Bio-Based, Self-Healing, Recyclable, Reconfigurable Multifunctional Polymers with Both One-Way and Two-Way Shape Memory Properties

Self-healing and recyclable vitrimers enabled by dual-dynamic cross-linked networks with biomass citric acid-diaminodecane salt modified hydrotalcites

Traditional petroleum-based synthetic leather exhibits multiple limitations, including non-sustainability, non-biodegradability, environmental contamination and resource inefficiency. Bio-based polymers serve as sustainable matrix materials for synthetic leather production, effectively mitigating petroleum dependence while enabling sustainable manufacturing. In this work, epoxidized natural rubber (ENR)/citric acid (CA)-decanediamine (DA) salt intercalated layered double hydroxides (LDHs) nanocomposites were prepared. The nanocomposites were specifically designed as surface-layer components for bio-based synthetic leathers. LDHs with interlayer spacing (17.9 Å) were synthesized through ion exchange, enabling effective exfoliation and homogeneous dispersion within the ENR matrix. The crosslinking characteristics, mechanical and dynamic properties of ENR composites under different CA-DA salt modified LDHs (CA-DA LDHs) concentrations were surveyed in detail. The shortest vulcanization time (t90 = 21.9 min) and highest torque were observed in ENR vitrimers containing 30 wt% nano-filler loading. A progressive increase in crosslink density and mechanical performance was recorded with increasing CA-DA LDHs contents. ENR30 demonstrated the maximum tensile strength of 8.0 MPa, significantly exceeding the 1.3 MPa measured for unfilled ENR0, which was attributed primarily to the enhanced crosslink networks formation and optimized LDHs dispersion characteristics. Notably, the dynamic properties of ENR were conferred by dual reconfigurable cross-linked network comprising β-hydroxy ester bonds and hydrogen-bonding interactions, which facilitated rapid stress relaxation (τ* = 53 s at 200 °C for ENR30) and thermally induced topological rearrangement. This architectural design enabled recovery efficiencies exceeding 90 % after multiple reprocessing cycles, demonstrating excellent network reconfigurability. With the combination of mechanical strength and dynamic activity, ENR vitrimers exhibit potential as the bio-based surface layer in synthetic leather to replace traditional petroleum-based leather.

Shape Memory Networks With Tunable Self-Stiffening Kinetics Enabled by Polymer Melting-Recrystallization

Shape memory polymers (SMPs) are deformable materials capable of recovering from a programmed temporary shape to a permanent shape under specific stimuli. However, shape recovery of SMPs is often accompanied by the evolution of materials from a stiff to soft state, leading to a significant decrease in strength/modulus and thereby impacting their practical applications. Although some attempts are made to pursue the SMPs with self-stiffening capability after shape recovery, the modulus increase ratio is much limited. Inspired by the recrystallization process of CaCO3 during crab molting, a novel and universal strategy is developed to construct water-free self-stiffening SMPs by using a single thermal stimulus through harnessing the polymer melting-recrystallization. The shape recovery is achieved through the melting of polymer primary crystals, followed by the self-stiffening via polymer recrystallization at the same recovery temperature, in which the modulus increase rate and ratio can be programmed in a wide range. Additionally, conceptual applications of these self-stiffening SMPs as artificial stents with self-enhancing supporting function are successfully demonstrated. This work is believed to provide new insights for developing the advanced shape memory devices.

Smart Polymeric Composite Thermal Switch for Geothermal Energy Harvesting

Geothermal energy represents a promising sustainable power source that harnesses Earth's natural heat through water circulation systems. A critical challenge in geothermal power generation is controlling the water heating process through formation of cracks in hot zones. This requires an innovative thermal switch or reversible proppant that can regulate water flow and ensure optimal heat absorption before extraction for electricity generation. In this study, we designed and synthesized a composite thermal switch with a polymeric artificial muscle embedded in a fluoroelastomer matrix. In this design, the fluoroelastomer protects the artificial muscle from superhot water (200 °C or above) damage and also provides tensile stress to the muscle; the artificial muscle provides the desired reversible actuation. In this study, poly(vinylidene fluoride-co-bexafluoropropylene) (PVDF-HFP) was cross-linked by dicumyl peroxide (DCP) to form a fluoroelastomer PVDF-HFP/DCP. A Nylon fiber was twisted until it was used to coil as the artificial muscle. Under zero external loading, the composite thermal switch exhibited a maximum contraction upon heating (CUH) of about 10.76% and expansion upon cooling (EUC) of about 10.89% when the temperature cycled from 25 to 200 °C. Furthermore, the CUH and EUC were about 2.12 and 3.36%, respectively, when the temperature cycled from 150 to 200 °C. The composite thermal switch still exhibited excellent reversible actuation and chemical stability after soaking in 200 °C water within a pressure vessel for 4 weeks. A design-oriented structural mechanics model was also developed to evaluate the various design parameters on the reversible actuation of the smart thermal switch. To further highlight the performance of PVDF-HFP/DCP, we also prepared three other fluorinated rubbers as controls. This composite thermal switch shows promise as a smart proppant or valve for enhanced geothermal systems, offering the potential to improve heat extraction efficiency through controlled fracture conductivity.

