Renee Zhao

All Publications

• A multiscale anisotropic polymer network model coupled with phase field fracture INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING Arunachala, P., Vajari, S., Neuner, M., Sim, J., Zhao, R., Linder, C. 2024

  View details for DOI 10.1002/nme.7488

  View details for Web of Science ID 001197250300001

• Recent Advances in 4D Printing of Advanced Materials and Structures for Functional Applications. Advanced materials (Deerfield Beach, Fla.) Wan, X., Xiao, Z., Tian, Y., Chen, M., Liu, F., Wang, D., Liu, Y., Bartolo, P. J., Yan, C., Shi, Y., Zhao, R. R., Qi, H. J., Zhou, K. 2024: e2312263

  Abstract

  Four-dimensional (4D) printing has attracted tremendous worldwide attention during the past decade. This technology enables the shape, property, or functionality of printed structures to change with time in response to diverse external stimuli, making the original static structures alive. The revolutionary 4D-printing technology offers remarkable benefits in controlling the geometric and functional reconfiguration, thereby showcasing immense potential across diverse fields, including biomedical engineering, electronics, robotics, and photonics. Here, a comprehensive review of the latest achievements on 4D printing using various types of materials and different additive manufacturing techniques is presented. The state-of-the-art strategies implemented in harnessing various 4D-printed structures are highlighted, which involve materials design, stimuli, functionalities, and applications. The machine learning approach explored for 4D printing is also discussed. Finally, the perspectives on the current challenges and future trends toward further development in 4D printing are summarized. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/adma.202312263

  View details for PubMedID 38439193

• Magneto-Mechanical Metamaterials: A Perspective JOURNAL OF APPLIED MECHANICS-TRANSACTIONS OF THE ASME Sim, J., Zhao, R. 2024; 91 (3)

  View details for DOI 10.1115/1.4063816

  View details for Web of Science ID 001156410400005

• Perspective: Machine Learning in Design for 3D/4D Printing JOURNAL OF APPLIED MECHANICS-TRANSACTIONS OF THE ASME Sun, X., Zhou, K., Demoly, F., Zhao, R., Qi, H. 2024; 91 (3)

  View details for DOI 10.1115/1.4063684

  View details for Web of Science ID 001156410400007

• Elephant Trunk Inspired Multimodal Deformations and Movements of Soft Robotic Arms ADVANCED FUNCTIONAL MATERIALS Leanza, S., Lu-Yang, J., Kaczmarski, B., Wu, S., Kuhl, E., Zhao, R. 2024

  View details for DOI 10.1002/adfm.202400396

  View details for Web of Science ID 001175732900001

• Effects of symmetry-breaking mechanisms on the flow field around magnetic-responsive material appendages that mimic swimming strokes PHYSICAL REVIEW FLUIDS Mohaghar, M., Connor, A. A., Wu, S., Zhao, R., Webster, D. R. 2024; 9 (2)

  View details for DOI 10.1103/PhysRevFluids.9.023101

  View details for Web of Science ID 001171509300006

• Physics-aware differentiable design of magnetically actuated kirigami for shape morphing. Nature communications Wang, L., Chang, Y., Wu, S., Zhao, R. R., Chen, W. 2023; 14 (1): 8516

  Abstract

  Shape morphing that transforms morphologies in response to stimuli is crucial for future multifunctional systems. While kirigami holds great promise in enhancing shape-morphing, existing designs primarily focus on kinematics and overlook the underlying physics. This study introduces a differentiable inverse design framework that considers the physical interplay between geometry, materials, and stimuli of active kirigami, made by soft material embedded with magnetic particles, to realize target shape-morphing upon magnetic excitation. We achieve this by combining differentiable kinematics and energy models into a constrained optimization, simultaneously designing the cuts and magnetization orientations to ensure kinematic and physical feasibility. Complex kirigami designs are obtained automatically with unparalleled efficiency, which can be remotely controlled to morph into intricate target shapes and even multiple states. The proposed framework can be extended to accommodate various active systems, bridging geometry and physics to push the frontiers in shape-morphing applications, like flexible electronics and minimally invasive surgery.

  View details for DOI 10.1038/s41467-023-44303-x

  View details for PubMedID 38129420

  View details for PubMedCentralID 7500935

• Mechanics of hard-magnetic soft materials: A review MECHANICS OF MATERIALS Lu, L., Sim, J., Zhao, R. 2024; 189

  View details for DOI 10.1016/j.mechmat.2023.104874

  View details for Web of Science ID 001132903000001

• Curved Ring Origami: Bistable Elastic Folding for Magic Pattern Reconfigurations JOURNAL OF APPLIED MECHANICS-TRANSACTIONS OF THE ASME Dai, J., Lu, L., Leanza, S., Hutchinson, J. W., Zhao, R. 2023; 90 (12)

  View details for DOI 10.1115/1.4062221

  View details for Web of Science ID 001104813800011

• Tailoring the mechanical and combustion performance of B/HTPB composite solid fuel with covalent interfaces COMPOSITES SCIENCE AND TECHNOLOGY Jiang, Y., Leem, J., Robinson, A. M., Wu, S., Huynh, A. H., Ka, D., Zhao, R., Xia, Y., Zheng, X. 2024; 245

  View details for DOI 10.1016/j.compscitech.2023.110350

  View details for Web of Science ID 001126206100001

• Multiple equilibrium states of a curved-sided hexagram: Part I-stability of states JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS Lu, L., Dai, J., Leanza, S., Zhao, R., Hutchinson, J. W. 2023; 180

