Multifunctional Thermoplastic Polyurea Based on the Synergy of Dynamic Disulfide Bonds and Hydrogen Bond Cross-Links

Rapidly self-healing electronic skin for machine learning-assisted physiological and movement evaluation

Emerging electronic skins (E-Skins) offer continuous, real-time electrophysiological monitoring. However, daily mechanical scratches compromise their functionality, underscoring urgent need for self-healing E-Skins resistant to mechanical damage. Current materials have slow recovery times, impeding reliable signal measurement. The inability to heal within 1 minute is a major barrier to commercialization. A composition achieving 80% recovery within 1 minute has not yet been reported. Here, we present a rapidly self-healing E-Skin tailored for real-time monitoring of physical and physiological bioinformation. The E-Skin recovers more than 80% of its functionality within 10 seconds after physical damage, without the need of external stimuli. It consistently maintains reliable biometric assessment, even in extreme environments such as underwater or at various temperatures. Demonstrating its potential for efficient health assessment, the E-Skin achieves an accuracy exceeding 95%, excelling in wearable muscle strength analytics and on-site AI-driven fatigue identification. This study accelerates the advancement of E-Skin through rapid self-healing capabilities.

Boosting the Actuation Performance of a Dynamic Supramolecular Polyurethane-Urea Elastomer via Kinetic Control

The ongoing soft actuation has accentuated the demand for dielectric elastomers (DEs) capable of large deformation to replace the traditional rigid mechanical apparatus. However, the low actuation strain of DEs considerably limits their practical applications. This work developed high-performance polyurethane-urea (PUU) elastomers featuring large actuation strains utilizing an approach of kinetic control over the microphase separation structure during the fabrication process. Additionally, disulfide (DS) bonds were incorporated as dynamic chemical linkages to effectively heal the mechanical damage in the resulting elastomer (PUUDS). Alteration in processing conditions creates notable differences in the rate of phase separation among the multiphase materials. A faster phase separation rate is associated with a reduced degree of microphase separation, increased spacing within hard domains, a higher proportion of disordered hydrogen bonds, and hydrogen bonding index. These changes synergistically improved the electromechanical properties of the PUUDS elastomers, thereby enhancing their actuation performance. The sample processed under the fastest phase separation condition showed the lowest Young's modulus and a pronounced dielectric response at low frequencies. The electrostriction effect accounts for 89% of the total electromechanical coupling, achieving a significant reduction in the driving voltage during actuation. The maximum actuation strain recorded was 21.6% at an electric field of 45 MV/m. Benefiting from the fully reversible dynamic network, the damaged PUUDS elastomer can be healed and restored to its original elongation at break after 3 h at room temperature. Practical application was demonstrated through the development of a miniature butterfly model constructed from a single-layer PUUDS elastomer, showcasing potential applications in soft robotics. These findings highlight the critical role of kinetic control in optimizing the performance of advanced DEs.

Degradable and Recyclable Hydrogels for Sustainable Bioelectronics

Hydrogel bioelectronics has been widely used in wearable sensors, electronic skin, human-machine interfaces, and implantable tissue-electrode interfaces, providing great convenience for human health, safety, and education. The generation of electronic waste from bioelectronic devices jeopardizes human health and the natural environment. The development of degradable and recyclable hydrogels is recognized as a paradigm for realizing the next generation of environmentally friendly and sustainable bioelectronics. This review first summarizes the wide range of applications for bioelectronics, including wearable and implantable devices. Then, the employment of natural and synthetic polymers in hydrogel bioelectronics is discussed in terms of degradability and recyclability. Finally, this work provides constructive thoughts and perspectives on the current challenges toward hydrogel bioelectronics, providing valuable insights and guidance for the future evolution of sustainable hydrogel bioelectronics.

