A rigid and healable polymer cross-linked by weak but abundant Zn(II)-carboxylate interactions

Controlling the Relaxation Dynamics of Polymer Networks by Combining Associative and Dissociative Dynamic Covalent Bonds

Dynamic polymer networks offer a promising solution to key challenges in polymers such as recyclability, processability, and damage repair. However, the trade-off between combining facile processability, fast self-healing, and high creep resistance remains a major obstacle to implementation. To overcome this, two very distinct dynamic covalent chemistries, Diels-Alder and transesterification, is combined in a single network. The resulting dual dynamic networks offer an unprecedented set of properties and control over the relaxation times. The system decouples the relaxation dynamics of the network from the spatial motifs, and the tuning of the ratio between chemistries enables to control of the relaxation dynamics over six orders of magnitude. Taking advantage of this control, the composition and rheological behavior is optimized to drastically improve the resolution for extrusion-based additive manufacturing of dynamic covalent networks. Additionally, two well-defined and separated stress relaxation peaks are observed at compositions close to 50% of each dynamic chemistry, accentuating the double character of the system's relaxation dynamics. This atypical situation, enables to preparation of self-healing materials with negligible creep, and with shape-memory properties solely leveraging the two distinct relaxation dynamics, instead of the glass transition temperature or the melting point.

Mechanically skin-like and water-resistant self-healing bioelastomer for high-tension wound healing

The biomedical application of self-healing materials in wet or (under)water environments is quite challenging because the insulation and dissociation effects of water molecules significantly reduce the reconstruction of material-interface interactions. Rapid closure with uniform tension of high-tension wounds is often difficult, leading to further deterioration and scarring. Herein, a new type of thermosetting water-resistant self-healing bioelastomer (WRSHE) was designed by synergistically incorporating a stable polyglycerol sebacate (PGS) covalent crosslinking network and triple hybrid dynamic networks consisting of reversible disulfide metathesis (SS), and dimethylglyoxime urethane (Dou) and hydrogen bonds. And a resveratrol-loaded WRSHE (Res@WRSHE) was developed by a swelling, absorption, and crosslinked network locking strategy. WRSHEs exhibited skin-like mechanical properties in terms of nonlinear modulus behavior, biomimetic softness, high stretchability, and good elasticity, and they also achieved ultrafast and highly efficient self-healing in various liquid environments. For wound-healing applications of high-tension full-thickness skin defects, the convenient surface assembly by self-healing of WRSHEs provides uniform contraction stress to facilitate tight closure. Moreover, Res@WRSHEs gradually release resveratrol, which helps inflammatory response reduction, promotes blood vessel regeneration, and accelerates wound repair.

Softening implantable bioelectronics: Material designs, applications, and future directions

Implantable bioelectronics, integrated directly within the body, represent a potent biomedical solution for monitoring and treating a range of medical conditions, including chronic diseases, neural disorders, and cardiac conditions, through personalized medical interventions. Nevertheless, contemporary implantable bioelectronics rely heavily on rigid materials (e.g., inorganic materials and metals), leading to inflammatory responses and tissue damage due to a mechanical mismatch with biological tissues. Recently, soft electronics with mechanical properties comparable to those of biological tissues have been introduced to alleviate fatal immune responses and improve tissue conformity. Despite their myriad advantages, substantial challenges persist in surgical handling and precise positioning due to their high compliance. To surmount these obstacles, softening implantable bioelectronics has garnered significant attention as it embraces the benefits of both rigid and soft bioelectronics. These devices are rigid for easy standalone implantation, transitioning to a soft state in vivo in response to environmental stimuli, which effectively overcomes functional/biological problems inherent in the static mechanical properties of conventional implants. This article reviews recent research and development in softening materials and designs for implantable bioelectronics. Examples featuring tissue-penetrating and conformal softening devices highlight the promising potential of these approaches in biomedical applications. A concluding section delves into current challenges and outlines future directions for softening implantable device technologies, underscoring their pivotal role in propelling the evolution of next-generation bioelectronics.

Combination Nanomedicine Strategy for Preventing High-Risk Corneal Transplantation Rejection

High-risk (HR) corneal transplantation presents a formidable challenge, with over 50% of grafts experiencing rejection despite intensive postoperative care involving frequent topical eyedrop administration up to every 2 h, gradually tapering over 6-12 months, and ongoing maintenance dosing. While clinical evidence underscores the potential benefits of inhibiting postoperative angiogenesis, effective antiangiogenesis therapy remains elusive in this context. Here, we engineered controlled-release nanomedicine formulations comprising immunosuppressants (nanoparticles) and antiangiogenesis drugs (nanowafer) and demonstrated that these formulations can prevent HR corneal transplantation rejection for at least 6 months in a clinically relevant rat model. Unlike untreated corneal grafts, which universally faced rejection within 2 weeks postsurgery, a single subconjunctival injection of the long-acting immunosuppressant nanoparticle alone effectively averted graft rejection for 6 months, achieving a graft survival rate of ∼70%. Notably, the combination of an immunosuppressant nanoparticle and an anti-VEGF nanowafer yielded significantly better efficacy with a graft survival rate of >85%. The significantly enhanced efficacy demonstrated that a combination nanomedicine strategy incorporating immunosuppressants and antiangiogenesis drugs can greatly enhance the ocular drug delivery and benefit the outcome of HR corneal transplantation with increased survival rate, ensuring patient compliance and mitigating dosing frequency and toxicity concerns.

