A Fascinating Metallo-Supramolecular Polymer Network with Thermal/Magnetic/Light-Responsive Shape-Memory Effects Anchored by Fe3O4 Nanoparticles

Photoreactive silver-containing supramolecular polymers that form self-assembled nanogels for efficient antibacterial treatment

In this study, an efficient synthetic strategy and potential route to obtain a photo-reactive silver-containing cytosine-functionalized polypropylene glycol polymer (Ag-Cy-PPG) was developed by combining a hydrophilic oligomeric polypropylene glycol (PPG) backbone with dual pH-sensitive/photo-reactive cytosine-silver-cytosine (Cy-Ag-Cy) linkages. The resulting photo-responsive Ag-Cy-PPG holds great promise as a multifunctional biomedical material that generates spherical-like nanogels in water; the nanogels exhibit high antibacterial activity and thus may significantly enhance the efficacy of antibacterial treatment. Due to the formation of photo-dimerized Cy-Ag-Cy cross-linkages after UV irradiation, Ag-Cy-PPG converts into water-soluble cross-linked nanogels that possess a series of interesting chemical and physical properties, such as intense and stable fluorescence behavior, highly sensitive pH-responsive characteristics, on/off switchable phase transition behavior, and well-controlled release of silver ions (Ag+) in mildly acidic aqueous solution. Importantly, antibacterial tests clearly demonstrated that irradiated Ag-Cy-PPG nanogels exhibited strong antibacterial activity at low doses (MIC values of < 50 μg/mL) against gram-positive and gram-negative bacterial pathogens, whereas non-irradiated Ag-Cy-PPG nanogels did not inhibit the viability of bacterial pathogens. These results indicate that irradiated Ag-Cy-PPG nanogels undergo a highly sensitive structural change in the bacterial microenvironment due to their relatively unstable π-conjugated structures (compared to non-irradiated nanogels); this change results in a rapid structural response that promotes intracellular release of Ag+ and induces potent antibacterial ability. Overall, this newly created metallo-supramolecular system may potentially provide an efficient route to dramatically enhance the therapeutic effectiveness of antibacterial treatments.

Shape Memory Polyester Scaffold Promotes Bone Defect Repair through Enhanced Osteogenic Ability and Mechanical Stability

Bone tissue engineering involving scaffolds is recognized as the ideal approach for bone defect repair. However, scaffold materials exhibit several limitations, such as low bioactivity, less osseointegration, and poor processability, for developing bone tissue engineering. Herein, a bioactive and shape memory bone scaffold was fabricated using the biodegradable polyester copolymer's four-dimensional fused deposition modeling. The poly(ε-caprolactone) segment with a transition temperature near body temperature was selected as the molecular switch to realize the shape memory effect. Another copolymer segment, i.e., poly(propylene fumarate), was introduced for post-cross-linking and improving the regulation effect of the resulting bioadaptable scaffold on osteogenesis. To mimic the porous structures and mechanical properties of the native spongy bone, the pore size of the printed scaffold was set as ∼300 μm, and a comparable compression modulus was achieved after photo-cross-linking. Compared with the pristine poly(ε-caprolactone), the scaffold made from fumarate-functionalized copolymer considerably enhanced the adhesion and osteogenic differentiation of MC3T3-E1 cells in vitro. In vivo experiments indicated that the bioactive shape memory scaffold could quickly adapt to the defect geometry during implantation via shape change, and bone regeneration at the defect site was remarkably promoted, providing a promising strategy to treat bone defects in the clinic, substantial bone defects with irregular geometry.

Recent Advances in Magnetic Polymer Composites for BioMEMS: A Review

The objective of this review is to investigate the potential of functionalized magnetic polymer composites for use in electromagnetic micro-electro-mechanical systems (MEMS) for biomedical applications. The properties that make magnetic polymer composites particularly interesting for application in the biomedical field are their biocompatibility, their adjustable mechanical, chemical, and magnetic properties, as well as their manufacturing versatility, e.g., by 3D printing or by integration in cleanroom microfabrication processes, which makes them accessible for large-scale production to reach the general public. The review first examines recent advancements in magnetic polymer composites that possess unique features such as self-healing capabilities, shape-memory, and biodegradability. This analysis includes an exploration of the materials and fabrication processes involved in the production of these composites, as well as their potential applications. Subsequently, the review focuses on electromagnetic MEMS for biomedical applications (bioMEMS), including microactuators, micropumps, miniaturized drug delivery systems, microvalves, micromixers, and sensors. The analysis encompasses an examination of the materials and manufacturing processes involved and the specific fields of application for each of these biomedical MEMS devices. Finally, the review discusses missed opportunities and possible synergies in the development of next-generation composite materials and bioMEMS sensors and actuators based on magnetic polymer composites.