State-of-the-Art Polyurea Coatings: Synthesis Aspects, Structure-Properties Relationship, and Nanocomposites for Ballistic Protection Applications

This review presents polyurea (PU) synthesis, the structure-properties relationship, and characterization aspects for ballistic protection applications. The synthesis of polyurea entails step-growth polymerization through the reaction of an isocyanate monomer/prepolymer and a polyamine, each component possessing a functionality of at least two. A wide range of excellent properties such as durability and high resistance against atmospheric, chemical, and biological factors has made this polymer an outstanding option for ballistic applications. Polyureas are an extraordinary case because they contain both rigid segments, which are due to the diisocyanates used and the hydrogen points formed, and a flexible zone, which is due to the chemical structure of the polyamines. These characteristics motivate their application in ballistic protection systems. Polyurea-based coatings have also demonstrated their abilities as candidates for impulsive loading applications, affording a better response of the nanocomposite-coated metal sheet at the action of a shock wave or at the impact of a projectile, by suffering lower deformations than neat metallic plates.

Multifunctional Hydrogels for the Healing of Diabetic Wounds

The healing of diabetic wounds is hindered by various factors, including bacterial infection, macrophage dysfunction, excess proinflammatory cytokines, high levels of reactive oxygen species, and sustained hypoxia. These factors collectively impede cellular behaviors and the healing process. Consequently, this review presents intelligent hydrogels equipped with multifunctional capacities, which enable them to dynamically respond to the microenvironment and accelerate wound healing in various ways, including stimuli -responsiveness, injectable self-healing, shape -memory, and conductive and real-time monitoring properties. The relationship between the multiple functions and wound healing is also discussed. Based on the microenvironment of diabetic wounds, antibacterial, anti-inflammatory, immunomodulatory, antioxidant, and pro-angiogenic strategies are combined with multifunctional hydrogels. The application of multifunctional hydrogels in the repair of diabetic wounds is systematically discussed, aiming to provide guidelines for fabricating hydrogels for diabetic wound healing and exploring the role of intelligent hydrogels in the therapeutic processes.

Liquid-Free, Self-Repairable, Recyclable, and Highly Stretchable Colorless Solid Ionic Conductive Elastomers for Strain/Temperature Sensors

Solid-state ionic conductive elastomers (ICEs) can fundamentally overcome the disadvantages of hydrogels and ionogels (their liquid components tend to leak or evaporate), and are considered to be ideal materials for flexible ionic sensors. In this study, a liquid-free ionic polyurethane (PU) type conductive elastomer (ICE-2) was synthesized and studied. The PU type matrix with microphase separation endowed ICE-2 with excellent mechanical versatility. The disulfide bond exchange reaction in the hard phase and intermolecular hydrogen bonds contributed to damage repairing ability. ICE-2 exhibited good ionic conductivity (2.86×10-6  S/cm), high transparency (average transmittance >89 %, 400~800 nm), excellent mechanical properties (tensile strength of 3.06 MPa, elongation at break of 1760 %, and fracture energy of 14.98 kJ/m2 ), appreciable self-healing ability (healing efficiency >90 %), satisfactory environmental stability, and outstanding recyclability. The sensor constructed by ICE-2 could not only realize the perception of temperature changes, but also accurately and sensitively detect various human activities, including joint movements and micro-expression changes. This study provides a simple and effective strategy for the development of flexible and soft ionic conductors for sensors and human-machine interfaces.

Hemiaminal dynamic covalent networks with rapid stress relaxation, reprocessability and degradability endowed by the synergy of disulfide and hemiaminal bonds

This work proposes a strategy to address the challenge of achieving rapid reprocessability of vitrimers at mild temperatures by introducing dynamic disulfide and hemiaminal bonds into hemiaminal dynamic covalent networks (HDCNs). The resulting HDCNs, termed HDCNs-DTDA, were prepared through a facile polycondensation between formaldehyde and 4,4'-dithiodianiline. The dual dynamic bond system in the HDCNs-DTDA enables rapid stress relaxation under mild temperature (65 °C for 54 s), which is significantly faster than that observed in HDCNs containing a single dynamic bond (HDCNs-DDM). The HDCNs-DTDA also exhibit a glass transition temperature of 96 °C, excellent solvent resistance and high recovery rates (97%) of tensile strength after reprocessing. In addition, HDCNs-DTDA can be easily degraded in HCl and thiol solutions at room temperature to enable chemical recyclability. Finally, HDCNs-DTDA demonstrates fast shape memory behaviors using thermal stimulation.

