Polymers with dual light-triggered functions of shape memory and healing using gold nanoparticles

Environmental-friendly, flexible silk fibroin-based film as dual-responsive shape memory material

Bio-based shape memory materials have attracted wide attention due to their biocompatibility, degradability and safety. However, designing and manufacturing wearable bio-based shape memory films with excellent flexibility and toughness is still a challenge. In this work, silk fibroin substrate with a β-sheet structure was combined with a tri-block shape memory copolymer to prepare a transparent composited shape memory film. The silk fibroin-based film showed a dual-responsive shape memory function, which can respond to both temperature and water stimuli. This film has a sensitive water-responsive shape memory, which starts deforming after exposure to water for 3 s and fully recovers in 30 s. In addition, the composite film shows highly stretchable (>300 %) and could maintain its high tensile properties after 5 cycles of regeneration. The films also exhibited rapid degradation ability. This study provides new insights for the design of dual-responsive shape memory materials by combining biocompatible matrix and multi-block SMP to simultaneously enhance the mechanical properties, which can be used for intelligent packaging, medical supplies, soft actuators and wearable devices.

4D Printed Protein-AuNR Nanocomposites with Photothermal Shape Recovery

4D printing is the 3D printing of objects that change chemically or physically in response to an external stimulus over time. Photothermally responsive shape memory materials are attractive for their ability to undergo remote activation. While photothermal methods using gold nanorods (AuNRs) have been used for shape recovery, 3D patterning of these materials into objects with complex geometries using degradable materials has not been addressed. Here, we report on the fabrication of 3D printed shape memory bioplastics with photo-activated shape recovery. Protein-based nanocomposites based on bovine serum albumin (BSA), poly (ethylene glycol) diacrylate and gold nanorods were developed for vat photopolymerization. These 3D printed bioplastics were mechanically deformed under high loads, and the proteins served as mechanoactive elements that unfolded in an energy-dissipating mechanism that prevented fracture of the thermoset. The bioplastic object maintained its metastable shape-programmed state under ambient conditions. Subsequently, up to 99% shape recovery was achieved within 1 min of irradiation with near-infrared light. Mechanical characterization and small angle X-ray scattering (SAXS) analysis suggest that the proteins mechanically unfold during the shape programming step and may refold during shape recovery. These composites are promising materials for the fabrication of biodegradable shape-morphing devices for robotics and medicine.

Triphenylphosphonium conjugated gold nanotriangles impact Pi3K/AKT pathway in breast cancer cells: a photodynamic therapy approach

Although gold nanoparticles based photodynamic therapy (PDT) were reported to improve efficacy and specificity, the impact of surface charge in targeting cancer is still a challenge. Herein, we report gold nanotriangles (AuNTs) tuned with anionic and cationic surface charge conjugating triphenylphosphonium (TPP) targeting breast cancer cells with 5-aminoleuvinic acid (5-ALA) based PDT, in vitro. Optimized surface charge of AuNTs with and without TPP kill breast cancer cells. By combining, 5-ALA and PDT, the surface charge augmented AuNTs deliver improved cellular toxicity as revealed by MTT, fluorescent probes and flow cytometry. Further, the 5-ALA and PDT treatment in the presence of AuNTs impairs cell survival Pi3K/AKT signaling pathway causing mitochondrial dependent apoptosis. The cumulative findings demonstrate that, cationic AuNTs with TPP excel selective targeting of breast cancer cells in the presence of 5-ALA and PDT.

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.

Research Progress of Shape Memory Polymer and 4D Printing in Biomedical Application

As a kind of smart material, shape memory polymer (SMP) shows great application potential in the biomedical field. Compared with traditional metal-based medical devices, SMP-based devices have the following characteristics: 1) The adaptive ability allows the biomedical device to better match the surrounding tissue after being implanted into the body by minimally invasive implantation; 2) it has better biocompatibility and adjustable biodegradability; 3) mechanical properties can be regulated in a large range to better match with the surrounding tissue. 4D printing technology is a comprehensive technology based on smart materials and 3D printing, which has great application value in the biomedical field. 4D printing technology breaks through the technical bottleneck of personalized customization and provides a new opportunity for the further development of the biomedical field. This paper summarizes the application of SMP and 4D printing technology in the field of bone tissue scaffolds, tracheal scaffolds, and drug release, etc. Moreover, this paper analyzes the existing problems and prospects, hoping to provide a preliminary discussion and useful reference for the application of SMP in biomedical engineering.

