (adma.202307963) provided an overview of how AM promotes the fabrication of soft grippers, which are an important component of soft robots. Tissue engineering applications are another sub-field where AM finds tremendous potential. Yuan et al. (adma.202403641) presented an in-depth review of 3D printing of smart scaffolds with stimulus-responsive properties, which can generate tailored and controllable therapeutic effects for bone tissue engineering and regeneration. This special issue has a strong focus on materials in 3D printing. Liquid crystal elastomers (LCEs) have attracted significant attention in recent years due to their capability of large reversible actuation upon external stimuli. LCEs are typically actuated by heat. However, typical heating methods, such as water baths, are relatively slow. Maurin et al. (adma.202302765) proposed an LCE-liquid metal (LM) composite where the LM was used to heat the 3D-printed LCEs ultrarapidly through eddy current under a high-frequency magnetic field. In their demonstrations, the LCE structures could be activated in less than a second. Photothermal heating by incorporating nanoparticles into resin is another common method for LCE actuators. Gold nanorods (AuNRs) are typically used due to their high photothermal efficiency. Skillin et al. (adma.202313745) grafted AuNR with poly(ethylene glycol) (PEG) that greatly improved the dispersion of AuNR in the LCE resin. Because of this, the LCE-AuNR nanocomposites with very low PEG-AuNR content (0.01 wt.%) were shown to be highly efficient photothermal actuators with rapid response (within a second). Chen et al. (adma.202303969) incorporated photochromic titanium-based nanocrystals (TiNC) into an LCE ink. Upon UV irradiation, TiNC could change color from white to black and absorb infrared (IR) light to generate heat. The 3D-printed structures could thus be globally or locally programmed, erased, and reprogrammed for color and shape change. Kotikian et al. (adma.202310743) used a multi-nozzle 3D printer to fabricate LCE lattice structures with spatially programmed nematic director order. These structures demonstrated different interesting shape morphing upon actuation. Escobar and White (adma.202401140) developed actuators by twisting LCE fibers. These actuators showed dramatically increased deformation rate, specific work, and achievable force output. Liquid metals , because of their high conductivity and large deformation capability almost without resistance, have attracted significant research interest in recent years. For example, Maurin et al. (adma.202302765) utilized this feature and spray-printed large patches of the LM so that eddy current could be generated for rapid heating. Wu et al. (adma.202307632) utilized digital light processing (DLP) method to print conductive patterns with high resolution (≈20 µm) by using LM particles. By a simple 5–10s UV irradiation, highly conductive and stretchable patterns could be printed using a photo-cross-linkable LM particle ink. Wu et al. (adma.202307546) used selective laser sintering (SLS) to fabricate a lattice structure, which was then coated by LM. After the lattice was magnetized by a magnetic field, any deformation of the lattice could generate a voltage change for sensing. LMs also have many other interesting merits. Krisnadi et al. (adma.202308862) found that mixing a small amount of water (as low as 1%) with LM foams could lead to significant foaming where the volume could increase by 4–5 times yet still retain good conductivity. They further used this feature to create a 4D printing where the conductors could grow, fill cavities, and change shape and density over time. This special issue also introduces some interesting new materials for 3D printing. Materials or structures capable of growth have attracted much research interest in recent years. In addition to the work by Krisnadi et al. (adma.202308862), Wang et al. (adma.202309818) developed a hydrogel ink that contained yeast and magnetic particles. After a structure was fabricated, it could be deformed by a magnetic field, and then the growth of yeast could then fix the deformation. The growth could be reversed by removing the yeast cell walls. The directed growth and recovery process could be repeated several times. Sustainability has also drawn significant attention in the AM community. Yue et al. (adma.202310040) developed a biobased δ-valerolactone as a platform photoprecursor for DLP printing. Both thermoplastic and thermoset structures could be printed. These printed structures could be recovered to monomers at more than 90% yield by a simple heating. Volumetric printing has also seen rapid development in recent years, but the resins (or inks) usable with this emerging method remain limited. In this special issue, Lian et al. (adma.202304846) developed a bioink from porcine and human renal cortex to fabricate renal decellularized extracellular matrix (dECM) hydrogels using volumetric printing. One requirement for the resin in volumetric printing is high viscosity, which limits the choice of resins. Riffe et al. (adma.202309026) addressed this challenge by using sacrificial gelatin to modulate resin viscosity to support the cell-compatible volumetric printing of macromers based on poly(ethylene glycol), hyaluronic acid, and polyacrylamide. The gelatin could be removed by washing at an elevated temperature. They further expanded this approach to multimaterial volumetric printing. The AM field has also seen many new methods that have led to new capabilities. Godshall et al. (adma.202307881) used a custom heated material extrusion device to print aerogels of engineering thermoplastics through in-situ thermally induced phase separation. The printed aerogels had tailorable porosities (50.0–74.8%) and densities (0.345–0.684 g cm−3), with moduli ranging from 26.3 to 135.0 MPa. Using AM in space has always been a fascinating research area. There are tremendous challenges that one needs to overcome due to the difference in the environments between on-ground and space. Mo et al. (adma.202309618) developed a 3D bioprinting device that could be operated on a satellite. They also created corresponding bioink and suspension medium that supported the on-satellite printing and in situ culture of complex tumor models. Additionally, they developed a control algorithm based on machine learning to enable the automatic control of 3D printing, autofocusing, fluorescence imaging, and data transfer back to the ground. Metal AM has seen wide applications in automobile and aerospace industries. However, one important aspect of metal AM is how to improve the properties of printed parts. Hu et al. (adma.202307825) significantly improved the mechanical performance of Al6xxx alloy by introducing a nucleation agent during the AM process, followed by a heat treatment. This led to a substantial enhancement in plastic stability. Niu et al. (adma.202310160) presented an approach to inhibit cracks by manipulating stacking