Excellent Shape Memory Properties Research Articles

Strengthening-Durable Trade-Off and Self-Healing, Recyclable Shape Memory Polyurethanes Enabled by Dynamic Boron-Urethane Bonds.

Addressing the demand for integrating strength and durability reinforcement in shape memory polyurethane (SMPU) for diverse applications remains a significant challenge. Here we synthesized a series of SMPUs with ultra-high strength, self-healing and recyclability, and excellent shape memory properties through introducing dynamic boron-urethane bonds. The introducing of boric acid (BA) to polyurethane leading to the formation of dynamic covalent bonds (DCB) boron-urethane, that confer a robust cross-linking structure on the SMPUs led to the formation of ordered stable hydrogen-bonding network within the SMPUs. The flexible crosslinking with DCB represents a novel strategy for balancing the trade-off between strength and durability, with their strengths reaching up to 82.2MPa while also addressing the issue of durability in prolonged usage through the provision of self-healing and recyclability. The self-healing and recyclability of SMPU were demonstrated through rapid dynamic exchange reaction of boron-urethane bonds, systematically investigated by dynamic mechanical analysis (DMA). This study sheds light on the essential role of such PU with self-healing and recyclability, contributing to the extension of the PU's service life. The findings of this work provide a general strategy for overcoming traditional trade-offs in preparing SMPUs with both high strength and good durability. This article is protected by copyright. All rights reserved.

Analysing the shape memory behaviour of GnP-enhanced nanocomposites: A comparative study between experimental and finite element analysis

Abstract Shape memory polymers (SMPs) are capable of enduring significant deformations and returning to their original form upon activation by certain external stimuli. However, their restricted mechanical and thermal capabilities have limited their broader application in engineering fields. To address this, the integration of graphene nanoplatelets (GnPs) with SMPs has proven effective in enhancing their mechanical and thermal properties while maintaining inherent shape memory functions. The study evaluated shape memory nanocomposites (SMNCs) using dynamic mechanical, thermogravimetric, and static tensile, flexural, and shape memory tests, along with scanning electron microscopy to analyse tensile fractures. The results indicate that the optimal content of GnP is 0.6 wt%, resulting in excellent shape memory, thermal, and mechanical properties. Specifically, this composition demonstrates a shape recovery ratio of 94.02%, a storage modulus of 4580.07 MPa, a tensile strength of 61.42 MPa, and a flexural strength of 116.37 MPa. Additionally, the incorporation of GnPs into epoxy reduces recovery times by up to 52% at the 0.6 wt% concentration. While there is a slight decrease in the shape fixity ratio from 98.77% to 93.02%, the shape recoverability remains consistently high across all samples. Current finite element (FE) models often necessitate complex, problem-specific user subroutines, which can impede the straightforward application of research findings in real-world settings. To address this, the current study introduces an innovative finite element simulation method using the widely used ABAQUS software to model the thermomechanical behaviour of SMNCs, importantly incorporating the time-dependent viscoelastic behaviour of the material. The effectiveness of this new approach was tested by comparing experimental results from bending test of SMNCs cantilever beam with outcomes derived from FE simulations. The strong agreement between the experimental data and simulation results confirmed the precision and reliability of this novel technique.

Effect of hybrid ratio on shape memory properties of graphene oxide‐carbon/glass fiber composites prepared based on vacuum infiltration hot‐press forming experimental system