Polydopamine Nanoparticle-Reinforced Near-Infrared Light-Triggered Shape Memory Polycaprolactone-Polydopamine Polyurethane for Biomedical Implant Applications

Near-infrared (NIR) light-triggered shape memory polymers are expected to have a more promising prospect in biomedical applications compared with traditional heat-triggered shape memory polymers. In this work, a new kind of polyurethane with NIR light-triggered shape memory property was prepared by using polycaprolactone (PCL), polydopamine nanoparticles (PDANPs), hexamethylene diisocyanate (HDI), and 1,4-butanediol (BDO). The synthesized PCL-PDA polyurethanes, especially when the weight content of PDANPs was 0.17%, showed excellent mechanical properties because the PDANPs were well-dispersed in polyurethanes by the chain extension reaction. Moreover, it also showed an NIR light-triggered rapid shape recovery because of the photothermal effect of polydopamine. The in vitro and in vivo tests showed that the PCL-PDA polyurethane would not inhibit cell proliferation nor induce a strong host inflammatory response, revealing the non-cytotoxicity and good biocompatibility of the material. In addition, the PCL-PDA polyurethane exhibited excellent in vivo NIR light-triggered shape memory performance under an 808 nm laser with low intensity (0.33 W cm^-2), which was harmless to the human skin. These results demonstrated the potential of the PCL-PDA polyurethane in biomedical implant applications.

Importance of the Structural and Physicochemical Properties of Silica Nanoshells in the Photothermal Effect of Silica-Coated Au Nanoparticles Suspensions

In this work, monodisperse silica-coated gold nanoparticles (NPs) were synthesized and used for obtaining aqueous colloidal dispersions with an optimum relationship between colloidal stability and photothermal activity. The idea behind this design was to produce systems with the advantages of the presence of a silica shell (biocompatibility, potential for surface modification, and protecting effect) with a minimal loss of optical and thermal properties. With this aim, the photothermal properties of NPs with silica shells of different thicknesses were analyzed under conditions of high radiation extinction. By using amorphous, gel-like silica coatings, thicknesses higher than 40 nm could be obtained without an important loss of the light absorption capacity of the colloids and with a significant photothermal response even at low NP concentrations. The effects produced by changes in the solvent and in the NP concentration were also analyzed. The results show that the characteristics of the shell control both, the photothermal effect and the optical properties of the colloidal dispersions. As the presence of a silica shell strongly enhances the possibilities of adding cargo molecules or probes, these colloids can be considered of high interest for biomedical therapies, sensing applications, remote actuation, and other technological applications.

Biobased Composites with High Lignin Content and Excellent Mechanical Properties toward the Ingenious Photoresponsive Actuator

The fabrication of biobased smart materials from renewable biomasses is of great importance for sustainable development. Although lignin possesses photothermal conversion potential, the development of lignin-based actuators with large contraction and fast photoresponse has various hurdles. Herein, simply by blending with castor oil-derived polyamide elastomers, a lignin-based photoresponsive actuator can be obtained, which accomplishes up to 18% light-driven contraction under loading within 3 s. The crystals in polymer matrix serve as switch segments, firmly locking the stress-induced strain energy, which is swiftly released due to photothermal processes and induced a huge contraction. The composite, LP₄-50, can contract and induce dynamic bending in multiple directions when irradiated locally with a near-infrared 808 nm laser. Furthermore, at standard 1 sun irradiation (100 mW/cm²), LP₄-50 was successfully employed to power a thermoelectric generator. This strategy establishes the groundwork for further research into the photothermal characteristics of lignin and encourages new applications in stimulus-responsive actuators.

A Photoorganizable Triple Shape Memory Polymer for Deployable Devices

Inspired by the action and healing process from living organisms, developing deployable devices using stimuli-responsive materials, or "smart" deployable devices, is desired to realize remote-controlled programmable deformation with additional in situ repair to perform multiple tasks while extending their service life in aerospace. In this work, a photoorganizable triple shape memory polymer (POTSMP) is reported, which is composed of an azobenzene-containing thermoplastic polyurethane. Upon UV and visible illumination, this POTSMP performs arbitrary programming of two temporary shapes and precise and stepwise shape recovery, exhibiting various temporary shapes adapted to different aerospace applications. On the other hand, rapid light-reconfiguration in seconds, including light-reshaping and light-welding, is achieved in response to UV irradiation, allowing in situ localized process and repair of permanent shape. Combining these photoorganizable operations, deformable devices with complex 2D/3D structures are facilely manufactured with no need of special molds. It is envisioned that this POTSMP can expand the potential of photoresponsive TSMPs in smart deployable devices.

