Biosynthetic self-healing materials for soft machines

Coupling of Spectrin Repeat Modules for the Assembly of Nanorods and Presentation of Protein Domains

Modular protein engineering is a powerful approach for fabricating high-molecular-weight assemblies and biomaterials with nanoscale precision. Herein, we address the challenge of designing an extended nanoscale filamentous architecture inspired by the central rod domain of human dystrophin, which protects sarcolemma during muscle contraction and consists of spectrin repeats composed of three-helical bundles. A module of three tandem spectrin repeats was used as a rigid building block self-assembling via coiled-coil (CC) dimer-forming peptides. CC peptides were precisely integrated to maintain the spectrin α-helix continuity in an appropriate frame to form extended nanorods. An orthogonal set of customizable CC heterodimers was harnessed for modular rigid domain association, which could be additionally regulated by metal ions and chelators. We achieved a robust assembly of rigid rods several micrometers in length, determined by atomic force microscopy and negative stain transmission electron microscopy. Furthermore, these rigid rods can serve as a scaffold for the decoration of diverse proteins or biologically active peptides along their length with adjustable spacing up to tens of nanometers, as confirmed by the DNA-PAINT super-resolution microscopy. This demonstrates the potential of modular bottom-up protein engineering and tunable CCs for the fabrication of functionalized protein biomaterials.

A robust, high-temperature-resistant, protective cellulose gel enabled by multiscale structural engineering

Given the escalating environmental and safety concerns, friendly protective materials with exceptional mechanical properties, biodegradability, and insensitivity to high temperature have received more and more attention. Here, we report a robust cellulosic gel through the multi-scale integration of cellulose molecular skeleton, nano-reinforced diatomite, and in situ polymerized polyacrylamide molecule. The bottom-up yet cross-scale approach facilitates the formation of cellulosic gel characterized by a highly interconnected hydrogen bond network and nano-enhanced domain, resulting in a tensile strength of up to 13.83 MPa, a Young's modulus exceeding 280 MPa, and an impact strength around 12.38 KJ m-1. Furthermore, this gel exhibits structural stability at temperatures up to 130 °C, good flame retardancy, and complete biodegradability within a span of 35 days. The robust cellulosic gel, acting as a pliable protector, demonstrates exceptional protection for human joints. Our study presents a highly efficient and scalable pathway towards the development of sustainable and robust biomass gels, holding immense potential in intelligent-protective wearables and advanced materials science and engineering.

Mechanical Regulation of Polymer Gels

The mechanical properties of polymer gels devote to emerging devices and machines in fields such as biomedical engineering, flexible bioelectronics, biomimetic actuators, and energy harvesters. Coupling network architectures and interactions has been explored to regulate supportive mechanical characteristics of polymer gels; however, systematic reviews correlating mechanics to interaction forces at the molecular and structural levels remain absent in the field. This review highlights the molecular engineering and structural engineering of polymer gel mechanics and a comprehensive mechanistic understanding of mechanical regulation. Molecular engineering alters molecular architecture and manipulates functional groups/moieties at the molecular level, introducing various interactions and permanent or reversible dynamic bonds as the dissipative energy. Molecular engineering usually uses monomers, cross-linkers, chains, and other additives. Structural engineering utilizes casting methods, solvent phase regulation, mechanochemistry, macromolecule chemical reactions, and biomanufacturing technology to construct and tailor the topological network structures, or heterogeneous modulus compositions. We envision that the perfect combination of molecular and structural engineering may provide a fresh view to extend exciting new perspectives of this burgeoning field. This review also summarizes recent representative applications of polymer gels with excellent mechanical properties. Conclusions and perspectives are also provided from five aspects of concise summary, mechanical mechanism, biofabrication methods, upgraded applications, and synergistic methodology.

Ionic aggregates induced room temperature autonomous self-healing elastic tape for reducing ankle sprain

Traditional kinesiology tape (KT) is an elastic fabric tape that clinicians and sports trainers widely use for managing ankle sprains. However, inadequate mechanical properties, adhesive strength, water resistance, and micro-damage generation could affect the longevity of the tape on the skin during physical activity and sweating. Therefore, autonomous room-temperature self-healing elastomers with robust mechanical properties and adequate adhesion to the skin are highly desirable to replace traditional KT. Ionic aggregates were introduced into the polymer matrix via electrostatic attraction between polymer colloid and polyelectrolyte to achieve such elastic tape. These ionic aggregates act as physical crosslink points to enhance mechanical properties and dissociate at room temperature to provide self-healing functions. The obtained elastic tape possesses a tensile strength of 3.7 MPa, elongation of 940 %, toughness of 16.6 MJ∙m-3, and self-healing efficiency of 90 % for 2 h at room temperature. It also exhibits adequate reversible adhesion on the skin via van der Waals force and electrostatic interaction in both dry and wet conditions. The new elastic tapes have great potential in biomedical engineering for preventing and rehabilitating ankle sprain.

Thermomechanical and Morphological Properties of Loligo vulgaris Squid Sucker Ring Teeth

Climate change is accelerating the increase of temperatures across the planet and resulting in the warming of oceans. Ocean warming threatens the survival of many aquatic species, including squids, and has introduced physiological, behavioral, and developmental changes, as well as physical changes in their biological materials composition, structure, and properties. Here, we characterize and analyze how the structure, morphology, and mechanical properties of European common squid Loligo vulgaris sucker ring teeth (SRT) are affected by temperature. SRT are predatory teethed structures located inside the suction cups of squids that are used to capture prey and are composed of semicrystalline structural proteins with a high modulus (GPa-range). We observed here that this biological material reversibly softens with temperature, undergoing a glass transition at ∼35°C, to a MPa-range modulus. We analyzed the SRT protein nanostructures as a function of temperature, as well as microscale and macroscale morphological changes, to understand their impact in the material properties. The results suggested that even small deviations from their habitat temperatures can result in significant softening of the material (up to 40% in modulus loss). Temperature changes following recent global climate trends and predictions might affect environmental adaptation in squid species and pose emerging survival challenges to adapt to increasing ocean temperatures.

Study of Nonlinear Optical Properties of a Self-Healing Organic Crystal

Recently a noncentrosymmetric single crystal of a dibenzoate derivative, namely, dimethyl-4,4'-(methylenebis(azanediyl))dibenzoate, with second harmonic generation activities at 405 nm and ultrafast self-healing activity was reported by Mondal et al. in Nature Communications in 2023. Here, the linear and nonlinear optical properties of this notable molecular crystal were simulated using 1,611,464 atoms in the Supermolecule approach at the DFT/CAM-B3LYP/aug-cc-pVTZ level. Our results for the second order nonlinear optical properties of dimethyl-4,4'-(methylenebis(azanediyl))dibenzoate show that the second harmonic generation is more significant at 532 nm. In addition, the density functional theory calculations of the electro-optical parameters for the crystals in the pristine state and after the fracture mechanical self-healing process show small differences, confirming the efficiency of the self-healing process. Additionally, the crystal displays significant third-order nonlinear optical properties, particularly pronounced at a shorter wavelength of 330 nm. Thus, the self-healing dimethyl-4,4'-(methylenebis(azanediyl))dibenzoate crystal shows relevant second and third order nonlinear optical properties which make it a very interesting material for optical applications.