Magnetite Nanoparticles Functionalized with Thermoresponsive Polymers as a Palladium Support for Olefin and Nitroarene Hydrogenation

A thermoresponsive and recyclable nanomaterial was synthesized by surface modification of magnetite nanoparticles (MNPs) with poly(N-isopropylacrylamide-co-diethylaminoethyl methacrylate) (P(NIPAAm-co-DEAEMA)), having PNIPAAm as a thermoresponsive moiety and PDEAEMA for catalyst binding. Palladium (Pd) nanoparticles were incorporated into this material, and the resulting nanocatalyst was efficient in the hydrogenation of olefins and nitro compounds with turnover frequencies (TOFs) up to 750 h^-1. Consistent catalytic activity in 10 consecutive runs was observed when performing the hydrogenation at 45 °C, i.e., above the lower critical solution temperature (LCST) of the copolymer (37 °C), followed by cooling to 15 °C, i.e., below the LCST of the copolymer.

Narrow response temperature range with excellent reversible shape memory effect for semi-crystalline networks as soft actuators

Complex and controlled reversible actuation inevitably relies on changing thermal fields (direct or indirect) for semi-crystalline reversible shape memory networks. Unfortunately, the non-tunability of thermal signals often brings potential limitations to actuators' applications. In practice, a wide response temperature range (T-range) formed by T_high and T_low in the remarkable reversible actuation is an obvious fact. Herein, we demonstrate the tunability of the transition temperatures while stably maintaining excellent actuation abilities. We further verified that the narrow T-range (24 °C) that had not been reported could present more than 17% reversible strain. Special parameter optimization provides opportunities for potential non-implantable biomedical applications. Therefore, based on target 2W-SMP, a vehicle concept with the drug release and vehicle recovery ability was proposed, proving our approach's feasibility.

A Review of Smart Superwetting Surfaces Based on Shape-Memory Micro/Nanostructures

Bioinspired smart superwetting surfaces with special wettability have aroused great attention from fundamental research to technological applications including self-cleaning, oil-water separation, anti-icing/corrosion/fogging, drag reduction, cell engineering, liquid manipulation, and so on. However, most of the reported smart superwetting surfaces switch their wettability by reversibly changing surface chemistry rather than surface microstructure. Compared with surface chemistry, the regulation of surface microstructure is more difficult and can bring novel functions to the surfaces. As a kind of stimulus-responsive material, shape-memory polymer (SMP) has become an excellent candidate for preparing smart superwetting surfaces owing to its unique shape transformation property. This review systematically summarizes the recent progress of smart superwetting SMP surfaces including fabrication methods, smart superwetting phenomena, and related application fields. The smart superwettabilities, such as superhydrophobicity/superomniphobicity with tunable adhesion, reversible switching between superhydrophobicity and superhydrophilicity, switchable isotropic/anisotropic wetting, slippery surface with tunable wettability, and underwater superaerophobicity/superoleophobicity with tunable adhesion, can be obtained on SMP micro/nanostructures by regulating the surface morphology. Finally, the challenges and future prospects of smart superwetting SMP surfaces are discussed.

Configurational Entropy Regulation in Polyolefin Elastomer/Paraffin Wax Vitrimers by Thermally Responsive Liquid-Solid Transition for Force Storage

The work output of shape memory polymers during shape shifting is desired for practical application as actuators. Herein, a polyolefin elastomer (POE) and paraffin wax (PW) are co-cross-linked by dynamic boronic ester bonds to enhance the network elasticity and the stress transfer between the two phases, endowing high force storage capacity to the prepared vitrimers. Depending on the phase of PW, one-way force storage is realized by programming at a low temperature (25 °C), owing to which solid PW can promote the locking of POE chains in a low-entropy state, while reversible force storage can be realized by programming at a high temperature (75 °C), owing to which the relaxation of chains facilitated by liquid PW can promote the construction of a stable structure. Based on one-way force storage, a weight-lifting machine with a weight of 20 mg prestrained at 25 °C can lift a 100 g weight, showing a lifting ratio of no less than 5000, with a high work output of 0.98 J/g. A high-temperature alarm can be triggered at varied temperatures (43-56 °C) through controlled force release by adjusting the PW content and programmed prestrains. Based on the reversible force storage, crawling robots and artificial muscles with a work output of 0.025 J/g are demonstrated. The dynamic cross-linking network also confers mold-free self-healing capability to POE/PW vitrimers, and the repair efficiency is enhanced compared with the POE vitrimer due to the improved POE chain motion by liquid PW. The realized one-way and reversible force storage and self-healing by POE/PW vitrimers pave the way for the application of SMPs in the fields of soft robotic actuators.