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.

Challenges and Opportunities of Self-Healing Polymers and Devices for Extreme and Hostile Environments

Engineering materials and devices can be damaged during their service life as a result of mechanical fatigue, punctures, electrical breakdown, and electrochemical corrosion. This damage can lead to unexpected failure during operation, which requires regular inspection, repair, and replacement of the products, resulting in additional energy consumption and cost. During operation in challenging, extreme, or harsh environments, such as those encountered in high or low temperature, nuclear, offshore, space, and deep mining environments, the robustness and stability of materials and devices are extremely important. Over recent decades, significant effort has been invested into improving the robustness and stability of materials through either structural design, the introduction of new chemistry, or improved manufacturing processes. Inspired by natural systems, the creation of self-healing materials has the potential to overcome these challenges and provide a route to achieve dynamic repair during service. Current research on self-healing polymers remains in its infancy, and self-healing behavior under harsh and extreme conditions is a particularly untapped area of research. Here, the self-healing mechanisms and performance of materials under a variety of harsh environments are discussed. An overview of polymer-based devices developed for a range of challenging environments is provided, along with areas for future research.

Shape-Memory Polymer Nanocomposites of Poly(ε-caprolactone) with the Polystyrene-block-polybutadiene-block-polystyrene-tri-block Copolymer Encapsulated with Metal Oxides

Shape-memory polymer composite (SMPC) blends with thermo-responsive shape memorizing capability have received increasing interest and have been a grooming research area due to their various potential applications. In this work, we report three thermo-responsive SMPCs derived from poly(ε-caprolactone) (PCL) and the polystyrene-block-polybutadiene-block-polystyrene-tri-block copolymer (SBS) encapsulated with CuO, Fe₂O₃, and CuFe₂O₄, namely, SMPC-CuO, SMPC-Fe ₂ O ₃ , and SMPC-CuFe ₂ O ₄ , respectively. We have also synthesized the neat shape-memory polymer matrix SMP in the context of the effect of the metal oxide encapsulates on the shape-memory property. Neat SBS rubber and PCL are used as the polymer-elastomer blend matrix to form SMP. The objective of this study is to understand the effect of these three metal oxide nanofillers encapsulated within the SMP matrix and their thermal, mechanical, and shape-memory properties. Morphological, thermal, mechanical, and shape-memory properties of the prepared SMPCs are completely characterized. It is revealed that the addition of nano-metallic-oxide fillers into the polymeric matrix significantly improved the overall properties of SMPCs. The tensile test confirmed that SMPC-CuFe ₂ O ₄ possesses a high tensile modulus and is found to be very rigid when compared to other SMPCs. The shape fixing property is found in the increasing order as follows: SMPC-CuO > SMPC-Fe ₂ O ₃ > SMP > SMPC-CuFe ₂ O ₄ . The better thermal, mechanical, and shape-memory performances were shown by the SMPC-Fe ₂ O ₃ composite, and thus, it can be considered as the better shape-memory polymer nanocomposite among all others. An optimum storage modulus was attained by SMPC-Fe ₂ O ₃ among the SMPCs. More interestingly, we have developed a microvalve actuator system using SMPC-Fe ₂ O ₃ , which could be useful for promising microsystem applications.

A Review of Shape Memory Polymers and Composites: Mechanisms, Materials, and Applications

Over the past decades, interest in shape memory polymers (SMPs) has persisted, and immense efforts have been dedicated to developing SMPs and their multifunctional composites. As a class of stimuli-responsive polymers, SMPs can return to their initial shape from a programmed temporary shape under external stimuli, such as light, heat, magnetism, and electricity. The introduction of functional materials and nanostructures results in shape memory polymer composites (SMPCs) with large recoverable deformation, enhanced mechanical properties, and controllable remote actuation. Because of these unique features, SMPCs have a broad application prospect in many fields covering aerospace engineering, biomedical devices, flexible electronics, soft robotics, shape memory arrays, and 4D printing. Herein, a comprehensive analysis of the shape recovery mechanisms, multifunctionality, applications, and recent advances in SMPs and SMPCs is presented. Specifically, the combination of functional, reversible, multiple, and controllable shape recovery processes is discussed. Further, established products from such materials are highlighted. Finally, potential directions for the future advancement of SMPs are proposed.