Cephalopod-Inspired Nanomaterials for Optical and Thermal Regulation: Mechanisms, Applications and Perspectives

The manipulation of interactions between light and matter plays a crucial role in the evolution of organisms and a better life for humans. As a result of natural selection, precise light-regulatory systems of biology have been engineered that provide many powerful and promising bioinspired strategies. As the "king of disguise", cephalopods, which can perfectly control the propagation of light and thus achieve excellent surrounding-matching via their delicate skin structure, have made themselves an exciting source of inspiration for developing optical and thermal regulation nanomaterials. This review presents cutting-edge advancements in cephalopod-inspired optical and thermal regulation nanomaterials, highlighting the key milestones and breakthroughs achieved thus far. We begin with the underlying mechanisms of the adaptive color-changing ability of cephalopods, as well as their special hierarchical skin structure. Then, different types of bioinspired nanomaterials and devices are comprehensively summarized. Furthermore, some advanced and emerging applications of these nanomaterials and devices, including camouflage, thermal management, pixelation, medical health, sensing and wireless communication, are addressed. Finally, some remaining but significant challenges and potential directions for future work are discussed. We anticipate that this comprehensive review will promote the further development of cephalopod-inspired nanomaterials for optical and thermal regulation and trigger ideas for bioinspired design of nanomaterials in multidisciplinary applications.

Fibres-threads of intelligence-enable a new generation of wearable systems

Fabrics represent a unique platform for seamlessly integrating electronics into everyday experiences. The advancements in functionalizing fabrics at both the single fibre level and within constructed fabrics have fundamentally altered their utility. The revolution in materials, structures, and functionality at the fibre level enables intimate and imperceptible integration, rapidly transforming fibres and fabrics into next-generation wearable devices and systems. In this review, we explore recent scientific and technological breakthroughs in smart fibre-enabled fabrics. We examine common challenges and bottlenecks in fibre materials, physics, chemistry, fabrication strategies, and applications that shape the future of wearable electronics. We propose a closed-loop smart fibre-enabled fabric ecosystem encompassing proactive sensing, interactive communication, data storage and processing, real-time feedback, and energy storage and harvesting, intended to tackle significant challenges in wearable technology. Finally, we envision computing fabrics as sophisticated wearable platforms with system-level attributes for data management, machine learning, artificial intelligence, and closed-loop intelligent networks.

Magnetically Controllable Paper-Based Soft Robots for Colorimetric Detection of Heavy Metal Ions

Magnetically controllable soft robots are of great interest because they have unique properties compared with conventional rigid counterparts and can be used in diverse applications such as intelligent electronics, bionics, personalized medicine, and cargo grasping. However, the fabrication of such multifunctional soft robots has been challenging because of the integration of dissimilar materials into the robot body. Herein, we designed and fabricated a soft robotic multifunctional system using conventional papers and elastomeric polymers for the colorimetric detection of heavy metal ions (Hg2+ and Fe3+) in water samples. The magnetic actuation of the platforms was shown to correlate with the type of underlying paper and magnetic particle content in the mixtures. Moreover, it was observed that actuation can also be manipulated by controlling the magnetic field strength. A proof-of-concept robotic paper-based Hg2+, Zn2+, and Fe3+ ion detection was demonstrated by combining colorimetric paper sensors and magneto-papers. Our study highlights the significant potential of paper as a material for the fabrication of effective and multifunctional untethered soft robots.

A Soft, Fatigue-free, and Self-healable Ionic Elastomer via the Synergy of Skin-like Assembly and Bouligand Structure

Soft ionic elastomers that are self-healable, fatigue-free, and environment-tolerant are ideal structural and sensing materials for artificial prosthetics, soft electronics, and robotics to survive unpredictable service conditions. However, most synthetic strategies failed to unite rapid healing, fatigue resistance, and environmental robustness, limited by their singular compositional/structural designs. Here, we present a soft, tough, fatigue-resistant, and self-healable ionic elastomer (STFSI elastomer), which fuses skin-like binary assembly and Bouligand helicoidal structure into a composite of thermoplastic polyurethane (TPU) fibers and a supramolecular ionic biopolymer. The interlocked binary assembly enables skin-like softness, high stretchability, and strain-adaptive stiffening through a matrix-to-scaffold stress transfer. The Bouligand structure contributes to superhigh fracture toughness (101.6 kJ m-2) and fatigue resistance (4937 J m-2) via mechanical toughening by interlayer slipping and twisted crack propagation path. Besides, the STFSI elastomer is self-healable through a "bridging" method and environment-tolerant (-20 °C, strong acid/alkali, saltwater). To demonstrate the versatile structural and sensing applications, we showcase a safety cushion with efficient damping and suppressed rebounding, and a robotic sensor with excellent fatigue crack tolerance and instant sensation recovery upon cutting-off damage. Our presented synthetic strategy is generalizable to other fiber-reinforced tough polymers for applications involving demanding mechanical/environmental conditions.

Dynamic Covalent Bonded Gradient Structured Actuators with Mechanical Robustness and Self-Healing Ability

Flexible actuators with excellent adaptability and interaction safety have a wide range of application prospects in many fields. However, current flexible actuators have problems such as fragility and poor actuating ability. Here, inspired by the features of nacre structure, a gradient structured flexible actuator is proposed with mechanical robustness and self-healing ability. By introducing dynamic boronic ester bonds at the interface between MXene nanosheets and epoxy natural rubber matrix, the resulting nanocomposites with ordered micro-nano structures exhibit excellent tensile strength (25.03 MPa) and satisfactory repair efficiency (81.2%). In addition, the gradient distribution structure of MXene nanosheets endows the actuator with stable photothermal conversion capability, which can quickly respond to near-infrared light stimulation. The interlayer dynamic covalent bond crosslinking enables good response speed after multiple bending and is capable of functional self-healing after damage. This work introduces gradient structure and dynamic covalent bonding into flexible actuators, which provides a reference for the fabrication of self-healing soft robots, wearable, and other healable functional materials.