  View details for DOI 10.1016/j.jmps.2023.105406

  View details for Web of Science ID 001062135700001

• Multiple equilibrium states of a curved-sided hexagram: Part II-Transitions between states JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS Lu, L., Dai, J., Leanza, S., Hutchinson, J. W., Zhao, R. 2023; 180

  View details for DOI 10.1016/j.jmps.2023.105407

  View details for Web of Science ID 001065055000001

• Origami With Rotational Symmetry: A Review on Their Mechanics and Design APPLIED MECHANICS REVIEWS Lu, L., Leanza, S., Zhao, R. 2023; 75 (5)

  View details for DOI 10.1115/1.4056637

  View details for Web of Science ID 001084533300001

• Liquid Crystal Elastomer - Liquid Metal Composite: Ultrafast, Untethered, And Programmable Actuation by Induction Heating. Advanced materials (Deerfield Beach, Fla.) Maurin, V., Chang, Y., Ze, Q., Leanza, S., Wang, J., Zhao, R. R. 2023: e2302765

  Abstract

  Liquid crystal elastomers (LCEs) are a class of stimuli-responsive materials that have been intensively studied for applications including artificial muscles, shape morphing structures, and soft robotics, due to their capability of large, programmable, and fully reversible actuation strains. To fully take advantage of LCEs, rapid, untethered, and programmable actuation methods are highly desirable. Here, we report a liquid crystal elastomer-liquid metal (LCE-LM) composite, which enables ultrafast and programmable actuations by eddy current induction heating. The composite consists of LM sandwiched between two LCE layers printed via direct ink writing (DIW). When subjected to a high-frequency alternating magnetic field, the composite is actuated in milliseconds. By moving the magnetic field, the eddy current is spatially controlled for selective actuation. Additionally, sequential actuation is achievable by programming the LM thickness distribution in a sample. With these capabilities, the LCE-LM composite is further exploited for multimodal deformation of a pop-up structure, on-ground omnidirectional robotic motion, and in-water targeted object manipulation and crawling. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/adma.202302765

  View details for PubMedID 37656872

• Magneto-Mechanical Bilayer Metamaterial with Global Area-Preserving Density Tunability for Acoustic Wave Regulation. Advanced materials (Deerfield Beach, Fla.) Sim, J., Wu, S., Dai, J., Zhao, R. R. 2023: e2303541

  Abstract

  2D metamaterials have immense potential in acoustics, optics, and electromagnetic applications due to their unique properties and ability to conform to curved substrates. Active metamaterials have attracted significant research attention because of their on-demand tunable properties and performances through shape reconfigurations. 2D active metamaterials often achieve active properties through internal structural deformations, which lead to changes in overall dimensions. This demands corresponding alterations of the conforming substrate, or the metamaterial fails to provide complete area coverage, which can be a significant limitation for their practical applications. To date, achieving area-preserving active 2D metamaterials with distinct shape reconfigurations remains a prominent challenge. In this paper, we present magneto-mechanical bilayer metamaterials that demonstrate area density tunability with area-preserving capability. The bilayer metamaterials consist of two arrays of magnetic soft materials with distinct magnetization distributions. Under a magnetic field, each layer behaves differently, which allows the metamaterial to reconFigure its shape into multiple modes and to significantly tune its area density without changing its overall dimensions. The area-preserving multimodal shape reconfigurations are further exploited as active acoustic wave regulators to tune bandgaps and wave propagations. The bilayer approach thus provides a new concept to the design of area-preserving active metamaterials for broader applications. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/adma.202303541

  View details for PubMedID 37335806

• Autonomous alignment and healing in multilayer soft electronics using immiscible dynamic polymers. Science (New York, N.Y.) Cooper, C. B., Root, S. E., Michalek, L., Wu, S., Lai, J. C., Khatib, M., Oyakhire, S. T., Zhao, R., Qin, J., Bao, Z. 2023; 380 (6648): 935-941

  Abstract

  Self-healing soft electronic and robotic devices can, like human skin, recover autonomously from damage. While current devices use a single type of dynamic polymer for all functional layers to ensure strong interlayer adhesion, this approach requires manual layer alignment. In this study, we used two dynamic polymers, which have immiscible backbones but identical dynamic bonds, to maintain interlayer adhesion while enabling autonomous realignment during healing. These dynamic polymers exhibit a weakly interpenetrating and adhesive interface, whose width is tunable. When multilayered polymer films are misaligned after damage, these structures autonomously realign during healing to minimize interfacial free energy. We fabricated devices with conductive, dielectric, and magnetic particles that functionally heal after damage, enabling thin-film pressure sensors, magnetically assembled soft robots, and underwater circuit assembly.

  View details for DOI 10.1126/science.adh0619

  View details for PubMedID 37262169

• Active Materials for Functional Origami. Advanced materials (Deerfield Beach, Fla.) Leanza, S., Wu, S., Sun, X., Qi, H. J., Zhao, R. R. 2023: e2302066

  Abstract

  In recent decades, origami has been explored to aid in the design of engineering structures. These structures span multiple scales and have been demonstrated to be used towards various areas such as aerospace, metamaterial, biomedical, robotics, and architectural applications. Conventionally, origami or deployable structures have been actuated by hands, motors, or pneumatic actuators, which can result in heavy or bulky structures. On the other hand, active materials, which reconfigure in response to external stimulus, eliminate the need for external mechanical loads and bulky actuation systems. Thus, in recent years, active materials incorporated with deployable structures have shown promise for remote actuation of light weight, programmable origami. In this review, active materials such as shape memory polymers and alloys, hydrogels, liquid crystal elastomers, magnetic soft materials, and covalent adaptable network polymers, their actuation mechanisms, as well as how they have been utilized for active origami and where these structures are applicable is discussed. Additionally, the state-of-the-art fabrication methods to construct active origami are highlighted. The existing structural modeling strategies for origami, the constitutive models used to describe active materials, and the largest challenges and future directions for active origami research are summarized. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/adma.202302066

