Surface-initiated self-healing of polymers in aqueous media

Strong Hydrophobic Interaction of High Molecular Weight Chitosan in Aqueous Solution

Chitosan is a versatile bioactive polysaccharide in various industries, such as pharmaceuticals and environmental applications, owing to its abundance, biodegradability, biocompatibility, and antibacterial properties. To effectively harness its potential for various purposes, it is crucial to understand the mechanisms of its interaction in water. This study investigates the interactions between high molecular weight (HMW, >150 kDa) chitosan and four different functionalized self-assembled monolayers (SAMs) at three different pHs (3.0, 6.5, and 8.5) using a surface forces apparatus (SFA). We report that HMW chitosan exhibits the strongest adhesion to methyl-terminated SAM (CH3-SAM) at all pHs, showing potential for strong hydrophobic interactions against other molecules containing hydrophobic moieties. Noting that hydrogen bonding has been considered the dominating interaction mechanism of chitosan, the consequence of this study provides valuable insights into its applications in developing chitosan-based eco-friendly materials.

Stretchable, Self-Healable, and Durable Conductive Elastomer Derived from a Rationally Designed Covalently Cross-Linked Network

Silver nanowire (Ag NW)-based elastic conductors have been considered a promising candidate for key stretchable electrodes in wearable devices. However, the weak interface interaction of Ag NWs and elastic substrates leads to poor durability of electronic devices. For everyday usage, an additional self-healing ability is required to resist scratching and damage. Therefore, robust Ag NW-based elastic conductors possessing stretchability, self-healing, and stability are highly desirable and challenging. Here, we present a universal interface tailoring strategy that introduces thiols onto the dynamically cross-linked elastic substrate surface. The surface thiol groups strongly interact with Ag NWs through Ag-S bonds, forming the stable conductive layer on the elastic substrate. At elevated temperatures, the Ag NWs are partially embedded in the surface of the elastic substrate and a buffer layer is formed to release the concentrated stress. As a result, the formed Ag NW-based elastic conductor displays the combination of good conductivity, high stretchability (>1000%), efficient self-healing capability (>95%), and remarkable stability. Besides, the Ag NW-based elastic conductor combining the good properties mentioned above is suitable for fabricating a sensitive and durable strain sensor against cyclic strain. The presented strategy can be considered a versatile and effective route to generating other surface thiol-rich covalently cross-linked elastomers with dynamic disulfide bonds.

Catechol redox maintenance in mussel adhesion

Catechol-functionalized proteins in mussel holdfasts are essential for underwater adhesion and cohesion and have inspired countless synthetic polymeric materials and devices. However, as catechols are prone to oxidation, long-term performance and stability of these inventions awaits effective antioxidation strategies. In mussels, catechol-mediated interactions are stabilized by 'built-in' homeostatic redox reservoirs that restore catechols oxidized to quinones. Mussel byssus has a typical 'core-shell' architecture in which the core is a degradable fibrous block copolymer consisting of collagen and fibroin coated by robust protein networks stabilized by bis-catecholato-metal and tris-catecholato-metal ion complexes. The coating is well-adapted to protect the core against abrasion, hydrolysis and microbial attack, but it is not impervious to oxidative damage, which, during function, is promptly repaired by redox poise via coacervated catechol-rich and thiol-rich reducing interlayers and inclusions. However, when the e- and H+ equivalents from these reducing reservoirs are depleted, coating damage accumulates, leading to exposure of the vulnerable core to environmental attack. Heeding and translating these strategies is essential for deploying catechols with longer service lifetimes and designing more sustainable next-generation polymeric adhesives.

Adhesion Mechanism, Applications, and Challenges of Ocular Tissue Adhesives

Corneal injury is prevalent in ophthalmology, with mild cases impacting vision and severe cases potentially resulting in permanent blindness. In clinical practice, standard treatments for corneal injury involve transplantation surgery combined with pharmacological therapy. However, surgical sutures exhibit several limitations, which can be overcome using tissue adhesives. With recent advances in biomedical materials, the use of ophthalmic tissue adhesives has expanded beyond wound closure, including tissue filling and drug delivery. Furthermore, the use of tissue adhesives has demonstrated promising outcomes in drug delivery, ophthalmic disease diagnosis, and biological scaffolds. This study briefly introduces common adhesion mechanisms and their applications in ophthalmology, aiming to increase interest in tissue adhesives and clinical ophthalmic treatment.

Self-healing Hydrophobic Antifouling Polymers with Fe3+-Catechol Coordination Interaction

Hydrophobic antifouling polymers capable of self-healing performance are highly desirable for industrial applications. However, the construction of self-healing, hydrophobic antifouling polymers is challenging considering their complex fouling environments, which are humid in aqueous environment. In this work, a self-healing hydrophobic polymer containing Fe3+-catechol coordination applicable to antifouling is synthesized. The hydrophobic fluoroalkyl segments in the polymers formed unique domains dispersed in a polydimethylsiloxane matrix. The as-synthesized polymers can completely restore their tensile strength, and their self-healing efficiency is above 90% in both artificial seawater and pure water because of the dynamic Fe3+-catechol coordination interactions. The as-synthesized polymer exhibited self-healing and antifouling properties against common marine bacteria. The colony adhesion and self-healing processes of the damaged coating in artificial seawater containing marine bacteria are characterized by laser confocal microscopy. This strategy may be useful for the development of future polymeric antifouling materials.

Study on the discoloration phenomenon caused by iron ion oxidation in Boston ivy pads and its effect on adhesion force

Boston ivy has received much attention from researchers owing to its exceptional climbing abilities. However, many aspects of their adhesion behavior remain unresolved. Our research has discovered a phenomenon of oxidation and discoloration in Boston ivy pads, which leads to a significant decrease in adhesion force. In this study, we conducted a comprehensive investigation into the oxidation discoloration phenomenon. Through XPS analysis, we confirmed that the transition from Fe2+ to Fe3+ in the pad is the primary cause of the oxidation discoloration reaction. Furthermore, by conducting in situ adhesion testing using AFM, we observed a decrease in adhesion during the oxidation of iron ions. The magnitude of adhesion is closely related to the amount of pyrocatechol. Following the oxidation reaction, iron ions chelate with more pyrocatechol, resulting in a decrease in the available pyrocatechol content for adhesion. To validate this mechanism, we designed and prepared a biomimetic composite adhesion surface of a PDMS hydrogel. This composite surface improved oxidation resistance through the hydrogel, demonstrating improved adhesion performance. These findings offer promising prospects for the application of bionic materials in various fields.