AbstractShape memory composites now have a wide range of applications in aerospace, medical devices, and smart structures. Seven graphene‐carbon oxide/glass fiber (GO‐CF/GF) hybrid reinforced shape memory composites were prepared using vacuum infiltration hot pressing system (VIHPS) and the shape memory properties of the materials were investigated in 100°C test. By comparing and analyzing the microstructure and shape memory properties of composites containing different volume fractions of GFs, the mechanism of the influence of different hybrid contents of GFs on the organizational properties and shape memory properties was investigated. The results show that when the reinforcement of the composites were all carbon fibers, the composites had the largest elasticity modulus, harder material and the fixation rate of 77.15%, the recovery rate of 95.17%, the porosity of 0.80% and the shape recovery force of 7.98 N. When the reinforcement of the composites were glass fibers, the composites had the smallest elasticity modulus, softer material and the fixation rate of 94.89%, the recovery rate of 77.21%, the porosity of 13.56% and the recovery force of 2.28 N. The results of this test can lay a foundation for subsequent research on fibers with different mixing ratios.Highlights The GO‐CF/GF/EP prepared by VIHPS has excellent shape memory properties. Fiber hybrid ratio affects the composite's porosity and its properties. Fiber hybrid ratio affects the composite's shape fixation, recovery, and memory force. The shape fixation of G6 decreases the lowest with test cycles. Carbon fiber content changes the zero‐stress plane of GO‐CF/GF/EP.

Anti-swellable, stretchable, self-healable, shape-memory and supramolecular conductive TA-based hydrogels for amphibious motion sensors

Conductive hydrogel endures as an ideal candidate for flexible electronic devices. However, conventional conductive hydrogels cannot incorporate superior sensitivity under low deformation, biocompatibility and underwater sensing into one system, which widely obstructs their applications in an aqueous environment. Herein, we designed a supramolecular conductive poly(vinyl alcohol) (PVA) and tannic acid (TA) based PVA/TA hydrogel. Due to the effective hydrogen bonding between PVA and TA, the hydrogel possesses some unique properties, including anti-swelling, stretching, self-healing and shape-memory. The PVA/TA supramolecular hydrogel demonstrates an excellent electrical performance where the conductivity and gauge factor (GF) are obtained at 5.5 × 10-4 S/cm and 1.3 in dry and 5.0 × 10-4 S/cm and 1.2 in wet conditions, respectively. The multifunctional hydrogel manifests excellent mechanical properties, where the maximum tensile strength of the hydrogels is 700 kPa at an elongation of 4700 %. Additionally, the hydrogel possesses excellent shape-memory and self-healable properties. Moreover, the hydrogel depicts outstanding biocompatibility, anti-swellable properties and exerts long-term stability underwater to detect human motions. Based on excellent anti-swelling and stability, high electrical conductivity and extraordinary stretching capability, the hydrogels may consider as promising candidates for applications in amphibious motion sensors.

Crosslinking of polyethylene with polysilsesquioxane via carbamate linkages: Synthesis, shape recovery, and reprocessing properties

AbstractIn this contribution, we reported the crosslinking of polyethylene (PE) with dynamic silyl ether bonds. First, polycyclooctene copolymers bearing hydroxyl groups were synthesized via the ring‐opening metathesis copolymerization of cyclooctene with 5‐norbornene‐2‐methanol. The hydroxy‐functionalized polycyclooctene copolymers were further hydrogenated into the corresponding hydroxy‐functionalized PE copolymers. The PE copolymers were allowed to react with 3‐isocyanatopropyltriethoxysilane to obtain the PE copolymers bearing triethoxysilane groups. By taking advantage of hydrolysis and condensation of triethoxysilane groups grafted onto PE chains, the PE copolymers were well crosslinked; polysilsesquioxane (PSSQ) segments behaved as the crosslinking linkages in the networks. Notably, the PE networks were reprocessable (or recyclable) while zinc trifluoromethanesulfonate [Zn(OTf)2] was incorporated. The reprocessing properties of the PE networks were quite dependent on the crosslinking densities. The reprocessing behavior of the networks is attributable to the introduction of two dynamic chemistries: (i) the metathesis of silyl ether bonds which was catalyzed with Zn(OTf)2 and (ii) transcarbamoylation of carbamates which was catalyzed with dibutyltin dilaurate. Owing to the crosslinking, the PE networks displayed excellent shape memory properties. For the shape memory networks, notably, the original shapes can be reprogrammed with the aid of the exchange of the dynamic covalent bonds introduced into the systems.

