High toughness, healable, self-cleaning polydimethylsiloxane elastomers with "rigid-while-flexible" mutual network structure

Polydimethylsiloxane (PDMS) elastomers with high mechanical and healing properties are developed as smart materials for electrical power systems and electronic devices to address electrical or mechanical damage. However, the challenge is to reconcile the conflicting molecular mechanisms of mechanical and healing properties in the development of PDMS elastomers. This study adopts the "rigid-while-flexible" mutual network structure by copolymerizing the rigid polyimide (PI) with flexible segments with dynamic reversible crosslinking designed on the PDMS backbones. This elastomer (designated PSiPI) exhibits high toughness, tensile strength and elongation at break, as well as excellent healing efficiency and recyclability. Moreover, the PSiPI elastomer also exhibits good insulation and corona damage healing properties. Taking advantage of the recyclability and healing properties of PSiPI elastomers, healable superhydrophobic coatings with contact angles greater than 150° have been prepared by compositing PSiPI elastomers with SiO2. Likewise, combining the elastomer with conductive materials can create a healing flexible conductor. This "rigid-while-flexible" design approach provides important inspiration for the development of high-performance, sustainable and environmentally friendly PDMS elastomers for electrical and electronic applications.

Investigation of Multiple Shape Memory Behaviors, Thermal and Physical Properties of Benzoxazine Blended with Diamino Polysiloxane

In this research, benzoxazine (BA-a) and diamino polysiloxane (PSX750) blends were prepared at 0-50 wt% of BA-a. The interactions between two polymeric components were investigated via a Fourier Transform Infrared Spectrometer (FT-IR). The thermal properties of the blends were also determined with Dynamic Mechanical Analyzer (DMA) and Thermogravimetric Analyzer (TGA). The mechanical properties and shape memory behaviors of the blends were also investigated. The FTIR spectra exhibited the shift of the peak from 1672 to the range of 1634-1637 cm-1, which could be identified as hydrogen bonds between two polymeric domains at the contents from 30 to 50 wt%. The DMA thermograms revealed two glass transition temperatures, which could indicate a partially miscible system. The char yield values were increased, while the decomposition temperatures were decreased with an increasing benzoxazine content. Interestingly, the blends at the contents of 10 and 20 wt% presented dual-shape memory behaviors, whereas triple- or multiple-shape memory behaviors were observed with benzoxazine contents of 30 to 50 wt%. For the high-temperature recovery state, a shape memory ratio of 97.5% with a recovery time of 65 s and a shape fixity ratio of 66.7% was recorded at the content of 50 wt%. For the low-temperature recovery state, a shape recovery ratio of 98.9% was observed at the same content. Moreover, the values of the recovery ratio for four shape-recovery cycles revealed multiple shape memory behaviors with high recovery ratios in the range of 95-98%.

Solvent-Free Environmentally Friendly Method to Prepare Thermo-Reversible Fully Bio-Based Elastomers

Most rubber products come from petrochemical resources, which are increasingly in short supply. Rubber products that formed irreversible chemical bonds in the vulcanization process are difficult to recycle, resulting in a serious waste of resources. Therefore, it is important to prepare a kind of reprocessable biobased elastomers. Using furfuryl methacrylate (FMA) as the modified monomer, poly(dibutyl itaconate-myrcene-furfuryl methacrylate) (PDBIMFA) was synthesized by high-temperature emulsion polymerization successfully. The structure and compositions of PDBIMFA were characterized by Fourier transform infrared and 1H NMR, and the effects of different FMA contents on the structures and properties of PDBIMFA were systematically studied. Based on the Diels-Alder reaction, bismaleimide (BMI) and carbon black (CB) were introduced into PDBIMFA as cross-linking agents and reinforcing fillers, respectively, by the melt blending method, and PDBIMFA-BMI elastomer materials and CB/PDBIMFA-BMI elastomer composites with thermo-reversible cross-linking characteristics were prepared. The effects of the ratio of FMA and BMI on the mechanical properties of PDBIMFA-BMI were studied. PDBIMFA-BMI and CB/PDBIMFA-BMI were reprocessed twice, and the recovery rate of tensile strength was both more than 90%. The addition of CB was found to play a reinforcing role in the elastomer and with the introduction of the amount of CB, the reprocessability of composite remained at a good level. It is hoped that this research will provide a new strategy for the sustainable development of bio-based elastomer materials.