Tough Self-Healing Materials via In Situ Growth of Zeolitic Imidazolate Framework-8 Nanocrystals in Polymers

Construction of self-healing materials with improved mechanical performance is a great challenge. A strong and tough self-healing composite is fabricated via in situ growth of zeolitic imidazole framework-8 (ZIF-8) nanocrystals in imidazole-containing polymer networks. By adjusting the stoichiometric ratio of the zinc salt to 2-methylimidazole, composites with various mechanical performances are obtained. The existence of ZIF-8 nanocrystals via in situ growth in the polymer networks is confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The zinc-imidazole interactions between the ZIF-8 nanocrystals and the polymer are confirmed by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The composites can repair themselves under mild conditions owing to dynamic zinc-imidazole interactions. The self-healing efficiency of composites can reach up to 91% under the condition of 60 °C for 48 h. In contrast to the pure zinc cation crosslinking system, the composite containing ZIF-8 nanocrystals prepared via in situ growth exhibited enhanced tensile strength and toughness by 43% and 100%, respectively. This study proves that incorporating the metal-organic frameworks (MOFs) materials into a self-healing system via an in situ growth strategy is highly promising for designing self-healing materials with improved mechanical performance.

Rugged Island-Bridge Inorganic Electronics Mounted on Locally Strain-Isolated Substrates

Various strain isolation strategies that combine rigid and stretchable regions for stretchable electronics were recently proposed, but the vulnerability of inorganic materials to mechanical stress has emerged as a major impediment to their performance. We report a strain-isolation system that combines heteropolymers with different elastic moduli (i.e., hybrid stretchable polymers) and utilize it to construct a rugged island-bridge inorganic electronics system. Two types of prepolymers were simultaneously cross-linked to form an interpenetrating polymer network at the rigid-stretchable interface, resulting in a hybrid stretchable polymer that exhibited efficient strain isolation and mechanical stability. The system, including stretchable micro-LEDs and microheaters, demonstrated consistent operation under external strain, suggesting that the rugged island-bridge inorganic electronics mounted on a locally strain-isolated substrate offer a promising solution for replacing conventional stretchable electronics, enabling devices with a variety of form factors.

High thermal conductivity regenerated cellulose/carboxylated carbon nanotubes composite films with semi-insulating properties prepared via ionic coordination and hydrothermal synthesis of zinc oxide

With the rapid development of miniaturization and integration of electronic products, its heat dissipation has become the focus of research. In order to improve the heat dissipation efficiency of electronic components, flexible thermal conduction materials are constantly studied. Cellulose has good flexibility and load capacity, which is often used in the preparation of thermal conduction materials. In this paper, carboxylated multi-walled carbon nanotubes (C-MWCNTs) were modified by metal ion coordination and hydrothermal synthesis of zinc oxide (ZnO) to prepare semi-insulating thermal conduction fillers, which were dispersed into regenerated cellulose (RC) to cast to be composite films. The results show that the two modification methods can reduce the probability of phonon scattering and block the electron transport path, so as to improve the thermal conductivity (TC) and electrical insulation properties of the composite films. Especially for the RC/C-MWCNTs@ZnO composite films, when the total filler content is 20 wt%, the in-plane TC can reach 11.89 ± 0.19 (W/(m·K)), and the surface electrical resistivity (ρs) is (5.24 ± 0.17) × 106 Ω. Compared with the RC/C-MWCNTs composite films, the in-plane TC and ρs of the RC/C-MWCNTs@ZnO composites films are increased by about 94.92 % and 555 %, respectively. Therefore, the developed RC-based composite film has broad application prospects in thermal management.

3D-Printed Architectured Silicones with Autonomic Self-Healing and Creep-Resistant Behavior

Self-healing silicones that are able to restore functionalities and extend the lifetime of soft devices hold great potential in many applications. However, currently available silicones need to be triggered to self-heal or suffer from creep-induced irreversible deformation during use. Here, a platform is proposed to design and print silicone objects that are programmed at the molecular and architecture levels to achieve self-healing at room temperature while simultaneously resisting creep. At the molecular scale, dioxaborolanes moieties are incorporated into silicones to synthesize self-healing vitrimers, whereas conventional covalent bonds are exploited to make creep-resistant elastomers. When combined into architectured printed parts at a coarser length scale, the layered materials exhibit fast healing at room temperature without compromising the elastic recovery obtained from covalent polymer networks. A patient-specific vascular phantom and fluidic chambers are printed to demonstrate the potential of architectured silicones in creating damage-resilient functional devices using molecularly designed elastomer materials.