Layered co-continuous structure in bone scaffold fabricated by laser additive manufacturing for enhancing electro-responsive shape memory properties

Porous scaffold based on electro-responsive shape memory polymers (ESMPs) possesses great potential applications in minimally invasive surgery for bone defect repair because it provides the ability for remote control and internal heating. However, it's difficult to obtain co-continuous structure in bone scaffold for achieving excellent electro-responsive shape memory properties. In this study, layered co-continuous structure with thermoplastic polyurethane (TPU) loaded with multi-walled carbon nanotubes (MWCNTs) (referred to as cTPU) layer and l-polylactic acid (PLLA) layer alternate stacking was obtained via layer-by-layer fabrication technology, and the porous scaffold was fabricated via selective laser sintering (SLS). The thermal and electrical shape memory properties of the scaffolds with different contents of MWCNT were evaluated by dynamic mechanical analysis (DMA) and U-bending experiments. The results indicated that the layered co-continuous structure improved phase continuity and confined MWCNTs to one side, enhancing the electrically driven properties and shape memory properties. The scaffold with 1.5 wt% MWCNTs achieved shape fixed and recovery rates of 95.6% and 90.2%, respectively. With the further increasing of MWCNTs content, the shape memory properties decreased due to the agglomeration of MWCNTs in the cTPU phase, which affected the phase continuity of cTPU. The DMA results confirmed the good mechanical properties of the scaffold, and the cell culture experiment results demonstrated excellent cytocompatibility for cell attachment and growth. This work provides a feasible method to fabricate electro-responsive shape memory bone scaffold with layered co-continuous structure, which exhibits great potential in applications of bone defect repair.

Tetherless and Batteryless Soft Navigators and Grippers.

Remotely controllable soft actuators have promising potential applications in many fields including soft robotics, exploration, and invasion medical treatment. Shape memory polymers could store and release energy, resulting in shape deformation, and have been regarded as promising candidates to fabricate untethered soft robots. Herein, an untethered and battery-free soft navigator and gripper based on a shape memory hydrogel is presented. The shape memory hydrogel is obtained through hydrogen bonding between gelatin and tannic acid, and the hydrogel displays excellent shape memory properties on the basis of hydrogen bonding and the coil-triple helix transition of gelatin. Moreover, Fe3O4 nanoparticles are introduced to endow the hydrogel magnetic responsiveness and photothermal conversion capacity. Finally, the shape memory hydrogel in a stretched state is assembled with an inert hydrogel to achieve a bilayer hydrogel actuator, which could produce complex shape transformation due to the shape recovery of the shape memory layer induced by heat or light. Taking advantage of the magnetically control and light-responsive shape deformation, remotely controllable soft grippers that could navigate through tortuous paths and grasp objects from a hard-to-reach place have been accomplished. This approach will inspire the design and fabrication of novel shape memory hydrogels as remotely controllable soft robots.

Hyaluronidase-Responsive Bactericidal Cryogel for Promoting Healing of Infected Wounds: Inflammatory Attenuation, ROS Scavenging, and Immune Regulation.

Wounds infected with multidrug-resistant (MDR) bacteria are increasingly threatening public health and challenging clinical treatments because of intensive bacterial colonization, excessive inflammatory responses, and superabundant oxidative stress. To overcome this malignant burden and promote wound healing, a multifunctional cryogel (HA/TA2/KR2) composed of hyaluronic acid (HA), tannic acid (TA), and KR-12 peptides is designed. The cryogel exhibited excellent shape-memory properties, strong absorption performance, and hemostatic capacity. In vitro experiments demonstrated that KR-12 in the cryogel can be responsively released by stimulation with hyaluronidase produced by bacteria, reaching robust antibacterial activity against Escherichia coli (E. coli), MDR Pseudomonas aeruginosa (MDR-PA), and methicillin-resistant Staphylococcus aureus (MRSA)by disrupting bacterial cell membranes. Furthermore, the synergetic effect of KR-12 and TA can efficiently scavenge ROS and decrease expression of pro-inflammatory cytokines (tumor necrosis factor (TNF)-α & interleukin (IL)-6), as well as modulate the macrophage phenotype toward the M2 type. In vivo animal tests indicated that the cryogel can effectively destroy bacteria in the wound and promote healing process via accelerating angiogenesis and re-epithelialization. Proteomic analysis revealed the underlying mechanism by which the cryogel mainly reshaped the infected wound microenvironment by inhibiting the Nuclear factor kappa B (NF-κB) signaling pathway and activating the Janus kinase-Signal transducer and activator of transcription (JAK-STAT6) signaling pathway. Therefore, the HA/TA2/KR2 cryogel is a promising dressing candidate for MDR bacteria-infected wound healing.