fault energy (SFE) in a high-entropy alloy from the laser powder bed fusion (LPBF) AM process. They introduced a small amount of Al doping, which could effectively lower SFE, efficiently dissipate thermal stress during LPBF processing, as well as enhance the resistance to crack propagation. Noronha et al. (adma.202308715) used a design approach to improve the mechanical properties while maintaining the lightweight. Specifically, they integrated thin-plate lattice with hollow-strut lattice (HSL) metamaterials, which enhance the resistance of the irregular HSL nodes to deformation and uniformly distribute the applied stresses in the new topology for significantly improved strength. One important aspect of improving the properties is to understand those properties. However, AM field faces the challenges of no or few standard testing methods to gain insights into properties. Koch et al. (adma.202308497) took advantage of the recent development of two-photon polymerization (2PP) 3D printing technique to create macro-sized specimens (centimeter range) and tested three different photopolymers using a high-throughput 2PP system. They characterized the mechanical, thermo-mechanical, and fracture properties of 2PP processed materials, which laid the foundation for future expansion of the 2PP technique to broader industrial applications. As shown in the work by Noronha et al. (adma.202308715), design plays an important role in AM for improving mechanical properties. Deng et al. (adma.202308149) further demonstrated the importance of design in obtaining direction-dependent elastic properties in nonperiodic 3D architectures. This is a challenging problem as it is computationally expensive and experimentally nontrivial. They combined artificial intelligence (AI) and 2PP to design and fabricate 3D porous scaffolds with prescribed elastic properties. Multimaterial printing is highly desirable in AM but is challenging to achieve. Smith and MacCurdy (adma.202308491) took a design approach to achieve continuous change in multiple mechanical properties in composite materials AM. By using multi-inkjet printing, they obtained materials that span four orders of magnitude in modulus and two orders of magnitude in toughness. 4D printing has emerged in recent years as one of the most active subfields of AM. It combines AM with active materials so that the printed structures can change shapes or properties as a function of time (the 4th dimension). Wan et al. (adma.202312263) conducted a comprehensive review of the development 4D printing in the past five years and provided perspectives on future development of this subfield. The work by Maurin et al (adma.202302765), Chen et al. (adma.202303969), Kotikian et al. (adma.202310743), Krisnadi et al. (adma.202308862), and Wang et al. (adma.202309818), also demonstrated features of 4D printing. Shi et al. (adma.202307601) developed a gelatin/sodium-alginate/magnetic (GSM) bioink for 4D printing with the application of sutureless internal tissue sealing. The ink could be precisely placed by the gastroscope with the assistance of an external magnetic field. In addition, the magnetic field could bring the solidified material together, resulting in a sutureless sealing. Bioprinting has seen tremendous growth in the past few years. This is also reflected in this special issue. Chen et al. (adma.202307686) reviewed multimaterial 3D/4D printing for tissue engineering applications. Yuan et al. (adma.202403641) provided an in-depth review of 3D printing of smart scaffolds with stimulus-responsive properties, which can generate tailored and controllable therapeutic effects for bone tissue engineering and regeneration. The works by Lian et al. (adma.202304846), Riffe et al.(adma.202309026), Mo et al. (adma.202309618), and Shi et al. (adma.202307601) were all aiming at bioprinting. In addition, Li et al. (adma.202308875) developed a nanocomposite bioink that consisted of magnesium peroxide and poly (lactide-co-glycolide) for low-temperature printing. The printed structure could release magnesium ions in a time-sequential manner to prevent tumor recurrence, inhibit bacterial infection, and promote bone defect repair. Camarero-Espinosa et al. (adma.202310258) 3D-printed scaffolds inspired by the bone marrow niche that could recapitulate the natural healing process after injury. They conducted in vivo tests of these niche-inspired scaffolds in different animal models. Garreta et al. (adma.202400306) fabricated dECM from porcine and human renal cortex to enrich cell-to-ECM crosstalk during the onset of kidney organoid differentiation from human pluripotent stem cells (hPSCs). They found that the printed renal dECM together with hPSC-derived renal progenitor cells presented new approaches for 2D and 3D kidney organoid differentiation, exhibiting renal differentiation features and the formation of an endogenous vascular component. Hwang et al. (adma.202400364) presented a bioprinting-assisted tissue assembly (BATA) approach to fabricating biological tissues with complex structures. As a demonstration, they fabricated a model for the left ventricular twist that exhibits synchronized contraction between layers and mimics the native cardiac architecture. As mentioned earlier, AM is a highly active field. The collections in this special issue may represent only a small portion of the excellent work being done, but we hope that they can give other researchers a glimpse into this dynamic and rapidly developing field. The authors declare no conflict of interest. Kun Zhou is a Professor of Mechanical Engineering in the School of Mechanical and Aerospace Engineering at Nanyang Technological University and is a member of European Academy of Science. He currently serves as Programme Director (Marine & Offshore) in Singapore Centre for 3D Printing. He received both his B.Eng. and M.Eng. degrees from Tsinghua University, China and his Ph.D. from Nanyang Technological University. He has been conducting multidisciplinary research at the crossroads of mechanics, additive manufacturing, materials science, and molecular physics. Ruike Renee Zhao is an Assistant Professor of Mechanical Engineering at Stanford University where she directs the Soft Intelligent Materials Laboratory. Renee received her Ph.D. and postdoc training from Brown University and MIT, respectively. Her research focuses on the development of stimuli-responsive soft composites for applications in soft robotics, miniaturized biomedical devices, flexible electronics, and deployable and morphing structures. H. Jerry Qi is the Woodruff Endowed Professor of Mechanical Engineering at Georgia Institute of Technology and is the site director of NSF IUCRC Center SHAP3D on 3D printing. He received his doctoral degree from MIT. He joined University of Colorado Boulder in 2004 and moved to Georgia Tech in 2014. His research is nonlinear mechanics of active polymers and their integration with 3D printing for active structures and sustainability.