  View details for PubMedID 37120795

• Easy snap-folding of hexagonal ring origami by geometric modifications JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS Lu, L., Leanza, S., Dai, J., Sun, X., Zhao, R. 2023; 171

  View details for DOI 10.1016/j.jmps.2022.105142

  View details for Web of Science ID 000892615200004

• 4D Printing of Freestanding Liquid Crystal Elastomers via Hybrid Additive Manufacturing. Advanced materials (Deerfield Beach, Fla.) Peng, X., Wu, S., Sun, X., Yue, L., Montgomery, S. M., Demoly, F., Zhou, K., Zhao, R. R., Qi, H. J. 2022: e2204890

  Abstract

  Liquid crystal elastomers (LCE) are appealing candidates among active materials for 4D printing, due to their reversible, programmable, and rapid actuation capabilities. Recent progress has been made on direct ink writing (DIW) or digital light processing (DLP) to print LCEs with certain actuation. However, it remains a challenge to achieve complicated structures, such as spatial lattices with large actuation, due to the limitation of printing LCEs on the build platform or the previous layer. Herein, we propose a novel method to 4D print freestanding LCEs on-the-fly by using laser-assisted DIW with an actuation strain up to -40%. This process is further hybridized with the DLP method for optional structural or removable supports to create active 3D architectures in a one-step additive process. We demonstrate that various objects, including hybrid active lattices, active tensegrity, an actuator with tunable stability, and 3D spatial LCE lattices, can be additively fabricated. The combination of DIW-printed functionally freestanding LCEs with the DLP-printed supporting structures thus provides new design freedom and fabrication capability for applications including soft robotics, smart structures, active metamaterials, and smart wearable devices. This article is protected by copyright. All rights reserved.

  View details for DOI 10.1002/adma.202204890

  View details for PubMedID 35962737

• Hexagonal Ring Origami Assemblies: Foldable Functional Structures With Extreme Packing JOURNAL OF APPLIED MECHANICS-TRANSACTIONS OF THE ASME Leanza, S., Wu, S., Dai, J., Zhao, R. 2022; 89 (8)

  View details for DOI 10.1115/1.4054693

  View details for Web of Science ID 000821123400007

• Deep Learning-Accelerated Designs of Tunable Magneto-Mechanical Metamaterials ACS APPLIED MATERIALS & INTERFACES Ma, C., Chang, Y., Wu, S., Zhao, R. 2022; 14 (29): 33892-33902

  View details for DOI 10.1021/acsami.2c0905233892

  View details for Web of Science ID 000841727800001

• Deep Learning-Accelerated Designs of Tunable Magneto-Mechanical Metamaterials. ACS applied materials & interfaces Ma, C., Chang, Y., Wu, S., Zhao, R. R. 2022

  Abstract

  Metamaterials are artificially structured materials with unusual properties, such as negative Poisson's ratio, acoustic band gap, and energy absorption. However, metamaterials made of conventional materials lack tunability after fabrication. Thus, active metamaterials using magneto-mechanical actuation for untethered, fast, and reversible shape configurations are developed to tune the mechanical response and property of metamaterials. Although the magneto-mechanical metamaterials have shown promising capabilities in tunable mechanical stiffness, acoustic band gaps, and electromagnetic behaviors, the existing demonstrations rely on the forward design methods based on experience or simulations, by which the metamaterial properties are revealed only after the design. Considering the massive design space due to the material and structural programmability, a robust inverse design strategy is desired to create the magneto-mechanical metamaterials with preferred tunable properties. In this work, we develop an inverse design framework where a deep residual network replaces the conventional finite-element analysis for acceleration, realizing metamaterials with predetermined global strains under magnetic actuations. For validation, a direct-ink-writing printing method of the magnetic soft materials is adopted to fabricate the designed complex metamaterials. The deep learning-accelerated design framework opens avenues for the designs of magneto-mechanical metamaterials and other active metamaterials with target mechanical, acoustic, thermal, and electromagnetic properties.

  View details for DOI 10.1021/acsami.2c09052

  View details for PubMedID 35833606

• Magnetically Actuated Reconfigurable Metamaterials as Conformal Electromagnetic Filters ADVANCED INTELLIGENT SYSTEMS Wu, S., Eichenberger, J., Dai, J., Chang, Y., Ghalichechian, N., Zhao, R. 2022

  View details for DOI 10.1002/aisy.202200106

  View details for Web of Science ID 000821629000001

• Phase diagram and mechanics of snap-folding of ring origami by twisting INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES Sun, X., Wu, S., Dai, J., Leanza, S., Yue, L., Yu, L., Jin, Y., Qi, H., Zhao, R. 2022; 248

  View details for DOI 10.1016/j.ijsolstr.2022.111685

  View details for Web of Science ID 000803791100003

• Spinning-enabled wireless amphibious origami millirobot. Nature communications Ze, Q., Wu, S., Dai, J., Leanza, S., Ikeda, G., Yang, P. C., Iaccarino, G., Zhao, R. R. 2022; 13 (1): 3118

  Abstract

  Wireless millimeter-scale origami robots have recently been explored with great potential for biomedical applications. Existing millimeter-scale origami devices usually require separate geometrical components for locomotion and functions. Additionally, none of them can achieve both on-ground and in-water locomotion. Here we report a magnetically actuated amphibious origami millirobot that integrates capabilities of spinning-enabled multimodal locomotion, delivery of liquid medicine, and cargo transportation with wireless operation. This millirobot takes full advantage of the geometrical features and folding/unfolding capability of Kresling origami, a triangulated hollow cylinder, to fulfill multifunction: its geometrical features are exploited for generating omnidirectional locomotion in various working environments through rolling, flipping, and spinning-induced propulsion; the folding/unfolding is utilized as a pumping mechanism for controlled delivery of liquid medicine; furthermore, the spinning motion provides a sucking mechanism for targeted solid cargo transportation. We anticipate the amphibious origami millirobots can potentially serve as minimally invasive devices for biomedical diagnoses and treatments.