Biodegradable photo-crosslinked polycaprolactone/polydopamine elastomers with excellent light driven programmable shape memory and chemical degradation properties

Fabrication of biodegradable shape memory polymer with remotely controllable shape actuation is of great significance in the biomedical field but remains challenging. Herein, we present a simple strategy to fabricate a monolayer-based stretchable and mechanically robust polycaprolactone/polydopamine elastomer via efficient thiol-ene click chemistry. The resultant elastomers exhibit desirable photothermal transfer efficiency and can enable rapid temperature increase over the melting temperature of polymeric matrix, and quantitative results demonstrate that the crosslinked film exhibited excellent shape memory properties with shape fixity (Rf) and shape recovery ratios (Rr) approaching 92.3 % and 95.6 %, respectively. Combined with photo stimuli, anisotropic polymer chain relaxation of the prestretched film can generate asymmetric contractions and eventually give rise to ut out-of-plane bending actuations upon photo stimulation, meanwhile, numerical simulation reveals the interaction mechanism of light with film. Beyond this, we further demonstrate that the bending angle is correlated with the parameters of prestretch strain, film thickness as well as irradiation time, and the maximum value can reach 158° with prestretch strain of 200 % and film thickness of 0.3 mm. In particular, the bent structures could be reversibly deformed into plane state via photo-directed corresponding opposite surfaces. Remarkably, the in vitro degradation properties of the elastomers on PBS-T buffer solutions demonstrated that the degradation was composed of induction stage and acceleration stage. This work will pave way for designing biodegradable light-induced shape memory materials toward biomedical device fields and so on.

Poly(ethylene-co-vinyl acetate)/Fe3O4 with near-infrared light active shape memory behavior

The use of near-infrared (NIR) to drive shape memory composites can compensate for the shortcomings of heat-driven shape memory composites in environmental applications such as outer space, in vivo and in cold regions. Here we report, a shape memory composites that can respond to NIR light stimulation were prepared by blending EVA with Fe3O4 nanoparticles. With the addition of Fe3O4 nanoparticles, the EVA/Fe3O4 composites exhibited excellent NIR light responsiveness. When the mass fraction of Fe3O4 is 1 % of EVA, it shows excellent shape memory properties with 95.1 % one-way shape fixity ratio and 97.9 % one-way shape recovery ratio. The non-contact manipulation and segmented response of the EVA/Fe3O4 composites were achieved by irradiation with NIR light.

Shape memory and hemostatic silk-laponite scaffold for alveolar bone regeneration after tooth extraction trauma

Persistent bleeding and the absence of alveolar bone stress following tooth loss can hinder socket healing, complicating future dental implant procedures, and potentially leading to neighboring tooth instability. Therefore, developing materials that promote alveolar bone regeneration and possess both hemostatic and osteogenic properties is crucial for preserving the extraction sites. This study introduces a silk-based laponite composite scaffold material with proficient hemostatic and osteogenic functions, and excellent shape-memory properties for efficient extraction- site filling. In vitro studies research demonstrated that the scaffold's inherent negative charge of the scaffold significantly enhanced blood coagulation and thrombin generation. Moreover, its porous structure and slightly rough inner surface promoted blood cell adhesion and, improved the hemostatic performance. Furthermore, the scaffold facilitated stem cell osteogenic differentiation by activating the TRPM7 channel through the released of magnesium ions. In vivo tests using rat models confirmed its effectiveness in promoting coagulation and mandibular regeneration. Thus, this study proposes a promising approach for post-extraction alveolar bone regenerative repair. The composite scaffold material, with its hemostatic and osteogenic capabilities and shape-memory features, can potentially enhance dental implant success and overall oral health.