Enhanced Tensile Properties, Biostability, and Biocompatibility of Siloxane-Cross-Linked Polyurethane Containing Ordered Hard Segments for Durable Implant Application

This work developed a series of siloxane-modified polyurethane (PU-Si) containing ordered hard segments by a facile method. The polyaddition between poly(ε-caprolactone) and excess diurethane diisocyanate was carried out to synthesize a polyurethane prepolymer with terminal isocyanate groups, which was then end-capped by 3-aminopropyl triethoxysilane to produce alkoxysilane-terminated polyurethane; the target products of PU-Si were obtained with hydrolysis and the condensation of alkoxysilane groups. The chemical structures were confirmed by FT-IR and XPS, and the effect of the siloxane content or cross-linked degree on the physicochemical properties of the PU-Si films was investigated in detail. The formation of the network structure linked by Si-O-Si bonds and interchain denser hydrogen bonds endowed PU-Si films with fine phase compatibility, low crystallinity, high thermal stability, and excellent tensile properties. Due to the high cross-linked degree and low interfacial energy, the films displayed a high surface water contact angle and low equilibrium water absorption, which resulted in slow hydrolytic degradation rates. Furthermore, the evaluation of protein adsorption and platelet adhesion on the PU-Si film surface presented high resistance to biofouling, indicating superior surface biocompatibility. Consequently, the siloxane-cross-linked polyurethane, which possessed excellent tensile properties, high biostability, and superior biocompatibility, showed great potential to be explored as biomaterials for durable implants.

Intrinsically Self-Healing Polymers: From Mechanistic Insight to Current Challenges

Self-healing materials open new prospects for more sustainable technologies with improved material performance and devices' longevity. We present an overview of the recent developments in the field of intrinsically self-healing polymers, the broad class of materials based mostly on polymers with dynamic covalent and noncovalent bonds. We describe the current models of self-healing mechanisms and discuss several examples of systems with different types of dynamic bonds, from various hydrogen bonds to dynamic covalent bonds. The recent advances indicate that the most intriguing results are obtained on the systems that have combined different types of dynamic bonds. These materials demonstrate high toughness along with a relatively fast self-healing rate. There is a clear trade-off relationship between the rate of self-healing and mechanical modulus of the materials, and we propose design principles of polymers toward surpassing this trade-off. We also discuss various applications of intrinsically self-healing polymers in different technologies and summarize the current challenges in the field. This review intends to provide guidance for the design of intrinsic self-healing polymers with required properties.

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.

A Lamellibranchia-inspired epidermal electrode for electrophysiology

The capability to accurately monitor electrophysiological signals and instantly provide feedback to users is crucial for wearable healthcare. However, commercial gel electrodes suffer from drying out and irritation on skin with time, severely affecting signal quality for practical use. Toward a gel-free electrophysiology, epidermal electrodes that can accurately detect biosignals and simultaneously achieve the multifunctional properties of on-skin electronics needs are highly desirable. In this work, inspired by Lamellibranchia, which can adhere tightly to various surfaces using their extensible, adhesive and self-healing byssal threads, we developed a gel-free epidermal electrode to acquire high-quality electrophysiological signals based on a novel polymer substrate design. This polymer (STAR) features extreme stretchability (>2300% strain), high transparency (>90% transmittance at λ = 550 nm), gentle adhesion (adhesion strengths: tens of kPa), and rapid self-healing ability (95% healing efficiency in 10 min). Combined with silver nanowires as conductors, STAR was employed as a self-healing, stretchable and adhesive epidermal electrode for electrophysiological signal recording, showing a signal-to-noise ratio (SNR) even higher than that of commercial electrodes, and being able to control an artificial limb as an intermediate for human-machine interface. We believe our Lamellibranchia inspired STAR will pave a new way to design multifunctional polymers for epidermal electronics, accelerating the development of emerging wearable healthcare.