  View details for DOI 10.1038/s41467-022-30802-w

  View details for PubMedID 35701405

• Hexagonal ring origami-Snap-folding with large packing ratio EXTREME MECHANICS LETTERS Wu, S., Dai, J., Leanza, S., Zhao, R. 2022; 53

  View details for DOI 10.1016/j.eml.2022.101713

  View details for Web of Science ID 000821200100010

• Multi-Color 3D Printing via Single-Vat Grayscale Digital Light Processing ADVANCED FUNCTIONAL MATERIALS Peng, X., Yue, L., Liang, S., Montgomery, S., Lu, C., Cheng, C., Beyah, R., Zhao, R., Qi, H. 2022

  View details for DOI 10.1002/adfm.202112329

  View details for Web of Science ID 000782590200001

• Soft robotic origami crawler. Science advances Ze, Q., Wu, S., Nishikawa, J., Dai, J., Sun, Y., Leanza, S., Zemelka, C., Novelino, L. S., Paulino, G. H., Zhao, R. R. 2022; 8 (13): eabm7834

  Abstract

  Biomimetic soft robotic crawlers have attracted extensive attention in various engineering fields, owing to their adaptivity to different terrains. Earthworm-like crawlers realize locomotion through in-plane contraction, while inchworm-like crawlers exhibit out-of-plane bending-based motions. Although in-plane contraction crawlers demonstrate effective motion in confined spaces, miniaturization is challenging because of limited actuation methods and complex structures. Here, we report a magnetically actuated small-scale origami crawler with in-plane contraction. The contraction mechanism is achieved through a four-unit Kresling origami assembly consisting of two Kresling dipoles with two-level symmetry. Magnetic actuation is used to provide appropriate torque distribution, enabling a small-scale and untethered robot with both crawling and steering capabilities. The crawler can overcome large resistances from severely confined spaces by its anisotropic and magnetically tunable structural stiffness. The multifunctionality of the crawler is explored by using the internal cavity of the crawler for drug storage and release. The magnetic origami crawler can potentially serve as a minimally invasive device for biomedical applications.

  View details for DOI 10.1126/sciadv.abm7834

  View details for PubMedID 35353556

• Machine Learning-Evolutionary Algorithm Enabled Design for 4D-Printed Active Composite Structures ADVANCED FUNCTIONAL MATERIALS Sun, X., Yue, L., Yu, L., Shao, H., Peng, X., Zhou, K., Demoly, F., Zhao, R., Qi, H. 2021

  View details for DOI 10.1002/adfm.202109805

  View details for Web of Science ID 000720738000001

• Deciphering and engineering tissue folding: A mechanical perspective ACTA BIOMATERIALIA Zhu, Y., Deng, S., Zhao, X., Xia, G., Zhao, R., Chan, H. 2021; 134: 32-42

  Abstract

  The folding of tissues/organs into complex shapes is a common phenomenon that occurs in organisms such as animals and plants, and is both structurally and functionally important. Deciphering the process of tissue folding and applying this knowledge to engineer folded systems would significantly advance the field of tissue engineering. Although early studies focused on investigating the biochemical signaling events that occur during the folding process, the physical or mechanical aspects of the process have received increasing attention in recent years. In this review, we will summarize recent findings on the mechanical aspects of folding and introduce strategies by which folding can be controlled in vitro. Emphasis will be placed on the folding events triggered by mechanical effects at the cellular and tissue levels and on the different cell- and biomaterial-based approaches used to recapitulate folding. Finally, we will provide a perspective on the development of engineering tissue folding toward preclinical and clinical translation. STATEMENT OF SIGNIFICANCE: Tissue folding is a common phenomenon in a variety of organisms including human, and has been shown to serve important structural and functional roles. Understanding how folding forms and applying the concept in tissue engineering would represent an advance of the research field. Recently, the physical or mechanical aspect of tissue folding has gained increasing attention. In this review, we will cover recent findings of the mechanical aspect of folding mechanisms, and introduce strategies to control the folding process in vitro. We will also provide a perspective on the future development of the field towards preclinical and clinical translation of various bio fabrication technologies.

  View details for DOI 10.1016/j.actbio.2021.07.044

  View details for Web of Science ID 000710075800003

  View details for PubMedID 34325076

• Stretchable origami robotic arm with omnidirectional bending and twisting. Proceedings of the National Academy of Sciences of the United States of America Wu, S., Ze, Q., Dai, J., Udipi, N., Paulino, G. H., Zhao, R. 2021; 118 (36)