Glycopeptide-based multifunctional nanofibrous hydrogel that facilitates the healing of diabetic wounds infected with methicillin-resistant Staphylococcus aureus

Diabetic wound management remains a significant challenge in clinical care due to bacterial infections, excessive inflammation, presence of excessive reactive oxygen species (ROS), and impaired angiogenesis. The use of multifunctional wound dressings has several advantages in diabetic wound healing. Moreover, the balance of macrophage polarization plays a crucial role in promoting skin regeneration. However, few studies have focused on the development of multifunctional wound dressings that can regulate the inflammatory microenvironment and promote diabetic wound healing. In this study, an extracellular matrix-inspired glycopeptide hydrogel composed of glucomannan and polypeptide was proposed for regulating the local microenvironment of diabetic wound sites. The hydrogel network, which was formed via Schiff base and hydrogen bonding interactions, effectively inhibited inflammation and promoted angiogenesis during wound healing. The hydrogels exhibited sufficient self-healing ability and had the potential to scavenge ROS and to activate the mannose receptor (MR), thereby inducing macrophage polarization toward the M2 phenotype. The experimental results confirm that the glycopeptide hydrogel is an effective tool for managing diabetic wounds by showing antibacterial, ROS scavenging, and anti-inflammatory effects, and promoting angiogenesis to facilitate wound repair and skin regeneration in vivo. STATEMENT OF SIGNIFICANCE: •The designed wound dressing combines the advantage of natural polysaccharide and polypeptide. •The hydrogel promotes M2-polarized macrophages, antibacterial, scavenges ROS, and angiogenesis. •The multifunctional glycopeptide hydrogel dressing could accelerating diabetic wound healing in vivo.

Skin-Inspired All-Natural Biogel for Bioadhesive Interface

Natural material-based hydrogels are considered ideal candidates for constructing robust bio-interfaces due to their environmentally sustainable nature and biocompatibility. However, these hydrogels often encounter limitations such as weak mechanical strength, low water resistance, and poor ionic conductivity. Here, inspired by the role of natural moisturizing factor (NMF) in skin, a straightforward yet versatile strategy is proposed for fabricating all-natural ionic biogels that exhibit high resilience, ionic conductivity, resistance to dehydration, and complete degradability, without necessitating any chemical modification. A well-balanced combination of gelatin and sodium pyrrolidone carboxylic acid (an NMF compound) gives rise to a significant enhancement in the mechanical strength, ionic conductivity, and water retention capacity of the biogel compared to pure gelatin hydrogel. The biogel manifests temperature-controlled reversible fluid-gel transition properties attributed to the triple-helix junctions of gelatin, which enables in situ gelation on diverse substrates, thereby ensuring conformal contact and dynamic compliance with curved surfaces. Due to its salutary properties, the biogel can serve as an effective and biocompatible interface for high-quality and long-term electrophysiological signal recording. These findings provide a general and scalable approach for designing natural material-based hydrogels with tailored functionalities to meet diverse application needs.

Strongly plasticized gelatin-based hydrogel for flexible encapsulation of complex-shaped electronic devices

The growth of environmentally sensitive complex-shaped electronic devices (ECEDs) has led to a surging demand for flexible electromagnetic wave (EMW) absorbers. Herein, the water loss property of hydrogel was ingeniously applied for the flexible encapsulation (FE) of ECEDs. To be specific, saturated state (SGT) hydrogels were prepared by chemical cross-linking, and the hydrogen bond dissipation network promoted FE. Additionally, SGT has an effective absorption bandwidth (EAB) of 6.04 GHz at 1.65 mm due to the presence of dipole polarization. With the loss of water, SGT transitions to its natural state (NGT), and the decreasing conductivity leads to better impedance matching. NGT exhibited a broader EAB (9.20 GHz at 2.65 mm) and also strength and lightness (density of 0.3 g cm-3). Furthermore, the semi-automatic reversible cyclic transformation between SGT and NGT gels further broadens application scenarios. GT gel combines self-encapsulation and self-optimized performance as a potential EMW absorber for FE.

Ancestral terpene cyclases: From fundamental science to applications in biosynthesis

Terpenes constitute one of the largest family of natural products with potent applications as renewable platform chemicals and medicines. The low activity, selectivity and stability displayed by terpene biosynthetic machineries can constitute an obstacle towards achieving expedient biosynthesis of terpenoids in processes that adhere to the 12 principles of green chemistry. Accordingly, engineering of terpene synthase enzymes is a prerequisite for industrial biotechnology applications, but obstructed by their complex catalysis that depend on reactive carbocationic intermediates that are prone to undergo bifurcation mechanisms. Rational redesign of terpene synthases can be tedious and requires high-resolution structural information, which is not always available. Furthermore, it has proven difficult to link sequence space of terpene synthase enzymes to specific product profiles. Herein, the author shows how ancestral sequence reconstruction (ASR) can favorably be used as a protein engineering tool in the redesign of terpene synthases without the need of a structure, and without excessive screening. A detailed workflow of ASR is presented along with associated limitations, with a focus on applying this methodology on terpene synthases. From selected examples of both class I and II enzymes, the author advocates that ancestral terpene cyclases constitute valuable assets to shed light on terpene-synthase catalysis and in enabling accelerated biosynthesis.

Seahorse-Tail-Inspired Soft Pneumatic Actuator: Development and Experimental Characterization

The study of bio-inspired structures and their reproduction has always fascinated humans. The advent of soft robotics, thanks to soft materials, has enabled considerable progress in this field. Over the years, polyps, worms, cockroaches, jellyfish, and multiple anthropomorphic structures such as hands or limbs have been reproduced. These structures have often been used for gripping and handling delicate objects or those with complex unknown a priori shapes. Several studies have also been conducted on grippers inspired by the seahorse tail. In this paper, a novel biomimetic soft pneumatic actuator inspired by the tail of the seahorse Hippocampus reidi is presented. The actuator has been developed to make a leg to sustain a multi-legged robot. The prototyping of the actuator was possible by combining a 3D-printed reinforcement in thermoplastic polyurethane, mimicking the skeletal apparatus, within a silicone rubber structure, replicating the functions of the external epithelial tissue. The latter has an internal channel for pneumatic actuation that acts as the inner muscle. The study on the anatomy and kinematic behaviour of the seahorse tail suggested the mechanical design of the actuator. Through a test campaign, the actuator prototype was characterized by isotonic tests with an external null load, isometric tests, and activation/deactivation times. Specifically, the full actuator distension of 154.5 mm occurs at 1.8 bar, exerting a maximum force of 11.9 N, with an activation and deactivation time of 74.9 and 94.5 ms, respectively.

Towards high performance and durable soft tactile actuators

Soft actuators are gaining significant attention due to their ability to provide realistic tactile sensations in various applications. However, their soft nature makes them vulnerable to damage from external factors, limiting actuation stability and device lifespan. The susceptibility to damage becomes higher with these actuators often in direct contact with their surroundings to generate tactile feedback. Upon onset of damage, the stability or repeatability of the device will be undermined. Eventually, when complete failure occurs, these actuators are disposed of, accumulating waste and driving the consumption of natural resources. This emphasizes the need to enhance the durability of soft tactile actuators for continued operation. This review presents the principles of tactile feedback of actuators, followed by a discussion of the mechanisms, advancements, and challenges faced by soft tactile actuators to realize high actuation performance, categorized by their driving stimuli. Diverse approaches to achieve durability are evaluated, including self-healing, damage resistance, self-cleaning, and temperature stability for soft actuators. In these sections, current challenges and potential material designs are identified, paving the way for developing durable soft tactile actuators.

