Mechanochemical Regulated Origami with Tough Hydrogels by Ion Transfer Printing

Engineering viscoelastic mismatch for temporal morphing of tough supramolecular hydrogels

Viscoelasticity is a generic characteristic of soft biotissues and polymeric materials, endowing them with unique time- and rate-dependent properties. Here, by spatiotemporally tailoring the viscoelasticity in tough supramolecular hydrogels, we demonstrate reprogrammable morphing of the gels based on differential viscoelastic recovery processes that lead to internal strain mismatch. The spatial heterogeneity of viscoelasticity is encoded through integrating dissimilar hydrogels or by site-specific treatment of a singular hydrogel. The temporal morphing behavior of tough gels, including a fast deformation process and then a slow shape-recovery process, is related to the kinetics of associative interactions and the entropic elasticity of supramolecular networks after pre-stretching and release, which takes place spontaneously in the absence of external stimuli. Such a kinetically driven morphing mechanism resolves the trade-off between the mechanical robustness and shape-changing speed in tough hydrogels with dense entanglements and physical associations, and should be applicable to other viscoelastic materials. A numerical theory for the temporal morphing of tough supramolecular gels has been formulated by dynamic coupling of viscoelastic recovery and mechanics of deformations, which is further implemented to predict the sophisticated morphed structures. Furthermore, magnetic particles are incorporated into the morphed tough hydrogels to devise versatile soft actuators and robots for specific applications.

Robust hydrogel adhesives for emergency rescue and gastric perforation repair

Development of biocompatible hydrogel adhesives with robust tissue adhesion to realize instant hemorrhage control and injury sealing, especially for emergency rescue and tissue repair, is still challenging. Herein, we report a potent hydrogel adhesive by free radical polymerization of N-acryloyl aspartic acid (AASP) in a facile and straightforward way. Through delicate adjustment of steric hindrance, the synergistic effect between interface interactions and cohesion energy can be achieved in PAASP hydrogel verified by X-ray photoelectron spectroscopy (XPS) analysis and simulation calculation compared to poly (N-acryloyl glutamic acid) (PAGLU) and poly (N-acryloyl amidomalonic acid) (PAAMI) hydrogels. The adhesion strength of the PAASP hydrogel could reach 120 kPa to firmly seal the broken organs to withstand the external force with persistent stability under physiological conditions, and rapid hemostasis in different hemorrhage models on mice is achieved using PAASP hydrogel as physical barrier. Furthermore, the paper-based Fe³⁺ transfer printing method is applied to construct PAASP-based Janus hydrogel patch with both adhesive and non-adhesive surfaces, by which simultaneous wound healing and postoperative anti-adhesion can be realized in gastric perforation model on mice. This advanced hydrogel may show vast potential as bio-adhesives for emergency rescue and tissue/organ repair.

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The hydrogel with good mechanical properties and adhesiveness is designed.

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The hydrogel adhesive can act as physical barrier for emergency rescue.

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The Janus hydrogel can realize efficient gastric perforation repair on mice.

4D Multiscale Origami Soft Robots: A Review

Time-dependent shape-transferable soft robots are important for various intelligent applications in flexible electronics and bionics. Four-dimensional (4D) shape changes can offer versatile functional advantages during operations to soft robots that respond to external environmental stimuli, including heat, pH, light, electric, or pneumatic triggers. This review investigates the current advances in multiscale soft robots that can display 4D shape transformations. This review first focuses on material selection to demonstrate 4D origami-driven shape transformations. Second, this review investigates versatile fabrication strategies to form the 4D mechanical structures of soft robots. Third, this review surveys the folding, rolling, bending, and wrinkling mechanisms of soft robots during operation. Fourth, this review highlights the diverse applications of 4D origami-driven soft robots in actuators, sensors, and bionics. Finally, perspectives on future directions and challenges in the development of intelligent soft robots in real operational environments are discussed.