  Abstract

  Inspired by the embodied intelligence observed in octopus arms, we introduce magnetically controlled origami robotic arms based on Kresling patterns for multimodal deformations, including stretching, folding, omnidirectional bending, and twisting. The highly integrated motion of the robotic arms is attributed to inherent features of the reconfigurable Kresling unit, whose controllable bistable deploying/folding and omnidirectional bending are achieved through precise magnetic actuation. We investigate single- and multiple-unit robotic systems, the latter exhibiting higher biomimetic resemblance to octopus' arms. We start from the single Kresling unit to delineate the working mechanism of the magnetic actuation for deploying/folding and bending. The two-unit Kresling assembly demonstrates the basic integrated motion that combines omnidirectional bending with deploying. The four-unit Kresling assembly constitutes a robotic arm with a larger omnidirectional bending angle and stretchability. With the foundation of the basic integrated motion, scalability of Kresling assemblies is demonstrated through distributed magnetic actuation of double-digit number of units, which enables robotic arms with sophisticated motions, such as continuous stretching and contracting, reconfigurable bending, and multiaxis twisting. Such complex motions allow for functions mimicking octopus arms that grasp and manipulate objects. The Kresling robotic arm with noncontact actuation provides a distinctive mechanism for applications that require synergistic robotic motions for navigation, sensing, and interaction with objects in environments with limited or constrained access. Based on small-scale Kresling robotic arms, miniaturized medical devices, such as tubes and catheters, can be developed in conjunction with endoscopy, intubation, and catheterization procedures using functionalities of object manipulation and motion under remote control.

  View details for DOI 10.1073/pnas.2110023118

  View details for PubMedID 34462360

• Ring Origami: Snap-Folding of Rings with Different Geometries ADVANCED INTELLIGENT SYSTEMS Wu, S., Yue, L., Jin, Y., Sun, X., Zemelka, C., Qi, H., Zhao, R. 2021; 3 (9)

  View details for DOI 10.1002/aisy.202100107

  View details for Web of Science ID 000680583300001

• Magnetic Dynamic Polymers for Modular Assembling and Reconfigurable Morphing Architectures ADVANCED MATERIALS Kuang, X., Wu, S., Ze, Q., Yue, L., Jin, Y., Montgomery, S., Yang, F., Qi, H., Zhao, R. 2021; 33 (30): e2102113

  Abstract

  Shape-morphing magnetic soft materials, composed of magnetic particles in a soft polymer matrix, can transform shape reversibly, remotely, and rapidly, finding diverse applications in actuators, soft robotics, and biomedical devices. To achieve on-demand and sophisticated shape morphing, the manufacture of structures with complex geometry and magnetization distribution is highly desired. Here, a magnetic dynamic polymer (MDP) composite composed of hard-magnetic microparticles in a dynamic polymer network with thermally responsive reversible linkages, which permits functionalities including targeted welding for magnetic-assisted assembly, magnetization reprogramming, and permanent structural reconfiguration, is reported. These functions not only provide highly desirable structural and material programmability and reprogrammability but also enable the manufacturing of functional soft architected materials such as 3D kirigami with complex magnetization distribution. The welding of magnetic-assisted modular assembly can be further combined with magnetization reprogramming and permanent reshaping capabilities for programmable and reconfigurable architectures and morphing structures. The reported MDP are anticipated to provide a new paradigm for the design and manufacture of future multifunctional assemblies and reconfigurable morphing architectures and devices.

  View details for DOI 10.1002/adma.202102113

  View details for Web of Science ID 000663379700001

  View details for PubMedID 34146361

• Adaptive and multifunctional hydrogel hybrid probes for long-term sensing and modulation of neural activity NATURE COMMUNICATIONS Park, S., Yuk, H., Zhao, R., Yim, Y., Woldeghebriel, E. W., Kang, J., Canales, A., Fink, Y., Choi, G. B., Zhao, X., Anikeeva, P. 2021; 12 (1): 3435

  Abstract

  To understand the underlying mechanisms of progressive neurophysiological phenomena, neural interfaces should interact bi-directionally with brain circuits over extended periods of time. However, such interfaces remain limited by the foreign body response that stems from the chemo-mechanical mismatch between the probes and the neural tissues. To address this challenge, we developed a multifunctional sensing and actuation platform consisting of multimaterial fibers intimately integrated within a soft hydrogel matrix mimicking the brain tissue. These hybrid devices possess adaptive bending stiffness determined by the hydration states of the hydrogel matrix. This enables their direct insertion into the deep brain regions, while minimizing tissue damage associated with the brain micromotion after implantation. The hydrogel hybrid devices permit electrophysiological, optogenetic, and behavioral studies of neural circuits with minimal foreign body responses and tracking of stable isolated single neuron potentials in freely moving mice over 6 months following implantation.

  View details for DOI 10.1038/s41467-021-23802-9

  View details for Web of Science ID 000664803900004

  View details for PubMedID 34103511

  View details for PubMedCentralID PMC8187649

• Preface: Forum on Novel Stimuli-Responsive Materials for 3D Printing ACS APPLIED MATERIALS & INTERFACES Qi, H., Ionov, L., Zhao, R. 2021; 13 (11): 12637-12638

  View details for DOI 10.1021/acsami.1c03782

  View details for Web of Science ID 000634759500001

  View details for PubMedID 33761585

• Magnetic Multimaterial Printing for Multimodal Shape Transformation with Tunable Properties and Shiftable Mechanical Behaviors ACS APPLIED MATERIALS & INTERFACES Ma, C., Wu, S., Ze, Q., Kuang, X., Zhang, R., Qi, H., Zhao, R. 2021; 13 (11): 12639-12648

  Abstract

  Magnetic soft materials (MSMs) have shown potential in soft robotics, actuators, metamaterials, and biomedical devices because they are capable of untethered, fast, and reversible shape reconfigurations as well as controllable dynamic motions under applied magnetic fields. Recently, magnetic shape memory polymers (M-SMPs) that incorporate hard magnetic particles in shape memory polymers demonstrated superior shape manipulation performance by realizing reprogrammable, untethered, fast, and reversible shape transformation and shape locking in one material system. In this work, we develop a multimaterial printing technology for the complex structural integration of MSMs and M-SMPs to explore their enhanced multimodal shape transformation and tunable properties. By cooperative thermal and magnetic actuation, we demonstrate multiple deformation modes with distinct shape configurations, which further enable active metamaterials with tunable physical properties such as sign-change Poisson's ratio. Because of the multiphysics response of the M-MSP/MSM metamaterials, one distinct feature is their capability of shifting between various global mechanical behaviors such as expansion, contraction, shear, and bending. We anticipate that the multimaterial printing technique opens new avenues for the fabrication of multifunctional magnetic materials.