Physical and thermo-mechanical properties of shape memory polyurethane containing reversible chemical cross-links

Orthodontic chains are one of the main parts of orthodontic braces. In this study, in order to obtain a suitable polymer for this application as well as troubleshoot the main drawbacks such as stress relaxation and water absorption, thermoplastic polyurethane (TPU) elastomers with various compositions were synthesized and characterized by Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) analyses. Mechanical properties of samples were evaluated by tensile, elasticity, and stress relaxation tests. According to the required properties for orthodontic chain application, PU2000-311 which contains reversible crosslinks, was selected as the most favorable sample among other pure samples. Moreover, to reduce the water absorption content of PU2000-311, its nanocomposite containing 1 wt% of silica nanoparticles was prepared via solution casting method. As water content angle and field emission scanning electron microscopy (FESEM) images illustrate, incorporation of 1 wt% of modified silica nanoparticles has increased PU2000-311-1S hydrophobicity. In vitro oral environment study showed crystability of samples has recovered great portion of relaxed force. Stress relaxation study indicated samples are applicable in oral temperature range and temperature changes have assisted recovery of relaxed force and reduced treatment period. Finally, shape memory study showed that optimum samples could recover 100% of their original shape.

Preparation, characterization and properties of intrinsic self-healing elastomers

Significant advances have been made in the development of self-healing synthetic polymer materials in recent years. This review article discusses the recent progress in preparation, characterization and properties of different kinds of intrinsic self-healing elastomers based on reversible covalent bonds and dynamic supramolecular chemistry. Healing conditions, mechanical property recovery and healing efficiency are the main discussion topics. Potential applications, challenges and future prospects in self-healing elastomer fields are also discussed in the last part of this review.

Advances in intrinsic self-healing polyurethanes and related composites

Fascinating and challenging, the development of repairable materials with long-lasting, sustainable and high-performance properties is a key-parameter to provide new advanced materials. To date, the concept of self-healing includes capsule-based healing systems, vascular healing systems, and intrinsic healing systems. Polyurethanes have emerged as a promising class of polymeric materials in this context due to their ease of synthesis and their outstanding properties. This review thereby focuses on the current research and developments in intrinsic self-healing polyurethanes and related composites. The chronological development of such advanced materials as well as the different strategies employed to confer living-like healing properties are discussed. Particular attention will be paid on chemical reactions utilized for self-healing purposes. Potential applications, challenges and future prospects in self-healing polyurethane fields are also provided.

Modulating the thermomechanical properties and self-healing efficiency of siloxane-based soft polymers through metal–ligand coordination

An efficient strategy to modulate the thermomechanical properties and self-healing of soft polymers has been developed by rationally selecting the metal used for supramolecular crosslinking.

A colorless, transparent and self-healing polyurethane elastomer modulated by dynamic disulfide and hydrogen bonds

A self-healing PU elastomer modulated by disulfide and hydrogen bonding with high transparency of 97% was reported.

Imine and metal-ligand dynamic bonds in soft polymers for autonomous self-healing capacitive-based pressure sensors

In this work, a facile and simple yet effective method to generate intrinsic autonomous self-healing polymers was developed, leading to new materials that can be easily fine-tuned both mechanically and chemically. The new materials were designed to incorporate two dynamic and reversible types of chemical bonds, namely dynamic imine and metal-coordinating bonds, to enable autonomous self-healing, controlled degradability and ultra-high tunable stretchability (up to 800% strain) based on the ratio of metal to ligand incorporated. Through an easy condensation reaction, imine bonds are generated at the end-termini of a short siloxane chain. The new dynamic system was characterized by a variety of techniques, including tensile-pull strain testing, atomic force microscopy and UV-Vis spectroscopy, which showed that the highly dynamic imine bonds, combined with coordination with Fe²⁺ ions, allow for the material to regenerate 88% of its mechanical strength after physical damage. The materials were also controlled to be degraded in mild acidic conditions. Lastly, application in self-healable electronics was demonstrated through the fabrication of a capacitive-based pressure sensor, which shows good sensitivity and dynamic response (∼0.33 kPa^-1) before and after healing.