Light-Guided Growth of Gradient Hydrogels with Programmable Geometries and Thermally Responsive Actuations

Hydrogel actuators have gained considerable interest and experienced significant advancements in recent years. However, the programming of their actuating behaviors is still challenging. Herein, we report the development and regulation of gradient structures of hydrogels for programmable thermally responsive actuating behaviors. The hydrogel actuators are developed by controlling the photoreduction of Fe³⁺ ions coordinated with carboxylate groups from the substrates and their limited diffusion into the precursor solutions to act as both initiators and crosslinkers. The developed hydrogels show well-defined external geometries and controllable thicknesses under spatiotemporal control of ultraviolet irradiation. The shapes and the actuation amplitudes of the hydrogel actuators can be independently regulated by controlling the formation and photodissociation of Fe³⁺-carboxylate coordination in the formed gradient networks. Some interesting applications such as the lifting of an object with a specific shape and directional walking are realized. The proposed method can be extended to other hydrogel actuators with different compositions and stimuli-responsive behaviors.

Anti-Freezing, Non-Drying, Localized Stiffening, and Shape-Morphing Organohydrogels

Artificial shape-morphing hydrogels are emerging toward various applications, spanning from electronic skins to healthcare. However, the low freezing and drying tolerance of hydrogels hinder their practical applications in challenging environments, such as subzero temperatures and arid conditions. Herein, we report on a shape-morphing system of tough organohydrogels enabled by the spatially encoded rigid structures and its applications in conformal packaging of “island–bridge” stretchable electronics. To validate this method, programmable shape morphing of Fe (III) ion-stiffened Ca-alginate/polyacrylamide (PAAm) tough organohydrogels down to −50 °C, with long-term preservation of their 3D shapes at arid or even vacuum conditions, was successfully demonstrated, respectively. To further illustrate the potency of this approach, the as-made organohydrogels were employed as a material for the conformal packaging of non-stretchable rigid electronic components and highly stretchable liquid metal (galinstan) conductors, forming a so-called “island–bridge” stretchable circuit. The conformal packaging well addresses the mechanical mismatch between components with different elastic moduli. As such, the as-made stretchable shape-morphing device exhibits a remarkably high mechanical durability that can withstand strains as high as 1000% and possesses long-term stability required for applications under challenging conditions.

A facile approach for anisotropic hydrogel with light-regulated stiffness and its application to achieve mechanical toughening

Many load-bearing tissues in nature obtain high toughness by fabricating anisotropic structures with spatially regulated composition and modulus at macroscale. This reality inspires a toughening strategy for hydrogel based on the controlling of modulus heterogeneity. Herein, a facile approach to realize light-regulated spatial modulus heterogeneity with large contrast in hydrogel is proposed. Ferric citric acid complex is used as a light-responsive ionic crosslinker, which can first stiffen an alginate/polyacrylamide hydrogel by coordinating with the alginate to form another network, then realize light-triggered softening through photoreduction of ferric ions. Based on this, a stripe-patterned hydrogel with alternating stiff and soft segments can be fabricated through photopatterning. The modulus contrast between the stiff and soft phases can be adjusted by control of several influence factors and the maximum modulus contrast reach up to 87 times. As a result, the toughness of the stripe-patterned hydrogel is enhanced by 3.5 times comparing to that hydrogel without pattern. This approach shows great potential in synthesis of smart hydrogel with light-programmable mechanical performances, and may be widely applicable for the hydrogels with functional groups that can coordinate with metal ions. This article is protected by copyright. All rights reserved.

Recent Progress in Active Mechanical Metamaterials and Construction Principles

Active mechanical metamaterials (AMMs) (or smart mechanical metamaterials) that combine the configurations of mechanical metamaterials and the active control of stimuli-responsive materials have been widely investigated in recent decades. The elaborate artificial microstructures of mechanical metamaterials and the stimulus response characteristics of smart materials both contribute to AMMs, making them achieve excellent properties beyond the conventional metamaterials. The micro and macro structures of the AMMs are designed based on structural construction principles such as, phase transition, strain mismatch, and mechanical instability. Considering the controllability and efficiency of the stimuli-responsive materials, physical fields such as, the temperature, chemicals, light, electric current, magnetic field, and pressure have been adopted as the external stimuli in practice. In this paper, the frontier works and the latest progress in AMMs from the aspects of the mechanics and materials are reviewed. The functions and engineering applications of the AMMs are also discussed. Finally, existing issues and future perspectives in this field are briefly described. This review is expected to provide the basis and inspiration for the follow-up research on AMMs.