  View details for DOI 10.1021/acsami.0c13863

  View details for Web of Science ID 000634759500002

  View details for PubMedID 32897697

• Local Shape-Preserving Formation Maneuver Control of Multi-agent Systems: From 2D to 3D Wan, C., Jing, G., Dai, R., Zhao, R., IEEE IEEE. 2021: 6251-6257

  View details for DOI 10.1109/CDC45484.2021.9683637

  View details for Web of Science ID 000781990305070

• Multifunctional magnetic soft composites: a review. Multifunctional materials Wu, S., Hu, W., Ze, Q., Sitti, M., Zhao, R. 2020; 3 (4): 042003

  Abstract

  Magnetically responsive soft materials are soft composites where magnetic fillers are embedded into soft polymeric matrices. These active materials have attracted extensive research and industrial interest due to their ability to realize fast and programmable shape changes through remote and untethered control under the application of magnetic fields. They would have many high-impact potential applications in soft robotics/devices, metamaterials, and biomedical devices. With a broad range of functional magnetic fillers, polymeric matrices, and advanced fabrication techniques, the material properties can be programmed for integrated functions, including programmable shape morphing, dynamic shape deformation-based locomotion, object manipulation and assembly, remote heat generation, as well as reconfigurable electronics. In this review, an overview of state-of-the-art developments and future perspectives in the multifunctional magnetically responsive soft materials is presented.

  View details for DOI 10.1088/2399-7532/abcb0c

  View details for PubMedID 33834121

• Magneto-Mechanical Metamaterials with Widely Tunable Mechanical Properties and Acoustic Bandgaps ADVANCED FUNCTIONAL MATERIALS Montgomery, S., Wu, S., Kuang, X., Armstrong, C. D., Zemelka, C., Ze, Q., Zhang, R., Zhao, R., Qi, H. 2021; 31 (3)

  View details for DOI 10.1002/adfm.202005319

  View details for Web of Science ID 000575925100001

• Untethered control of functional origami microrobots with distributed actuation PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Novelino, L. S., Ze, Q., Wu, S., Paulino, G. H., Zhao, R. 2020; 117 (39): 24096-24101

  Abstract

  Deployability, multifunctionality, and tunability are features that can be explored in the design space of origami engineering solutions. These features arise from the shape-changing capabilities of origami assemblies, which require effective actuation for full functionality. Current actuation strategies rely on either slow or tethered or bulky actuators (or a combination). To broaden applications of origami designs, we introduce an origami system with magnetic control. We couple the geometrical and mechanical properties of the bistable Kresling pattern with a magnetically responsive material to achieve untethered and local/distributed actuation with controllable speed, which can be as fast as a tenth of a second with instantaneous shape locking. We show how this strategy facilitates multimodal actuation of the multicell assemblies, in which any unit cell can be independently folded and deployed, allowing for on-the-fly programmability. In addition, we demonstrate how the Kresling assembly can serve as a basis for tunable physical properties and for digital computing. The magnetic origami systems are applicable to origami-inspired robots, morphing structures and devices, metamaterials, and multifunctional devices with multiphysics responses.

  View details for DOI 10.1073/pnas.2013292117

  View details for Web of Science ID 000576664200020

  View details for PubMedID 32929033

  View details for PubMedCentralID PMC7533839

• Self-adaptive flexible valve as passive flow regulator EXTREME MECHANICS LETTERS Zhang, Q., Peng, X., Weng, S., Zhang, R., Fang, D., Zhao, R., Qi, H. 2020; 39

  View details for DOI 10.1016/j.eml.2020.100824

  View details for Web of Science ID 000564535600002

• Micromechanics Study on Actuation Efficiency of Hard-Magnetic Soft Active Materials JOURNAL OF APPLIED MECHANICS-TRANSACTIONS OF THE ASME Zhang, R., Wu, S., Ze, Q., Zhao, R. 2020; 87 (9)

  View details for DOI 10.1115/1.4047291

  View details for Web of Science ID 000562836800008

• Evolutionary Algorithm-Guided Voxel-Encoding Printing of Functional Hard-Magnetic Soft Active Materials ADVANCED INTELLIGENT SYSTEMS Wu, S., Hamel, C. M., Ze, Q., Yang, F., Qi, H., Zhao, R. 2020; 2 (8)

  View details for DOI 10.1002/aisy.202000060

  View details for Web of Science ID 000669782900009

• Magnetoactuated Reconfigurable Antennas on Hard-Magnetic Soft Substrates and E-Threads IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION Alharbi, S., Ze, Q., Zhao, R., Kiourti, A. 2020; 68 (8): 5882-5892

  View details for DOI 10.1109/TAP.2020.2988937

  View details for Web of Science ID 000557411300014

• Magnetic Shape Memory Polymers with Integrated Multifunctional Shape Manipulation ADVANCED MATERIALS Ze, Q., Kuang, X., Wu, S., Wong, J., Montgomery, S., Zhang, R., Kovitz, J. M., Yang, F., Qi, H., Zhao, R. 2020; 32 (4): e1906657

  Abstract

  Shape-programmable soft materials that exhibit integrated multifunctional shape manipulations, including reprogrammable, untethered, fast, and reversible shape transformation and locking, are highly desirable for a plethora of applications, including soft robotics, morphing structures, and biomedical devices. Despite recent progress, it remains challenging to achieve multiple shape manipulations in one material system. Here, a novel magnetic shape memory polymer composite is reported to achieve this. The composite consists of two types of magnetic particles in an amorphous shape memory polymer matrix. The matrix softens via magnetic inductive heating of low-coercivity particles, and high-remanence particles with reprogrammable magnetization profiles drive the rapid and reversible shape change under actuation magnetic fields. Once cooled, the actuated shape can be locked. Additionally, varying the particle loadings for heating enables sequential actuation. The integrated multifunctional shape manipulations are further exploited for applications including soft magnetic grippers with large grabbing force, reconfigurable antennas, and sequential logic for computing.