Responsive Protection of Magnesium Alloys From Multicorrosive Media by Constructing Nanofluidic Channels in Self-Repairing Coatings

Low-density magnesium (Mg) alloys are excellent engineering materials, and can significantly reduce energy consumption by replacing existing steel and aluminum materials. However, Mg species are susceptible to corrosion, especially in harsh environments (high-temperature or acidic), severely limiting the range of practical applications. Here, 2D covalent organic framework (COF) is synthesized with pore diameters ranging from 1.5 to 2.9 nm to obtain ultrafast nanofluidic channels. Loaded with silver (Ag+) ions, 2-mercaptobenzimidazole (2-MB) inhibitors are immobilized in the COF channels through the silver bridges. Based on the strong metal-complexing capability, Ag+ ions precipitated with various corrosive media (Cl-, Br-, I-, SO3 2-, S2-, S2O3 2- SO4 2-, CO3 2-, PO4 3-); meanwhile, the 2-MB inhibitors are rapidly released through the nanofluidic channels, forming a passivation film as a corrosion barrier to protect the Mg substrate. After integration with commercial polyethersulfone (PES), the COF-based coating exhibits high repairing capability achieving 100% damage restoration within 7 h, outperforming all existing coatings of Mg alloys. Notably, the coating shows almost complete protection of Mg alloys after being treated in respective 473 K, acidic (pH ≈4.0), and alkaline (pH ≈10.0) environments.

Enhanced Intrinsic Self-Healing Performance of Mussel Inspired Coating via In-Situ Cation Capture

Under damp or aquatic conditions, the corrosion products deposited on micro-cracks/pore sites bring about the failure of intrinsically healable organic coatings. Inspired by mussels, a composite coating of poly (methyl methacrylate-co-butyl acylate-co-dopamine acrylamide)/phenylalanine-functionalized boron nitride (PMBD/BN-Phe) is successfully prepared on the reinforcing steel, which exhibits excellent anti-corrosion and underwater self-healing capabilities. The self-healing property of PMBD is derived from the synergistic effect of hydrogen bonding and metal-ligand coordination bonding, and thereby the continuous generation of corrosion products can be significantly suppressed through in situ capture of cations by the catechol group. Furthermore, the corrosion protection ability can be remarkably improved by the labyrinth effect of BN and the inhibition role of Phe, and the desired interfacial compatibility can be formed by the hydrogen bonds between BN-Phe and PMBD matrix. The corrosion current density (icorr) of PMBD/BN-Phe coating is determined as 7.95 × 10-11 A cm-2. The low-frequency impedance modulus (|Z|f  =  0.0 1 Hz is remained at 3.47 × 109 Ω cm2, indicating an ultra-high self-healing efficiency (≈89.5%). It is anticipated to provide a unique strategy for development of an underwater self-healing coating and robust durability for application in anti-corrosion engineering of marine buildings.

Mussel-Bioinspired Lignin Adhesive for Wearable Bioelectrodes

As a natural "binder," lignin fixes cellulose in plants to foster growth and longevity. However, isolated lignin has a poor binding ability, which limits its biomedical applications. In this study, inspired by mussel adhesive proteins, acidic/basic amino acids (AAs) are introduced in alkali lignin (AL) to form ionic-π/spatial correlation interactions, followed by demethylation to create catechol residues for enhanced adhesion activity. Atomic force microscopy reveals that catechol residues are the primary adhesion structures, with basic AAs exhibiting superior synergistic effects compared to acidic AAs. Demethylated lysine-grafted AL exhibits the strongest adhesion force toward skin tissue. Molecular dynamic simulation and density functional theory calculations indicate that adhesion against skin tissue mainly results from hydrogen bonds and cation-π interactions, with the adhesion mechanism being based on the Gibbs free energy of the Schiff base reaction. In summary, a biomimetic electrode based on lignin inspired by mussel adhesive proteins is prepared; the presented method offers a straightforward strategy for the development of biomimetic adhesives. Furthermore, this mussel-inspired adhesive can be used as a wearable bioelectrode in biomedical applications.

Polymeric silk fibroin hydrogel as a conductive and multifunctional adhesive for durable skin and epidermal electronics

Silk fibroin (SF)-based hydrogels are promising multifunctional adhesive candidates for real-world applications in tissue engineering, implantable bioelectronics, artificial muscles, and artificial skin. However, developing conductive SF-based hydrogels that are suitable for the micro-physiological environment and maintain their physical and chemical properties over long periods of use remains challenging. Herein, we developed an ion-conductive SF hydrogel composed of glycidyl methacrylate silk fibroin (SilMA) and bioionic liquid choline acylate (ChoA) polymer chains, together with the modification of acrylated thymine (ThyA) and adenine (AdeA) functional groups. The resulting polymeric ion-conductive SF composite hydrogel demonstrated high bioactivity, strong adhesion strength, good mechanical compliance, and stretchability. The formed hydrogel network of ChoA chains can coordinate with the ionic strength in the micro-physiological environment while maintaining the adaptive coefficient of expansion and stable mechanical properties. These features help to form a stable ion-conducting channel for the hydrogel. Additionally, the hydrogel network modified with AdeA and ThyA, can provide a strong adhesion to the surface of a variety of substrates, including wet tissue through abundant hydrogen bonding. The biocompatible and ionic conductive SF composite hydrogels can be easily prepared and incorporated into flexible skin or epidermal sensing devices. Therefore, our polymeric SF-based hydrogel has great potential and wide application to be an important component of many flexible electronic devices for personalized healthcare.

Ultra-Fast-Healing Glassy Hyperbranched Plastics Capable of Restoring 26.4 MPa Tensile Strength within One Minute at Room Temperature

The growing concern regarding widespread plastic pollution has propelled the development of sustainable self-healing plastics. Although considerable efforts have been dedicated to fabricating self-healing plastics, achieving rapid healing at room temperature is extremely challenging. Herein, we have developed an ultra-fast-healing glassy polyurethane (UGPU) by designing a hyperbranched molecular structure with a high density of multiple hydrogen bonds (H-bonds) on compliant acyclic heterochains and introducing trace water to form water bridge across the fractured surfaces. The compliant acyclic heterochains allow the dense multiple hydrogen bonds to form a frozen network, enabling tensile strength of up to 70 MPa and storage modulus of 2.5 GPa. The hyperbranched structure can drive the reorganization of the H-bonding network through the high mobility of the branched chains and terminals, thereby leading to self-healing ability at room temperature. Intriguingly, the presence of trace water vapor facilitates the formation of activated layers and the rearrangement of networks across the fractured UGPU sections, thereby enabling ultra-fast self-healing at room temperature. Consequently, the restored tensile strength after healing for 1 minute achieves a historic-record of 26.4 MPa. Furthermore, the high transparency (>90 %) and ultra-fast healing property of UGPU make it an excellent candidate for advanced optical and structural materials.