Self-Healable Supramolecular Vanadium Pentoxide Reinforced Polydimethylsiloxane-Graft-Polyurethane Composites

The self-healing ability can be imparted to the polymers by different mechanisms. In this study, self-healing polydimethylsiloxane-graft-polyurethane (PDMS-g-PUR)/Vanadium pentoxide (V₂O₅) nanofiber supramolecular polymer composites based on a reversible hydrogen bonding mechanism are prepared. V₂O₅ nanofibers are synthesized via colloidal route and characterized by XRD, SEM, EDX, and TEM techniques. In order to prepare PDMS-g-PUR, linear aliphatic PUR having one ⁻COOH functional group (PUR-COOH) is synthesized and grafted onto aminopropyl functionalized PDMS by EDC/HCl coupling reaction. PUR-COOH and PDMS-g-PUR are characterized by ¹H NMR, FTIR. PDMS-g-PUR/V₂O₅ nanofiber composites are prepared and characterized by DSC/TGA, FTIR, and tensile tests. The self-healing ability of PDMS-graft-PUR and composites are determined by mechanical tests and optical microscope. Tensile strength data obtained from mechanical tests show that healing efficiencies of PDMS-g-PUR increase with healing time and reach 85.4 ± 1.2 % after waiting 120 min at 50 °C. The addition of V₂O₅ nanofibers enhances the mechanical properties and healing efficiency of the PDMS-g-PUR. An increase of healing efficiency and max tensile strength from 85.4 ± 1.2% to 95.3 ± 0.4% and 113.08 ± 5.24 kPa to 1443.40 ± 8.96 kPa is observed after the addition of 10 wt % V₂O₅ nanofiber into the polymer.

Photo-Crosslinked Polymeric Matrix with Antimicrobial Functions for Excisional Wound Healing in Mice

Wound infection extends the duration of wound healing and also causes systemic infections such as sepsis, and, in severe cases, may lead to death. Early prevention of wound infection and its appropriate treatment are important. A photoreactive modified gelatin (GE-BTHE) was synthesized by gelatin and a conjugate formed from the 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) and the 2-hydroxyethyl methacrylate (HEMA). Herein, we investigated the photocurable polymer solution (GE-BTHE mixture) containing GE-BTHE, poly(ethylene glycol) diacrylate (PEGDA), chitosan, and methylene blue (MB), with antimicrobial functions and photodynamic antimicrobial chemotherapy for wound dressing. This photocurable polymer solution was found to have fast film-forming property attributed to the photochemical reaction between GE-BTHE and PEGDA, as well as the antibacterial activity in vitro attributed to the ingredients of chitosan and MB. Our in vivo results also demonstrated that untreated wounds after 3 days had the same scab level as the GE-BTHE mixture-treated wounds after 20 s of irradiation, which indicates that the irradiated GE-BTHE mixture can be quickly transferred into artificial scabs to protect wounds from an infection that can serve as a convenient excisional wound dressing with antibacterial efficacy. Therefore, it has the potential to treat nonhealing wounds, deep burns, diabetic ulcers and a variety of mucosal wounds.

Polymer nanocomposite-enabled high-performance triboelectric nanogenerator with self-healing capability

Triboelectric nanogenerators (TENG) have been proven to be effective for the collection of low-frequency vibrational energy in the environment. However, most polymer materials as friction layers are highly susceptible to mechanical damage during operation, which reduces the performance and lifetime of TENG. Herein, we report a high-performance, flexible triboelectric nanogenerator with reproducible self-healing electronic characteristics. Based on its soft and flexible polymers, the self-healing triboelectric nanogenerator (SH-TENG) can achieve a peak power of 2.5 W m-2 and triboelectric charge density of about 100 μC m-2. High-conductance Ag nanowires (AgNWs) are semi-embedded in the polymer to fabricate all-in-one friction layers and for an enhanced self-healing process. Both the output voltage and current of the healed device can reach up to about 99% of their original values even after five cutting/healing cycles. The fabricated SH-TENG has excellent stability and flexibility, which presents a significant step towards the fabrication of reliable triboelectric nanogenerators with recoverability and low maintenance costs.