Biocompatible polyurethanes with thermally-induced shape memory properties derived from three-arm branched poly(ε-caprolactone-co-γ-butyrolactone)-b-poly(lactide) block copolymers

A series of poly(lactide)-based polyurethanes with cross-linked network structure was synthesized through the chain extension of three-arm branched poly(ε-caprolactone-co-γ-butyrolactone)-b-poly(lactide) (3PBCL-b-PLA) block copolymers with various molecular weights and optical activities of PLA blocks. The structure of the synthesized poly(lactide)-based polyurethanes was analyzed, and it was confirmed that they contained the cross-linked network structure. Effects of the molecular weight and optical activity of PLA block on the various properties such as crystallization, mechanical property, shape memory performance, thermal stability and hydration ability were discussed. By simultaneously adjusting the molecular weight and optical activity of PLA blocks, the crystallization of flexible PCBL blocks and rigid PLA blocks in the synthesized cross-linked polyurethanes was effectively controlled, which was the basis for constructing poly(lactide)-based polyurethanes with a broad ranged mechanical property, excellent shape memory properties and controllable hydration ability. The synthesized polyurethanes exhibited adjusted tensile strength and elongation at break in the range of 11.2–32.4 MPa and 41–753 %, with the water content varying from 1.1 % to 20.1 %, respectively. The shape fixity ratio and shape recovery ratio of L-PU2.9 could reach 90.9 % and 96.0 %, respectively. The effect of stereocomplex-crystallization on the properties of poly(lactide)-based polyurethane was also analyzed. Stereocomplexed polyurethane based on 3PCL-b-PLA block copolymer enantiomers with short PLA block was constructed, which achieves fully stereocomplexation in a wide mixing ratio (20–50 %). It was found that the formation of a small number of stereocomplex-crystals can change the properties of poly(lactide)-based polyurethane in a wide range. Eventually, it was demonstrated by in vitro hemolysis test, cytotoxicity test and live/death staining that the synthetic poly(lactide)-based polyurethanes exhibited excellent biocompatibility. These results suggested that these biocompatible shape memory poly(lactide)-based polyurethanes with tunable mechanical properties and hydration ability demonstrated the promising potential as an excellent implantation for biomedical application.

Co-continuous structure enhanced magnetic responsive shape memory PLLA/TPU blend fabricated by 4D printing

ABSTRACT Combining poly (L-lactic acid) (PLLA) with thermoplastic polyurethane elastomer (TPU) can integrate the advantages of excellent biocompatibility and intrinsic shape memory ability of PLLA and high elasticity and excellent shape memory properties of TPU in the application of minimally invasive surgery for bone tissue engineering. However, TPU easily forms a sea-island-like structure in PLLA matrix, decreasing shape memory properties. In this study, a co-continuous structure of TPU phase in PLLA matrix was constructed by adding Fe3O4 nanoparticles due to the changed interfacial tension and flow behavior of TPU, which endowed the TPU/PLLA/Fe3O4 blend fabricated via selective laser sintering (SLS) with excellent shape memory properties. As a result, the morphology of TPU in the blend changed from sea-island-like structure to complete co-continuous structure with increasing Fe3O4 content (0 to 10wt%), and shape recovery ratios in 50 °C water increased from 66.67 to 95.92%. The introduction of Fe3O4 endowed the blend with magnetic responsive shape memory in alternating magnetic field because Fe3O4 could heat it by generating heat from relative friction and particle collisions. Besides, the tensile modulus and hardness of the specimen with 10wt% Fe3O4 nanoparticles increased. In addition, the blend demonstrated excellent biocompatibility by promoting cell adhesion, spreading, and proliferation.