Multifunctional Thermoplastic Polyurea Based on the Synergy of Dynamic Disulfide Bonds and Hydrogen Bond Cross-Links

Integrating the self-healing property with the shape-memory effect is a strategy that extends the service lifetime of shape-memory materials. However, this strategy is inadequate to reshape and recycle through the self-healing property or liquid-state remoldability. For more types of damage, solid-state plasticity is needed as a complementary mechanism to broaden the reprocessing channels of smart materials. In this study, multifunctional thermoplastic polyureas cross-linked by urea hydrogen bonds are prepared, which possess the multipathway remodeling property. The shape transition can be triggered after heating above 65 °C. The synergistic effect of dynamic disulfide bonds and hydrogen bonds causes the thermoplastic polyureas to possess characteristics similar to those of associative covalent adaptable networks. Thus, the polyureas can repair the damage or reconfigure the shape at 75 °C in 15 min by solid-state plasticity, instead of going into a viscous flow state. Soft grippers with various shapes are prepared by integration of solid-state plasticity, and the structure and function of the grippers can be repaired. The integration of solid-state plasticity and the self-healing property broadens the paths of shape-memory polymers in recyclability and reshapability.

Programmable Stimuli-Responsive Actuators for Complex Motions in Soft Robotics: Concept, Design and Challenges

During the last years, great progress was made in material science in terms of concept, design and fabrication of new composite materials with conferred properties and desired functionalities. The scientific community paid particular interest to active soft materials, such as soft actuators, for their potential as transducers responding to various stimuli aiming to produce mechanical work. Inspired by this, materials engineers today are developing multidisciplinary approaches to produce new active matters, focusing on the kinematics allowed by the material itself more than on the possibilities offered by its design. Traditionally, more complex motions beyond pure elongation and bending are addressed by the robotics community. The present review targets encompassing and rationalizing a framework which will help a wider scientific audience to understand, sort and design future soft actuators and methods enabling complex motions. Special attention is devoted to recent progress in developing innovative stimulus-responsive materials and approaches for complex motion programming for soft robotics. In this context, a challenging overview of the new materials as well as their classification and comparison (performances and characteristics) are proposed. In addition, the great potential of soft transducers are outlined in terms of kinematic capabilities, illustrated by the related application. Guidelines are provided to design actuators and to integrate asymmetry enabling motions along any of the six basic degrees of freedom (translations and rotations), and strategies towards the programming of more complex motions are discussed. As a final note, a series of manufacturing methods are described and compared, from molding to 3D and 4D printing. The review ends with a Perspectives section, from material science and microrobotic points of view, on the soft materials’ future and close future challenges to be overcome.

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.

A near-infrared light-triggered shape-memory polymer for long-time fluorescence imaging in deep tissues

Implanting a stent in the body through a minimally invasive operation and tracking its location in real-time is still a challenge. Herein, a near-infrared (NIR) light-triggered shape-memory polymer possessing a long-time fluorescence imaging function has been developed by cross-linking 6-arm poly(ethylene glycol)-poly(ε-caprolactone) using a croconate dye YHD798 as the chemical crosslinker and NIR-absorption perssad. Due to the extraordinary photothermal conversion property of YHD798, the temperature of the material raised from 20 °C to 120 °C under 808 nm near-infrared irradiation at 0.4 W cm^-2, leading to shape recovery in 50 s in a programmed shape-transition process. YHD798 also exerted an aggregation-induced emission effect, endowing the polymer with a clear NIR fluorescence imaging function even when covered by a 2 mm pork slab and could be used for the real-time visualization of the implanted device fabricated from this polymer in deep tissues of the body. When a tubular stent that was fabricated from this polymer, was implanted into the carotid artery of a Sprague-Dawley rat, it could recover to its permanent shape under 808 nm laser irradiation in 60 s owing to the shape-memory function and facilitated NIR-I fluorescence imaging after implantation for a week owing to the croconate dye. This work provides a new strategy for designing and developing smart polymers with NIR-light-triggered shape-memory effect and long-term fluorescence imaging function for biomedical applications.