3D Printing of Self-Healing Materials

This review article presents a comprehensive overview of the latest advances in the field of 3D printable structures with self-healing properties. Three-dimensional printing (3DP) is a versatile technology that enables the rapid manufacturing of complex geometric structures with precision and functionality not previously attainable. However, the application of 3DP technology is still limited by the availability of materials with customizable properties specifically designed for additive manufacturing. The addition of self-healing properties within 3D printed objects is of high interest as it can improve the performance and lifespan of structural components, and even enable the mimicking of living tissues for biomedical applications, such as organs printing. The review will discuss and analyze the most relevant results reported in recent years in the development of self-healing polymeric materials that can be processed via 3D printing. After introducing the chemical and physical self-healing mechanism that can be exploited, the literature review here reported will focus in particular on printability and repairing performances. At last, actual perspective and possible development field will be critically discussed.

Superstretchable Liquid-Metal Electrodes for Dielectric Elastomer Transducers and Flexible Circuits

Dielectric elastomer transducers (DETs), with a dielectric elastomer (DE) film sandwiched between two compliant electrodes, are highly sought after in the fields of soft robotics, energy harvesting, and human-machine interaction. To achieve a high-performance DET, it is essential to develop electrodes with high conductivity, strain-insensitive resistance, and adaptability. Herein, we design an electrode (Supra-LMNs) based on multiple dynamic bond cross-linked supramolecular networks (Ns) and liquid metal (LM), which realizes high conductivity (up to 16,000 S cm-1), negligible resistance changes at high strain (1.3-fold increase at 1000% strain), instantaneous self-healability at ambient temperature, and rapid recycling. The conductive pathway can be activated through simple friction by transmitting stress through the silver nanowires (AgNWs) and cross-linking sites of LM particles. This method is especially attractive for printing circuits on flexible substrates, especially DE films. Utilized as dielectric elastomer generator (DEG) electrodes, it reduces the charge loss by 3 orders of magnitude and achieves high generating energy density and energy conversion efficiency on a low-resistance load. Additionally, serving as sensor (DES) and actuator (DEA) electrodes, it enables a highly sensitive sensing capability and complex interaction.

Functional PDMS Elastomers: Bulk Composites, Surface Engineering, and Precision Fabrication

Polydimethylsiloxane (PDMS)-the simplest and most common silicone compound-exemplifies the central characteristics of its class and has attracted tremendous research attention. The development of PDMS-based materials is a vivid reflection of the modern industry. In recent years, PDMS has stood out as the material of choice for various emerging technologies. The rapid improvement in bulk modification strategies and multifunctional surfaces has enabled a whole new generation of PDMS-based materials and devices, facilitating, and even transforming enormous applications, including flexible electronics, superwetting surfaces, soft actuators, wearable and implantable sensors, biomedicals, and autonomous robotics. This paper reviews the latest advances in the field of PDMS-based functional materials, with a focus on the added functionality and their use as programmable materials for smart devices. Recent breakthroughs regarding instant crosslinking and additive manufacturing are featured, and exciting opportunities for future research are highlighted. This review provides a quick entrance to this rapidly evolving field and will help guide the rational design of next-generation soft materials and devices.

Self-Healing Polymeric Materials and Composites for Additive Manufacturing

Self-healing polymers have received widespread attention due to their ability to repair damage autonomously and increase material stability, reliability, and economy. However, the processability of self-healing materials has yet to be studied, limiting the application of rich self-healing mechanisms. Additive manufacturing effectively improves the shortcomings of conventional processing while increasing production speed, accuracy, and complexity, offering great promise for self-healing polymer applications. This article summarizes the current self-healing mechanisms of self-healing polymers and their corresponding additive manufacturing methods, and provides an outlook on future developments in the field.

Toughening CO2 -Derived Copolymer Elastomers Through Ionomer Networking

Utilizing carbon dioxide (CO2 ) to make polycarbonates through the ring-opening copolymerization (ROCOP) of CO2 and epoxides valorizes and recycles CO2 and reduces pollution in polymer manufacturing. Recent developments in catalysis provide access to polycarbonates with well-defined structures and allow for copolymerization with biomass-derived monomers; however, the resulting material properties are underinvestigated. Here, new types of CO2 -derived thermoplastic elastomers (TPEs) are described together with a generally applicable method to augment tensile mechanical strength and Young's modulus without requiring material re-design. These TPEs combine high glass transition temperature (Tg ) amorphous blocks comprising CO2 -derived poly(carbonates) (A-block), with low Tg poly(ε-decalactone), from castor oil, (B-block) in ABA structures. The poly(carbonate) blocks are selectively functionalized with metal-carboxylates where the metals are Na(I), Mg(II), Ca(II), Zn(II) and Al(III). The colorless polymers, featuring <1 wt% metal, show tunable thermal (Tg ), and mechanical (elongation at break, elasticity, creep-resistance) properties. The best elastomers show >50-fold higher Young's modulus and 21-times greater tensile strength, without compromise to elastic recovery, compared with the starting block polymers. They have wide operating temperatures (-20 to 200 °C), high creep-resistance and yet remain recyclable. In the future, these materials may substitute high-volume petrochemical elastomers and be utilized in high-growth fields like medicine, robotics, and electronics.