Facile Preparation and Study of Self-Healing Water-Absorbing Expanding Elastomers

The absorbent expansion elastomer plays a crucial role in engineering sealing and holds a promising future in this field as infrastructure continues to develop. Traditional materials have their limitations, especially when used in large construction projects where the integrity and reliability of the material are of utmost importance. In this work, a self-healing water-absorbing expansion elastomer was developed for continuous production at a large scale to monitor the sealing conditions of massive infrastructure projects. At room temperature, the material exhibited a repairing efficiency of 57.77 % within 2 h, which increased to 84.02 % after 12 h. This extended reaction time allowed for effective repairs when defects were detected. The material's strength can attain 3 MPa, placing it at the upper echelon among common self-healing materials, thereby granting it a certain level of durability in its application environment. The material's volume expansion rate reached 200-400 % to achieve effective sealing, and the functional filling of the filler endowed the material itself with a favorable external force induction effect and prevented heat accumulation. The conductive detection performance of the absorbent expansion elastomer was improved by utilizing triple self-healing strategies, including dipole-dipole interaction, ion cross-linked network, and externally-aided restoration materials. These strategies were combined with a double packing strategy to enhance the material's properties. This innovative elastomer can be applied in various fields such as tunnel construction, infrastructure development, aerospace sealing, and railway transportation, showcasing significant potential for diverse engineering applications.

Integrating hydrogels manipulate ECM deposition after spinal cord injury for specific neural reconnections via neuronal relays

A bioinspired hydrogel composed of hyaluronic acid-graft-dopamine (HADA) and a designer peptide HGF-(RADA)4-DGDRGDS (HRR) was presented to enhance tissue integration following spinal cord injury (SCI). The HADA/HRR hydrogel manipulated the infiltration of PDGFRβ+ cells in a parallel pattern, transforming dense scars into an aligned fibrous substrate that guided axonal regrowth. Further incorporation of NT3 and curcumin promoted axonal regrowth and survival of interneurons at lesion borders, which served as relays for establishing heterogeneous axon connections in a target-specific manner. Notable improvements in motor, sensory, and bladder functions resulted in rats with complete spinal cord transection. The HADA/HRR + NT3/Cur hydrogel promoted V2a neuron accumulation in ventral spinal cord, facilitating the recovery of locomotor function. Meanwhile, the establishment of heterogeneous neural connections across the hemisected lesion of canines was documented in a target-specific manner via neuronal relays, significantly improving motor functions. Therefore, biomaterials can inspire beneficial biological activities for SCI repair.

Reconfiguring hydrogel assemblies using a photocontrolled metallopolymer adhesive for multiple customized functions

Stimuli-responsive hydrogels with programmable shape changes are promising materials for soft robots, four-dimensional printing, biomedical devices and artificial intelligence systems. However, these applications require the fabrication of hydrogels with complex, heterogeneous and reconfigurable structures and customizable functions. Here we report the fabrication of hydrogel assemblies with these features by reversibly gluing hydrogel units using a photocontrolled metallopolymer adhesive. The metallopolymer adhesive firmly attached individual hydrogel units via metal-ligand coordination and polymer chain entanglement. Hydrogel assemblies containing temperature- and pH-responsive hydrogel units showed controllable shape changes and motions in response to these external stimuli. To reconfigure their structures, the hydrogel assemblies were disassembled by irradiating the metallopolymer adhesive with light; the disassembled hydrogel units were then reassembled using the metallopolymer adhesive with heating. The shape change and structure reconfiguration abilities allow us to reprogramme the functions of hydrogel assemblies. The development of reconfigurable hydrogel assemblies using reversible adhesives provides a strategy for designing intelligent materials and soft robots with user-defined functions.

Self-Healing Hydrogel Bioelectronics

Hydrogels have emerged as powerful building blocks to develop various soft bioelectronics because of their tissue-like mechanical properties, superior bio-compatibility, the ability to conduct both electrons and ions, and multiple stimuli-responsiveness. However, hydrogels are vulnerable to mechanical damage, which limits their usage in developing durable hydrogel-based bioelectronics. Self-healing hydrogels aim to endow bioelectronics with the property of repairing specific functions after mechanical failure, thus improving their durability, reliability, and longevity. This review discusses recent advances in self-healing hydrogels, from the self-healing mechanisms, material chemistry, and strategies for multiple properties improvement of hydrogel materials, to the design, fabrication, and applications of various hydrogel-based bioelectronics, including wearable physical and biochemical sensors, supercapacitors, flexible display devices, triboelectric nanogenerators (TENGs), implantable bioelectronics, etc. Furthermore, the persisting challenges hampering the development of self-healing hydrogel bioelectronics and their prospects are proposed. This review is expected to expedite the research and applications of self-healing hydrogels for various self-healing bioelectronics.

Enhancing Adhesion Properties of Commodity Polymers through Thiol-Catechol Connectivities: A Case Study on Polymerizing Polystyrene-Telechelics via Thiol-Quinone Michael-Polyaddition

Segmented block copolymers with adhesive functionality bridges in between are synthesized through the combination of controlled radical polymerization (CRP) and thiol-quinone Michael-polyaddition. CRP provides a set of α,ω-dithiol polystyrenes (PS), which react as telechelics with a low molecular weight bisquinone, resulting in thiol-catechol connectivities (TCCs). By introducing as little as 3 mol % of TCC functionalities, the bonding of the polymer on dry and wet aluminum surfaces is significantly improved while keeping the integrity of the PS segments undisturbed to constitute favorable bulk properties. This improvement is evidenced by reaching up to 3.8 MPa adhesive strength, representing a 600% increase compared to nonfunctional PS.