Photoresponsive Shape Memory Hydrogels for Complex Deformation and Solvent-Driven Actuation

A new design for photoresponsive shape memory hydrogels and their possible applications are demonstrated in the present study. We show that the photodissociable Fe³⁺-carboxylate coordination can be utilized as a molecular switch to realize photocontrol of shape memory on both macroscopic and microscopic scales and enable a number of functions. Indeed, Fe³⁺-carboxylate coordination can fix a large tensile strain (up to 680%) of the sodium alginate/polyacrylamide hydrogel through cross-linking of sodium alginate chains, and subsequent UV irradiation allows strain energy release in spatially selected regions through reduction of Fe³⁺ to Fe²⁺. By manipulating light irradiation, complex 3D structures are obtained from 2D hydrogel sheets, and they exhibit complex solvent-driven actuation behaviors due to a light-changeable modulus and cross-linking density in the hydrogel. Based on the same approach, micropatterns can be inscribed on the hydrogel surface using mask-assisted irradiation, and they exhibit chain orientation-mediated anisotropic topography change upon solvent exchange. Moreover, light-controlled strain energy release also enables changing hydrogel surface wettability by solvent replacement. The demonstrated mechanism for photoresponsive hydrogels is highly efficient and applicable to many systems, which offers new perspectives in developing hydrogels with multiple photoresponsive functions.

Photothermally and magnetically controlled reconfiguration of polymer composites for soft robotics

New materials are advancing the field of soft robotics. Composite films of magnetic iron microparticles dispersed in a shape memory polymer matrix are demonstrated for reconfigurable, remotely actuated soft robots. The composite films simultaneously respond to magnetic fields and light. Temporary shapes obtained through combined magnetic actuation and photothermal heating can be locked by switching off the light and magnetic field. Subsequent illumination in the absence of the magnetic field drives recovery of the permanent shape. In cantilevers and flowers, multiple cycles of locking and unlocking are demonstrated. Scrolls show that the permanent shape of the film can be programmed, and they can be frozen in intermediate configurations. Bistable snappers can be magnetically and optically actuated, as well as biased, by controlling the permanent shape. Grabbers can pick up and release objects repeatedly. Simulations of combined photothermal heating and magnetic actuation are useful for guiding the design of new devices.

Plasmonic Ti3C2Tx MXene Enables Highly Efficient Photothermal Conversion for Healable and Transparent Wearable Device

Skin-mountable and transparent devices are highly desired for next-generation electronic applications but are susceptible to unexpected ruptures or undesired scratches, which can drastically reduce the device lifetime. Developing wearable and transparent materials with healable function that can recover their original functionality after mechanical damage under mild and noninvasive repairing operation is thus imperative. Herein, we demonstrate that the incorporation of ultrasmall quantities of plasmonic silver nanoparticle (AgNP)@MXene nanosheet hybrids to serve as photothermal fillers in waterborne elastic polyurethane enables high transparency as well as effective light-triggered healing capabilities for wearable composite coatings. The AgNP@MXene hybrid functions as a highly effective photon captor, energy transformer, and molecular heater due to the amalgamation of (1) ultrahigh photothermal conversion efficiency, high thermal conductivity, and structural properties of MXene, (2) the outstanding plasmonic effect of AgNPs, and (3) the synergistic effects from their hybrids. The resulting wearable composite coating with ultralow loading of plasmonic AgNP@MXene hybrids (0.08 wt % or 0.024 vol %) can produce a significant temperature increase of ∼111 ± 2.6 °C after the application of 600 mW cm^-2 light irradiation for 5 min, while maintaining a high optical transmittance of ∼83% at a thickness of ∼60 μm. This local temperature increase can rapidly heal the mechanical damage to the composite coating, with a healing efficiency above 97%.

AIE Supramolecular Assembly with FRET Effect for Visualizing Drug Delivery

Here, we constructed a nanostructured pH/redox dual-responsive supramolecular drug carrier with both aggregation-induced emission (AIE) and Forster resonance energy transfer (FRET) effects, which enabled selective drug release and monitoring drug delivery and release processes. Taking the hyperbranched polyamide amine (H-PAMAM) with intrinsic AIE effects as the core, poly(ethylene glycol) (PEG) was bridged on its periphery by dithiodipropionic acid. Then, through the host-guest interaction of PEG and α-cyclodextrin, the supramolecular nanoparticles with AIE effects were constructed to load the anticancer drug doxorubicin (DOX). The supramolecular assembly has sufficiently large DOX loading due to the abundant cavities formed by branched structures. The hyperbranched core H-PAMAM has strong fluorescence, and the dynamic track of drug carriers and the dynamic drug release process can be monitored by the AIE and FRET effects between H-PAMAM and DOX, respectively. Furthermore, the introduction of disulfide bonds and the pH sensitivity of H-PAMAM enable the achievement of rapid selective release of loaded DOX at the tumor while remaining stable under normal physiological conditions. In vitro cytotoxicity indicates that the drug-loaded supramolecular assembly has a good therapeutic effect on cancer. In addition, the H-PAMAM core is different from the traditional AIE functional group, which has no conjugated structure, such as a benzene ring, thereby providing better biocompatibility. This technology will have broad applications as a new drug delivery system.