Fabrication of patterned magnetic hydrogels by ion transfer printing

Magnetic hydrogels have found a myriad of applications in bioengineering and soft robotics. As the function of magnetic hydrogels is affected by the distribution of magnetic nanoparticles, it is imperative to propose a strategy for fabricating patterned magnetic hydrogels. However, previous strategies can only achieve very simple distribution by using external magnetic fields to guide the chain-like assembly of nanoparticles. It remains challenging to realize the complex distribution of magnetic nanoparticles in a hydrogel. Here we propose an ion transfer printing strategy to prepare patterned magnetic hydrogels, taking advantage of the ion permeation and nanoparticle precipitation in the hydrogel. The polyacrylamide (PAAm) hydrogel is loaded with Fe²⁺/Fe³⁺ ions and covered with a patterned filter paper with OH^- ions to generate Fe₃O₄ nanoparticles locally. The effect of the ion concentration and covering time on the generation of nanoparticles is investigated by using a reaction-diffusion model. Furthermore, the magnetothermal response of the patterned magnetic hydrogels has been characterized to reveal the distribution and thermogenesis of magnetic nanoparticles. We hope that the fabricated magnetic hydrogels with complex patterns can open up new opportunities for applications.

A bio-inspired self-recoverable polyampholyte hydrogel with low temperature sensing

Hydrogel-based flexible sensors have been extensively investigated, but inevitably, some hydrogels will not work properly at low temperature or recover their original property after deformation. In this work, a polyampholyte hydrogel was successfully prepared by introducing zwitterionic monomers with hydrophobic association. The electrostatic interaction based on polyelectrolyte provides excellent stretchability, fatigue resistance and self-recovery. It was important that the hydrogel, as an excellent strain sensor, exhibited a high electrical conductivity of 0.041 S cm-1, a low temperature resistance of -31.7 °C, and a high sensitivity in the strain range of 0-500%. The hydrogel sensor is used for human motion detection, including joint movement, vocalization, and walking. Predictably, the hydrogel will provide stable performance in a complex temperature environment and exhibited a wide range of applications in physiological signal monitoring, electronic skin and soft robots.

Stimuli responsive dynamic transformations in supramolecular gels

Supramolecular gels are formed by the self-assembly of small molecules under the influence of various non-covalent interactions. As the interactions are individually weak and reversible, it is possible to perturb the gels easily, which in turn enables fine tuning of their properties. Synthetic supramolecular gels are kinetically trapped and usually do not show time variable changes in material properties after formation. However, such materials potentially become switchable when exposed to external stimuli like temperature, pH, light, enzyme, redox, and chemical analytes resulting in reconfiguration of gel matrix into a different type of network. Such transformations allow gel-to-gel transitions while the changes in the molecular aggregation result in alteration of physical and chemical properties of the gel with time. Here, we discuss various methods that have been used to achieve gel-to-gel transitions by modifying a pre-formed gel material through external perturbation. We also describe methods that allow time-dependent autonomous switching of gels into different networks enabling synthesis of next generation functional materials. Dynamic modification of gels allows construction of an array of supramolecular gels with various properties from a single material which eventually extend the limit of applications of the gels. In some cases, gel-to-gel transitions lead to materials that cannot be accessed directly. Finally, we point out the necessity and possibility of further exploration of the field.

Heterogeneous Hydrogel Structures with Spatiotemporal Reconfigurability using Addressable and Tunable Voxels

Stimuli-responsive hydrogels can sense environmental cues and change their volume accordingly without the need for additional sensors or actuators. This enables a significant reduction in the size and complexity of resulting devices. However, since the responsive volume change of hydrogels is typically uniform, their robotic applications requiring localized and time-varying deformations have been challenging to realize. Here, using addressable and tunable hydrogel building blocks-referred to as soft voxel actuators (SVAs)-heterogeneous hydrogel structures with programmable spatiotemporal deformations are presented. SVAs are produced using a mixed-solvent photopolymerization method, utilizing a fast reaction speed and the cononsolvency property of poly(N-isopropylacrylamide) (PNIPAAm) to produce highly interconnected hydrogel pore structures, resulting in tunable swelling ratio, swelling rate, and Young's modulus in a simple, one-step casting process that is compatible with mass production of SVA units. By designing the location and swelling properties of each voxel and by activating embedded Joule heaters in the voxels, spatiotemporal deformations are achieved, which enables heterogeneous hydrogel structures to manipulate objects, avoid obstacles, generate traveling waves, and morph to different shapes. Together, these innovations pave the way toward tunable, untethered, and high-degree-of-freedom hydrogel robots that can adapt and respond to changing conditions in unstructured environments.