A Multiple Remotely Controlled Platform from Recyclable Polyurethane Composite Network with Shape-Memory Effect and Self-Healing Ability

Stimuli-responsive materials can transform from temporary to permanent shapes by specific external triggers. However, the damage might inevitably occur to them when exposed to complex environments, causing a significant reduction in their lifetime and quality. In this study, recyclable remotely controlled shape-changing polyurethane composite with self-healing compacity is developed from polyethylene glycol, polytetrahydrofuran diol using isophorone diisocyanate as crosslinker. After the incorporation of magnetite nanoparticles (MNPs), remote heating could be generated by near-infrared irradiation and alternating magnetic fields. The results show that MNPs are uniformly distributed in the smart networks, resulting in tunable temperature changes of the polymer composite material under various direct/indirect triggering in bending experiments, presenting different shape recovery rates. Moreover, to enhance the self-healing capability, a disulfide bond is introduced into the polymer networks, and the results show that highly efficient and rapid healing could be achieved from tensile tests, scanning electron microscopy as well as optical microscopy. Additionally, the synergistic effect of transesterification and the dynamic exchange of disulfide bonds brin the networks reproducibility for recycling use. The obtained material is promising to be an alternative material for soft robots and smart sensors.

Magnetic Self-Healing Composites: Synthesis and Applications

Magnetic composites and self-healing materials have been drawing much attention in their respective fields of application. Magnetic fillers enable changes in the material properties of objects, in the shapes and structures of objects, and ultimately in the motion and actuation of objects in response to the application of an external field. Self-healing materials possess the ability to repair incurred damage and consequently recover the functional properties during healing. The combination of these two unique features results in important advances in both fields. First, the self-healing ability enables the recovery of the magnetic properties of magnetic composites and structures to extend their service lifetimes in applications such as robotics and biomedicine. Second, magnetic (nano)particles offer many opportunities to improve the healing performance of the resulting self-healing magnetic composites. Magnetic fillers are used for the remote activation of thermal healing through inductive heating and for the closure of large damage by applying an alternating or constant external magnetic field, respectively. Furthermore, hard magnetic particles can be used to permanently magnetize self-healing composites to autonomously re-join severed parts. This paper reviews the synthesis, processing and manufacturing of magnetic self-healing composites for applications in health, robotic actuation, flexible electronics, and many more.

Constructing a shape memory network with controllable stability and dynamic features through cation–π interactions

A dynamic shape memory network, PCL-Pyr, with excellent shape memory effects, mechanical performance and reprocessability was constructed based on cation–π interactions.

High-strength, high-toughness, self-healing thermosetting shape memory polyurethane enabled by dual dynamic covalent bonds

Smart materials that integrate multiple functions into one system will broaden the application range of materials, but there are still challenges to obtain a material with excellent shape memory, toughness,...

Materials for Smart Soft Actuator Systems

In contrast to conventional hard actuators, soft actuators offer many vivid advantages, such as improved flexibility, adaptability, and reconfigurability, which are intrinsic to living systems. These properties make them particularly promising for different applications, including soft electronics, surgery, drug delivery, artificial organs, or prosthesis. The additional degree of freedom for soft actuatoric devices can be provided through the use of intelligent materials, which are able to change their structure, macroscopic properties, and shape under the influence of external signals. The use of such intelligent materials allows a substantial reduction of a device's size, which enables a number of applications that cannot be realized by externally powered systems. This review aims to provide an overview of the properties of intelligent synthetic and living/natural materials used for the fabrication of soft robotic devices. We discuss basic physical/chemical properties of the main kinds of materials (elastomers, gels, shape memory polymers and gels, liquid crystalline elastomers, semicrystalline ferroelectric polymers, gels and hydrogels, other swelling polymers, materials with volume change during melting/crystallization, materials with tunable mechanical properties, and living and naturally derived materials), how they are related to actuation and soft robotic application, and effects of micro/macro structures on shape transformation, fabrication methods, and we highlight selected applications.