Self-Healing Silicone Materials: Looking Back and Moving Forward

This review is dedicated to self-healing silicone materials, which can partially or entirely restore their original characteristics after mechanical or electrical damage is caused to them, such as formed (micro)cracks, scratches, and cuts. The concept of self-healing materials originated from biomaterials (living tissues) capable of self-healing and regeneration of their functions (plants, human skin and bones, etc.). Silicones are ones of the most promising polymer matrixes to create self-healing materials. Self-healing silicones allow an increase of the service life and durability of materials and devices based on them. In this review, we provide a critical analysis of the current existing types of self-healing silicone materials and their functional properties, which can be used in biomedicine, optoelectronics, nanotechnology, additive manufacturing, soft robotics, skin-inspired electronics, protection of surfaces, etc.

Complexation of Sulfonate-Containing Polyurethane and Polyacrylic Acid Enables Fabrication of Self-Healing Hydrogel Membranes with High Mechanical Strength and Excellent Elasticity

Artificial hydrogel membranes with good biocompatibility are strongly needed in biological fields. The preparation of biocompatible hydrogel membranes simultaneously possessing high mechanical strength, excellent elasticity, and satisfactory self-healing properties remains a challenge. Herein, we demonstrate the preparation of such hydrogel membranes by complexation of sulfonate-containing polyurethane (SPU) and poly(acrylic acid) (PAA) in the presence of Zn²⁺ ions followed by swelling in water (denoted as SPU-PAA/Zn). Originating from the synergy of the coordination and hydrogen-bonding interactions and the reinforcement effect of the in situ formed hydrophobic domains, the SPU-PAA/Zn hydrogel membrane exhibits a high tensile strength of ∼7.1 MPa and a toughness of ∼30.4 MJ m^-3. Moreover, the hydrogel membrane is highly elastic, which can restore to its initial state from an ∼500% strain within 40 min rest at room temperature without any external assistance. The dynamic noncovalent interactions and hydrophobic domains allow the fractured hydrogel membrane to heal and completely regain its original integrity and mechanical properties at room temperature. Both in vitro and in vivo tests confirm that the hydrogel membrane exhibits satisfactory biocompatibility and could be potentially used as a biological barrier membrane in surgical operations or artificial organs.

Efficient High-Refractive-Index Azobenzene Dendrimers Based on a Hierarchical Supramolecular Approach

Real-time manipulation of light in a diffractive optical element made with an azomaterial, through the light-induced reconfiguration of its surface based on mass transport, is an ambitious goal that may enable new applications and technologies. The speed and the control over photopatterning/reconfiguration of such devices are critically dependent on the photoresponsiveness of the material to the structuring light pattern and on the required extent of mass transport. In this regard, the higher the refractive index (RI) of the optical medium, the lower the total thickness and inscription time can be. In this work, we explore a flexible design of photopatternable azomaterials based on hierarchically ordered supramolecular interactions, used to construct dendrimer-like structures by mixing specially designed sulfur-rich, high-refractive-index photoactive and photopassive components in solution. We demonstrate that thioglycolic-type carboxylic acid groups can be selectively used as part of a supramolecular synthon based on hydrogen bonding or readily converted to carboxylate and participate in a Zn(II)-carboxylate interaction to modify the structure of the material and fine-tune the quality and efficiency of photoinduced mass transport. Compared with a conventional azopolymer, we demonstrate that it is possible to fabricate high-quality, thinner flat diffractive optical elements to reach the desired diffraction efficiency by increasing the RI of the material, achieved by maximizing the content of high molar refraction groups in the chemical structure of the monomers.

High-Performance, Degradable, Self-Healing Bio-Based Nanocomposite Coatings with Antibacterial and Antioxidant Properties

The purpose of this study is to obtain a bio-based coating with good functional activity and self-healing ability, demonstrating its potential in food, materials, and other application fields. Plastic coatings can cause serious environmental pollution. It was a good solution to replace plastic coatings with degradable coatings. However, the development of degradable coatings in the fields of food and materials was limited due to their insufficient antibacterial ability and weak comprehensive properties. Therefore, chitosan nanoparticles (NPs) loaded with gallic acid (GA) were self-assembled with gelatin (GE) to prepare high-performance, degradable, self-healing bio-based nanocomposite coatings with antibacterial and antioxidant properties. The oxygen permeability of GE nanocomposite coatings decreased gradually with the addition of NPs, and the barrier properties increased significantly. At the same time, due to the excellent antioxidant and antibacterial ability of GA, the antioxidant effect of the nanocomposite coatings increased by 119%, and the antibacterial rate against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) increased by 32% and 58%, respectively, compared with the pure GE coatings. In addition, the nanocomposite coatings can be repaired within 24 h after being scratched at room temperature. Finally, GA coated with chitosan nanoparticles can significantly delay the escape of GA, and the retardation of gallic acid release exceeded 89% in simulated solutions after 24 h immersion, extending the service life of the nanocomposite coatings.