Ultrafast underwater self-healing piezo-ionic elastomer via dynamic hydrophobic-hydrolytic domains

The development of advanced materials capable of autonomous self-healing and mechanical stimulus sensing in aquatic environments holds great promise for applications in underwater soft electronics, underwater robotics, and water-resistant human-machine interfaces. However, achieving superior autonomous self-healing properties and effective sensing simultaneously in an aquatic environment is rarely feasible. Here, we present an ultrafast underwater molecularly engineered self-healing piezo-ionic elastomer inspired by the cephalopod's suckers, which possess self-healing properties and mechanosensitive ion channels. Through strategic engineering of hydrophobic C-F groups, hydrolytic boronate ester bonds, and ions, the material achieves outstanding self-healing efficiencies, with speeds of 94.5% (9.1 µm/min) in air and 89.6% (13.3 µm/min) underwater, coupled with remarkable pressure sensitivity (18.1 kPa-1) for sensing performance. Furthermore, integration of this mechanosensitive device into an underwater submarine for signal transmission and light emitting diode modulation demonstrates its potential for underwater robotics and smarter human-machine interactions.

From Nature-Sourced Polysaccharide Particles to Advanced Functional Materials

Polysaccharides constitute over 90% of the carbohydrate mass in nature, which makes them a promising feedstock for manufacturing sustainable materials. Polysaccharide particles (PSPs) are used as effective scavengers, carriers of chemical and biological cargos, and building blocks for the fabrication of macroscopic materials. The biocompatibility and degradability of PSPs are advantageous for their uses as biomaterials with more environmental friendliness. This review highlights the progresses in PSP applications as advanced functional materials, by describing PSP extraction, preparation, and surface functionalization with a variety of functional groups, polymers, nanoparticles, and biologically active species. This review also outlines the fabrication of PSP-derived macroscopic materials, as well as their applications in soft robotics, sensing, scavenging, water harvesting, drug delivery, and bioengineering. The paper is concluded with an outlook providing perspectives in the development and applications of PSP-derived materials.

Design and build of small-scale magnetic soft-bodied robots with multimodal locomotion

Small-scale magnetic soft-bodied robots can be designed to operate based on different locomotion modes to navigate and function inside unstructured, confined and varying environments. These soft millirobots may be useful for medical applications where the robots are tasked with moving inside the human body. Here we cover the entire process of developing small-scale magnetic soft-bodied millirobots with multimodal locomotion capability, including robot design, material preparation, robot fabrication, locomotion control and locomotion optimization. We describe in detail the design, fabrication and control of a sheet-shaped soft millirobot with 12 different locomotion modes for traversing different terrains, an ephyra jellyfish-inspired soft millirobot that can manipulate objects in liquids through various swimming modes, a larval zebrafish-inspired soft millirobot that can adjust its body stiffness for efficient propulsion in different swimming speeds and a dual stimuli-responsive sheet-shaped soft millirobot that can switch its locomotion modes automatically by responding to changes in the environmental temperature. The procedure is aimed at users with basic expertise in soft robot development. The procedure requires from a few days to several weeks to complete, depending on the degree of characterization required.

Formation and mechanics of fire ant rafts as an active self-healing membrane

The unique ability of fire ants to form a raft to survive flooding rain has enchanted biologists as well as researchers in other disciplines. It was established during the last decade that a three-dimensional aggregation of fire ants exhibits viscoelasticity with respect to external compression and shearing among numerous unusual mechanical properties. Continuing these works, we will study the ant raft in its natural form, i.e., composing no more than two layers. This allowed us to focus on the cracks that are unique to membranes and see how their patterns are influenced by the fact that these ants are mobile and can self-repair the damage to keep their raft from disintegration. In the beginning, we show that vertical and horizontal shaking can also prompt fire ants to aggregate. The canonical view that the stability of ant raft relies on the Cheerios effect and a combination of other parameters is tested. The force-displacement experiment is performed to show that two distinct mechanical responses and fracture patterns, characteristic of ductile and brittle materials, can be elicited, depending on the magnitude of the pull speed. During the process, we counted the number of ants that actively participated in the stress-strain relation and used this information to roughly sketch out the force chain. The latter information reveals that the pull force expedites the alignment of fire ants, in analogy to the effect of an electric field on liquid crystal polymers. To highlight the self-healing nature, we employ the creep experiment to study how the length and Young's modulus of the raft change or relax with time. One major finding is that the raft can exhibit zero Poisson's ratio without resorting to specific geometry structures. This is enabled by the active recruitment of ants from the top layer to the bottom layer to keep the raft from disintegrating.

A self-healing hydrogel wound dressing based on oxidized Bletilla striata polysaccharide and cationic gelatin for skin trauma treatment

Skin trauma presents significant treatment challenges in clinical settings. Hydrogels made from naturally-derived polysaccharide have demonstrated great potential in wound healing. Here, a novel in-situ crosslinked self-healing hydrogel was prepared using oxidized Bletilla striata polysaccharide (BSP) and cationic gelatin via a Schiff-base reaction without the need for any chemical crosslinkers. Similar to the natural extracellular matrix, the BSP-gelatin hydrogel (BG-gel) exhibited typical viscoelastic characteristics. The rheological properties, mechanical behavior, porous structure, and degradation performance of BG-gel could be adjusted by changing the aldehyde group content of BSP. Importantly, the hydrogel showed superior hemostatic performance in mouse tail amputation and rat liver incision models. It significantly facilitated wound healing by promoting hair follicles regeneration, blood vessels repair, collagen deposition, and inducing skin tissue remodeling via increased CD31 expression in a full-thickness skin wound rat model. This multifunctional hydrogel holds potential as a wound dressing for skin trauma, offering both hemostasis and expedited healing.

Cephalopod inspired self-healing protein foams for oil-water separation

Cephalopods are remarkable creatures, captivating scientists with their advanced neurophysiology, complex behavior, and miraculously effective camouflage. Research into cephalopods has led to many discoveries in neuroscience, cell biology, and materials science. Specifically, squids provide us with remarkable self-healing Squid Ring Teeth protein, which is applied herein to extend the life span of foams. Despite the advantages of porosity in surface science applications, porosity impairs mechanical properties by making materials more prone to structural damage -which traditional polymeric foams also suffer from. Drawing inspiration from Squid Ring Teeth, we developed self-healing tandem repeat proteins to overcome these challenges. By leveraging porosity and self-healing properties inspired by Squid Ring Teeth, we created bioengineered protein foams with high separation capacity (5.1 g g-1) and efficiency (≈94%). The foams healed entirely within minutes which regained over 100% strength after repair. These advances promise applications for efficient continuous water treatment through durable filter cartridges.