An Ultrasoft Self-Fused Supramolecular Polymer Hydrogel for Completely Preventing Postoperative Tissue Adhesion

The intermolecular H-bonding density heavily influences the gelation and rheological behavior of hydrogen-bonded supramolecular polymer hydrogels, thus offering a delicate pathway to tailor their physicochemical properties for meeting a specific biomedical application. Herein, one methylene spacer between two amides in the side chain of N-acryloyl glycinamide (NAGA) is introduced to generate a variant monomer, N-acryloyl alaninamide (NAAA). Polymerization of NAAA in aqueous solution affords an unprecedented ultrasoft and highly swollen supramolecular polymer hydrogel due to weakened H-bonds caused by an extra methylene spacer, which is verified by variable-temperature Fourier transform infrared (FTIR) spectroscopy and simulation calculation. Intriguingly, poly(N-acryloyl alaninamide) (PNAAA) hydrogel can be tuned to form a transient network with a self-fused and excellent antifouling capability that results from the weakened dual amide H-bonding interactions and enhanced water-amide H-bonding interactions. This self-fused PNAAA hydrogel can completely inhibit postoperative abdominal adhesion and recurrent adhesion after adhesiolysis in vivo. This transient hydrogel network allows for its disintegration and excretion from the body. The molecular mechanism studies reveal the signal pathway of PNAAA hydrogel in inhibiting inflammatory response and regulating fibrinolytic system balance. This self-fused, antifouling ultrasoft supramolecular hydrogel is promising as a barrier biomaterial for completely preventing postoperative tissue adhesion.

Thermal/Near-Infrared Light Dual-Responsive Reversible Two-Way Shape Memory cEVA/2D-MoO2 Composite for Multifunctional Applications

Light-responsive reversible two-way shape memory polymers (2W-SMPs) are highly promising for many fields due to indirect heating, clean, and remote control. In this work, a composite with both thermal- and near-infrared (NIR) light-induced reversible two-way shape memory effect (2W-SME) is prepared by doping extremely little quantities of 2D non-layered molybdenum dioxide nanosheets (2D-MoO₂ ) into semicrystalline poly(ethylene-co-vinyl acetate) (EVA) networks. This is the first report on light-induced reversible two-way shape memory composites employing 2D-MoO₂ as photothermal fillers. Upon switching the NIR light on and off, due to the excellent photothermal feature and stability of 2D-MoO₂ , the composite exhibits remarkable light-induced reversible 2W-SME. A light-driven actuator for sensing applications is designed based on the composite and the circuit, where the lamp acting as an alarm can raise and fade upon responding to NIR light. A completely flexible, fuel-free self-walking soft robot is designed based on the advantages of the light-responsive reversible 2W-SMPs. Additionally, the composite acting as a light-fueled crane is able to lift and lower a load that is 3846 times its own weight. The results demonstrate that the prepared composite has a promising prospect for applications as actuators, self-walking soft robot and crane.

Effects of ionic liquid types on the tribological, mechanical, and thermal properties of ionic liquid modified graphene/polyimide shape memory composites

Different ionic liquid modified graphene nanosheets (IG) were induced into polyimide (PI) to improve the tribological, thermal, and mechanical properties of shape memory IG/PI composites. The results demonstrated that when using 1-aminoethyl-3-methylimidazole bromide to modify graphene nanosheets (IG-1), the laser-driven shape recovery rate of IG-1/PI composites (IGPI-1) reached 73.02%, which was 49.36% higher than that of pure PI. In addition, the IGPI-1 composite materials reached the maximum shape recovery rate within 15 s. Additionally, under dry sliding, the addition of IG can significantly improve the tribological properties of composite materials. IGPI-1 exhibited the best self-lubricating properties. Compared with pure PI, the friction coefficient (0.19) and wear rate (2.62 × 10–5) mm3/Nm) were reduced by 44.1% and 24.2%, respectively, and the T10% of IGPI-1 increased by 32.2°C. The Tg of IGPI-1 reached 256.5°C, which was 8.4°C higher than that of pure PI. In addition, the tensile strength and modulus of IGPI-1 reached 82.3 MPa and 1.18 GPa, which were significantly increased by 33.6% and 29.8%, respectively, compared with pure PI. We hope that this work will be helpful for the preparation of shape memory materials with excellent tribological, thermal, and mechanical properties.