Mechanically Adaptive Materials Based on Dynamic Chemical Bonds

Adaptiveness is an important feature for biological creatures to survive and interact with variable environments. Mechanically adaptive polymers (MAPs), which have been developed recently inspired by this adaptive nature, can regulate their mechanical properties in response to external stimuli or environmental changes. Specifically, MAPs based on dynamic chemical bonds have been synthesized and reported as an emerging material because of the intrinsic self-adaptability, outstanding mechanical properties and durable applications. This review primarily focuses on the recent advancements in the fabrication of MAPs through the utilization of dynamic covalent bonds and non-covalent bonds. A comprehensive summary of the methodologies and mechanisms employed to attain high energy dissipation in MAPs is provided. Subsequently, the review offers incisive analyses of the intrinsic functionalities of MAPs, such as high impact-stiffening, damping, and buffering capabilities. Finally, the developmental achievements within this domain are recapitulated, the potential challenges, and future research perspectives in MAPs are deliberated.

Fabricating Remote-Controllable Dynamic Ionomer/CNT Networks via Cation-π Interaction for Multi-Responsive Shape Memory and Self-Healing Capacities

Shape memory polymers (SMPs) with remotely controllable triggering capabilities are crucial for actuating applications in biomedical and aeronautic devices. This work presents a novel ionomer/carbon nanotube (CNT) composite network with exceptional remotely controllable shape memory effects (SMEs) and self-healing capabilities. By integrating quaternary ammonium (QA) units covalently bonded to crystalline polycaprolactone (PCL) segments through a chain extension reaction, we not only enabled the formation of ion clusters that act as netpoints in PCLQA ionomers to achieve superior SMEs, but also facilitated the generation of cation-π interactions when the multiresponsive CNTs were incorporated into the PCLQA ionomer matrix. This resulted in a robust physical PCLQA@CNT network stabilized by ionic clusters and cation-π interactions, along with significantly enhanced CNT dispersion. The PCLQA@CNT composites demonstrated remarkably improved mechanical performance (tensile strength, σb > 40 MPa; elongation at break, εb > 1900%), excellent thermally induced SME (shape fixity ratio of 99.6% and shape recovery ratio of 92.3%), and exceptional antibacterial effects (>99% against Escherichia coli and Staphylococcus aureus). Furthermore, the physical dynamic interactions endowed PCLQA@CNT networks with reproducibility and welding capability. The remotely controllable shape memory and self-healing behaviors via NIR and electrical stimulation were verified and demonstrated. This work paves the way for developing remotely controllable shape memory materials for advanced intelligent devices and applications.

Chemically Recyclable, Reprocessable, and Mechanically Robust Reversible Cross-Linked Polyurea Plastics for Fully Recyclable Aramid Fiber Reinforced Composites

Aramid fiber reinforced composites (AFRCs) have received increasing attention because of their excellent comprehensive performance including high mechanical strength, high modulus, and light weight. However, full recycling of AFs from ARCFs is difficult to achieve. Herein, fully recyclable ARCFs are fabricated using reversible cross-linked polyurea plastics (PUHA) as the matrix. PUHA plastics are fabricated by cross-linking linear polyurea using hemiaminal groups. By changing the main chain structures, two types of PUHA plastics are prepared with excellent mechanical performance, which is comparable to that of traditional engineering plastics. PUHA plastics can be reprocessed at least five times without losing their original mechanical properties because of the dynamic exchangeability of the hemiaminal groups. Meanwhile, PUHA plastics can be rapidly depolymerized into linear polyurea under acidic conditions. When PUHA plastics are used as a matrix to fabricate AFRCs, the AFRCs exhibit excellent mechanical strength. Moreover, due to the simple chemical recycling ability of PUHA plastics, AFRCs can be fully decomposed into intact AFs and linear polyurea with high purity. This work presents the use of reversible cross-linked polyurea plastics in the fabrication of fully recyclable AFRCs and provides the future direction of developing fully recyclable and high-performance fiber-reinforced composites.

A cellulose-based light-management film incorporated with benzoxazine resin/tannic acid exhibiting UV/blue light double blocking and enhanced mechanical property

Cellulose, as a biomass resource, has attracted increasingly attention and extensive research by virtue of its widely sources, ideal degradability, good mechanical properties and easy modification due to its rich hydroxyl groups. Nevertheless, it is still a challenge to attain high performance cellulose-based composite film materials with diverse functional combinations. In this work, we developed a multifunctional cellulose-based film via a facile impregnation-curing strategy. Here, benzoxazine resin (BR) is used as an optically functional component to endow the microfibrillated cellulose (MFC) film with powerful light management capabilities including UV and blue light double shielding, high transmittance, and high haze. Meanwhile, the introduction of tannic acid (TA) substantially enhanced the mechanical properties of the film, including tensile strength and toughness, by constructing energy-sacrificial bonds. An effective self-healing of the film was achieved by controlling the degree of BR curing. The final films exhibited 98.24 % UV shielding and 89.98 % blue light blocking, good mechanical properties including a tensile strength of 202.21 MPa and tensile strain of 7.1 %, as well as desirable thermal healing properties supported by incompletely cured BR. This work may provide new insights into the high-value utilization of biomass resources.