Liquid Crystal Elastomer–Liquid Metal Composite In article number 2302765, Ruike Renee Zhao and co-workers present a novel liquid crystal elastomer-liquid metal (LCE-LM) composite enabling ultrafast, reversible, remote, and programmable actuation through eddy current induction heating. The programmability of the LCE-LM composite is exploited for multimodal pop-up deformations through sequential actuation and soft robotic locomotion mimicking turtle fin deformation through selective actuation strategy.

Blockage of blood flow in arteries or veins by blood clots can lead to serious medical conditions. Mechanical thrombectomy (MT), minimally invasive endovascular procedures that utilize aspiration, stent retriever, or cutting mechanisms for clot removal have emerged as an effective treatment modality for ischemic stroke, myocardial infarction, pulmonary embolism, and peripheral vascular disease. However, state-of-the-art MT technologies still fail to remove clots in approximately 10% to 30% of patients, especially when treating large-size clots with high fibrin content. In addition, the working mechanism of most current MT techniques results in rupturing or cutting of clots which could lead to clot fragmentation and distal emboli. Here, we report a new MT technology based on an unprecedented mechanism, in which a milli-spinner mechanically debulks the clot by densifying its fibrin fiber network and discharging red blood cells to significantly reduce the clot volume for complete clot removal. This mechanism is achieved by the spin-induced compression and shearing of the clot. We demonstrate its effective clot-debulking performance with clot volumetric reduction of up to 90% on various sizes of clots with diverse clot compositions. Milli-spinner MT in both in-vitro pulmonary and cerebral artery flow models and in-vivo swine models demonstrate high-fidelity revascularization. The milli-spinner MT is the first reported mechanism that directly modifies the clot microstructure to facilitate clot removal, which also results in markedly improved MT efficacy compared to the existing MT mechanisms that are based on clot rupturing and cutting. This technology introduces a unique mechanical way of debulking and removing clots for future MT device development, especially for the treatment of ischemic stroke, pulmonary emboli, and peripheral thrombosis.