Photocured Materials with Self-Healing Function through Ionic Interactions for Flexible Electronics

Photocured materials with self-healing function have the merit of long lifetime and environmentally benign preparation process and thus find potential applications in various fields. Herein, a novel imidazolium-containing photocurable monomer, (6-(3-(3(2-hydroxyethyl)-1 H-imidazol-3-ium bromide)propanoyloxy)hexyl acrylate, IM-A), was designed and synthesized. Self-healing polymers were prepared by fast photocuring with IM-A, isobornyl acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, and 2-hydroxyethyl acrylate as the monomers. The mechanical and self-healing properties of the polymers were tuned by varying the contents of IM-A and other monomers. The as-prepared self-healing polymer IB7-IM5 exhibited a tensile strength of 3.1 MPa, elongation at break of 205%, healing efficiency of 93%, and a wide healing temperature range from room temperature to 120 °C. The self-healing polymer was also employed as a flexible substrate to fabricate a flexible electronic device, which could be healed and completely restore its conductivity after the device was damaged.

Silicone-Containing Biodegradable Smart Elastomeric Thermoplastic Hyperbranched Polyurethane

Silicone-containing biobased hyperbranched polyurethane thermoplastic elastomers at different compositions were reported for the first time. The structures of the polymers were evaluated from Fourier transform infrared spectroscopy, NMR, X-ray diffraction, and energy-dispersive X-ray spectroscopy analyses. The synthesized elastomers possess high molecular weight (1.11-1.38 × 10⁵ g·mol^-1) and low glass transition temperature (from -40.0 to -27.3 °C). These polymers exhibited multistimuli responsive excellent repeatable intrinsic self-healing (100% efficiency), shape recovery (100%), and efficient self-cleaning (contact angle 102°-107°) abilities along with exceptional elongation at break (2834-3145%), high toughness (123.3-167.8 MJ·m^-3), good impact resistance (18.3-20.3 kJ·m^-1), and adequate tensile strength (5.9-6.9 MPa). Furthermore, high thermal stability (253-263 °C) as well as excellent UV and chemical resistance was also found for the polymers. Most interestingly, controlled bacterial biodegradation under exposure of Pseudomonas aeruginosa bacterial strains demonstrated them as sustainable materials. Therefore, such biobased novel thermoplastic polyurethane elastomers with self-healing, self-cleaning, and shape memory effects possess great potential for their advanced multifaceted applications.

Polydimethylsiloxane incorporated with reduced graphene oxide (rGO) sheets for wound dressing application: Preparation and characterization

Toward fabricating a novel multifunctional wound dressing material, we incorporated a series of contents of reduced graphene oxide (rGO) sheets into polydimethylsiloxane (PDMS) matrix to prepare the rGO-PDMS composite membrane and be used for wound dressing. The pore structure, dispersion of rGO, physical properties, water vapor transmission rate (WVTR), cytotoxicity and antibacterial activity were studied. Finally, the effect of the rGO-PDMS composite membrane on wound healing was investigated on a murine full-thickness skin wound model. The rGO-PDMS composite membrane exhibited bionic performance (ordered pore structure and suitable WVTR), improved mechanical properties, good compatibility and effective antibacterial activity. In vivo experiment indicated that the rGO-PDMS composite membrane could accelerate wound healing via enhancement of the re-epithelialization and granulation tissue formation. These findings suggest that rGO doping PDMS uniquely resulted in a multifunctional material for potential use in wound dressing.

A Highly Stretchable Self-Healing Poly(dimethylsiloxane) Elastomer with Reprocessability and Degradability

It is a challenge to synthesize materials that possess the properties of high stretchability and self-healability. Herein a new poly(dimethylsiloxane) elastomer with high stretchability, room-temperature self-healability, repeatable reprocessability, and controlled degradability is reported by incorporating an aromatic disulfide bond and imine bond. The as-prepared elastomer can be stretched to over 2200% of its original length. Without external stimuli, a damaged sheet can completely heal in 4 h. In addition, the elastomer can be reprocessed multiple times without obvious performance degradation and degraded controllably by three ways. All these properties of the elastomer can be ascribed to the unique dual-dynamic-covalent sacrificial system.

Thermo-reversible self-healing in a fluorous crosslinked copolymer

Self-healing in a fluorous copolymer material enhances its safety index and extends its working lifetime.

Thermoresponsive hybrid double-crosslinked networks using magnetic iron oxide nanoparticles as crossing points

Preparation and characterization of stimuli-sensitive hybrid double-crosslinked hydrogels based on iron oxide nanoparticles as the nano-crosslinkers and a difuran-functionalized PEO as the diene partner for the thermoreversible Diels–Alder reaction.