Self-healing Polymeric Materials Research Articles

Recent Advances in Self-healing Polymer Materials: Routes and Strategies

Abstract:: The most intriguing area of scientific study and engineering applications is to synthetize materials that can autonomously heal damage similar to biological tissues. Since the concept of self-healing materials was established, several variations of self-healing polymer materials have been developed based on distinct healing techniques. This review outlines the most recent breakthroughs in self-healing polymers and utilizes the opportunity to categories the descriptions of self-healing technologies in the literatures according to extrinsic and intrinsic routes (noncovalent bonds, physical interaction, and covalent bonds). The major focus is on the routes and strategies used to generate self-healing polymer materials. In addition, the strengths and weaknesses of polymer materials with different self-healing routes and strategies in terms of mechanical and self-healing properties were summarized. Furthermore, we also reviewed the progress of the development from a single selfhealing mechanism to multiple self-healing mechanisms to achieve balanced comprehensive performance. Finally, the future trajectory of self-healing polymers is envisioned.

Practical Applications of Self-Healing Polymers Beyond Mechanical and Electrical Recovery.

Self-healing polymeric materials, which can repair physical damage, offer promising prospects for protective applications across various industries. Although prolonged durability and resource conservation are key advantages, focusing solely on mechanical recovery may limit the market potential of these materials. The unique physical properties of self-healing polymers, such as interfacial reduction, seamless connection lines, temperature/pressure responses, and phase transitions, enable a multitude of innovative applications. In this perspective, the diverse applications of self-healing polymers beyond their traditional mechanical strength are emphasized and their potential in various sectors such as food packaging, damage-reporting, radiation shielding, acoustic conservation, biomedical monitoring, and tissue regeneration is explored. With regards to the commercialization challenges, including scalability, robustness, and performance degradation under extreme conditions, strategies to overcome these limitations and promote successful industrialization are discussed. Furthermore, the potential impacts of self-healing materials on future research directions, encompassing environmental sustainability, advanced computational techniques, integration with emerging technologies, and tailoring materials for specific applications are examined. This perspective aims to inspire interdisciplinary approaches and foster the adoption of self-healing materials in various real-life settings, ultimately contributing to the development of next-generation 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.

Highly entangled elastomer with ultra-fast self-healing capability and high mechanical strength

Self-healing polymeric material, which can heal the cracks repeatedly and thus definitely prolong their lifetime in practical applications, has attracted intensive interesting in recent years. However, it is still a great challenge to both achieve fast self-healing ability and high mechanical strength. Considering the mechanism of fast self-healing is the re-bonding of dynamic bonds in the fracture surfaces, the dense physical cross-linking might be a good option for fast self-healing polymer to solve the trade-off between self-healing ability and mechanical strength. To this end, the highly entangled polymer chains are thereby introduced to improve the mechanical strength of the elastomer by simply increasing the monomer concentration. As expected, the mechanical strength of the resultant elastomers increases with monomer concentration, accompanied by a slight decline in self-healing ability. In addition, further increment of the mechanical strength to 18.4 Mpa is achieved by introducing anisotropic structure into the highly entangled polymers by pre-stretching. Most importantly, the resultant polymer exhibits high recovery and fast self-healing ability with a healing efficiency of 86.2 % after only 30 s healing at room temperature. Moreover, the highly entangled polymer chains also improve the actuation performance of the elastomer with anisotropic structure, which can lift up about 1000 times of its own weight reversibly upon heating–cooling cycles with a maximum tensile stroke of ca. 28 %.

Properties and Applications of Self-Healing Polymeric Materials: A Review.

Self-healing polymeric materials, engineered to autonomously self-restore damages from external stimuli, are at the forefront of sustainable materials research. Their ability to maintain product quality and functionality and prolong product life plays a crucial role in mitigating the environmental burden of plastic waste. Historically, initial research on the development of self-healing materials has focused on extrinsic self-healing systems characterized by the integration of embedded healing agents. These studies have primarily focused on optimizing the release of healing agents and ensuring rapid self-healing capabilities. In contrast, recent advancements have shifted the focus towards intrinsic self-healing systems that utilize their inherent reactivity and interactions within the matrix. These systems offer the advantage of repeated self-healing over the same damaged zone, which is attributed to reversible chemical reactions and supramolecular interactions. This review offers a comprehensive perspective on extrinsic and intrinsic self-healing approaches and elucidates their unique properties and characteristics. Furthermore, various self-healing mechanisms are surveyed, and insights from cutting-edge studies are integrated.

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.

Mechanical Robust, Self-Healable Polyurethane Elastomer Enabled by Hierarchical Hydrogen Bonds and Disulfide Bonds.