Supramolecular Elastomers with Excellent Dielectric Properties and High Recyclability Based on the Coordinative Bond

The enhancement in dielectric properties and self-healing ability for dielectric materials has been a challenging subject these years. Herein, a series of self-healed dielectric elastomers by combining the ferric ions and carboxyl-containing poly(sulfone siloxane)s is reported. Experimental results indicate the excellent dielectric properties of obtained elastomers, as the dielectric constant up to 12.8. SEM micrographs exhibit that carboxyl groups and ferric ions can aggregate together to generate clusters, which further result in interfacial polarization. Besides, high polarity dipole units including sulfonyl units and carboxyl groups contribute to dipole polarization. The overlay of the two mentioned polarization eventually results in the high dielectric property. The dielectric constant obviously increases with the contents of carboxyl groups and ferric ions. Moreover, the samples are feasible for recycling and reprocessing with high self-healing efficiency, owing to the reversibility of the coordination bond. A self-healing efficiency of 92.1% in tensile strength of the obtained samples can be reached after 2 h treatment at 60 °C. And the elastomers can also conveniently recover most mechanical properties after solution treatment. This work may offer a promising method for preparing dielectric elastomers with high dielectric properties and self-healing ability.

Stress-Induced Shape-Shifting Materials Possessing Autonomous Self-Healing and Scratch-Resistant Ability

Covalent adaptable networks (CANs) capable of both shape-shifting and self-healing ability offer a viable alternative to 4D printing technology to gain access to various complex shapes in a simplified manner. However, most of the reported CANs exhibit shape-shifting ability in the presence of temperature, light or chemical stimuli, which restricts their further utilization as realization of such a controlled environment is not feasible under complex scenarios. Herewith, we report a set of CANs based on a room-temperature exchangeable thia-Michael adduct, which undergoes rearrangement in network topology on application of external stress. These CANs with tensile strength (≤6 MPa) and modulus (≤71.4 MPa) adopt to any programmed shape under application of nominal stress. The CANs also exhibit stress-induced recyclability, self-welding and self-healing ability under ambient conditions. The transparency and ambient condition self-healing ability render these CANs to be utilized as scratch-resistant coatings on display items.

Self-Healing, High-Strength, and Antimicrobial Polysiloxane Based on Amino Acid Hydrogen Bond

Recent years have witnessed the rapid development of self-healing and recyclable materials because they can extend the life of the material. For polysiloxane materials, exploring polysiloxanes with high-strength and self-healing properties remains a challenge. In this work, a high-strength and self-healing polysiloxane containing N-acetyl-L-cysteine (NACL) side groups is prepared. The NACL is used to form strong hydrogen bonds to build a self-healing network. Molecular simulations help explain the reasons and processes for the repair of modified polysiloxanes. On the one hand, the obtained modified polysiloxanes have good self-healing properties. The self-healing efficiency of modified polysiloxane can reach 96.9%. As the number of NACL increases, the tensile strength of the modified polysiloxane increases. For PMVS-30%NACL, the tensile strength can reach 4.36 MPa, and the strain can reach 586%. On the other hand, modified polysiloxane has an apparent inhibitory effect on Staphylococcus aureus. With the increase in the number of NACL, the antibacterial effect of modified polysiloxane is more obvious. Furthermore, NACL is a bio-based amino acid with excellent biocompatibility. This work expands the idea of designing and synthesizing high-strength polysiloxanes with antibacterial properties. It has great potential in the field of polysiloxane antimicrobial coatings.

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.

Zinc(II) Carboxylate Coordination Polymers with Versatile Applications

This review considers the applications of Zn(II) carboxylate-based coordination polymers (Zn-CBCPs), such as sensors, catalysts, species with potential in infections and cancers treatment, as well as storage and drug-carrier materials. The nature of organic luminophores, especially both the rigid carboxylate and the ancillary N-donor bridging ligand, together with the alignment in Zn-CBCPs and their intermolecular interaction modulate the luminescence properties and allow the sensing of a variety of inorganic and organic pollutants. The ability of Zn(II) to act as a good Lewis acid allowed the involvement of Zn-CBCPs either in dye elimination from wastewater through photocatalysis or in pathogenic microorganism or tumor inhibition. In addition, the pores developed inside of the network provided the possibility for some species to store gaseous or liquid molecules, as well as to deliver some drugs for improved treatment.