Tough hybrid microgel-reinforced hydrogels dependent on the size and modulus of the microgels

Microgel-reinforced (MR) hydrogels are tough hydrogels with dispersed rigid microgels embedded in a continuous soft matrix. MR gels have the great potential to provide not only mechanical toughness but also the desired functional matrix by incorporation of various functional microgels. Understanding the toughening mechanism of the MR hydrogels is critical for the rational design of the desired functionally tough MR gels. However, our current knowledge of the toughening mechanism of MR gels mainly comes from the MR hydrogels with both chemically crosslinked dispersed microgels and a continuous matrix. Little is known about the hybrid MR gels with physically crosslinked microgels embedded in a chemically crosslinked matrix. Herein, we synthesize such hybrid MR hydrogels with the ionic crosslinked calcium alginate microgels incorporated into the chemically crosslinked polyacrylamide (PAAm) matrix. The alginate microgels show strong size and modulus effects on the toughening enhancement: the larger microgels could toughen the MR gels more than the small ones, and the microgels with medium modulus could maximize the toughness of the MR gels. By comparison of the mechanical performances of the MR and the corresponding double network (DN) hydrogels, we have proposed that the hybrid MR gels may have the same toughening mechanism as the bulk DN gel. This work tries to better understand the structure-property relationships of both MR and DN gels and help in the design of more functionally tough MR gels with the desired properties.

Recent progress on hydrogel actuators

This review outlines progress in hydrogels with well-defined heterogeneity in structures and responsiveness by using sequential synthesis, photolithography, 3D/4D printing, and macroscopic assembling for programmable shape morphing or actuations.

Trends in Micro-/Nanorobotics: Materials Development, Actuation, Localization, and System Integration for Biomedical Applications

Micro-/nanorobots (m-bots) have attracted significant interest due to their suitability for applications in biomedical engineering and environmental remediation. Particularly, their applications in in vivo diagnosis and intervention have been the focus of extensive research in recent years with various clinical imaging techniques being applied for localization and tracking. The successful integration of well-designed m-bots with surface functionalization, remote actuation systems, and imaging techniques becomes the crucial step toward biomedical applications, especially for the in vivo uses. This review thus addresses four different aspects of biomedical m-bots: design/fabrication, functionalization, actuation, and localization. The biomedical applications of the m-bots in diagnosis, sensing, microsurgery, targeted drug/cell delivery, thrombus ablation, and wound healing are reviewed from these viewpoints. The developed biomedical m-bot systems are comprehensively compared and evaluated based on their characteristics. The current challenges and the directions of future research in this field are summarized.

Programmable Deformations of Biomimetic Composite Hydrogels Embedded with Printed Fibers

Shape deformations are prevalent in nature, which are closely related to the heterogeneous structures with a feature of fibrous elements embedded in a matrix. The microfibers with specific orientations act as either passive geometrical constraints in an active matrix or active elements in a passive matrix, which generate programmed internal stresses and drive shape morphing under external stimuli. Morphing materials can be designed in a biomimetic way, yet it is challenging to fabricate composite hydrogels with well-distributed fibers by a facile strategy. Here, we demonstrate the fabrication of microfiber-embedded hydrogels facilitated by the extrusion-based printing technology. Programmed deformations are achieved in these hydrogels with microfibers distributed in the upper and/or bottom layers of the gel matrix. Under external stimuli, the microfibers and the gel matrix have different responses that produce internal stresses and result in programmable deformations of the composite gel. Multiple shape transformations are realized in the hydrogel by embedding multiple types of responsive microfibers in the passive or active matrix, which is fabricated with the assistance of multinozzle printing. A soft hook is designed to show the capacity of the composite hydrogel to hold and move an object in a saline solution. This facile and versatile strategy provides an alternative way to prepare biomimetic hydrogels with potential applications in biomedical devices, flexible electronics, and soft robots.