The fabrication of mechanically robust and self-healing polymeric materials remains a formidable challenge. To address the drawbacks, a core strategy is proposed based on the dynamic hard domains formed by hierarchical hydrogen bonds and disulfide bonds. The dynamic hard domains dissipate considerable stress energy during stretching. Meanwhile, the synergistic effect of hierarchical hydrogen bonds and disulfide bonds greatly enhances the relaxation dynamics of the PU network chains, thus accelerating network reorganization. Therefore, this designed strategy effectively solves the inherent drawback between cohesive energy and relaxation dynamics of the PU network. As a result, the PU elastomer has excellent mechanical properties (9.9 MPa and 44.87 MJ/m3) and high self-healing efficiency (96.2%). This approach provides a universal but valid strategy to fabricate high-performance self-healing polymeric materials. Meanwhile, such materials can be extended to emerging fields such as flexible robotics and wearable electronics.

Bio-Based Self-Healing Polymeric Materials Derived from Furfuryl Alcohol Based on the Diels-Alder Reversible Reaction

Bio-Based Self-Healing Polymeric Materials Derived from Furfuryl Alcohol Based on the Diels-Alder Reversible Reaction

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

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

Aromatic disulfide-induced self-reinforcing polyurethane elastomer with self-healability

Developing new strategies to improve the mechanical robustness of self-healing polymer materials to meet engineering requirements remains a great challenge and research focus. Herein, a self-reinforcing strategy of self-healing polyurethane (PU) elastomer is presented to achieve simultaneous giant tensile strength (33.3 ± 1.7 MPa) and toughness (141.9 ± 3.7 MJ m−3). Two chain extenders, diethyl 2,2-bis(hydroxymethyl)malonate (BDMH) and bis(4-hydroxyphenyl) disulfide, are elaborately regulated in the molecular structure to balance the mechanical and self-healing properties. On the one hand, BDMH containing abundant ester groups provide a large number of hydrogen bond (H-bond) acceptors. On the other hand, the incorporation of aromatic disulfide forms reversible hierarchical H-bonds confined to loosely-stacked hard domains and improves the physical crosslinking density, thus realizing the self-reinforcing of PU elastomer based on the strain-induced crystallization (SIC) of polytetramethylene ether glycol (PTMEG) as the soft segment. Hierarchical H-bonds with dynamic nature acting as sacrificial bonds can dissociate and regenerate and dissipate a large amount of energy, thus contributing to mechanical robustness and self-healing properties. In addition to constructing a self-healing PU elastomer with mechanical robustness, a remarkable progress over previous work is that we perform fundamental study at the molecular level and reveal the three-stage evolution of H-bonds and aggregation structure during stretching, thus revealing the SIC behavior and mechanism, which provides a theoretical basis for the strengthening and toughening of self-healing PU elastomer.

Self-Healing Polymer Electrolytes for Next-Generation Lithium Batteries

The integration of polymer materials with self-healing features into advanced lithium batteries is a promising and attractive approach to mitigate degradation and, thus, improve the performance and reliability of batteries. Polymeric materials with an ability to autonomously repair themselves after damage may compensate for the mechanical rupture of an electrolyte, prevent the cracking and pulverization of electrodes or stabilize a solid electrolyte interface (SEI), thus prolonging the cycling lifetime of a battery while simultaneously tackling financial and safety issues. This paper comprehensively reviews various categories of self-healing polymer materials for application as electrolytes and adaptive coatings for electrodes in lithium-ion (LIBs) and lithium metal batteries (LMBs). We discuss the opportunities and current challenges in the development of self-healable polymeric materials for lithium batteries in terms of their synthesis, characterization and underlying self-healing mechanism, as well as performance, validation and optimization.

Advances in the Diels-Alder Reaction in Self-Healing Polymeric Materials

Polymeric functional materials are widely used in all aspects of everyday life. However, they are subject to a variety of environmental influences such as chemical attack, mechanical abrasion or impact and thermal decomposition, resulting in a significant shortening of the service life of polymer materials. Using traditional repair methods, the damaged part of the material is only reattached or reinforced at a macro level. Currently, more and more research is focused on smart composite materials with self-healing properties. This eliminates hidden problems in the use of the material, thereby extending its service life and broadening the range of applications. The Diels-Alder (DA) reaction is a [4+2] cycloaddition reaction between a conjugated diene and a substituted alkene. It has become a hot research topic in the field of self-healing due to its mild reaction conditions and lack of catalyst. In this paper, the progress of research on self-healing polymeric materials is reviewed with a focus on applications in DA reactions. The research progress in this field is reviewed based on the chemical structures of the prepared DA reaction-based polymers, and the development of DA reaction based self-healing polymers is investigated. Finally, the development of selfhealing polymers based on DA reactions is given as an outlook.

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.