  View details for DOI 10.1002/adma.201906657

  View details for Web of Science ID 000501295500001

  View details for PubMedID 31814185

• Symmetry-Breaking Actuation Mechanism for Soft Robotics and Active Metamaterials ACS APPLIED MATERIALS & INTERFACES Wu, S., Ze, Q., Zhang, R., Hu, N., Cheng, Y., Yang, F., Zhao, R. 2019; 11 (44): 41649-41658

  Abstract

  Magnetic-responsive composites that consist of a soft matrix embedded with hard-magnetic particles have recently been demonstrated as robust soft active materials for fast-transforming actuation. However, the deformation of the functional components commonly attains only a single actuation mode under external stimuli, which limits their capability of achieving tunable properties. To greatly enhance the versatility of soft active materials, we exploit a new class of programmable magnetic-responsive composites incorporated with a multifunctional joint design that allows asymmetric multimodal actuation under an external stimulation. We demonstrate that the proposed asymmetric multimodal actuation enables a plethora of novel applications ranging from the basic one-dimensional/two-dimensional (2D) active structures with asymmetric shape-shifting to biomimetic crawling robots, swimming robots with efficient dynamic performance, and 2D metamaterials with tunable properties. This new asymmetric multimodal actuation mechanism will open up new avenues for the design of next-generation multifunctional soft robots, biomedical devices, and acoustic metamaterials.

  View details for DOI 10.1021/acsami.9b13840

  View details for Web of Science ID 000495769900071

  View details for PubMedID 31578851

• Mechanics of hard-magnetic soft materials JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS Zhao, R., Kim, Y., Chester, S. A., Sharma, P., Zhao, X. 2019; 124: 244-263

  View details for DOI 10.1016/j.jmps.2018.10.008

  View details for Web of Science ID 000459368300014

• Soft wall-climbing robots SCIENCE ROBOTICS Gu, G., Zou, J., Zhao, R., Zhao, X., Zhu, X. 2018; 3 (25)

  Abstract

  Existing robots capable of climbing walls mostly rely on rigid actuators such as electric motors, but soft wall-climbing robots based on muscle-like actuators have not yet been achieved. Here, we report a tethered soft robot capable of climbing walls made of wood, paper, and glass at 90° with a speed of up to 0.75 body length per second and multimodal locomotion, including climbing, crawling, and turning. This soft wall-climbing robot is enabled by (i) dielectric-elastomer artificial muscles that generate fast periodic deformation of the soft robotic body, (ii) electroadhesive feet that give spatiotemporally controlled adhesion of different parts of the robot on the wall, and (iii) a control strategy that synchronizes the body deformation and feet electroadhesion for stable climbing. We further demonstrate that our soft robot could carry a camera to take videos in a vertical tunnel, change its body height to navigate through a confined space, and follow a labyrinth-like planar trajectory. Our soft robot mimicked the vertical climbing capability and the agile adaptive motions exhibited by soft organisms.

  View details for DOI 10.1126/scirobotics.aat2874

  View details for Web of Science ID 000453903300001

  View details for PubMedID 33141690

• Controlled crack propagation for atomic precision handling of wafer-scale two-dimensional materials SCIENCE Shim, J., Bae, S., Kong, W., Lee, D., Qiao, K., Nezich, D., Park, Y., Zhao, R., Sundaram, S., Li, X., Yeon, H., Choi, C., Kum, H., Yue, R., Zhou, G., Ou, Y., Lee, K., Moodera, J., Zhao, X., Ahn, J., Hinkle, C., Ougazzaden, A., Kim, J. 2018; 362 (6415): 665-+

  Abstract

  Although flakes of two-dimensional (2D) heterostructures at the micrometer scale can be formed with adhesive-tape exfoliation methods, isolation of 2D flakes into monolayers is extremely time consuming because it is a trial-and-error process. Controlling the number of 2D layers through direct growth also presents difficulty because of the high nucleation barrier on 2D materials. We demonstrate a layer-resolved 2D material splitting technique that permits high-throughput production of multiple monolayers of wafer-scale (5-centimeter diameter) 2D materials by splitting single stacks of thick 2D materials grown on a single wafer. Wafer-scale uniformity of hexagonal boron nitride, tungsten disulfide, tungsten diselenide, molybdenum disulfide, and molybdenum diselenide monolayers was verified by photoluminescence response and by substantial retention of electronic conductivity. We fabricated wafer-scale van der Waals heterostructures, including field-effect transistors, with single-atom thickness resolution.