Self-Healing of Polarizing Films via the Synergy between Gold Nanorods and Vitrimer

Conventional self-healing is about the recovery of shape and mechanical properties. In contrast, recovery of functional properties is still a great challenge, especially for optical functional materials, as the known self-healing methods are incompatible with optical properties. By utilizing the synergistic effect between Au nanorods and vitrimer, the alignment of Au nanorods can be achieved in the crosslinked polymer. The optical properties of the resulting polarizing film, such as light transmittance and polarization degree, can be fully recovered without an external repair agent. With simple laser irradiation to induce the photothermal effect of Au nanorods, the shape-memory effect of vitrimer returns the Au nanorods to their initial orientation, and the plasticity achieves in situ self-healing of the cutting area. The self-healing of polarizing film provides a new research direction and reference for the application of self-healing systems in functional materials.

Thermally and Near-Infrared Light-Induced Shape Memory Polymers Capable of Healing Mechanical Damage and Fatigued Shape Memory Function

The fabrication of shape memory polymers that are mechanically robust and capable of being induced by near-infrared (NIR) light and healing mechanical damage and the fatigued shape memory function remains a challenge. In this study, thermally and NIR-light-induced shape memory polymers with self-healing ability and satisfactory mechanical robustness are fabricated by dispersing poly(acrylic acid) (PAA)-grafted graphene oxide (GO) (PAA-GO) into poly(vinyl alcohol) (PVA) matrix. The PVA/PAA-GO_3% films with a PAA-GO content of 3.0 wt % have a fracture stress of ∼70.4 MPa and a Young's modulus of ∼2.8 GPa. The PVA/PAA-GO_3% films exhibit an excellent shape memory performance because PVA and PAA-GO form a stable network through hydrogen-bonding interaction between them. Meanwhile, the PVA/PAA-GO_3% films are capable of recovering from temporary shape to permanent shape under NIR light irradiation because of excellent photothermal conversion property of the GO nanosheets. More importantly, benefiting from the reversibility of hydrogen-bonding interactions between PVA and PAA-GO nanosheets, the shape memory PVA/PAA-GO_3% films are capable of healing physical damage and the fatigued shape memory function with the assistance of water, which greatly enhance their reliability as shape memory materials and prolong their service life.

Photothermal-Triggered Shape Memory Polymer Prepared by Cross-Linking Porphyrin-Loaded Micellar Particles

In this work, we fabricated porphyrin-loaded shape memory polymer (SMP) film by cross-linking micellar particles prepared by co-assembly of porphyrin compounds and amphiphilic macromolecules formulated by copolymerization of 2-butoxy ethanol (BCS), methyl methacrylate (MMA), butyl acrylate (BA) acrylic acid (AA), and diacetone acrylamide (DAAM). The experimental results revealed that this film was able to respond to the red light in terms of photothermal effect enabled by the porphyrin filler. The photothermal-triggered shape memory behaviors of the film were further examined in detail. It was noteworthy that this material was expected to have potential applications in the biomedical field due to the excellent biocompatibility of the porphyrin filler and the red-light source, which was optimal and safe enough for biomedical treatment.

“Carbolong” polymers with near infrared triggered, spatially resolved and rapid self-healing properties

Conjugated Möbius metalla-aromatic “carbolong” is incorporated into polymers to achieve spatially resolved, repeated and fast healing through a photothermal effect.

Gradient Polydopamine Coating: A Simple and General Strategy toward Multishape Memory Effects

Multi shape memory polymers (multi-SMPs) exhibit many potential applications such as aerospace, soft robotics, and biomedical devices because of their unique abilities. Although many works are done to broaden the preparations of multi-SMPs, the desire to a simple and versatile strategy as well as more complex shapes still exists. Moreover, a light-induced SMP shows more advantages than a thermal-induced one in many practical working circumstances. Herein, inspired by strong adhesion and efficient photothermal conversion of polydopamine (PDA) coating, we report a more simple and facile approach to prepare light-induced multi-SMPs by introducing a gradient PDA coating on a dual-SMP through time-controlled dipping. The photothermal converting properties with varying thicknesses of PDA under the tunable near-infrared light source are investigated. Then, light-induced multishape memory effects based on gradient PDA coatings are illustrated, where three designs of multi-SMPs - rectangle, triangle, and cross are prepared and demonstrated. Also, the evolutions of coating morphology during shape shifting are carefully studied. Finally, we present few complex designs of patterns and shapes as well as a design of potential application for the highly controllable smart devices. This strategy demonstrates a very simple and general strategy to design and prepare the light-induced multi-SMPs with complex shapes based on any thermal-responsive dual-SMPs.