Multistable structures have widespread applications in the design of deployable aerospace systems, mechanical metamaterials, flexible electronics, and multimodal soft robotics due to their capability of shape reconfiguration between multiple stable states. Recently, the snap-folding of rings, often in the form of circles or polygons, has shown the capability of inducing diverse stable configurations. The natural curvature of the rod segment (curvature in its stress-free state) plays an important role in the elastic stability of these rings, determining the number and form of their stable configurations during folding. Here, we develop a general theoretical framework for the elastic stability analysis of segmented rings (e.g., polygons) based on an energy variational approach. Combining this framework with finite element simulations, we map out all planar stable configurations of various segmented rings and determine the natural curvature ranges of their multistable states. The theoretical and numerical results are validated through experiments, which demonstrate that a segmented ring with a rectangular cross-section can show up to six distinct planar stable states. The results also reveal that, by rationally designing the segment number and natural curvature of the segmented ring, its one- or multiloop configuration can store more strain energy than a circular ring of the same total length. We envision that the proposed strategy for achieving multistability in the current work will aid in the design of multifunctional, reconfigurable, and deployable structures.

Shape transformations of active composites (ACs) depend on the spatial distribution of constituent materials. Voxel-level complex material distributions can be encoded by 3D printing, offering enormous freedom for possible shape-change 4D-printed ACs. However, efficiently designing the material distribution to achieve desired 3D shape changes is significantly challenging yet greatly needed. Here, we present an approach that combines machine learning (ML) with both gradient-descent (GD) and evolutionary algorithm (EA) to design AC plates with 3D shape changes. A residual network ML model is developed for the forward shape prediction. A global-subdomain design strategy with ML-GD and ML-EA is then used for the inverse material-distribution design. For a variety of numerically generated target shapes, both ML-GD and ML-EA demonstrate high efficiency. By further combining ML-EA with a normal distance-based loss function, optimized designs are achieved for multiple irregular target shapes. Our approach thus provides a highly efficient tool for the design of 4D-printed active composites.

One of the key problems in active materials is the control of shape through actuation. A fascinating example of such control is the elephant trunk, a long, muscular, and extremely dexterous organ with multiple vital functions. The elephant trunk is an object of fascination for biologists, physicists, and children alike. Its versatility relies on the intricate interplay of multiple unique physical mechanisms and biological design principles. Here, we explore these principles using the theory of active filaments and build, theoretically, computationally, and experimentally, a minimal model that explains and accomplishes some of the spectacular features of the elephant trunk.

Magnetic-shape memory polymers (M-SMPs) can not only undergo rapid and reversible deformation in response to magnetic actuation but also lock the actuated shape upon cooling, which has great potential in applications such as soft robotics, active metamaterials , and shape-morphing systems. In this work, we develop a constitutive model for M-SMPs with finite deformation . The constitutive model considers the Helmholtz free energy contributed by the thermally responsive shape memory polymers and the magnetically responsive particles, leading to a magneto-thermomechanical framework. It is shown that the developed model can capture the thermomechanical as well as magneto-elastic responses of M-SMPs at different temperatures. Simplified beam models for M-SMPs are presented to show the material's versatile functionalities including fast and reversible deformation, selective/sequential actuation, and shape locking. We envision that the constitutive framework and the simplified beam models presented in this work can serve as useful tools to guide the rational design of M-SMP-based functional structures and devices.