Near-Infrared Remotely Controllable Shape Memory Biodegradable Occluder Based on Poly(l-lactide-co-ε-caprolactone)/Gold Nanorod Composite

Biodegradable occluders, which can efficiently eliminate the complications caused by permanent foreign implants, are considered to be the next-generation devices for the interventional treatment of congenital heart disease. However, the controllability of the deployment process of degradable occluders remains a challenge. In this work, a near-infrared (NIR) remotely controllable biodegradable occluder is explored by integrating poly(l-lactide-co-ε-caprolactone) (PLCL) with poly(ethylene glycol)-modified gold nanorods (GNR/PEG). The caprolactone structural units can effectively increase the toughness of poly(l-lactide) and reduce the shape-memory transition temperature of the occluder to a more tissue-friendly temperature. Gold nanorods endow the PLCL-GNR/PEG composite with an excellent photothermal effect. The obtained occluder can be easily loaded into a catheter for transport and spatiotemporally expanded under irradiation with near-infrared light to block the defect site. Both in vitro and in vivo biological experiments showed that PLCL-GNR/PEG composites have good biocompatibility, and the PEGylated gold nanorods could improve the hemocompatibility of the composites to a certain extent by enhancing their hydrophilicity. As a thermoplastic shape-memory polymer, PLCL-GNR/PEG can be easily processed into various forms and structures for different patients and lesions. Therefore, PLCL-GNR/PEG has the potential to be considered as a competitive biodegradable material not only for occluders but also for other biodegradable implants.

Recent advances in self-healing polyurethane based on dynamic covalent bonds combined with other self-healing methods

To meet more application requirements, improving mechanical properties and self-healing efficiency has become the focus of current research on self-healing PU. The competitive relationship between self-healing ability and mechanical properties cannot be avoided by a single self-healing method. To address this problem, a growing number of studies have combined dynamic covalent bonding with other self-healing methods to construct the PU structure. This review summarizes recent studies on PU materials that combine typical dynamic covalent bonds with other self-healing methods. It mainly includes four parts: hydrogen bonding, metal coordination bonding, nanofillers combined with dynamic covalent bonding and multiple dynamic covalent bond bonding. The advantages and disadvantages of different self-healing methods and their significant role in improving self-healing ability and mechanical properties in PU networks are analyzed. At the same time, the possible challenges and research directions of self-healing PU materials in the future are discussed.

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.

Self-Healable Elastomeric Network with Dynamic Disulfide, Imine, and Hydrogen Bonds for Flexible Strain Sensor

Self-healable and stretchable elastomeric material is essential for the development of flexible electronics devices to ensure their stable performance. In this study, a strain sensor (PIH₂ T₁ -tri/CNT-3) composed of self-repairable crosslinked elastomer substrate (PIH₂ T₁ -tri, containing multiple reversible repairing sites such as disulfide, imine, and hydrogen bonds) and conductive layer (carbon nanotube, CNT) was prepared. The PIH₂ T₁ -tri elastomer had excellent self-healing ability (healing efficiency=91 %). It exhibited good mechanical integrity in terms of elongation at break (672 %), tensile strength (1.41 MPa). The Young's modulus (0.39 MPa) was close to that of human skin. The PIH₂ T₁ -tri/CNT-3 sensor also demonstrated an effective self-healing function for electrical conduction and sensing property. Meanwhile, it had high sensitivity (gauge factor (GF)=24.1), short response time (120 ms), and long-term durability (4000 cycles). This study offers a novel self-healable elastomer platform with carbon based conductive components to develop flexible strain sensors towards high performance soft electronics.

Disulfide Metathesis-Assisted Lithium-Ion Conduction for PEO-Based Polymer Electrolytes

The disulfide metathesis is a promising candidate in the dynamically exchanged strategy for improving the self-healing ability of polymer electrolytes (PEs). However, the enhancement effects on the ionic conductivities of PEs are generally ignored while introducing a dynamic covalent bond to PEs. Herein, the oligo(ethylene oxide)-based additive containing a disulfide bond (S-S additive) was synthesized via Michael addition reaction of cystamine and poly(ethylene glycol) methyl ether acrylate (PEGA). Short PEG chains complexed with Li⁺ in a S-S additive migrated rapidly in PEs because of the dynamically exchanged strategy of the disulfide bond. Moreover, disulfide bonds in a S-S additive possessed the ability to exchange with the cross-linked network containing disulfide bonds (S-S net). The as-prepared PEs exhibited a high room temperature ionic conductivity of 1.24 × 10^-4 S cm^-1, demonstrating that the disulfide metathesis-assisted Li⁺ conduction was feasible for enhancing ionic conductivities of PEs. Relative to other PEO-based PEs, these disulfide-containing PEs possessed a high Li⁺ transference number (0.54). Furthermore, the lithium-metal batteries (LMBs) assembled with PEs in the presence of a S-S additive presented stable cycle performance, indicating the promising potential of these PEs as candidates for next-generation LMBs.