Digital light 3D printing of a polymer composite featuring robustness, self-healing, recyclability and tailorable mechanical properties

Producing lightweight structures with high weight-specific strength and stiffness, self-healing abilities, and recyclability, is highly attractive for engineering applications such as aerospace, biomedical devices, and smart robots. Most self-healing polymer systems used to date for mechanical components lack 3D printability and satisfactory load-bearing capacity. Here, we report a new self-healable polymer composite for Digital Light Processing 3D Printing, by combining two monomers with distinct mechanical characteristics. It shows a desirable and superior combination of properties among 3D printable self-healing polymers, with tensile strength and elastic modulus up to 49 MPa and 810 MPa, respectively. Benefiting from dual dynamic bonds between the linear chains, a healing efficiency of above 80% is achieved after heating at a mild temperature of 60 °C without additional solvents. Printed objects are also endowed with multi-materials assembly and recycling capabilities, allowing robotic components to be easily reassembled or recycled after failure. Mechanical properties and deformation behaviour of printed composites and lattices can be tuned significantly to suit various practical applications by altering formulation. Lattice structures with three different architectures were printed and tested in compression: honeycomb, re-entrant, and chiral. They can regain their structural integrity and stiffness after damage, which is of great value for robotic applications. This study extends the performance space of composites, providing a pathway to design printable architected materials with simultaneous mechanical robustness/healability, efficient recoverability, and recyclability.

Block Poly(carbonate-ester) Ionomers as High-Performance and Recyclable Thermoplastic Elastomers

Thermoplastic elastomers based on polyesters/carbonates have the potential to maximize recyclability, degradability and renewable resource use. However, they often underperform and suffer from the familiar trade-off between strength and extensibility. Herein, we report well-defined reprocessable poly(ester-b-carbonate-b-ester) elastomers with impressive tensile strengths (60 MPa), elasticity (>800 %) and recovery (95 %). Plus, the ester/carbonate linkages are fully degradable and enable chemical recycling. The superior performances are attributed to three features: (1) Highly entangled soft segments; (2) Fully reversible strain-induced crystallization and (3) Precisely placed ZnII -carboxylates dynamically crosslinking the hard domains. The one-pot synthesis couples controlled cyclic monomer ring-opening polymerization and alternating epoxide/anhydride ring-opening copolymerization. Efficient convresion to ionomers is achieved by reacting vinyl-epoxides to install ZnII -carboxylates.

Advances and Challenges of Self-Healing Elastomers: A Mini Review

In the last few decades, self-healing polymeric materials have been widely investigated because they can heal the damages spontaneously and thereby prolong their service lifetime. Many ingenious synthetic procedures have been developed for fabricating self-healing polymers with high performance. This mini review provides an impressive summary of the self-healing polymers with fast self-healing speed, which exhibits an irreplaceable role in many intriguing applications, such as flexible electronics. After a brief introduction to the development of self-healing polymers, we divide the development of self-healing polymers into five stages through the perspective of their research priorities at different periods. Subsequently, we elaborated the underlying healing mechanism of polymers, including the self-healing origins, the influencing factors, and direct evidence of healing at nanoscopic level. Following this, recent advance in realizing the fast self-healing speed of polymers through physical and chemical approaches is extensively overviewed. In particular, the methodology for balancing the mechanical strength and healing ability in fast self-healing elastomers is summarized. We hope that it could afford useful information for research people in promoting the further technical development of new strategies and technologies to prepare the high performance self-healing elastomers for advanced applications.

Phase-locked constructing dynamic supramolecular ionic conductive elastomers with superior toughness, autonomous self-healing and recyclability

Stretchable ionic conductors are considerable to be the most attractive candidate for next-generation flexible ionotronic devices. Nevertheless, high ionic conductivity, excellent mechanical properties, good self-healing capacity and recyclability are necessary but can be rarely satisfied in one material. Herein, we propose an ionic conductor design, dynamic supramolecular ionic conductive elastomers (DSICE), via phase-locked strategy, wherein locking soft phase polyether backbone conducts lithium-ion (Li⁺) transport and the combination of dynamic disulfide metathesis and stronger supramolecular quadruple hydrogen bonds in the hard domains contributes to the self-healing capacity and mechanical versatility. The dual-phase design performs its own functions and the conflict among ionic conductivity, self-healing capability, and mechanical compatibility can be thus defeated. The well-designed DSICE exhibits high ionic conductivity (3.77 × 10⁻³ S m⁻¹ at 30 °C), high transparency (92.3%), superior stretchability (2615.17% elongation), strength (27.83 MPa) and toughness (164.36 MJ m⁻³), excellent self-healing capability (~99% at room temperature) and favorable recyclability. This work provides an interesting strategy for designing the advanced ionic conductors and offers promise for flexible ionotronic devices or solid-state batteries.

Stretchable ionic conductors are attractive candidates for flexible ionotronics but combining high conductivity with excellent mechanical properties is challenging. Herein, the authors combine these properties in a dynamic supramolecular ionic conductive elastomer enabling lithium-ion transport in the soft phase and dynamic disulfide and supramolecular hydrogen bonding in the hard segments.