Polarization of Stem Cells Directed by Magnetic Field-Manipulated Supramolecular Polymeric Nanofibers

Precise assembly of the cytoskeleton (e.g., actin, tubulin, and intermediate filaments) is of great importance for stem cell polarization and tissue regeneration. Recently, artificial manipulation of cytoskeleton assembly for remodeling stem cell polarization and ultimate cell fates attracts more and more interest of both chemists and biologists. Herein, we report the magnetic field-directed formation of biocompatible supramolecular polymeric nanofibers composed of two subunits: a β-cyclodextrin-bearing hyaluronic acid host polymer (HACD) and magnetic nanoparticles modified with actin-binding peptide and adamantane (MS-ABPAda). Transmission electron microscopy indicated that when HACD and MS-ABPAda were exposed to a magnetic field, they self-assembled into long nanofibers along the direction of the magnetic field, and the rate of nanofiber formation was linearly correlated with the strength of the magnetic field. Interestingly, when incubated with dental pulp stem cells, the nanofibers specifically drove tip extension and polarization of the cells, a phenomenon that can be attributed to targeting of actin-binding peptide to the actin cytoskeleton and subsequent polarization of the nanofibers. The successful application of these magnetic field-responsive supramolecular polymers on accurately driving polarization of mammalian cells is expected to be of great value for artificially manipulating cell fate and developing intelligent responsive materials in regenerative medicine.

Multifunctional magnetic soft composites: a review

Magnetically responsive soft materials are soft composites where magnetic fillers are embedded into soft polymeric matrices. These active materials have attracted extensive research and industrial interest due to their ability to realize fast and programmable shape changes through remote and untethered control under the application of magnetic fields. They would have many high-impact potential applications in soft robotics/devices, metamaterials, and biomedical devices. With a broad range of functional magnetic fillers, polymeric matrices, and advanced fabrication techniques, the material properties can be programmed for integrated functions, including programmable shape morphing, dynamic shape deformation-based locomotion, object manipulation and assembly, remote heat generation, as well as reconfigurable electronics. In this review, an overview of state-of-the-art developments and future perspectives in the multifunctional magnetically responsive soft materials is presented.

Combined light- and heat-induced shape memory behavior of anthracene-based epoxy elastomers

The development of multi-stimuli-responsive shape memory polymers has received increasing attention because of its scientific and technological significance. In this work, epoxy elastomers with reversible crosslinks are synthesized by polymerizing an anthracene-functionalized epoxy monomer, a diepoxy comonomer, and a dicarboxylic acid curing agent. The synthesized elastomers exhibit active responses to both light and heat enabled by the incorporated anthracene groups. When exposed to 365 nm UV light, additional crosslinking points are created by the photo-induced dimerization of pendant anthracene groups. The formation of the crosslinking points increases modulus and glass transition temperature of the elastomers, allowing for the fixation of a temporary shape at room temperature. The temporary shape remains stable until an external heat stimulus is applied to trigger the scission of the dimerized anthracene, which reduces the modulus and glass transition temperature and allows the elastomers to recover their original shapes. The effects of external stimuli on the thermal and dynamic mechanical properties of the elastomers are investigated experimentally and are correlated with molecular dynamics simulations that reveal the changes of structure and dynamics of the anthracene molecules and flexible chains.

Carbon-coated magnetic nanoparticles as a removable protection layer extending the operation lifetime of bilirubin oxidase-based bioelectrode

One of the factors hindering the development of enzymatic biosensors and biofuel cells in real-life applications is the time-dependant degradation of the biocatalysts on electrode surfaces. In this work, we present a new practical approach for extending the operation lifetimes of bioelectrocatalytic assemblies based on bilirubin oxidase (BOD). As evident by both spectroscopic and electrochemical measurements, an adsorption of carbon-coated magnetic nanoparticles (ccMNPs) onto a BOD/carbon nanotubes-deposited surface yields a stable bioelectrocathode system for mediatorless oxygen reduction. As compared to electrodes, which were stored without a preliminary interaction with the ccMNPs, an 80% increase in the active enzymatic content and the electrocatalytic performance was evident for the modified assemblies over a course of one month. As the full removal of the protective particles before the measurement requires only a single step applying an external magnetic force, the method is shown to be simple, reproducible, and easy to implement. Combined with the high efficiency in preserving the enzymatic stability and bioelectrocatalytic currents, the findings suggest a promising methodology for enhancing the lifetimes of bioelectronic applications.