Mechanically tough, adhesive, self-healing hydrogel promotes annulus fibrosus repair via autologous cell recruitment and microenvironment regulation

Annulus fibrosus (AF) defect is an important cause of disc re-herniation after discectomy. The self-regeneration ability of the AF is limited, and AF repair is always hindered by the inflammatory microenvironment after injury. Hydrogels represent one of the most promising materials for AF tissue engineering strategies. However, currently available commercial hydrogels cannot withstand the harsh mechanical load within intervertebral disc. In the present study, an innovative triple cross-linked oxidized hyaluronic acid (OHA)-dopamine (DA)- polyacrylamide (PAM) composite hydrogel, modified with collagen mimetic peptide (CMP) and supplied with transforming growth factor beta 1 (TGF-β1) (OHA-DA-PAM/CMP/TGF-β1 hydrogel) was developed for AF regeneration. The hydrogel exhibited robust mechanical strength, strong bioadhesion, and significant self-healing capabilities. Modified with collagen mimetic peptide, the hydrogel exhibited extracellular-matrix-mimicking properties and sustained the AF cell phenotype. The sustained release of TGF-β1 from the hydrogel was pivotal in recruiting AF cells and promoting extracellular matrix production. Furthermore, the composite hydrogel attenuated LPS-induced inflammatory response and promote ECM synthesis in AF cells via suppressing NFκB/NLRP3 pathway. In vivo, the composite hydrogel successfully sealed AF defects and alleviated intervertebral disk degeneration in a rat tail AF defect model. Histological evaluation showed that the hydrogel integrated well with host tissue and facilitated AF repair. The strategy of recruiting endogenous cells and providing an extracellular-matrix-mimicking and anti-inflammatory microenvironment using the mechanically tough composite OHA-DA-PAM/CMP/TGF-β1 hydrogel may be applicable for AF defect repair in the clinic. STATEMENT OF SIGNIFICANCE: Annulus fibrosus (AF) repair is challenging due to its limited self-regenerative capacity and post-injury inflammation. In this study, a mechanically tough and highly bioadhesive triple cross-linked composite hydrogel, modified with collagen mimetic peptide (CMP) and supplemented with transforming growth factor beta 1 (TGF-β1), was developed to facilitate AF regeneration. The sustained release of TGF-β1 enhanced AF cell recruitment, while both TGF-β1 and CMP could modulate the microenvironment to promote AF cell proliferation and ECM synthesis. In vivo, this composite hydrogel effectively promoted the AF repair and mitigated the intervertebral disc degeneration. This research indicates the clinical potential of the OHA-DA-PAM/CMP/TGF-β1 composite hydrogel for repairing AF defects.

Mussel-inspired PDA@PEDOT nanocomposite hydrogel with excellent mechanical strength, self-adhesive, and self-healing properties for a flexible strain sensor

Conductive hydrogel sensors have attracted attention for use in human motion monitoring detection, but integrating excellent biocompatibility, mechanical, self-adhesive, and self-healing properties, and high sensitivity into a hydrogel remains a challenge. In this work, a novel multifunctional conductive particle was designed and added to a polyacrylamide (PAM) matrix to prepare the hydrogel. It is worth noting that with the addition of polydopamine@poly(3,4-ethylenedioxythiophene) (PDA@PEDOT), the PAM/PDA@PEDOT hydrogel (PAPP hydrogel) showed excellent mechanical properties and high adhesion strength on different substrate surfaces. Meanwhile, the PAPP hydrogel shows outstanding self-healing properties, the mechanical properties of PAPP hydrogel broken from the middle recovered 92% tensile strength and 95% elongation at break after 12 h, respectively. Furthermore, assembled as strain wireless sensors, the PAPP sensor displays high sensitivity, where the gauge factor (GF) is 2.82, which can be used to accurately detect human facial micro-expressions and movements. Overall, the PAPP hydrogel with excellent mechanical, self-adhesive, and self-healing properties, and high sensitivity, demonstrated promise for use in wearable devices and bionic skins.

Synergistic Effect of Physical and Chemical Cross-Linkers Enhances Shape Fidelity and Mechanical Properties of 3D Printable Low-Modulus Polyesters

Three-dimensional (3D) printing is becoming increasingly prevalent in tissue engineering, driving the demand for low-modulus, high-performance, biodegradable, and biocompatible polymers. Extrusion-based direct-write (EDW) 3D printing enables printing and customization of low-modulus materials, ranging from cell-free printing to cell-laden bioinks that closely resemble natural tissue. While EDW holds promise, the requirement for soft materials with excellent printability and shape fidelity postprinting remains unmet. The development of new synthetic materials for 3D printing applications has been relatively slow, and only a small polymer library is available for tissue engineering applications. Furthermore, most of these polymers require high temperature (FDM) or additives and solvents (DLP/SLA) to enable printability. In this study, we present low-modulus 3D printable polyester inks that enable low-temperature printing without the need for solvents or additives. To maintain shape fidelity, we incorporate physical and chemical cross-linkers. These 3D printable polyester inks contain pendant amide groups as the physical cross-linker and coumarin pendant groups as the photochemical cross-linker. Molecular dynamics simulations further confirm the presence of physical interactions between different pendants, including hydrogen bonding and hydrophobic interactions. The combination of the two types of cross-linkers enhances the zero-shear viscosity and hence provides good printability and shape fidelity.

Compliant Clients: Catechols Exhibit Enhanced Solubility and Stability in Diverse Complex Coacervates

Polyelectrolyte coacervates, with their greater-than-water density, low interfacial energy, shear thinning viscosity, and ability to undergo structural arrest, mediate the formation of diverse load-bearing macromolecular materials in living organisms as well as in industrial material fabrication. Coacervates, however, have other useful attributes that are challenging to study given the metastability of coacervate colloidal droplets and a lack of suitable analytical methods. We adopt solution electrochemistry and nuclear magnetic resonance measurements to obtain remarkable insights about coacervates as solvent media for low-molecular-weight catechols. When catechols are added to dispersions of coacervated polyelectrolytes, there are two significant consequences: (1) catechols preferentially partition up to 260-fold into the coacervate phase, and (2) coacervates stabilize catechol redox potentials by up to +200 mV relative to the equilibrium solution. The results suggest that the relationship between phase-separated polyelectrolytes and their client molecules is distinct from that existing in aqueous solution and has the potential for insulating many redox-unstable chemicals.

Multifunctionality in Nature: Structure-Function Relationships in Biological Materials

Modern material design aims to achieve multifunctionality through integrating structures in a diverse range, resulting in simple materials with embedded functions. Biological materials and organisms are typical examples of this concept, where complex functionalities are achieved through a limited material base. This review highlights the multiscale structural and functional integration of representative natural organisms and materials, as well as biomimetic examples. The impact, wear, and crush resistance properties exhibited by mantis shrimp and ironclad beetle during predation or resistance offer valuable inspiration for the development of structural materials in the aerospace field. Investigating cyanobacteria that thrive in extreme environments can contribute to developing living materials that can serve in places like Mars. The exploration of shape memory and the self-repairing properties of spider silk and mussels, as well as the investigation of sensing-actuating and sensing-camouflage mechanisms in Banksias, chameleons, and moths, holds significant potential for the optimization of soft robot designs. Furthermore, a deeper understanding of mussel and gecko adhesion mechanisms can have a profound impact on medical fields, including tissue engineering and drug delivery. In conclusion, the integration of structure and function is crucial for driving innovations and breakthroughs in modern engineering materials and their applications. The gaps between current biomimetic designs and natural organisms are also discussed.