Magnetic Putty as a Reconfigurable, Recyclable, and Accessible Soft Robotic Material

Magnetically hard materials are widely used to build soft magnetic robots, providing large magnetic force/torque and macrodomain programmability. However, their high magnetic coercivity often presents practical challenges when attempting to reconfigure magnetization patterns, requiring a large magnetic field or heating. In this study, magnetic putty is introduced as a magnetically hard and soft material with large remanence and low coercivity. It is shown that the magnetization of magnetic putty can be easily reoriented with maximum magnitude using an external field that is only one-tenth of its coercivity. Additionally, magnetic putty is a malleable, autonomous self-healing material that can be recycled and repurposed. The authors anticipate magnetic putty could provide a versatile and accessible tool for various magnetic robotics applications for fast prototyping and explorations for research and educational purposes.

Autonomous self-healing organic crystals for nonlinear optics

Non-centrosymmetric molecular crystals have a plethora of applications, such as piezoelectric transducers, energy storage and nonlinear optical materials owing to their unique structural order which is absent in other synthetic materials. As most crystals are brittle, their efficiency declines upon prolonged usage due to fatigue or catastrophic failure, limiting their utilities. Some natural substances, like bone, enamel, leaf and skin, function efficiently, last a life-time, thanks to their inherent self-healing nature. Therefore, incorporating self-healing ability in crystalline materials will greatly broaden their scope. Here, we report single crystals of a dibenzoate derivative, capable of self-healing within milliseconds via autonomous actuation. Systematic quantitative experiments reveal the limit of mechanical forces that the self-healing crystals can withstand. As a proof-of-concept, we also demonstrate that our self-healed crystals can retain their second harmonic generation (SHG) with high efficiency. Kinematic analysis of the actuation in our system also revealed its impressive performance parameters, and shows actuation response times in the millisecond range.

Biomimetic Structural Proteins: Modular Assembly and High Mechanical Performance

Protein-based biomaterials attract growing interests due to their encoded and programmable robust mechanical properties, superelasticity, plasticity, shape adaptability, excellent interfacial behavior, etc., derived from sequence-guided backbone structures, particularly compared to chemically synthetic counterparts in materials science and biomedical engineering. For example, protein materials have been successfully fabricated as (1) artificial implants (man-made tendons, cartilages, or dental tissues), due to programmable chemistry and biocompatibility; (2) smart biodevices with temperature/light-response and self-healing effects; and (3) impact resistance materials having great mechanical performance due to biomimetics. However, the existing method of regenerating protein materials from natural sources has two critical issues, low yield and structural damage, making it unable to meet demands. Therefore, it is crucial to develop an alternative strategy for fabricating protein materials. Heterologous expression of natural proteins with a modular assembly approach is an effective strategy for material preparation. Standardized, easy-to-assemble protein modules with specific structures and functions are developed through experimental and computational tools based on natural functional protein sequences. Through recombination and heterologous expression, these artificial protein modules become keys to material fabrication. Undergoing an assembly process similar to supramolecular self-assembly of proteins in cells, biomimetic modules can be fabricated for formation of macroscopic materials such as fibers and adhesives. This strategy inspired by synthetic biology and supramolecular chemistry is important for improving target protein yields and assembly integrity. It also preserves and optimizes the mechanical functions of structural proteins, accelerating the design and fabrication of artificial protein materials.In this Account, we overview recent studies on fabricating biomimetic protein materials to elucidate the concept of modular assembly. We discuss the design of biomimetic structural proteins at the molecular level, providing a wealth of details determining the bulk properties of materials. Additinally, we describe the modular self-assembly and assembly driven by inducing molecules, and mechanical properties and applications of resulting fibers. We used these strategies to develop fiber materials with high tensile strength, high toughness, and properties such as anti-icing and high-temperature resistance. We also extended this approach to design protein-based adhesives with ultra-strong adhesion, biocompatibility, and biodegradability for surgical applications such as wound sealing and healing. Other protein materials, including films and hydrogels, have been developed through chemical assembly routes. Finally, we describe exploiting synthetic biology and chemistry to overcome bottlenecks in structural protein modular design, biosynthesis, and material assembly and our perspectives for future development in structural biomaterials.

Programmable nanocomposites of cellulose nanocrystals and zwitterionic hydrogels for soft robotics

Stimuli-responsive hydrogels have garnered significant attention as a versatile class of soft actuators. Introducing anisotropic properties, and shape-change programmability to responsive hydrogels promises a host of opportunities in the development of soft robots. Herein we report the synthesis of pH-responsive hydrogel nanocomposites with predetermined microstructural anisotropy, shape-transformation, and self-healing. Our hydrogel nanocomposites are largely composed of zwitterionic monomers and asymmetric cellulose nanocrystals. While the zwitterionic nature of the network imparts both self-healing and cytocompatibility to our hydrogel nanocomposites, the shear-induced alignment of cellulose nanocrystals renders their anisotropic swelling and mechanical properties. Thanks to the self-healing properties, we utilized a cut-and-paste approach to program reversible, and complex deformation into our hydrogels. As a proof-of-concept, we demonstrated the transport of light cargo using tethered and untethered soft robots made from our hydrogels. We believe the proposed material system introduce a powerful toolbox for the development of future generations of biomedical soft robots.

Protein fibers with self-recoverable mechanical properties via dynamic imine chemistry

The manipulation of internal interactions at the molecular level within biological fibers is of particular importance but challenging, severely limiting their tunability in macroscopic performances and applications. It thus becomes imperative to explore new approaches to enhance biological fibers' stability and environmental tolerance and to impart them with diverse functionalities, such as mechanical recoverability and stimulus-triggered responses. Herein, we develop a dynamic imine fiber chemistry (DIFC) approach to engineer molecular interactions to fabricate strong and tough protein fibers with recoverability and actuating behaviors. The resulting DIF fibers exhibit extraordinary mechanical performances, outperforming many recombinant silks and synthetic polymer fibers. Remarkably, impaired DIF fibers caused by fatigue or strong acid treatment are quickly recovered in water directed by the DIFC strategy. Reproducible mechanical performance is thus observed. The DIF fibers also exhibit exotic mechanical stability at extreme temperatures (e.g., -196 °C and 150 °C). When triggered by humidity, the DIFC endows the protein fibers with diverse actuation behaviors, such as self-folding, self-stretching, and self-contracting. Therefore, the established DIFC represents an alternative strategy to strengthen biological fibers and may pave the way for their high-tech applications.

Biohybrid Soft Robots Powered by Myocyte: Current Progress and Future Perspectives

Myocyte-driven robots, a type of biological actuator that combines myocytes with abiotic systems, have gained significant attention due to their high energy efficiency, sensitivity, biocompatibility, and self-healing capabilities. These robots have a unique advantage in simulating the structure and function of human tissues and organs. This review covers the research progress in this field, detailing the benefits of myocyte-driven robots over traditional methods, the materials used in their fabrication (including myocytes and extracellular materials), and their properties and manufacturing techniques. Additionally, the review explores various control methods, robot structures, and motion types. Lastly, the potential applications and key challenges faced by myocyte-driven robots are discussed and summarized.