Fractionation of Lignin for Selective Shape Memory Effects at Elevated Temperatures

We report a facile approach to control the shape memory effects and thermomechanical characteristics of a lignin-based multiphase polymer. Solvent fractionation of a syringylpropane-rich technical organosolv lignin resulted in selective lignin structures having excellent thermal stability coupled with high stiffness and melt-flow resistance. The fractionated lignins were reacted with rubber in melt-phase to form partially networked elastomer enabling selective programmability of the material shape either at 70 °C, a temperature that is high enough for rubbery matrix materials, or at an extremely high temperature, 150 °C. Utilizing appropriate functionalities in fractionated lignins, tunable shape fixity with high strain and stress recovery, particularly high-stress tolerance were maintained. Detailed studies of lignin structures and chemistries were correlated to molecular rigidity, morphology, and stress relaxation, as well as shape memory effects of the materials. The fractionation of lignin enabled enrichment of specific lignin properties for efficient shape memory effects that broaden the materials' application window. Electron microscopy, melt-rheology, dynamic mechanical analysis and ultra-small angle neutron scattering were conducted to establish morphology of acrylonitrile butadiene rubber (NBR)-lignin elastomers from solvent fractionated lignins.

Enhanced Mechanical Strength, Flexibility, and Shape-Restoring Rate of a Drug-Eluting Shape-Memory Polymer by Incorporation of Supramolecular Cross-Linkers

The purpose of this study is to develop mechanically robust soybean oil and polycaprolactone (PC)-based drug-eluting shape memory polymers (SMPs) containing polyrotaxane (PRX) cross-linkers. Essentially, the dynamic PRX cross-linker-containing methacrylate group is introduced to increase the cross-linking density and flexibility of the SMP to overcome its mechanical limitations. It was confirmed that the elongation and cross-linking density of the PRX-incorporated SMP were increased by 2-4 times compared to neat SMP. In addition, those high mechanical properties of the PRX-incorporated SMP could be maintained after the degradation of the PC by the drug-eluting process.

Self-Healing Dielectric Elastomers for Damage-Tolerant Actuation and Energy Harvesting

The actuation and energy-harvesting performance of dielectric elastomers are strongly related to their intrinsic electrical and mechanical properties. For future resilient smart transducers, a fast actuation response, efficient energy-harvesting performance, and mechanical robustness are key requirements. In this work, we demonstrate that poly(styrene-butadiene-styrene) (SBS) can be converted into a self-healing dielectric elastomer with high permittivity and low dielectric loss, which can be deformed to large mechanical strains; these are key requirements for actuation and energy-harvesting applications. Using a one-step click reaction at room temperature for 20 min, methyl-3-mercaptopropionate (M3M) was grafted to SBS and reached 95.2% of grafting ratios. The resultant M3M-SBS can be deformed to a high mechanical strain of 1000%, with a relative permittivity of ε_r = 7.5 and a low tan δ = 0.03. When used in a dielectric actuator, it can provide 9.2% strain at an electric field of 39.5 MV m^-1 and can also generate an energy density of 11 mJ g^-1 from energy harvesting. After being subjected to mechanical damage, the self-healed elastomer can recover 44% of its breakdown strength during energy harvesting. This work demonstrates a facile route to produce self-healing, high permittivity, and low dielectric loss elastomers for both actuation and energy harvesting, which is applicable to a wide range of diene elastomer systems.

Self-healing magnetic nanocomposites with robust mechanical properties and high magnetic actuation potential prepared from commodity monomers via graft-from approach

Herein, we report the design, synthesis and characterization of self-healing magnetic nanocomposites prepared from readily available commodity monomers.