Hydrogel-Based Bioelectronics and Their Applications in Health Monitoring

Flexible bioelectronics exhibit promising potential for health monitoring, owing to their soft and stretchable nature. However, the simultaneous improvement of mechanical properties, biocompatibility, and signal-to-noise ratio of these devices for health monitoring poses a significant challenge. Hydrogels, with their loose three-dimensional network structure that encapsulates massive amounts of water, are a potential solution. Through the incorporation of polymers or conductive fillers into the hydrogel and special preparation methods, hydrogels can achieve a unification of excellent properties such as mechanical properties, self-healing, adhesion, and biocompatibility, making them a hot material for health monitoring bioelectronics. Currently, hydrogel-based bioelectronics can be used to fabricate flexible bioelectronics for motion, bioelectric, and biomolecular acquisition for human health monitoring and further clinical applications. This review focuses on materials, devices, and applications for hydrogel-based bioelectronics. The main material properties and research advances of hydrogels for health monitoring bioelectronics are summarized firstly. Then, we provide a focused discussion on hydrogel-based bioelectronics for health monitoring, which are classified as skin-attachable, implantable, or semi-implantable depending on the depth of penetration and the location of the device. Finally, future challenges and opportunities of hydrogel-based bioelectronics for health monitoring are envisioned.

Mussel-Inspired, Underwater Self-Healing Ionoelastomers Based on α-Lipoic Acid for Iontronics

Weak adhesion and lack of underwater self-healability hinder advancing soft iontronics particularly in wet environments like sweaty skin and biological fluids. Mussel-inspired, liquid-free ionoelastomers are reported based on seminal thermal ring-opening polymerization of a biomass molecule of α-lipoic acid (LA), followed by sequentially incorporating dopamine methacrylamide as a chain extender, N,N'-bis(acryloyl) cystamine, and lithium bis(trifluoromethanesulphonyl) imide (LiTFSI). The ionoelastomers exhibit universal adhesion to 12 substrates in both dry and wet states, superfast self-healing underwater, sensing capability for monitoring human motion, and flame retardancy. The underwater self-repairabilitiy prolongs over three months without deterioration, and sustains even when mechanical properties greatly increase. The unprecedented underwater self-mendability benefits synergistically from the maximized availability of dynamic disulfide bonds and diverse reversible noncovalent interactions endowed by carboxylic groups, catechols, and LiTFSI, along with the prevented depolymerization by LiTFSI and tunability in mechanical strength. The ionic conductivity reaches 1.4 × 10^-6 -2.7 × 10^-5 S m^-1 because of partial dissociation of LiTFSI. The design rationale offers a new route for creating a wide range of LA- and sulfur-derived supramolecular (bio)polymers with superior adhesion, healability, and other functionalities, and thus has technological implications for coatings, adhesives, binders and sealants, biomedical engineering and drug delivery, wearable and flexible electronics, and human-machine interfaces.

Recombinant Lignin Peroxidase with Superior Thermal Stability and Melanin Decolorization Efficiency in a Typical Human Skin-Mimicking Environment

Recently, the desire for a safe and effective method for skin whitening has been growing in the cosmetics industry. Commonly used tyrosinase-inhibiting chemical reagents exhibit side effects. Thus, recent studies have focused on performing melanin decolorization with enzymes as an alternative due to the low toxicity of enzymes and their ability to decolorize melanin selectively. Herein, 10 different isozymes were expressed as recombinant lignin peroxidases (LiPs) from Phanerochaete chrysosporium (PcLiPs), and PcLiP isozyme 4 (PcLiP04) was selected due to its high stability and activity at pH 5.5 and 37 °C, which is close to human skin conditions. In vitro melanin decolorization results indicated that PcLiP04 exhibited at least 2.9-fold higher efficiency than that of well-known lignin peroxidase (PcLiP01) in a typical human skin-mimicking environment. The interaction force between melanin films measured by a surface forces apparatus (SFA) revealed that the decolorization of melanin by PcLiP04 harbors a disrupted structure, possibly interrupting π-π stacking and/or hydrogen bonds. In addition, a 3D reconstructed human pigmented epidermis skin model showed a decrease in melanin area to 59.8% using PcLiP04, which suggests that PcLiP04 exhibits a strong potential for skin whitening.

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.

Adhesion and Cohesion Differences between Catechol- and Pyrogallol-Functionalized Chitosan

Marine-inspired phenolic compounds that exhibit underwater adhesion are used as biomedical adhesives under wet conditions. While these applications mainly use catechol and pyrogallol moieties that contain different numbers of hydroxyl groups on their benzene rings, how this difference affects adhesion and cohesion is not well understood. Herein, the chitosan backbone is functionalized with catechol and pyrogallol at similar modification rates (to give chitosan-catechol (CS-CA) and chitosan-pyrogallol (CS-GA), respectively) and their interaction energies are compared by using a surface forces apparatus (SFA). The phenolic moieties decrease the rigidity of the chitosan chain and increase solubility; consequently, CS-CA and CS-GA are more cohesive and adhesive than chitosan at pH 7.4. Moreover, the additional hydroxyl group of GA provides a further interacting chance; hence, CS-GA is more cohesive and adhesive than CS-CA. This study provides in-depth insight into interactions involving chitosan derivatives bearing introduced phenolic moieties that will help to develop biomedical adhesives.

Photo-and Heat-Induced Dismantlable Adhesion Interfaces Prepared by Layer-by-Layer Deposition

The development of a dismantlable adhesion technology that allows switching between bonding and debonding states using external stimuli is important for realizing renewable and sustainable material cycles. Controlling the adhesion interface is an effective approach to manipulate the adhesion strength; however, research on dismantlable systems focusing on the interface has not been proceeded. Recently, we demonstrated a novel dismantlable system based on a stimuli-responsive molecular layer comprising cleavable anthracene dimers, which strengthen the initial adhesive force by forming chemical bonds between the substrate and adhesive and can be dismantled when required via stimulation-induced bond breaking. Here, we evaluate the use of the anthracene-based molecular layer with different components for verifying its versatility in the adhesive/dismantling system. The formation of the cleavable molecular layer by the stacking of relevant molecules enabled its usage with two types of adhesives, an epoxy adhesive and a silane-modified polymer adhesive. The initial adhesive strengths were improved in both types of molecular layers by creating chemical bonds at the adhesion interfaces. Light irradiation or heating stimuli for 1 min reduced the peel strength by up to 65%, and dismantling occurred in the cleavable photodimer layer. This study expands the versatile applicability of the molecular layer-based dismantling system.