Rigid and Strong Thermoresponsive Shape Memory Hydrogels Transformed from Poly(vinylpyrrolidone- co-acryloxy acetophenone) Organogels

Shape memory hydrogels (SMHs) have a wide range of potential practical applications. However, the mechanically weak and soft nature of most SMHs strongly impedes their applications. Here, we report a novel kind of thermal-responsive SMH with high tensile strength and high elastic moduli. Organogels are first prepared by the copolymerization of a hydrophilic monomer N-vinylpyrrolidone (NVP) and a hydrophobic monomer acryloxy acetophenone (AAP) in N, N'-dimethylformamide (DMF) solutions, and then, poly(vinylpyrrolidone- co-acryloxy acetophenone) [poly(NVP- co-AAP)] hydrogels are obtained by solvent exchange with water. Because of the strong and reversible hydrophobic association and π-π stacking of acetophenone groups, the poly(NVP- co-AAP) hydrogels exhibit tensile strengths up to 8.41 ± 0.83 MPa and Young's moduli up to 94.2 ± 1.3 MPa, which are more than 1 or 3 orders of magnitude higher than those of the organogels, respectively. The poly(NVP- co-AAP) hydrogels exhibit good shape memory behaviors, with a complete fixation ratio and a recovery ratio of 74-89%, as well as very fast shape-fixing and recovering rates (in seconds). These rigid and strong hydrogels are demonstrated to be an ideal shape memory material for surgical fixation devices to wrap around and support various shapes of limbs.

Fast IR-Actuated Shape-Memory Polymers Using in Situ Silver Nanoparticle-Grafted Cellulose Nanocrystals

In recent years, shape-memory polymers (SMPs) have gained a key position in the realm of actuating applications from daily life products to biomedical and aeronautic devices. Most of these SMPs rely mainly on shape changes upon direct heat exposure or after stimulus conversion (e.g., magnetic field and light) to heat, but this concept remains significantly limited when both remote control and fine actuation are demanded. In the present study, we propose to design plasmonic silver nanoparticles (AgNPs) grafted onto cellulose nanocrystals (CNCs) as an efficient plasmonic system for fast and remote actuation. Such CNC- g-AgNPs "nanorod-like" structures thereby allowed for a long-distance and strong coupling plasmonic effect between the AgNPs along the CNC axis, thus ensuring a fast photothermal shape-recovery effect upon IR light illumination. To demonstrate the fast and remote actuation promoted by these structures, we incorporated them at low loading (1 wt %) into poly(ε-caprolactone) (PCL)-based networks with shape-memory properties. These polymer matrix networks were practically designed from biocompatible PCL oligomers end-functionalized with maleimide and furan moieties in the melt on the basis of thermoreversible Diels-Alder reactions. The as-produced materials could find application in the realm of soft robotics for remote object transportation or as smart biomaterials such as self-tightening knots with antibacterial properties related to the presence of the AgNPs.

Gold nanorods or nanospheres? Role of particle shape on tuning the shape memory effect of semicrystalline poly(ε-caprolactone) networks

In this study, modified poly(ε-caprolactone) (PCL) tri-block copolymers were successfully synthesized through ring opening polymerization. The nanocomposite films containing either colloidal gold nanorods (AuNRs) or gold nanospheres (AuNSs) in the polymer matrix were fabricated without chemical modification to realize light-responsive shape memory behaviors. The localized surface plasmon resonance of AuNPs was utilized by irradiating the selective wavelength of light to create a photothermal effect. The polymer microstructures were investigated by NMR, and the thermal properties of the polymer networks were studied by TGA and DSC. The addition of AuNPs did not change the melting temperature, (T m) of the SMP. The AuNRs were fairly well dispersed within the PCL matrix as observed using SEM-EDAX analysis and as indicated from the uniform shape memory transitions of the SMP/AuNR nanocomposites. The shape memory behavior was quantitatively analyzed by cyclic thermomechanical tests using DMA. The laser-triggered shape memory properties of the nanocomposites were analyzed and the shape recovery process from a rectangular shaped film to a helical coil was demonstrated. The speed of SMP recovery was found to be dependent on the geometry and concentration of the AuNPs in the nanocomposite, as well as on the laser wavelength and intensity.