Synergetic improvement in the mechanical properties of polyurethanes with movable crosslinking and hydrogen bonds

Polyurethane (PU) materials with movable crosslinking were prepared by a typical two-step synthetic process using an acetylated γ-cyclodextrin (TAcγCD) diol compound. The soft segment of PU is polytetrahydrofuran (PTHF), and the hard segment consists of hexamethylene diisocyanate (HDI) and 1,3-propylene glycol (POD). The synthesized PU materials exhibited the typical mechanical characteristics of a movable crosslinking network, and the presence of hydrogen bonds from the urethane bonds resulted in a synergistic effect. Two kinds of noncovalent bond crosslinking increased the Young's modulus of the material without affecting its toughness. Fourier transform infrared spectroscopy and X-ray scattering measurements were performed to analyze the effect of introducing movable crosslinking on the internal hydrogen bond and the microphase separation structure of PU, and the results showed that the carbonyl groups on TAcγCD could form hydrogen bonds with the PU chains and that the introduction of movable crosslinking weakened the hydrogen bonds between the hard segments of PU. When stretched, the movable crosslinking of the PU materials suppressed the orientation of polymer chains (shish-kebab orientation) in the tensile direction. The mechanical properties of the movable crosslinked PU materials show promise for future application in the industrial field.

Controllable Physical Synergized Triboelectricity, Shape Memory, Self-Healing, and Optical Sensing with Rollable Form Factor by Zn cluster

To build devices offering users comfortable experience, it is important to focus on form factor and multifunctionality. In this study, for the first time, multifunctional Zn clusters with shape memory, self-healing, triboelectricity, and optical sensing synergized with rollable form factor are designed and fabricated by coordinating COO- and Zn2+ . As pore forming agent, Zn clusters produce hierarchical porous structure depending on Zn amount. Zn clusters are applied as message transmitters and charge containers in optical sensing and corona charge injection, respectively. Moreover, Zn clusters in PVB-COO-Zn serve as positive tribomaterial due to Zn ion doping effect, increasing the output performance as the Zn amount reaches 20 wt%. In addition, injecting positive charge into PVB-COO-Zn 20 lead to more than 24 times increase in output performance compared to those of non-porous structures. The reversibility of Zn clusters endows shape memory and self-healing, synergized with the rollable form factor. The rollability is implemented using the long alkyl chain and the energy absorption of porous structure, providing damage resistance. The advancements in this work provide opportunities for multifunctional and unique applications (shape memory rotating-triboelectric nanogenerator, rollable self-healing touchpad, hidden tag) synergized with rollability that accomplishes working in broadened condition in near future.

Rigidity-Tuned Full-Color Emission: Uncommon Luminescence Change from Polymer Free-Volume Variations

Probing the rigidity change of microenvironments via tracking embedded molecular fluorophore emissions represents a robust approach to monitor various polymer microstructural evolutions and biomolecular events with a high spatiotemporal resolution. However, reported fluorophores exclusively blueshift their emissions (termed as "rigidochromism") or merely alter intensities upon rigidification, suffering from inferior sensitivities, low-contrast outputs, and attenuated biocompatibilities. Here, phenanthridine-fused triazatruxene fluorophores (PTFs) with pronounced bathochromic emission (up to 135 nm) toward rigidifying media at a low loading of 5 ppm without sacrificing the quantum yields and lifetime are developed. PTFs effectively interact with polymeric matrixes through polar-π interactions and form charge-transfer complexes, resulting to a remarkable fluorescent color change from blue to red-orange over matrix rigidifying. Such a unique anti-rigidochromism enables a highly sensitive rigidity detection (i.e., a subtle polymer molecular-weight change (as low as 1000 Da vs up to 10 kDa for conventional probes) can result to obvious emission color changes). PTFs are able to noninvasively detect polymerization kinetics and in situ optically report polymer degradations. The broadly (nearly full-spectrum) tunable emission and the efficient coupling between anti-rigidochromism and polymer hierarchical structures/topologies render fluorescence with controlled wavelength and chirality, leading to an unprecedented free-volume-based data encryption and anti-counterfeiting technology with a superhigh security level.

Exploiting Sodium Coordination in Alternating Monomer Sequences to Toughen Degradable Block Polyester Thermoplastic Elastomers

Thermoplastic elastomers (TPEs) that are closed-loop recyclable are needed in a circular material economy, but many current materials degrade during recycling, and almost all are pervasive hydrocarbons. Here, well-controlled block polyester TPEs featuring regularly placed sodium/lithium carboxylate side chains are described. They show significantly higher tensile strengths than unfunctionalized analogues, with high elasticity and elastic recovery. The materials are prepared using controlled polymerizations, exploiting a single catalyst that switches between different polymerization cycles. ABA block polyesters of high molar mass (60–100 kg mol^–1; 21 wt % A-block) are constructed using the ring-opening polymerization of ε-decalactone (derived from castor oil; B-block), followed by the alternating ring-opening copolymerization of phthalic anhydride with 4-vinyl-cyclohexene oxide (A-blocks). The polyesters undergo efficient functionalization to install regularly placed carboxylic acids onto the A blocks. Reacting the polymers with sodium or lithium hydroxide controls the extent of ionization (0–100%); ionized polymers show a higher tensile strength (20 MPa), elasticity (>2000%), and elastic recovery (>80%). In one case, sodium functionalization results in 35× higher stress at break than the carboxylic acid polymer; in all cases, changing the quantity of sodium tunes the properties. A leading sample, 2-COONa75 (M_n 100 kg mol^–1, 75% sodium), shows a wide operating temperature range (−52 to 129 °C) and is recycled (×3) by hot-pressing at 200 °C, without the loss of mechanical properties. Both the efficient synthesis of ABA block polymers and precision ionization in perfectly alternating monomer sequences are concepts that can be generalized to many other monomers, functional groups, and metals. These materials are partly bioderived and have degradable ester backbone chemistries, deliver useful properties, and allow for thermal reprocessing; these features are attractive as future sustainable TPEs.