Non-isocyanate Polyurethane Coating with High Hardness, Superior Flexibility, and Strong Substrate Adhesion

Flexible hard coatings with strong adhesion are critical requirements for several foldable devices and marine applications; however, only a few such coatings have been reported. Herein, we report a non-isocyanate polyurethane (NIPU) coating prepared by the epoxy-oligosiloxane nanocluster-amine curing reaction and cyclic carbonate-amine polyaddition, where the former provides the coating with ceramic-like hardness and polymer-like flexibility while the latter polymerization results in NIPU with strong substrate adhesion. The coating is transparent (>92% transmittance), hard (5-7 H), and flexible (2 mm bending diameter). It has strong adhesion to various substrates including aluminum alloy, titanium, steel, glass, ceramic, epoxy, and polyethylene terephthalate (2-8 MPa), which can be attributed to the high density of polar groups in NIPU. Moreover, we can facilely endow the coating with anti-icing, self-cleaning, and anti-smudge capabilities by incorporating amine-terminated low-surface-tension polydimethylsiloxane (PDMS) to replace a part of the amine curing agent. Particularly, the mechanical properties of NIPU coatings are only slightly affected by the introduction of low-content PDMS since it intends to enrich on the surface. The novel coating has promising future for use in fields of foldable devices and marine applications.

Polydopamine-Reinforced Hemicellulose-Based Multifunctional Flexible Hydrogels for Human Movement Sensing and Self-Powered Transdermal Drug Delivery

The preparation of bio-based hydrogels with excellent mechanical properties, stable electrochemical properties, and self-adhesive properties remains a challenge. In this study, nano-polydopamine-reinforced hemicellulose-based hydrogels with typical multistage pore structures were prepared. The nanocomposite hydrogels exhibit stable mechanical properties and show no significant crushing phenomenon after 1000 cycles of cyclic compression. Its ultimate tensile strain was 101%, which is significantly higher than that of native skin. The shear adhesion strength of the hydrogel to skin tissue reaches 7.52 kPa, which is better than fibrin glue (Greenplast) (5 kPa), and the excellent adhesion property prolongs the service time of the hydrogel in biomedicine applications. The impedance of the hydrogel was reduced and the electrical conductivity was increased with the addition of nano-polydopamine. The prepared nanocomposite hydrogel can detect various body movements (even throat vibrations) in real time as a motion sensor while being able to rapidly load cationic drugs and facilitate transdermal introduction of electrically stimulated drug ions as a drug patch. It provides theoretical support for the fabrication of hemicellulose-based hydrogels with excellent properties through molecular design and nanoparticle reinforcement. This has important implications for the development of next-generation flexible materials suitable for health monitoring and self-administration.

Self-Healing Superwetting Surfaces, Their Fabrications, and Properties

The research on superwetting surfaces with a self-healing function against various damages has progressed rapidly in the recent decade. They are expected to be an effective approach to increasing the durability and application robustness of superwetting materials. Various methods and material systems have been developed to prepare self-healing superwetting surfaces, some of which mimic natural superwetting surfaces. However, they still face challenges, such as being workable only for specific damages, external stimulation to trigger the healing process, and poor self-healing ability in the water, marine, or biological systems. There is a lack of fundamental understanding as well. This article comprehensively reviews self-healing superwetting surfaces, including their fabrication strategies, essential rules for materials design, and self-healing properties. Self-healing triggered by different external stimuli is summarized. The potential applications of self-healing superwetting surfaces are highlighted. This article consists of four main sections: (1) the functional surfaces with various superwetting properties, (2) natural self-healing superwetting surfaces (i.e., plants, insects, and creatures) and their healing mechanism, (3) recent research development in various self-healing superwetting surfaces, their preparation, wetting properties in the air or liquid media, and healing mechanism, and (4) the prospects including existing challenges, our views and potential solutions to the challenges, and future research directions.

Mussel-Inspired Reversible Molecular Adhesion for Fabricating Self-Healing Materials

Nature offers inspiration for the development of high-performance synthetic materials. Extensive studies on the universal adhesion and self-healing behavior of mussel byssus reveal that a series of reversible molecular interactions occurring in byssal plaques and threads play an essential role, and the mussel-inspired chemistry can serve as a versatile platform for the design of self-healing materials. In this Perspective, we provide an overview of the recent progress in the detection, quantification, and utilization of mussel-inspired reversible molecular interactions, which includes the elucidation of their binding mechanisms via force-measuring techniques and the development of self-healing materials based on these dynamic interactions. Both conventional catechol-medicated interactions and newly discovered chemistry beyond the catechol groups are discussed, providing insights into the design strategies of advanced self-healing materials via mussel-inspired chemistry.

Self-healing polyacrylamide (PAAm) gels at room temperature based on complementary guanine and cytosine base pairs

The unique properties of self-healing materials hold great potential in many fields because they can repair themselves automatically and have an improved service time. In this study, polyacrylamide (PAAm) gels with complementary guanine and cytosine base pairs have been prepared. Herein, based on our previous research, cytosine (C) and guanine (G) (triple hydrogen) with biosafety were introduced to endow the PAAm with self-healing properties. Then, their self-healing properties were studied in detail and the results indicate that the optimized PAAm gel sample manifests a healing efficiency of 90% at room temperature. The excellent proportion of methacryloyloxyethyl isocyanate-cytosine/guanine (IEM-C/G) to AAm is 1 : 30, according to which the PAM-CG material exhibits enhanced stretchability and tensile strength. The major healing process occurs within 5 h at room temperature, and the material is completely healed after 20 h. Moreover, the healing time can be shortened at a higher temperature. The mechanical behaviors are tuned by changing the base pairs, and the gels exhibit recoverable mechanical performances. Therefore, this study provides a facile strategy for developing self-healing and biocompatible PAAm gels.