Light triggered interfacial damage self-healing of poly(p-phenylene benzobisoxazole) fiber composites

The interfacial microcracks in the resin matrix composites are difficult to be detected and repaired. However, the self-healing concept provides opportunities to fabricate composites with unusual properties. In the present study, photothermal conversion Ag-Cu₂S nanoparticles were immobilized onto poly(p-phenylene benzobisoxazole) (PBO) fibers via a polydopamine chemistry. Benefitting from the photothermal effects of Ag-Cu₂S, the obtained PBO fibers (Ag-Cu₂S-PBO) efficiently converted the light energy into heat under Xenon lamp irradiation. Then, single PBO fiber composites were prepared using thermoplastic polyurethane as the matrix. It was found that the interfacial damage caused by single fiber pull-out was simply self-healed by Xe light irradiation. This wonderful interfacial damage self-healing property was mainly attributed to the in situ heating generation via photothermal effects of Ag-Cu₂S in the composite interface. This paper reports a novel strategy to construct advanced composites with light-triggered self-healing properties, which will provide inspiration for preparing high performance composite materials.

Entanglement-Based Thermoplastic Shape Memory Polymeric Particles with Photothermal Actuation for Biomedical Applications

Triggering shape-memory functionality under clinical hyperthermia temperatures could enable the control and actuation of shape-memory systems in clinical practice. For this purpose, we developed light-inducible shape-memory microparticles composed of a poly(d,l-lactic acid) (PDLLA) matrix encapsulating gold nanoparticles (Au@PDLLA hybrid microparticles). This shape-memory polymeric system for the first time demonstrates the capability of maintaining an anisotropic shape at body temperature with triggered shape-memory effect back to a spherical shape at a narrow temperature range above body temperature with a proper shape recovery speed (37 < T < 45 °C). We applied a modified film-stretching processing method with carefully controlled stretching temperature to enable shape memory and anisotropy in these micron-sized particles. Accordingly, we achieved purely entanglement-based shape-memory response without chemical cross-links in the miniaturized shape-memory system. Furthermore, these shape-memory microparticles exhibited light-induced spatiotemporal control of their shape recovery using a laser to trigger the photothermal heating of doped gold nanoparticles. This shape-memory system is composed of biocompatible components and exhibits spatiotemporal controllability of its properties, demonstrating a potential for various biomedical applications, such as tuning macrophage phagocytosis as demonstrated in this study.

Healability Demonstrates Enhanced Shape-Recovery of Graphene-Oxide-Reinforced Shape-Memory Polymeric Films

The fabrication of shape-memory polymers or films that can simultaneously heal the mechanical damage and the fatigued shape-memory function remains challenging. In this study, mechanically robust healable shape-memory polymeric films that can heal the mechanical damage and the fatigued shape-memory function in the presence of water are fabricated by layer-by-layer assembly of branched poly(ethylenimine) (bPEI)-graphene oxide (GO) complexes with poly(acrylic acid) (PAA), followed by the release of the (PAA/bPEI-GO)*n films from the underlying substrates. The free-standing (PAA/bPEI-GO_0.02)*35 films made of bPEI-GO complexes with a mass ratio of 0.02 between GO nanosheets and bPEI are mechanically robust with a Young's modulus of 19.8 ± 2.1 GPa and a hardness of 0.92 ± 0.15 GPa and exhibit excellent humidity-induced healing and shape-memory functions. Benefiting from the highly efficient healing function, the (PAA/bPEI-GO_0.02)*35 films can heal cuts penetrating thorough the entire film and achieve an ∼100% shape-recovery ratio for a long-term shape-memory application. Meanwhile, the shape-memory function of the mechanically damaged (PAA/bPEI-GO_0.02)*35 films can be finely restored after being healed in water. The shape-memory functions of the (PAA/bPEI-GO_0.02)*35 films and their healing capacity originate from the reversibility of electrostatic and hydrogen-bonding interactions induced by water between PAA and bPEI-GO complexes.

Transiently malleable multi-healable hydrogel nanocomposites based on responsive boronic acid copolymers

Dynamic multi-responsive gel nanocomposites with rapid self-healing and cell encapsulation properties are presented.