Photoreversible Bond-Based Shape Memory Polyurethanes with Light-Induced Self-Healing, Recyclability, and 3D Fluorescence Encryption

Developing a shape memory polyurethane with high mechanical properties, excellent self-healing has become a huge challenge for the development of smart materials. Herein, we report the design and fabrication of a shape memory polyurethane network terminated with coumarin units (HEOMC-PU) to address this conundrum. The synthesized HEOMC-PU exhibits exceptional mechanical performance with a breaking elongation of 746% and toughness of 55.5 MJ·m-3. By utilizing the dynamically reversible behavior of coumarin units to repair the damaged network, the efficient self-healing performance (99.2%) of HEOMC-PU is obtained. In addition, the prepared network and light-induced dynamic reversibility endow the HEOMC-PU with both liquid-state remoldability and solid-state plasticity, respectively, enabling polyurethane to be recycled and processed multiple times. Furthermore, based on the fluorescence responsive characteristic of coumarin, HEOMC-PU with a fluorescent pattern can be deformed into specific three-dimensional configurations by combining photolithography, self-healing, and the shape memory effect. Such a multilevel and multidimensional anti-counterfeiting platform with rewritable fluorescent patterns and reconfigurable shapes can open up a new encryption approach for future intelligent anti-counterfeiting.

Enhanced Shape Memory Metal-Coordinated Poly(aryl ether ketone)s with Tunable Gradient-Deformation Behaviors as well as Self-Healing and Reprocessing Abilities

Reversible dynamic bonds are able to crack and recombine upon external stimuli, which endow polymers with exceptional self-healing, reprocessing, and reversible deformation ability. In this paper, we integrated the metal coordination bonds into shape memory poly(aryl ether ketone) (PAEK) to fabricate smart materials with multifunctionalities. Through tuning the metal ion content and species, the enhancement of shape memory behaviors was achieved, including the high recovery ratio (over 98%) and fixity ratio (over 98%), which was closely related to the synergic effect of the intrinsic motion ability of PAEK matrix and the cracking-recombination of coordination bonds. Besides, through the combination of the components with different Cu²⁺ contents, in addition to the components with Fe²⁺ coordination bonds, we fabricated the gradient shape memory structures with controllable shape memory and recovery behaviors. The manipulation of gradient coordination bonds resulted in different shape recovery speeds and directions. Furthermore, due to the dynamic cracking-recombination of coordination bonds, the metal-coordinated PAEK material exhibited the great self-healing and reprocessing performances, which were significant for largely extending its application range.

Janus membranes with asymmetric cellular adhesion behaviors for regenerating eardrum perforation

The tympanic membrane plays an important role in the human hearing system, which is easily perforated under unfavorable conditions, leading to loss of hearing and otitis media. Many autologous materials and artificial materials have been used to repair a perforated tympanic membrane, but these materials sometimes can cause severe hearing loss because of their adhesion to the ossicle during the healing process and the postoperative process. Herein, we report Janus membranes with asymmetric cellular adhesion behaviors for regenerating the eardrum. These Janus membranes are constructed by co-depositing a tannic acid (TA)/3-aminopropyltriethoxysilane (APTES) coating on one surface of the polypropylene microfiltration membrane. Cellular experiments indicate that the Janus membranes have good biocompatibility and asymmetric cellular adhesion properties. The repair of the tympanic membrane perforation experiment and laser Doppler vibrometer (LDV) measurements prove that the hydrophilic surface of Janus membranes repairs perforated eardrums, and meanwhile the hydrophobic surface can avoid adhering to the inner ear tissue for reducing hearing loss. The Janus membranes have good prospects in the treatment of tympanic membrane perforation.