Flexible thermal conductive Al2O3@siloxane composite with rapid self-healing property based on carboxyl-amine dynamic reversible bonds

Thermal interface materials (TIMs) are one of the efficacious ways to alleviate the heat accumulation problem of microelectronics devices. However, conventional TIMs based on polydimethylsiloxane (PDMS) always suffer from mechanical damage, leading to shortened service life or loss of thermal conductivity. In this work, we fabricated a high-thermal conductivity and fast self-healable Al₂O₃@siloxane composite by hydrosilylation reaction. The siloxane matrix consisted of thermosetting silicone rubber matrix (SR) and heat reversibility matrix (SCNR); the SR was synthesized via hydrosilylation between silicon hydrogen bond and vinyl, the SCNR was fabricated by thermal-curing between amino and carboxyl functionalized PDMS. Different sized spherical Al₂O₃ fillers were introduced into the SR/SCNR matrix system to construct the Al₂O₃@SR/SCNR composites. By adjusting the ratio of SR/SCNR, the obtained composites can achieve flexibility, self-healing and high filling simultaneously. It is notable that the self-healing efficiency of the composite is high, up to 95.6% within 3 minutes with 6.7 wt% mass ratio of SCNR/SR; these fast self-healing behaviors benefit from the assistance of thermal diffusion by 3D heat conduction pathways on the rearrangement of the dynamic cross-linked network. The resultant composites also exhibited the optimal thermal conductivity of 5.85 W mK⁻¹. This work provides a novel approach for constructing longer service life and high thermal conductivity multifunctional TIM based PDMS.

Thermal interface materials (TIMs) are one of the efficacious ways to alleviate the heat accumulation problem of microelectronics devices.

Ionic poly(dimethylsiloxane)-silica nanocomposites: Dispersion and self-healing

ABSTRACT

Poly(dimethylsiloxane) (PDMS)-based nanocomposites have attracted increasing attention due to their inherent outstanding properties. Nevertheless, the realization of high levels of dispersion of nanosilicas in PDMS represents a challenge arising from the poor compatibility between the two components. Herein, we explore the use of ionic interactions located at the interface between silica and a PDMS matrix by combining anionic sulfonate-functionalized silica and cationic ammonium-functionalized PDMS. A library of ionic PDMS nanocomposites was synthesized and characterized to highlight the impact of charge location, density, and molecular weight of ionic PDMS polymers on the dispersion of nanosilicas and the resulting mechanical reinforcement. The use of reversible ionic interactions at the interface of nanoparticles-polymer matrix enables the healing of scratches applied to the surface of the nanocomposites. Molecular dynamics simulations were used to estimate the survival probability of ionic cross-links between nanoparticles and the polymer matrix, revealing a dependence on polymer charge density.

IMPACT STATEMENT

Poly(dimethylsiloxane) (PDMS) has been widely used in diverse applications due to its inherent attractive and multifunctional properties including optical transparency, high flexibility, and biocompatibility. The combination of such properties in a single polymer matrix has paved the way toward a wide range of applications in sensors, electronics, and biomedical devices. As a liquid at room temperature, the cross-linking of the PDMS turns the system into a mechanically stable elastomer for several applications. Nanofillers have served as a reinforcing agent to design PDMS nanocomposites. However, due to significant incompatibility between silica and the PDMS matrix, the dispersion of nanosilica fillers has been challenging. One of the existing strategies to improve nanoparticle dispersion consists of grafting oppositely charged ionic functional groups to the nanoparticle surface and the polymer matrix, respectively, creating nanoparticle ionic materials. Here, this approach has been explored further to improve the dispersion of nanosilicas in a PDMS matrix. The designed ionic PDMS nanocomposites exhibit self-healing properties due to the reversible nature of ionic interactions. The developed synthetic approach can be transferred to other kinds of inorganic nanoparticles dispersed in a PDMS matrix, where dispersion at the nanometer scale is a prerequisite for specific applications such as encapsulants for light-emitting diodes (LEDs).

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1557/s43577-022-00346-x.

Zn(II) metal-organic architectures from ether-bridged tetracarboxylate linkers: assembly, structural variety and catalytic features

Semi-flexible aromatic polycarboxylic acids are gaining impetus in crystal engineering of functional coordination polymers (CPs). This work opens up the use of two ether-bridged tetracarboxylic acids, 3-(2,5-dicarboxyphenoxy)phthalic acid (H4dpa) and...