Photoregulated Gradient Structure and Programmable Mechanical Performances of Tough Hydrogels with a Hydrogen-Bond Network

Gradient materials exist widely in natural living organisms, affording fascinating biological and mechanical properties. However, the synthetic gradient hydrogels are usually mechanically weak or only have relatively simple gradient structures. Here, we report on tough nanocomposite hydrogels with designable gradient network structure and mechanical properties by a facile post-photoregulation strategy. Poly(1-vinylimidazole-co-methacrylic acid) hydrogels containing gold nanorods (AuNRs) are in a glassy state and show typical yielding and forced elastic deformation at room temperature. The gel slightly contracts its volume when the temperature is above the glass-transition temperature that results in a collapse of the chain segments and formation of denser intra- and interchain hydrogen bonds. Consequently, the mechanical properties of the gels are enhanced, when the temperature returns to room temperature. The mechanical performances of hydrogels can also be locally tuned by near-infrared light irradiation due to the photothermal effect of AuNRs. Hydrogels with arbitrary two-dimensional gradients can be facilely developed by site-specific photoirradiation. The treated and untreated regions with different stiffness and yielding stress possess construct behaviors in stretching or twisting deformations. A locally reinforced hydrogel with the kirigami structure becomes notch-insensitive and exhibits improved strength and stretchability because the treated regions ahead the cuts have better resistance to crack advancement. These tough hydrogels with programmable gradient structure and mechanics should find applications as structural elements, biological devices, etc.

Controllable, Bidirectional Water/Organic Vapors Responsive Actuators Fabricated by One-Step Thiol-Ene Click Polymerization

It is challenging to synthesize stimuli-responsive materials with the well-balanced performance of fast stimulus-response speed, good mechanical strength, multi-functionality, and deformation diversity as well. This work reports a facile, one-step thiol-ene click polymerization strategy for preparation of water/acetone vapor-responsive hierarchical films, by using diallyl terephthalate (P) as hydrophobic ene-monomer, 1,4-diallyl-1,4-diazabicyclo [2.2.2]octane-1,4-diium bromide (B) as hydrophilic ene-monomer, and pentaerythritol tetra(3-mercaptopropionate) (PETMP) as thiol monomer. Besides, by taking advantage of the specific hydrophilic/hydrophobic induction effect of substrate and adjusting the molar ratio of P to B, P₆₀ B₄₀ -HPI film is fabricated on hydrophilic substrate "with plasma treatment" whereas P₈₀ B₂₀ -HPO film is obtained on hydrophobic substrate "without plasma treatment". Their "upper-dense and lower-porous" structural feature ensured the excellent combination of fast stimuli-response speed endowed by the porous structure and good mechanical strength enhanced by the upper dense surface. Both films are bidirectional water/acetone vapor-responsive materials, but their bending directions responding to the stimuli factors are completely opposite. This strategy showed great potential in the development of smart stimuli-responsive materials.

Engineering hydrogels by soaking: from mechanical strengthening to environmental adaptation

The soaking strategy could not only strengthen hydrogels with superior mechanical properties but also provide the hydrogels with environmentally adapting properties.

Skin-Inspired Surface-Microstructured Tough Hydrogel Electrolytes for Stretchable Supercapacitors