COCu: A Robust Self-Regenerative Hydrogel with Applicability as Both Hydrated Gel Dressing and Dry Suture for Seamless Tissue Fixation and Repair

Self-regenerative hydrogels have recently been developed, and represent a special type of self-healing hydrogels with the ability to restore a dehydrated hydrogel with physical damage. In this study, a self-regenerative hydrogel (COCu) based on two chitosan polymers assembled by slow-released Cu²⁺ is developed. The COCu hydrogel displays an excellent regeneration ability after being dehydrated and fractured. By simple hydration at room temperature, the fragments of the dehydrated gel fuse into one seamless whole, thereby preserving the mechanical properties and functionalities of the original hydrogel. The regeneration process can be conducted repeatedly after different methods of dehydration (natural volatilization, heat drying, lyophilization) and various modes of deconstruction (flakes, powder, lumpy sponge, etc.). Furthermore, the COCu hydrogel provides ultra-stretchability, and it can be stretched into thin (0.01-0.1 mm) filaments, which, when dried (dtCOCu), can be used as suture lines. Moreover, when used as a dry suture, it regenerates into the hydrogel in the presence of the tissue fluid, forming an excellent sealant to immobilize tissues and seamlessly seal wounds. The fast self-regeneration allows for its facile application as both a hydrated gel dressing and dry suture, and offers customized strategies for fixing and repair of different wounds in soft tissues.

Semicrystalline polymer networks with a swelling-enhanced water-triggered two-way shape-memory effect for programmable deformation and smart actuation

A simple, effective and universal strategy is proposed to fabricate a water-triggered two-way shape-memory polymer with the highest angle reversibility of 45.2%, which can be applied as a soft gripper and water level monitor.

Disulfide bond-embedded polyurethane solid polymer electrolytes with self-healing and shape-memory performance

In this work, solid-state polymer electrolytes with both self-healing and shape-memory properties (SSSPEs) are designed and fabricated based on disulfide bond-containing polyurethane and poly(ethylene oxide) (PEO) segments.

Progress in Utilizing Dynamic Bonds to Fabricate Structurally Adaptive Self-Healing, Shape Memory, and Liquid Crystal Polymers

Stimuli-responsive structurally dynamic polymers are capable of mimicking the biological systems to adapt themselves to the surrounding environmental changes and subsequently exhibiting a wide range of responses ranging from self-healing to complex shape-morphing. Dynamic self-healing polymers (SHPs), shape-memory polymers (SMPs) and liquid crystal elastomers (LCEs), which are three representative examples of stimuli-responsive structurally dynamic polymers, have been attracting broad and growing interest in recent years because of their potential applications in the fields of electronic skin, sensors, soft robots, artificial muscles, and so on. We review recent advances and challenges in the developments towards dynamic SHPs, SMPs and LCEs, focusing on the chemistry strategies and the dynamic reaction mechanisms that enhance the performances of the materials including self-healing, reprocessing and reprogramming. We compare and discuss the different dynamic chemistries and their mechanisms on the enhanced functions of the materials, where three summary tables are presented: a library of dynamic bonds and the resulting characteristics of the materials. Finally, we provide a critical outline of the unresolved issues and future perspectives on the emerging developments. This article is protected by copyright. All rights reserved.

Dynamic Covalent Polyurethane Network Materials: Synthesis and Self-Healability

Polyurethane (PU) has not only been widely used in the daily lives, but also extensively explored as an important class of the essential polymers for various applications. In recent years, significant efforts have been made on the development of self-healable PU materials that possess high performance, extended lifetime, great reliability, and recyclability. A promising approach is the incorporation of covalent dynamic bonds into the design of PU covalently crosslinked polymers and thermoplastic elastomers that can dissociate and reform indefinitely in response to external stimuli or autonomously. This review summarizes various strategies to synthesize self-healable, reprocessable, and recyclable PU materials integrated with dynamic (reversible) Diels-Alder cycloadduct, disulfide, diselenide, imine, boronic ester, and hindered urea bond. Furthermore, various approaches utilizing the combination of dynamic covalent chemistries with nanofiller surface chemistries are described for the fabrication of dynamic heterogeneous PU composites.