A Novel Cryogenic Adhesive Retaining Fluidity at Dry-Ice Temperature for Low-Temperature Scanning Electron Microscopy

Scanning electron microscopy operated at cryogenic temperature (cryo-SEM) is a powerful tool for investigating surface and cross-sectional nanostructures of water-containing samples. Typically, cryo-SEM samples are frozen just before observation in specific metal carriers. However, pre-frozen samples are also of interest, such as frozen food and freeze-stored animal samples. In such cases, sample mounting with a defined orientation is required, but there has been a lack of ideal conductive adhesives that can be used without increasing the sample temperature. Here, we developed a mixture of graphite oxide and 1,3-butanediol as an adhesive, capable of gluing samples at dry-ice temperature and is frozen below that temperature. Dispersion of graphite oxide increased the conductivity and reduced the charge-up contrast. Acquisition of energy-dispersive X-ray spectrum, cross-sectional ion milling, and high-resolution imaging were successfully achieved using the adhesive. We tested and confirmed the usefulness of this new adhesive by applying it to cryo-SEM surface imaging of diatomite, freeze-fractured cross-sectional imaging of chicken liver, and ion milling cross-sectional imaging of a deep-sea snail. The new adhesive is not only useful for food science and field-preserved biological samples but also potentially applicable to wider fields such as archaeological and biological samples preserved under permafrost.

Probing and Manipulating Noncovalent Interactions in Functional Polymeric Systems

Noncovalent interactions, which usually feature tunable strength, reversibility, and environmental adaptability, have been recognized as driving forces in a variety of biological and chemical processes, contributing to the recognition between molecules, the formation of molecule clusters, and the establishment of complex structures of macromolecules. The marriage of noncovalent interactions and conventional covalent polymers offers the systems novel mechanical, physicochemical, and biological properties, which are highly dependent on the binding mechanisms of the noncovalent interactions that can be illuminated via quantification. This review systematically discusses the nanomechanical characterization of typical noncovalent interactions in polymeric systems, mainly through direct force measurements at microscopic, nanoscopic, and molecular levels, which provide quantitative information (e.g., ranges, strengths, and dynamics) on the binding behaviors. The fundamental understandings of intermolecular and interfacial interactions are then correlated to the macroscopic performances of a series of noncovalently bonded polymers, whose functions (e.g., stimuli-responsiveness, self-healing capacity, universal adhesiveness) can be customized through the manipulation of the noncovalent interactions, providing insights into the rational design of advanced materials with applications in biomedical, energy, environmental, and other engineering fields.

Co-assembling of natural drug-food homologous molecule into composite hydrogel for accelerating diabetic wound healing

Diabetic wound healing is a major clinical challenge due to its vulnerability to bacterial infection and the prolonged inflammation in the wound. Traditional dressings for the healing of diabetic wounds are often suffered from unsatisfactory efficacy and frequent dressing changes which may cause secondary damage. Therefore, it is necessary to find a wound dressing that balances material functionality, degradation, safety, and tissue regeneration. Our recent studies demonstrated that gallic acid (GA) could spontaneously form supramolecular hydrogels at a relatively high concentration. However, a single network of GA hydrogel is prone to degradation, poor adhesion, and poor swelling, and may not be suitable for wound healing dressings. In this study, a composite hydrogel (GAK) was constructed by introducing konjac glucomannan (KGM) into the gel system of gallic acid (GA) and applied to promote diabetic wound healing. The composite hydrogel (GAK) with superior surface adhesion, stability, and swelling properties than the single-network of GA hydrogel. Moreover, in vitro experiments showed that GAK hydrogel had excellent biocompatibility and exhibited antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Additionally, the GAK hydrogel could significantly accelerate angiogenesis, collagen deposition, and re-epithelialization during wound healing in diabetic mice, reducing the expression of related inflammatory proteins interleukin-1β (IL-1β), tumor necrosis factor-alpha (TNF-α), and cyclooxygenase-2 (COX-2), and improving the wound closure rate. The findings of this study suggest that this composite hydrogel (GAK) can be an ideal dressing material for accelerating diabetic wound healing.

Engineering Bio-Adhesives Based on Protein-Polysaccharide Phase Separation

Glue-type bio-adhesives are in high demand for many applications, including hemostasis, wound closure, and integration of bioelectronic devices, due to their injectable ability and in situ adhesion. However, most glue-type bio-adhesives cannot be used for short-term tissue adhesion due to their weak instant cohesion. Here, we show a novel glue-type bio-adhesive based on the phase separation of proteins and polysaccharides by functionalizing polysaccharides with dopa. The bio-adhesive exhibits increased adhesion performance and enhanced phase separation behaviors. Because of the cohesion from phase separation and adhesion from dopa, the bio-adhesive shows excellent instant and long-term adhesion performance for both organic and inorganic substrates. The long-term adhesion strength of the bio-glue on wet tissues reached 1.48 MPa (shear strength), while the interfacial toughness reached ~880 J m-2. Due to the unique phase separation behaviors, the bio-glue can even work normally in aqueous environments. At last, the feasibility of this glue-type bio-adhesive in the adhesion of various visceral tissues in vitro was demonstrated to have excellent biocompatibility. Given the convenience of application, biocompatibility, and robust bio-adhesion, we anticipate the bio-glue may find broad biomedical and clinical applications.

Polyvinyl alcohol/carboxymethyl chitosan hydrogel loaded with silver nanoparticles exhibited antibacterial and self-healing properties

Hydrogel materials are gradually increasing research in biological aspects due to their unique properties. In order to prepare hydrogels with the potential to be used in clinical wound therapy, the authors prepared a bifunctional hydrogel with antibacterial and self-healing properties. The hydrogel was composed of borax cross-linked polyvinyl alcohol (PVA) and carboxymethyl chitosan (CMCS), which realizes self-healing between polymers through hydrogen bonds and borate ester bonds. The double cross-linking of hydrogen bonds and borate ester bonds also endows the hydrogel with better mechanical properties (toughness and tensile stress can reach 22.30 MJ/m³ and 70.35 KPa, respectively). On this basis, adding highly stable silver nanoparticles (AgNPs) to the hydrogel can effectively inhibit the growth of E. coli and S. aureus. This idea provides the possibility for the application of hydrogels in the process of biological wound healing.

Preparation of a multifunctional organogel and its electrochemical properties

A facile methodology to fabricate a highly elastic organogel for supercapacitors is demonstrated. A stable polymer organogel was obtained in DMSO by a simple esterification reaction. This organogel showed high mechanical performance, flexibility, high elasticity, luminous performance and conductivity, as well as high potential values for application in the energy sector.