Bioinspired Fast Room-Temperature Self-Healing, Robust, Adhesive, and AIE Fluorescent Waterborne Polyurethane via Hierarchical Hydrogen Bonds and Use as a Strain Sensor

Developing a new generation of ecofriendly water-based polymeric materials that integrate mechanical robustness, fast room-temperature self-healing, adhesive, and fluorescence remains a formidable challenge. Herein, inspired by titin protein, a series of novel waterborne polyurethanes (WPU-CHZ-NAGA) containing irregular 6-fold and diamide hydrogen bonds are synthesized by introducing carbohydrazide (CHZ) and N,N-bis(2-hydroxyethyl)-3-amino propionyl glycinamide (HO-NAGA-OH) groups. The representative WPU-CHZ₂-NAGA₃ exhibits outstanding mechanical properties (tensile strength of 36.58 MPa, tearing energy of 81.2 kJ m^-2, and toughness of 125.82 MJ m^-3) and fast room-temperature self-healing ability with the aid of ethanol (≥90% within 8 h) originated from hierarchical hydrogen bonds. These properties are superior to those of most of the reported room-temperature self-healing polymer materials. Benefiting from plentiful hydrogen bonds, the WPU matrix achieves excellent adhesive properties without heating or adding curing agents. Interestingly, WPU-CHZ₂-NAGA₃ film emits inherent blue fluorescence due to the aggregation-induced emission effect of tertiary amine groups, and its potential applications in information encryption and anticounterfeiting are further demonstrated. Specially, a eutectic gel strain sensor is also fabricated with WPU-CHZ₂-NAGA₃ and deep eutectic solvent by a simple physical blending method, which can be used to monitor the movement of human fingers and wrists as well as the change in body temperature. In summary, this work provides new insight into the design and synthesis of multifunctional WPU with fast room-temperature self-healing and high mechanical properties.

Unusual Temperature Dependence of Water Sorption in Semicrystalline Hydrogels

Water vapor sorption is a ubiquitous phenomenon in nature and plays an important role in various applications, including humidity regulation, energy storage, thermal management, and water harvesting. In particular, capturing moisture at elevated temperatures is highly desirable to prevent dehydration and to enlarge the tunability of water uptake. However, owing to the thermodynamic limit of conventional materials, sorbents inevitably tend to capture less water vapor at higher temperatures, impeding their broad applications. Here, an inverse temperature dependence of water sorption in poly(ethylene glycol) (PEG) hydrogels, where their water uptake can be doubled with increasing temperature from 25 to 50 °C, is reported. With mechanistic modeling of water-polymer interactions, this unusual water sorption is attributed to the first-order phase transformation of PEG structures, and the key parameters for a more generalized strategy in materials development are identified. This work elucidates a new regime of water sorption with an unusual temperature dependence, enabling a promising engineering space for harnessing moisture and heat.

In Situ Grown Silver-Polymer Framework with Coordination Complexes for Functional Artificial Tissues

Self-sensing actuators are critical to artificial robots with biomimetic proprio-/exteroception properties of biological neuromuscular systems. Existing add-on approaches, which physically blend heterogeneous sensor/actuator components, fall short of yielding satisfactory solutions, considering their suboptimal interfaces, poor adhesion, and electronic/mechanical property mismatches. Here, a single homogeneous material platform is reported by creating a silver-polymer framework (SPF), thus realizing the seamless sensing-actuation unification. The SPF-enabled elastomer is highly stretchable (1200%), conductive (0.076 S m^-1 ), and strong (0.76 MPa in-strength), where the stretchable polymer matrix synthesis and in situ silver nanoparticles reduction are accomplished simultaneously. Benefiting from the multimodal sensing capability from its architecture itself (mechanical and thermal cues), self-sensing actuation (proprio-deformations and external stimuli perceptions) is achieved for the SPF-based pneumatic actuator, alongside an excellent load-lifting attribute (up to 3700 times its own weight), substantiating its advantage of the unified sensing-actuation feature in a single homogenous material. In view of its human somatosensitive muscular systems imitative functionality, the reported SPF bodes well for use with next-generation functional tissues, including artificial skins, human-machine interfaces, self-sensing robots, and otherwise dynamic materials.

Room-temperature self-healing polyurethane-cellulose nanocrystal composites with strong strength and toughness based on dynamic bonds

Self-healing materials suffer from a trade-off relationship between their self-healing ability and mechanical strength, which limits their applications. Therefore, we developed a room-temperature self-healing supramolecular composite based on polyurethane (PU) elastomer, cellulose nanocrystals (CNCs), and multiple dynamic bonds. In this system, the abundant hydroxyl groups on the surfaces of the CNCs form multiple hydrogen bonds with the PU elastomer, yielding a dynamic physical cross-linking network. This dynamic network enables self-healing without degrading the mechanical properties. As a result, the obtained supramolecular composites exhibited high tensile strength (24.5 ± 2.3 MPa), good elongation at break (1484.8 ± 74.9 %), favourable toughness (156.4 ± 31.1 MJ m^-3, which is equivalent to that of spider silk and 5.1-times higher than that of aluminium), and excellent self-healing efficiency (95 ± 1.9 %). Notably, the mechanical properties of the supramolecular composites were almost completely retained after reprocessing three times. Further, using these composites, flexible electronic sensors were prepared and tested. In summary, we have reported a method for preparing supramolecular materials having high toughness and room temperature self-healing ability that have applications in flexible electronics.

Skin-interfaced electronics: A promising and intelligent paradigm for personalized healthcare

Skin-interfaced electronics (skintronics) have received considerable attention due to their thinness, skin-like mechanical softness, excellent conformability, and multifunctional integration. Current advancements in skintronics have enabled health monitoring and digital medicine. Particularly, skintronics offer a personalized platform for early-stage disease diagnosis and treatment. In this comprehensive review, we discuss (1) the state-of-the-art skintronic devices, (2) material selections and platform considerations of future skintronics toward intelligent healthcare, (3) device fabrication and system integrations of skintronics, (4) an overview of the skintronic platform for personalized healthcare applications, including biosensing as well as wound healing, sleep monitoring, the assessment of SARS-CoV-2, and the augmented reality-/virtual reality-enhanced human-machine interfaces, and (5) current challenges and future opportunities of skintronics and their potentials in clinical translation and commercialization. The field of skintronics will not only minimize physical and physiological mismatches with the skin but also shift the paradigm in intelligent and personalized healthcare and offer unprecedented promise to revolutionize conventional medical practices.

Ultra-stretchable and biodegradable elastomers for soft, transient electronics

As rubber-like elastomers have led to scientific breakthroughs in soft, stretchable characteristics-based wearable, implantable electronic devices or relevant research fields, developments of degradable elastomers with comparable mechanical properties could bring similar technological innovations in transient, bioresorbable electronics or expansion into unexplored areas. Here, we introduce ultra-stretchable, biodegradable elastomers capable of stretching up to ~1600% with outstanding properties in toughness, tear-tolerance, and storage stability, all of which are validated by comprehensive mechanical and biochemical studies. The facile formation of thin films enables the integration of almost any type of electronic device with tunable, suitable adhesive strengths. Conductive elastomers tolerant/sensitive to mechanical deformations highlight possibilities for versatile monitoring/sensing components, particularly the strain-tolerant composites retain high levels of conductivities even under tensile strains of ~550%. Demonstrations of soft electronic grippers and transient, suture-free cardiac jackets could be the cornerstone for sophisticated, multifunctional biodegradable electronics in the fields of soft robots and biomedical implants.