Limonene-thioctic acid-ionic liquid polymer: A self-healing and antibacterial material for movement detection sensor

The healable smart electronic sensor can prolong its service life. Polymers with dynamic disulfide bonds are widely used in healable sensors because of their self-healing properties at room temperature, but the presence of terminal diradicals leads to their instability. Herein, attracted by the favorable reactivity of limonene (LIM) for nucleophilic proton addition, it is chosen to quench thiyl radical to prepare a self-healing polymeric material (poly TA-(EMIM)(ESO 4 )-LIM) for the sensor by thioctic acid (TA) and 1-ethyl-3-methylimidazolium ethyl sulfate [(EMIM)(ESO 4 )]. The polymeric material not only displayed long-term stability and moderate strain (640%) but also was equipped with a high adhesive strength towards various substrates. The existence of dynamic disulfide bonds and the hydrogen bonds conferred favorable self-healing capacity of the poly TA-(EMIM)(ESO 4 )-LIM. The fascinating conductivity sensitivity with gauge factors of 2.34 and 5.12 could be achieved under small deformation (0%−100%) and large deformation (100%−200%), respectively. Meanwhile, the polymeric material could detect the human movement of finger bending, elbow bending, and wrist bending, where a stable conductivity sensitivity could maintain after several cycles. Moreover, based on the natural and outstanding antibacterial activity of LIM, the antimicrobial capacity of the polymeric material is further enhanced (kill efficiency > 90%). These fascinating features make the poly TA-(EMIM)(ESO 4 )-LIM displayed great potential as an epidermal electronic for detecting human movement. • A polymeric material was obtained by limonene, thioctic acid, and ionic liquid. • The polymeric material could realize rapid network reconfiguration. • The polymeric material displayed over 90% kill efficiency towards bacteria. • The polymeric material displayed high sensitivity in detecting human movements.

Enhanced self-healing driving force in polymer materials by regulating molecular structure

For self-healing polymers, obtaining excellent healing ability and mechanical properties usually need complex chemical structure, external healing conditions, and high manufacturing difficulty. Therefore, self-healing efficiency and rate, mechanical strength, and simple structure design as well as no additional healing conditions of the material are contradictory properties and are difficult to optimize simultaneously. Herein, self-healable thermoplastic poly (urethane urea) elastomers driven by surface energy were fabricated by the introduction of asymmetric alicyclic structures and the healing properties in polymers were optimized by regulating surface energy. The results showed that with the increasing of isophorone diamine contents, the surface energy driving force increased from 36 kPa to 149 kPa, the healing time decreased from 30d to 5d, and healing efficiency, and tensile strength reached 100.9% and 4.04 MPa at room temperature. At the same time, polymers also obtained a high healing efficiency under high-temperature healing conditions. The healing mechanism is that asymmetric alicyclic structures with steric hindrance and ring flip promote the dissociation of hydrogen bonds, provide sufficient chain mobility, decrease the junction density, and improve the surface energy as well as the dissociation and reconstruction of hydrogen bonds. Energetic polymer composites using thermoplastic poly (urethane urea) elastomers as matrix obtained excellent healing properties. This study will offer a novel healing approach for developing advanced self-healing polymer materials.

Mechanically robust, instant self-healing polymers towards elastic entropy driven artificial muscles

Despite the substantial developments, it remains a huge challenge for the fabrication of soft actuators to achieve the systematic integrations of good actuating performance, high mechanical strength and self-healing ability at ambient temperature. Herein, we report the preparation of robust self-healing polymeric materials by introducing strong coordination bonds to the polymers with multiple hydrogen bonds and anisotropic chain structures. Due to the synergistic effect between the weak hydrogen and strong coordination bonds, the resultant polymer exhibits excellent mechanical strength (12.68 MPa) and instant (30 s) self-healing ability with a high healing efficiency of ca. 95 % at ambient temperature. Thanks to the entropic elasticity trapped by the anisotropic polymer chains, the resultant anisotropic polymer can be used as thermal-triggered artificial muscles with a tensile stroke of ca. 12 %. Even the healed sample can still achieve a tensile stroke of ca. 11 % repeatedly.

Self-Healing Polymeric Materials: On a Winding Road to Success

Self-Healing Polymeric Materials: On a Winding Road to Success

Reactivity and Release of Isocyanates from Microcapsules Used in Self-Healing Materials

Synthetic self-healing polymeric materials that can recover from physical or chemical damage autonomously have been explored in the past 20 years with the aim of reducing the environmental burden of polymers while exceeding the capabilities of current synthetic polymers. These smart materials contain an embedded healing agent that is exposed when the material is damaged and reacts with the outside environment to solidify in place, covering the damaged area and restoring the polymer’s properties. In this study, we investigated the reaction and release of a diisocyanate healing agent which is designed for underwater applications. Our results show that micellar and encapsulated isophorone diisocyanate (∼100 μm diameter) remain unreacted in water for at least 8 h. While this reaction rate indicates a potential for isocyanates to be released into the environment, no isocyanate was detected in flow through experiments with crushed microcapsules. Instead, the results suggest that polyurea, the product of the isocyanate and water reaction, can be released in the form of microparticles that are less than 25 μm in diameter. This study shows that the assumption of fast reaction kinetics and minimal chance of release into the environment of healing agent chemicals needs to be reconsidered.

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.

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

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