Double-network tough hydrogels have raised increasing interest in stretchable electronic applications as well as electronic skin (e-skin) owing to their excellent mechanical properties and functionalities. While hydrogels have been extensively explored as solid-state electrolytes, stretchable energy storage devices based on tough hydrogel electrolytes are still limited despite their high stretchability and strength. A key challenge remains in the robust electrode/electrolyte interface under large mechanical strains. Inspired by the skin structure that involves the microstructured interface for the tight connection between the dermis and epidermis, we demonstrated that a surface-microstructured tough hydrogel electrolyte composed of agar/polyacrylamide/LiCl (AG/PAAm/LiCl) could be exploited to allow stretchable supercapacitors with enhanced mechanical and electrochemical performance. The prestretched tough hydrogel electrolyte was treated to generate surface microstructures with a roughness of tens of micrometers simply via mechanical rubbing followed by the attachment of activated carbon electrodes on both sides to realize the fabrication of the stretchable supercapacitor. Through investigating the properties of the tough hydrogel electrolyte and the electrochemical performance of the as-fabricated supercapacitors under varied strains, the surface-microstructured hydrogel electrolyte was shown to enable robust adhesion to electrodes, improving electrochemical behavior and capacitance, as well as having better performance retention under repeated stretching cycles, which surpassed the pristine hydrogel with smooth surfaces. Our approach could provide an alternative and general strategy to improve the interfacial properties between the electrode and the hydrogel electrolyte, driving new directions for functional stretchable devices based on tough hydrogels.

Shape Morphing of Hydrogels in Alternating Magnetic Field

Shape-morphing hydrogels have found a myriad of applications in biomimetics, soft robotics, and biomedical engineering. A magnetic field is favorable for specific applications of hydrogels, since it is noncontact and biocompatible at high field strengths. However, most magnetosensitive shape-morphing structures are made of elastomers rather than hydrogels because the magnetization of magnetic hydrogels is usually too low to be actuated under a static magnetic field. Here, we propose a strategy to achieve the shape morphing of magnetic hydrogels. We actuate magnetothermal sensitive hydrogels by an alternating magnetic field (AMF), where magnetic poly( N-isopropylacrylamide) hydrogels can be heated by the AMF and can undergo giant volume shrinkage under high temperature. We design the distributing pattern of magnetic hydrogel strips on an elastomer substrate to realize various two-dimensional and three-dimensional shapes such as heart-shape, truss, tube, and helix. Complex three-dimensional origami structures have been demonstrated using elastomer-magnetic hydrogels as hinges. We further demonstrate the combination of magnetic navigation and magnetic shape morphing, by applying both a direct magnetic field and an alternating magnetic field. The strategy may open new opportunities for the shape morphing of functional hydrogels.

Electrobiofabrication: electrically based fabrication with biologically derived materials

While conventional material fabrication methods focus on form and strength to achieve function, the fabrication of material systems for emerging life science applications will need to satisfy a more subtle set of requirements. A common goal for biofabrication is to recapitulate complex biological contexts (e.g. tissue) for applications that range from animal-on-a-chip to regenerative medicine. In these cases, the material systems will need to: (i) present appropriate surface functionalities over a hierarchy of length scales (e.g. molecular features that enable cell adhesion and topographical features that guide differentiation); (ii) provide a suite of mechanobiological cues that promote the emergence of native-like tissue form and function; and (iii) organize structure to control cellular ingress and molecular transport, to enable the development of an interconnected cellular community that is engaged in cell signaling. And these requirements are not likely to be static but will vary over time and space, which will require capabilities of the material systems to dynamically respond, adapt, heal and reconfigure. Here, we review recent advances in the use of electrically based fabrication methods to build material systems from biological macromolecules (e.g. chitosan, alginate, collagen and silk). Electrical signals are especially convenient for fabrication because they can be controllably imposed to promote the electrophoresis, alignment, self-assembly and functionalization of macromolecules to generate hierarchically organized material systems. Importantly, this electrically based fabrication with biologically derived materials (i.e. electrobiofabrication) is complementary to existing methods (photolithographic and printing), and enables access to the biotechnology toolbox (e.g. enzymatic-assembly and protein engineering, and gene expression) to offer exquisite control of structure and function. We envision that electrobiofabrication will emerge as an important platform technology for organizing soft matter into dynamic material systems that mimic biology's complexity of structure and versatility of function.

Recent Progress in Biomimetic Anisotropic Hydrogel Actuators

Polymeric hydrogel actuators refer to intelligent stimuli-responsive hydrogels that could reversibly deform upon the trigger of various external stimuli. They have thus aroused tremendous attention and shown promising applications in many fields including soft robots, artificial muscles, valves, and so on. After a brief introduction of the driving forces that contribute to the movement of living creatures, an overview of the design principles and development history of hydrogel actuators is provided, then the diverse anisotropic structures of hydrogel actuators are summarized, presenting the promising applications of hydrogel actuators, and highlighting the development of multifunctional hydrogel actuators. Finally, the existing challenges and future perspectives of this exciting field are discussed.