Bioinspired Cationic-Aromatic Copolymer for Strong and Reversible Underwater Adhesion

Developing new underwater glue adhesives with robust and repeatable adhesion to various surfaces is promising and useful in marine life and medical treatments. In this work, we developed a novel glue based on a copolymer with a cation-co-aromatic sequence where the cationic units contain both catechol and positively charged sites. The glue consists of a crosslinked copolymer of poly(2-hydroxy-3-phenoxypropyl acrylate-co-3-(5-(3,4 dihydroxyphenyl)-4-oxo-3 N-pentyl)imidazolium) bromide in dimethyl sulfoxide. Solidification of the glue, triggered by contact with water, undergoes a coacervation stage and causes a drastic growth of its mechanical properties over time. The glue demonstrates fast-developing, strong, and repeatable underwater adhesion to different materials and can maintain its strength for a long time. The adhesion strength tends to increase with the surface energy of the substrate material, to a maximum value of 160 kPa found in plywood. Experiments conducted in aqueous media with different pH and ionic strengths, including physiological conditions and seawater, showed an even stronger adhesion than that evolved in deionized water. Thus, the developed glue is a promising candidate for use in marine life, tissue adhesives, and other freshwater and saline water applications.

Water-Enhanced and Remote Self-Healing Elastomers in Various Harsh Environments

The development of underwater remote stimulus-responsive self-healing polymer materials for applications in inaccessible and urgent situations is very challenging because water can readily disturb traditional noncovalent bonds and absorb heat, UV light, IR light, and electromagnetic wave energy at the wave band of micrometers and millimeters. Herein, visible-light-responsive diselenide bonds are employed as the healing moieties to produce a water-enhanced and remote self-healing elastomer triggered by a blue laser, which possesses excellent underwater transmission capability. During healing, the strain at break reaches ∼200% in 5 min and its toughness almost fully recovers within 1 h, which is estimated to be the fastest reported to date for healing silicone elastomers with a healing efficiency above 90%. The remote underwater pipeline sealing is instantly accomplished with the diselenide-containing elastomers by a blue laser 3 m away, thereby providing a direction for future emergent healing applications.

UV Curable Robust Durable Hydrophobic Coating Based on Epoxy Polyhedral Oligomeric Silsesquioxanes (EP-POSS) and Their Derivatives

Hydrophobic coatings have considerable potential applications in many fields. Ease of operation and high durability are essential for practical use. Fast curing and being solvent-free are a plus, and if they possess certain characteristics (antigraffiti, good adhesion, high hardness, heat resistance, wide range of applicability, etc.) at the same time, it is a dream solution. Herein, a facile one-step approach with the above features was reported for a UV curable robust hydrophobic coating based on Epoxy Polyhedral Oligomeric Silsesquioxanes (EP-POSSs). The structure and surface morphology of these EP-POSSs and their derivatives were systematically studied. Because of the core-in-cage structure which was constructed by repeating units of R-Si(O_1/2)₃ and the strong covalent bonds of Si-C and Si-O, the coatings displayed high pencil hardness (6-8H), high thermal stability with initial decomposition temperature around 350-400 °C, and a high water contact angle (up to 108.06°) even after outdoor exposure for a month. These POSSs and their derivatives are expected to find uses in various applications such as stain resistance, self-cleaning, scratch resistance, and cigarette moxibustion resistance of wood furniture, kitchenware, and medical and industrial appliances.

Multifunctional Hard Yet Flexible Coatings Fabricated Using a Universal Step-by-Step Strategy

Hard yet flexible coatings with multi-functionalities are useful for foldable displays and marine industries but rare. In this study, a highly cross-linked multifunctional hybrid coating with ceramic-like hardness and polymer-like flexibility is reported. The coating is prepared via a step-by-step strategy, where two types of epoxy-oligosiloxane nanoclusters are first synthesized by sol-gel chemistry, and amine-terminated curing agents are used to cross-link them at room temperature. The coating is highly transparent (>92% transmittance), hard (6-7H), and flexible (10 mm bending diameter) because of the unique combination of siloxane nanoclusters and polymer networks. Meanwhile, since the coating contains fouling-resistant telomer and low-surface-tension liquid lubricant polydimethylsiloxane (PDMS), it exhibits excellent anti-biofouling and self-cleaning properties. The results indicate that the mechanical and antifouling properties of the coating can be easily tuned and prove that the step-by-step strategy is a promising and universal method. The novel coatings can meet the needs of applications in foldable displays, marine industries, and other fields.

Tough and Highly Efficient Underwater Self-Repairing Hydrogels for Soft Electronics

The vulnerability of hydrogel electronic materials to mechanical damage due to their soft nature has necessitated the development of self-repairing hydrogel electronics. However, the development of such material with underwater self-repairing capability as well as excellent mechanical properties for application in aquatic environments is highly challenging and has not yet been fully realized. This study designs a tough and highly efficient underwater self-repairing supramolecular hydrogel by synergistically combining weak hydrogen bonds (H-bonds) and strong dipole-dipole interactions. The resultant hydrogel has high stretchability (up to 700%) and toughness (4.45 MJ m^-3 ), and an almost 100% fast strain self-recovery (10 min). The underwater healing process is rapid and autonomous (98% self-repair efficiency after 1 h of healing). Supramolecular hydrogels can be developed as soft electronic sensors for physiological signal detection (gestures, breathing, microexpression, and vocalization) and real-time underwater communication (Morse code). Importantly, the hydrogel sensor can function underwater after mechanical damage because of its highly efficient underwater self-repairing capability.

Efficient separation of bagasse lignin by freeze-thaw-assisted p-toluenesulfonic acid pretreatment

Lignin separation is an important procedure that benefits multiple industries and in particular biomass transformation efforts. In this study, bagasse lignin was separated by freeze-thaw-assisted p-toluenesulfonic acid (p-TsOH) pretreatment. The optimal conditions were freezing temperature -60 °C, freezing time 8.0 h, thawing temperature 15 °C, p-TsOH concentration 60%, pretreatment temperature 70 °C, and time 20 min. Lower acid concentrations and temperatures were used compared with traditional p-TsOH pretreatment. The efficiency and selectivity of lignin separation were improved. It was attributed to freeze-thawing, which provided a more efficient physical channel for the effective penetration of p-TsOH. The separation, extraction and purity of lignin were improved to 89.76%, 78.22% and 77.89%, respectively. High separation, high extraction, high purity and large molecular weight lignin samples were obtained. In addition, the recovery and reuse of p-TsOH was enhanced. This provided a new method for the efficient and clean separation of lignin.