Self-Healing of Recombinant Spider Silk Gel and Coating

Self-healing properties, originating from the natural healing process, are highly desirable for the fitness-enhancing functionality of biomimetic materials. Herein, we fabricated the biomimetic recombinant spider silk by genetic engineering, in which Escherichia coli (E. coli) was employed as a heterologous expression host. The self-assembled recombinant spider silk hydrogel was obtained through the dialysis process (purity > 85%). The recombinant spider silk hydrogel with a storage modulus of ~250 Pa demonstrated autonomous self-healing and high strain-sensitive properties (critical strain ~50%) at 25 °C. The in situ small-angle X-ray scattering (in situ SAXS) analyses revealed that the self-healing mechanism was associated with the stick-slip behavior of the β-sheet nanocrystals (each of ~2-4 nm) based on the slope variation (i.e., ~-0.4 at 100%/200% strains, and ~-0.9 at 1% strain) of SAXS curves in the high q-range. The self-healing phenomenon may occur through the rupture and reformation of the reversible hydrogen bonding within the β-sheet nanocrystals. Furthermore, the recombinant spider silk as a dry coating material demonstrated self-healing under humidity as well as cell affinity. The electrical conductivity of the dry silk coating was ~0.4 mS/m. Neural stem cells (NSCs) proliferated on the coated surface and showed a 2.3-fold number expansion after 3 days of culture. The biomimetic self-healing recombinant spider silk gel and thinly coated surface may have good potential in biomedical applications.

Machine-guided path sampling to discover mechanisms of molecular self-organization

Molecular self-organization driven by concerted many-body interactions produces the ordered structures that define both inanimate and living matter. Here we present an autonomous path sampling algorithm that integrates deep learning and transition path theory to discover the mechanism of molecular self-organization phenomena. The algorithm uses the outcome of newly initiated trajectories to construct, validate and-if needed-update quantitative mechanistic models. Closing the learning cycle, the models guide the sampling to enhance the sampling of rare assembly events. Symbolic regression condenses the learned mechanism into a human-interpretable form in terms of relevant physical observables. Applied to ion association in solution, gas-hydrate crystal formation, polymer folding and membrane-protein assembly, we capture the many-body solvent motions governing the assembly process, identify the variables of classical nucleation theory, uncover the folding mechanism at different levels of resolution and reveal competing assembly pathways. The mechanistic descriptions are transferable across thermodynamic states and chemical space.

Room-Temperature Self-Healing Soft Composite Network with Unprecedented Crack Propagation Resistance Enabled by a Supramolecular Assembled Lamellar Structure

Soft self-healing materials are compelling candidates for stretchable devices because of their excellent compliance, extensibility, and self-restorability. However, most existing soft self-healing polymers suffer from crack propagation and irreversible fatigue failure due to easy breakage of their dynamic amorphous, low-energy polymer networks. Herein, inspired by distinct structure-property relationship of biological tissues, a supramolecular interfacial assembly strategy of preparing soft self-healing composites with unprecedented crack propagation resistance is proposed by structurally engineering preferentially aligned lamellar structures within a dynamic and superstretchable poly(urea-ureathane) matrix (which is elongated to 24 750× its original length). Such a design affords a world-record fracture energy (501.6 kJ m^-2 ), ultrahigh fatigue threshold (4064.1 J m^-2 ), and outstanding elastic restorability (dimensional recovery from 13 times elongation), and preserving low modulus (1.2 MPa), high stretchability (3200%), and high room-temperature self-healing efficiency (97%). Thereby, the resultant composite represents the best of its kind and even surpasses most biological tissues. The lamellar 2D transition-metal carbide/carbonitride (MXene) structure also leads to a relatively high in-plane thermal conductivity, enabling composites as stretchable thermoconductive skins applied in joints of robotics to thermal dissipation. The present work illustrates a viable approach how autonomous self-healing, crack tolerance, and fatigue resistance can be merged in future material design.

Biodegradable electrohydraulic actuators for sustainable soft robots

Combating environmental pollution demands a focus on sustainability, in particular from rapidly advancing technologies that are poised to be ubiquitous in modern societies. Among these, soft robotics promises to replace conventional rigid machines for applications requiring adaptability and dexterity. For key components of soft robots, such as soft actuators, it is thus important to explore sustainable options like bioderived and biodegradable materials. We introduce systematically determined compatible materials systems for the creation of fully biodegradable, high-performance electrohydraulic soft actuators, based on various biodegradable polymer films, ester-based liquid dielectric, and NaCl-infused gelatin hydrogel. We demonstrate that these biodegradable actuators reliably operate up to high electric fields of 200 V/μm, show performance comparable to nonbiodegradable counterparts, and survive more than 100,000 actuation cycles. Furthermore, we build a robotic gripper based on biodegradable soft actuators that is readily compatible with commercial robot arms, encouraging wider use of biodegradable materials systems in soft robotics.

Aqueous spinning of robust, self-healable, and crack-resistant hydrogel microfibers enabled by hydrogen bond nanoconfinement

Robust damage-tolerant hydrogel fibers with high strength, crack resistance, and self-healing properties are indispensable for their long-term uses in soft machines and robots as load-bearing and actuating elements. However, current hydrogel fibers with inherent homogeneous structure are generally vulnerable to defects and cracks and thus local mechanical failure readily occurs across fiber normal. Here, inspired by spider spinning, we introduce a facile, energy-efficient aqueous pultrusion spinning process to continuously produce stiff yet extensible hydrogel microfibers at ambient conditions. The resulting microfibers are not only crack-insensitive but also rapidly heal the cracks in 30 s by moisture, owing to their structural nanoconfinement with hydrogen bond clusters embedded in an ionically complexed hygroscopic matrix. Moreover, the nanoconfined structure is highly energy-dissipating, moisture-sensitive but stable in water, leading to excellent damping and supercontraction properties. This work creates opportunities for the sustainable spinning of robust hydrogel-based fibrous materials towards diverse intelligent applications.