Shape-Memory Polymers Based on Carbon Nanotube Composites

For the past two decades, researchers have been exploring the potential benefits of combining shape-memory polymers (SMP) with carbon nanotubes (CNT). By incorporating CNT as reinforcement in SMP, they have aimed to enhance the mechanical properties and improve shape fixity. However, the remarkable intrinsic properties of CNT have also opened up new paths for actuation mechanisms, including electro- and photo-thermal responses. This opens up possibilities for developing soft actuators that could lead to technological advancements in areas such as tissue engineering and soft robotics. SMP/CNT composites offer numerous advantages, including fast actuation, remote control, performance in challenging environments, complex shape deformations, and multifunctionality. This review provides an in-depth overview of the research conducted over the past few years on the production of SMP/CNT composites with both thermoset and thermoplastic matrices, with a focus on the unique contributions of CNT to the nanocomposite's response to external stimuli.

Photothermal-responsive lignin-based polyurethane with mechanically robust, fast self-healing, solid-state plasticity and shape-memory performance

In light of the depletion of petrochemical resources and increase in environmental pollution, there has been a significant focus on utilizing natural biomass, specifically lignin, to develop sustainable and functional materials. This research presents the development of a lignin-based polyurethane (DLPU) with photothermal-responsiveness by incorporating lignin and oxime-carbamate bonds into polyurethane network. The abundant hydrogen bonds between lignin and the polyurethane matrix, along with its cross-linked structure, contribute to DLPU's excellent mechanical strength (30.2 MPa) and toughness (118.7 MJ·m-3). Moreover, the excellent photothermal conversion ability of DLPU (54.4 %) activates dynamic reversible behavior of oxime-carbamate bonds and hydrogen bonds, thereby endowing DLPU with exceptional self-healing performance. After 15 min of near-infrared irradiation, DLPU achieves self-healing efficiencies of 96.0 % for tensile strength and 96.3 % for elongation at break. Additionally, DLPU exhibits photocontrolled solid-state plasticity as well as an excellent phototriggered shape-memory effect (70 s), with shape fixity and recovery ratios reaching 98.8 % and 95.3 %, respectively. By exploiting the spatial controllability and photothermal-responsiveness of DLPU, we demonstrate multi-dimensional responsive materials with self-healing and shape-shifting properties. This work not only promotes the development of multi-functional polyurethanes but also provides a pathway for the high-value utilization of lignin.

Towards high performance and durable soft tactile actuators

Soft actuators are gaining significant attention due to their ability to provide realistic tactile sensations in various applications. However, their soft nature makes them vulnerable to damage from external factors, limiting actuation stability and device lifespan. The susceptibility to damage becomes higher with these actuators often in direct contact with their surroundings to generate tactile feedback. Upon onset of damage, the stability or repeatability of the device will be undermined. Eventually, when complete failure occurs, these actuators are disposed of, accumulating waste and driving the consumption of natural resources. This emphasizes the need to enhance the durability of soft tactile actuators for continued operation. This review presents the principles of tactile feedback of actuators, followed by a discussion of the mechanisms, advancements, and challenges faced by soft tactile actuators to realize high actuation performance, categorized by their driving stimuli. Diverse approaches to achieve durability are evaluated, including self-healing, damage resistance, self-cleaning, and temperature stability for soft actuators. In these sections, current challenges and potential material designs are identified, paving the way for developing durable soft tactile actuators.

Nanomedicine for Diagnosis and Treatment of Atherosclerosis

With the changing disease spectrum, atherosclerosis has become increasingly prevalent worldwide and the associated diseases have emerged as the leading cause of death. Due to their fascinating physical, chemical, and biological characteristics, nanomaterials are regarded as a promising tool to tackle enormous challenges in medicine. The emerging discipline of nanomedicine has filled a huge application gap in the atherosclerotic field, ushering a new generation of diagnosis and treatment strategies. Herein, based on the essential pathogenic contributors of atherogenesis, as well as the distinct composition/structural characteristics, synthesis strategies, and surface design of nanoplatforms, the three major application branches (nanodiagnosis, nanotherapy, and nanotheranostic) of nanomedicine in atherosclerosis are elaborated. Then, state-of-art studies containing a sequence of representative and significant achievements are summarized in detail with an emphasis on the intrinsic interaction/relationship between nanomedicines and atherosclerosis. Particularly, attention is paid to the biosafety of nanomedicines, which aims to pave the way for future clinical translation of this burgeoning field. Finally, this comprehensive review is concluded by proposing unresolved key scientific issues and sharing the vision and expectation for the future, fully elucidating the closed loop from atherogenesis to the application paradigm of nanomedicines for advancing the early achievement of clinical applications.