  View details for DOI 10.1126/science.aat8126

  View details for Web of Science ID 000450474500036

  View details for PubMedID 30309906

• Folding artificial mucosa with cell- laden hydrogels guided by mechanics models PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Chan, H., Zhao, R., Parada, G. A., Meng, H., Leong, K. W., Griffith, L. G., Zhao, X. 2018; 115 (29): 7503-7508

  Abstract

  The surfaces of many hollow or tubular tissues/organs in our respiratory, gastrointestinal, and urogenital tracts are covered by mucosa with folded patterns. The patterns are induced by mechanical instability of the mucosa under compression due to constrained growth. Recapitulating this folding process in vitro will facilitate the understanding and engineering of mucosa in various tissues/organs. However, scant attention has been paid to address the challenge of reproducing mucosal folding. Here we mimic the mucosal folding process using a cell-laden hydrogel film attached to a prestretched tough-hydrogel substrate. The cell-laden hydrogel constitutes a human epithelial cell lining on stromal component to recapitulate the physiological feature of a mucosa. Relaxation of the prestretched tough-hydrogel substrate applies compressive strains on the cell-laden hydrogel film, which undergoes mechanical instability and evolves into morphological patterns. We predict the conditions for mucosal folding as well as the morphology of and strain in the folded artificial mucosa using a combination of theory and simulation. The work not only provides a simple method to fold artificial mucosa but also demonstrates a paradigm in tissue engineering via harnessing mechanical instabilities guided by quantitative mechanics models.

  View details for DOI 10.1073/pnas.1802361115

  View details for Web of Science ID 000438892600050

  View details for PubMedID 29967135

  View details for PubMedCentralID PMC6055139

• Printing ferromagnetic domains for untethered fast-transforming soft materials NATURE Kim, Y., Yuk, H., Zhao, R., Chester, S. A., Zhao, X. 2018; 558 (7709): 274-+

  Abstract

  Soft materials capable of transforming between three-dimensional (3D) shapes in response to stimuli such as light, heat, solvent, electric and magnetic fields have applications in diverse areas such as flexible electronics1,2, soft robotics3,4 and biomedicine5-7. In particular, magnetic fields offer a safe and effective manipulation method for biomedical applications, which typically require remote actuation in enclosed and confined spaces8-10. With advances in magnetic field control 11 , magnetically responsive soft materials have also evolved from embedding discrete magnets 12 or incorporating magnetic particles 13 into soft compounds to generating nonuniform magnetization profiles in polymeric sheets14,15. Here we report 3D printing of programmed ferromagnetic domains in soft materials that enable fast transformations between complex 3D shapes via magnetic actuation. Our approach is based on direct ink writing 16 of an elastomer composite containing ferromagnetic microparticles. By applying a magnetic field to the dispensing nozzle while printing 17 , we reorient particles along the applied field to impart patterned magnetic polarity to printed filaments. This method allows us to program ferromagnetic domains in complex 3D-printed soft materials, enabling a set of previously inaccessible modes of transformation, such as remotely controlled auxetic behaviours of mechanical metamaterials with negative Poisson's ratios. The actuation speed and power density of our printed soft materials with programmed ferromagnetic domains are orders of magnitude greater than existing 3D-printed active materials. We further demonstrate diverse functions derived from complex shape changes, including reconfigurable soft electronics, a mechanical metamaterial that can jump and a soft robot that crawls, rolls, catches fast-moving objects and transports a pharmaceutical dose.

  View details for DOI 10.1038/s41586-018-0185-0

  View details for Web of Science ID 000435071400050

  View details for PubMedID 29899476

• Kirigami enhances film adhesion SOFT MATTER Zhao, R., Lin, S., Yuk, H., Zhao, X. 2018; 14 (13): 2515-2525

  Abstract

  Structures of thin films bonded on substrates have been used in technologies as diverse as flexible electronics, soft robotics, bio-inspired adhesives, thermal-barrier coatings, medical bandages, wearable devices and living devices. The current paradigm for maintaining adhesion of films on substrates is to make the films thinner, and more compliant and adhesive, but these requirements can compromise the function or fabrication of film-substrate structures. For example, there are limits on how thin, compliant and adhesive epidermal electronic devices can be fabricated and still function reliably. Here we report a new paradigm that enhances adhesion of films on substrates via designing rational kirigami cuts in the films without changing the thickness, rigidity or adhesiveness of the films. We find that the effective enhancement of adhesion by kirigami is due to (i) the shear-lag effect of the film segments; (ii) partial debonding at the film segments' edges; and (iii) compatibility of kirigami films with inhomogeneous deformation of substrates. While kirigami has been widely used to program thin sheets with desirable shapes and mechanical properties, fabricate electronics with enhanced stretchability and design the assembly of three-dimensional microstructures, this paper gives the first systematic study on kirigami enhancing film adhesion. We further demonstrate novel applications including a kirigami bandage, a kirigami heat pad and printed kirigami electronics.

  View details for DOI 10.1039/c7sm02338c

  View details for Web of Science ID 000435122100001

  View details for PubMedID 29537019

• Multimodal Surface Instabilities in Curved Film-Substrate Structures JOURNAL OF APPLIED MECHANICS-TRANSACTIONS OF THE ASME Zhao, R., Zhao, X. 2017; 84 (8)

  View details for DOI 10.1115/1.4036940

  View details for Web of Science ID 000404715200001

• The primary bilayer ruga-phase diagram I: Localizations in ruga evolution EXTREME MECHANICS LETTERS Zhao, R., Zhang, T., Diab, M., Gao, H., Kim, K. 2015; 4: 76-82

  View details for DOI 10.1016/j.eml.2015.04.006

  View details for Web of Science ID 000218745900009

• Ruga mechanics of creasing: from instantaneous to setback creases PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES Diab, M., Zhang, T., Zhao, R., Gao, H., Kim, K. 2013; 469 (2157)

  View details for DOI 10.1098/rspa.2012.0753

  View details for Web of Science ID 000321254400001