Protein-Based Biological Materials: Molecular Design and Artificial Production

Polymeric materials produced from fossil fuels have been intimately linked to the development of industrial activities in the 20th century and, consequently, to the transformation of our way of living. While this has brought many benefits, the fabrication and disposal of these materials is bringing enormous sustainable challenges. Thus, materials that are produced in a more sustainable fashion and whose degradation products are harmless to the environment are urgently needed. Natural biopolymers─which can compete with and sometimes surpass the performance of synthetic polymers─provide a great source of inspiration. They are made of natural chemicals, under benign environmental conditions, and their degradation products are harmless. Before these materials can be synthetically replicated, it is essential to elucidate their chemical design and biofabrication. For protein-based materials, this means obtaining the complete sequences of the proteinaceous building blocks, a task that historically took decades of research. Thus, we start this review with a historical perspective on early efforts to obtain the primary sequences of load-bearing proteins, followed by the latest developments in sequencing and proteomic technologies that have greatly accelerated sequencing of extracellular proteins. Next, four main classes of protein materials are presented, namely fibrous materials, bioelastomers exhibiting high reversible deformability, hard bulk materials, and biological adhesives. In each class, we focus on the design at the primary and secondary structure levels and discuss their interplays with the mechanical response. We finally discuss earlier and the latest research to artificially produce protein-based materials using biotechnology and synthetic biology, including current developments by start-up companies to scale-up the production of proteinaceous materials in an economically viable manner.

A Full-Device Autonomous Self-Healing Stretchable Soft Battery from Self-Bonded Eutectogels

Next-generation energy storage devices should be soft, stretchable, and self-healable. Previously reported self-healable batteries mostly possess limited stretchability and rely on healable electrodes or electrolytes rather than achieving full-device self-healability. Herein, an all-component self-bonding strategy is reported to obtain an all-eutectogel soft battery (AESB) that simultaneously achieves full-cell autonomous self-healability and omnidirectional intrinsic stretchability (>1000% areal strain) over a broad temperature range (-20~60 °C). Without requiring any external stimulus, the five-layered soft battery can efficiently recover both its mechanical and electrochemical performance at full-cell level. The developed AESB can be easily configured into various 3D architectures with highly interfacial compatible eutectogel electrodes, electrolyte, and substrate, presenting an excellent opportunity for the development of embodied energy technologies. The present work provides a general and user-friendly soft electronic material platform for fabricating a variety of intrinsic self-healing stretchable multi-layered electronics, which are promising beyond the field of energy storage, such as displays, sensors, circuits, and soft robots.

Self-Healing Polymeric Soft Actuators

Natural evolution has provided multicellular organisms with sophisticated functionalities and repair mechanisms for surviving and preserve their functions after an injury and/or infection. In this context, biological systems have inspired material scientists over decades to design and fabricate both self-healing polymeric materials and soft actuators with remarkable performance. The latter are capable of modifying their shape in response to environmental changes, such as temperature, pH, light, electrical/magnetic field, chemical additives, etc. In this review, we focus on the fusion of both types of materials, affording new systems with the potential to revolutionize almost every aspect of our modern life, from healthcare to environmental remediation and energy. The integration of stimuli-triggered self-healing properties into polymeric soft actuators endow environmental friendliness, cost-saving, enhanced safety, and lifespan of functional materials. We discuss the details of the most remarkable examples of self-healing soft actuators that display a macroscopic movement under specific stimuli. The discussion includes key experimental data, potential limitations, and mechanistic insights. Finally, we include a general table providing at first glance information about the nature of the external stimuli, conditions for self-healing and actuation, key information about the driving forces behind both phenomena, and the most important features of the achieved movement.

Providing New Insights on the Molecular Properties and Thermal Stability of Ovotransferrin and Lactoferrin

Ovotransferrin (OVT) is a multi-functional protein showing over 50% homology with Bovine lactoferrin (BLF) and human lactoferrin (HLF), which have the potential to be a substitute for lactoferrin (LF) due to the limited production of LF. To explore the substitutability of OVT, the molecular properties and thermal stability of OVT, BLF and HLF were characterized because these properties will affect the processing quality and biological activities of protein products when exposed to different processing conditions (e.g., temperature, pH, ion strength). The results showed that although obviously different isoelectric point (5.31, 9.12 and 8.75 for OVT, BLF and HLF, respectively), particle size distribution and hydrophobicity were found, they exhibited good dispersity because of high potential value. They showed an endothermic peak at 80.64 °C, 65.71 °C and 90.01 °C, respectively, and the denaturation temperature varied at different pH and ionic strength. OVT and BLF were more susceptible to heating at pH 5.0 as reflected by the decline of denaturation temperature (21.78 °C shift for OVT and 5.81 °C shift for BLF), while HLF could remain stable. Compared with BLF, OVT showed higher secondary structure stability at pH 7.0 and 9.0 with heating. For example, the α-helix content of OVT changed from 20.35% to 15.4% at pH 7.0 after heating, while that of BLF changed from 20.05% to 6.65%. The increase on fluorescence intensity and redshifts on the maximum wavelength after heating indicated the changes of tertiary structure of them. The turbidity measurements showed that the thermal aggregation degree of OVT was lower than BLF and HLF at pH 7.0 (30.98%, 59.53% and 35.66%, respectively) and pH 9.0 (4.83%, 12.80% and 39.87%, respectively). This work demonstrated the similar molecular properties and comparable thermal stability of OVT to BLF and HLF, which can offer a useful reference for the substitute of LF by OVT.

Vascular smooth muscle-inspired architecture enables soft yet tough self-healing materials for durable capacitive strain-sensor

Catastrophically mechanical failure of soft self-healing materials is unavoidable due to their inherently poor resistance to crack propagation. Here, with a model system, i.e., soft self-healing polyurea, we present a biomimetic strategy of surpassing trade-off between soft self-healing and high fracture toughness, enabling the conversion of soft and weak into soft yet tough self-healing material. Such an achievement is inspired by vascular smooth muscles, where core-shell structured Galinstan micro-droplets are introduced through molecularly interfacial metal-coordinated assembly, resulting in an increased crack-resistant strain and fracture toughness of 12.2 and 34.9 times without sacrificing softness. The obtained fracture toughness is up to 111.16 ± 8.76 kJ/m², even higher than that of Al and Zn alloys. Moreover, the resultant composite delivers fast self-healing kinetics (1 min) upon local near-infrared irradiation, and possesses ultra-high dielectric constants (~14.57), thus being able to be fabricated into sensitive and self-healing capacitive strain-sensors tolerant towards cracks potentially evolved in service.

Elastic Fluorescent Protein-Based Down-Converting Optical Films for Flexible Display

Protein-based material design provides great advantages to developing smart biomaterials with tunable structures and desired functions. They have been widely used in many biomedical applications including tissue engineering and drug delivery. However, protein-based materials are not yet widely used in optoelectronic materials despite their excellent optical and tunable mechanical properties. Here, we synthesized engineered fluorescent proteins (FPs) fused with elastic protein for the development of optoelectrical down-converting optical filters for flexible display materials. We synthesized sequence-specific FPs to tune blue, green, yellow, and red colors and fused them with elastic protein to tune mechanical properties. We fabricated flexible self-supporting film materials and characterized mechanical properties and down-converting optical properties. We also fabricated a hybrid light-emitting diode (LED) to down convert blue to desired green, red, and white colors. Furthermore, we constructed a flexible white LED using organic LED as a flexible substrate. Our modular synthesis approach of tunable bio-optoelectrical material approaches will be useful to design future biocompatible and flexible display materials and technologies.