Light-Induced Shape Morphing of Liquid Metal Nanodroplets Enabled by Polydopamine Coating

Shape morphing nanosystems have recently attracted much attention and a number of applications are developed, spanning from autonomous robotics to drug delivery. However, the fabrication of such nanosystems remains at an early stage owing to limited choices of strategies and materials. This work reports a facile method to fabricate liquid metal (LM) nanodroplets by sonication of bulk LM in an aqueous dopamine hydrochloride solution and their application in light-induced shape morphing at the nanoscale. In this method, dopamine acts as a surfactant, which stabilizes the LM nanodroplets dispersion during the sonication, and results in downsizing of the nanodroplets. Furthermore, by adding 2-amino-2-(hydroxymethyl)-1,3-propanediol to the suspension, self-polymerization of dopamine molecules occurs, resulting in the formation of polydopamine (PDA)-coated LM nanodroplets. Owing to the high photothermal conversion of the PDA, PDA-coated LM nanodroplets are transformed from spherical shapes to ellipsoids by NIR laser irradiation. This study paves a simple and reliable pathway for the preparation of functional LM nanodroplets and their application as shape-morphing nanosystems.

Magnetic double-network hydrogels for tissue hyperthermia and drug release

Magnetic-field driven soft materials have found extensive applications in fields such as soft robotics, shape morphing and biomedicine. Compared to magnetoactive elastomers (MAEs), magnetic hydrogels have shown significant advantages for in vivo applications, because of their better biocompatibility, as well as their soft and wet nature. However, the poor mechanical properties and ion sensitivity of conventional magnetic hydrogels will severely limit their applications especially under physiological conditions. Double network hydrogels are tough and stable, but do not respond to environmental stimuli. Here magnetic double network (M-DN) hydrogels have been developed with outstanding mechanical performances and ion-resistant stability. M-DN hydrogels show a high modulus of ∼0.4 MPa and a high toughness of ∼1500 J m^-2. The volume, magnetic and mechanical properties of M-DN hydrogels show negligible deterioration in ionic solutions. M-DN hydrogels exhibit magnetic responsiveness and have been used for tissue hyperthermia and drug release by magnetic induction heating. The induction heating behavior of M-DN hydrogels can be tuned to meet the clinical requirements, by changing the magnetic field strength or the composition of magnetic hydrogels. M-DN hydrogels may be inspiring to the development of responsive DN hydrogels and expand their more potential applications in load-bearing biomedical engineering.

Rational Fabrication of Anti-Freezing, Non-Drying Tough Organohydrogels by One-Pot Solvent Displacement

Tough hydrogels, polymeric network structures with excellent mechanical properties (such as high stretchability and toughness), are emerging soft materials. Despite their remarkably mechanical features, tough hydrogels exhibit two flaws (freezing around the icing temperatures of water and drying under arid conditions). Inspired by cryoprotectants (CPAs) used in the inhibition of the icing of water in biological samples, a versatile and straightforward method is reported to fabricate extreme anti-freezing, non-drying CPA-based organohydrogels with long-term stability by partially displacing water molecules within the pre-fabricated hydrogels. CPA-based Ca-alginate/polyacrylamide (PAAm) tough hydrogels were successfully fabricated with glycerol, glycol, and sorbitol. The CPA-based organohydrogels remain unfrozen and mechanically flexible even up to -70 °C and are stable under ambient conditions or even vacuum.

Shape morphing of anisotropy-encoded tough hydrogels enabled by asymmetrically-induced swelling and site-specific mechanical strengthening

Dually regulated shape morphing of anisotropy-encoded tough hydrogels to sequentially create complex three-dimensional origami structures.

Tough protein organohydrogels

Tough protein organohydrogels are fabricated by applying a solvent displacement-induced toughening (SDIT) strategy. By one-step SDIT, relatively weak and brittle protein hydrogels change to protein organohydrogels with remarkably high performance in anti-freezing, non-drying, topological healing, thermal plasticizing, mechanical toughness and stretchability.