Multireusable Thermoset with Anomalous Flame-Triggered Shape Memory Effect

While thermosets with high mechanical properties and shape memory capabilities have been developed in recent years, two main bottlenecks persist in their intrinsic nonreusability and flammability, especially for those shape memory thermosets used in recycling-required field with high glass transition temperatures ( T_g) and thus risky high temperatures to trigger shape recovery. Here, we report a new shape memory epoxy thermoset integrated with excellent fire retardancy, recyclability, high mechanical performance, and 100% shape recovery ratio. The shape memory effect of this new thermoset was directly triggered by high-temperature flame for the first time. Furthermore, the survival thermoset can be recycled by a simple solid-state recycling method and reused as reinforcing fillers for polyester. The highest recycling efficiency reached 85.4%, and the reinforced composite presented about four times higher storage modulus compared to that of neat sample. This work may open a door for application of thermoset shape memory polymers in many lightweight engineering structures and devices where fire hazard is a concern. The newly proposed concept of flame-triggered shape memory effect may also find applications in fire-protecting system.

One-way and two-way shape memory effects of a high-strain cis-1,4-polybutadiene–polyethylene copolymer based dynamic network via self-complementary quadruple hydrogen bonding

A polymer network based on a cis-1,4-polybutadiene–polyethylene copolymer exhibits multi- and two-way shape memory effects as well as a high-strain capacity.

Repeated Intrinsic Self-Healing of Wider Cracks in Polymer via Dynamic Reversible Covalent Bonding Molecularly Combined with a Two-Way Shape Memory Effect

To enable repeated intrinsic self-healing of wider cracks in polymers, a proof-of-concept approach is verified in the present work. It operates through two-way shape memory effect (SME)-aided intrinsic self-healing. Accordingly, a reversible C-ON bond is introduced into the main chain of crosslinked polyurethane (PU) containing an elastomeric dispersed phase (styrene-butadiene-styrene block copolymer, SBS). The PU/SBS blend was developed by the authors recently, and proved to possess an external stress-free two-way SME after programming. As a result, the thermal retractility offered by the SME coupled with the reversible C-ON bonds can be used for successive crack closure and remending based on synchronous fission/radical recombination of C-ON bonds. Moreover, multiwalled carbon nanotubes are incorporated to impart electrical conductivity to the insulating polymer. Repeated autonomic healing of wider cracks is thus achieved through narrowing of cracks followed by chemical rebonding under self-regulating Joule heating. No additional programming is needed after each healing event, which is superior to one-way SME-assisted self-healing. The outcomes set an example of integrating different stimuli-responsivities into single materials.

Reversible Actuation Ability upon Light Stimulation of the Smart Systems with Controllably Grafted Graphene Oxide with Poly (Glycidyl Methacrylate) and PDMS Elastomer: Effect of Compatibility and Graphene Oxide Reduction on the Photo-Actuation Performance

This study is focused on the controllable reduction of the graphene oxide (GO) during the surface-initiated atom transfer radical polymerization technique of glycidyl methacrylate (GMA). The successful modification was confirmed using TGA-FTIR analysis and TEM microscopy observation of the polymer shell. The simultaneous reduction of the GO particles was confirmed indirectly via TGA and directly via Raman spectroscopy and electrical conductivity investigations. Enhanced compatibility of the GO-PGMA particles with a polydimethylsiloxane (PDMS) elastomeric matrix was proven using contact angle measurements. Prepared composites were further investigated through the dielectric spectroscopy to provide information about the polymer chain mobility through the activation energy. Dynamic mechanical properties investigation showed an excellent mechanical response on the dynamic stimulation at a broad temperature range. Thermal conductivity evaluation also confirmed the further photo-actuation capability properties at light stimulation of various intensities and proved that composite material consisting of GO-PGMA particles provide systems with a significantly enhanced capability in comparison with neat GO as well as neat PDMS matrix.

Strategy for Constructing Shape-Memory Dynamic Networks through Charge-Transfer Interactions

Recently, charge transfer (CT) interactions have received attention for the fabrication of supramolecular architectures due to their inherent compatibilities, directional nature and solvent tolerance. In this study, we report a shape-memory dynamic network constructed by the CT interaction between π-electron-rich naphthalene embedded in poly(ethylene glycol) (PEG-Np) and π-electron-poor six-arm methyl-viologen-ended poly(ethylene glycol) (⁶PEG-MV), which was verified by ultraviolet-visible spectroscopy (UV-vis), fluorescence spectra and swelling tests. Interestingly, the mechanical properties of this CT complex were dramatically enhanced compared with the control without CT interaction. Moreover, the excellent shape-memory effect (SME) was realized due to the good crystallization of the PEG segment and stable netpoints based on the CT interaction. In addition, as we expected, this supramolecular polymer network is self-healable and reprocessable.