The axial buckling behavior is determined for an elastic beam or rod which has a uniform curvature in its natural state, is straightened by pure bending, and clamped at its ends. Buckling can be either identical to the classical two-dimensional behavior determined by Euler, or it can be three-dimensional involving twist and deflection out of the plane of natural curvature depending on the bending and torsional stiffnesses and the natural curvature. While the classical two-dimensional buckling behavior of Euler ’ s elastica is stable under applied load, the three-dimensional buckling behavior can be stable or unstable. Theoretical and experimental examples are presented illustrating the full range of possibilities.

DOFs, limited by the number of degrees of actuation (DOAs). The complexity of actuators restricts the number of DOAs that can be incorporated into soft robots. Active shape control is further complicated by the buckling of soft robots under compressive forces; this is particularly challenging for compliant continuum robots due to their long aspect ratios. In this study, we show how variable stiffness enables shape control of soft robots by addressing these challenges. Dynamically changing the stiffness of sections along a compliant continuum robot selectively "activates" discrete joints. By changing which joints are activated, the output of a single actuator can be reconfigured to actively control many different joints, thus decoupling the number of controllable DOFs from the number of DOAs. We demonstrate embedded positive pressure layer jamming as a simple method for stiffness change in inflated beam robots, its compatibility with growing robots, and its use as an "activating" technology. We experimentally characterize the stiffness change in a growing inflated beam robot and present finite element models that serve as guides for robot design and fabrication. We fabricate a multisegment everting inflated beam robot and demonstrate how stiffness change is compatible with growth through tip eversion, enables an increase in workspace, and achieves new actuation patterns not possible without stiffening.

Abstract The study of polymers has continued to gain substantial attention due to their expanding range of applications, spanning essential engineering fields to emerging domains like stretchable electronics, soft robotics, and implantable sensors. These materials exhibit remarkable properties, primarily stemming from their intricate polymer chain network, which, in turn, increases the complexity of precisely modeling their behavior. Especially for modeling elastomers and their fracture behavior, accurately accounting for the deformations of the polymer chains is vital for predicting the rupture in highly stretched chains. Despite the importance, many robust multiscale continuum frameworks for modeling elastomer fracture tend to simplify network deformations by assuming uniform behavior among chains in all directions. Recognizing this limitation, our study proposes a multiscale fracture model that accounts for the anisotropic nature of elastomer network responses. At the microscale, damage in the chains is assumed to be driven by both the chain's entropy and the internal energy due to molecular bond distortions. In order to bridge the stretching in the chains to the macroscale deformation, we employ the maximal advance path constraint network model, inherently accommodating anisotropic network responses. As a result, chains oriented differently can be predicted to exhibit varying stretch and, consequently, different damage levels. To drive macroscale fracture based on damages in these chains, we utilize the micromorphic regularization theory, which involves the introduction of dual local‐global damage variables at the macroscale. The macroscale local damage variable is obtained through the homogenization of the chain damage values, resulting in the prediction of an isotropic material response. The macroscale global damage variable is subjected to nonlocal effects and boundary conditions in a thermodynamically consistent phase field continuum formulation. Moreover, the total dissipation in the system is considered to be mainly due to the breaking of the molecular bonds at the microscale. To validate our model, we employ the double‐edge notched tensile test as a benchmark, comparing simulation predictions with existing experimental data. Additionally, to enhance our understanding of the fracturing process, we conduct uniaxial tensile experiments on a square film made up of polydimethylsiloxane (PDMS) rubber embedded with a hole and notches and then compare our simulation predictions with the experimental observations. Furthermore, we visualize the evolution of stretch and damage values in chains oriented along different directions to assess the predictive capacity of the model. The results are also compared with another existing model to evaluate the utility of our model in accurately simulating the fracture behavior of rubber‐like materials.