Rapid shape recovery and remodeling by tuning the topology of polycaprolactone-based polymer networks

Shape memory polymers (SMPs) designed with desired performance depend on a deeper understanding of network topology and macro characteristics. Although photoreversible dynamic covalent bonds are used for permanent shape reconstruction of SMPs due to their economical and rapid, the disordered network structure limits the ability to improve shape memory performance through structural adjust. In this work, the polycaprolactone networks with sliding structural components (polyrotaxane) and photoreversible components (coumarin) were prepared by preprogrammed precursors. The SMPs network topology is controlled by adjusting the length of molecular chain and sliding distance. Reversible bonding can realize complex shape designability and solid remodeling. Furthermore, the supramolecular structure of polyrotaxane can adjust the uneven stress distribution caused by network topology defects, so the material can instantly return to its original shape under more than 300 % strain, and its elongation at break is over 1600 %. Especially the thermo-mechanical properties of materials can be adjusted by simple preliminary monomer synthesis steps. The results revealed the material has excellent shape memory and controllable thermodynamic properties, which provides a new paradigm for the preparation of high performance SMPs.

Organic-inorganic polyureas with benzyl hindered urea bonds and POSS cages in the main chains: Synthesis, shape memory and reprocessing properties

The organic–inorganic polyureas with benzyl hindered urea bonds (HUBs) and POSS cages as the main-chain structural units were synthesized via the polyaddition of 4,4′-diphenylmethane diisocyanate with α,ω-dibenzyl diamines including α,ω-dibenzylamino-terminated poly(ethylene oxide), N,N’-dibenzylhexamethylene-1,6-diamine and 3,13-dibenzylaminoanilino double decker silsesquioxane. The organic–inorganic PUreas were microphase-separated, in which the POSS cages were self-assembled into the microdomains via POSS-POSS interactions. The POSS microdomains acted as the physical crosslinking points and thus the organic–inorganic PUreas behaved as the crosslinked elastomers; the physical crosslinking remained thermally stable even at elevated temperature as high as 200 °C. In spite of the high thermal stability, the networks can be reprocessed with the plasticity in solids via the dynamic exchange of benzyl HUBs. Due also to the physical crosslinking, the organic–inorganic PUreas possessed the excellent shape memory properties; the original shapes were re-configurable by taking advantage of the benzyl HUBs in the main chains.

3D printed epoxy/acrylate hybrid polymers with excellent mechanical and shape memory properties via UV and thermal cationic dual-curing mechanism

Fabricating shape memory polymers with complex configurations and high mechanical performance for application as structural materials remains a significant challenge. Here, an epoxy/acrylate hybrid material with remarkable mechanical properties and excellent shape memory performance is fabricated using vat photopolymerization printing technology through photo-thermal dual curing mechanism. The UV-curing component comprises of a polyurethane acrylate and a rigid active diluent to ensure robustness and toughness. Meanwhile, the thermal curing epoxy constituent utilizes a benzylanilinium salt as the cationic initiator for its storage and handling stability throughout the UV curing stage. The interpenetrating polymer network and the unique two-phase molecular microstructure impart the hybrid material with good shape memory and high mechanical properties. Many complex objects are fabricated using vat photopolymerization printing technology and employed in self-deploying antennas, intelligent mechanical grippers, and switches. Combining with excellent printability, mechanical and shape memory properties, the hybrid materials have great potential applications in various fields.

Preparation and Performance Study of Polyurethane/Epoxy Resin Interpenetrating Networks with Self‐Healing, Shape Memory, and High Damping Properties

AbstractInterpenetrating polymer networks (IPNs) possessing a wide damping temperature range are commonly employed as damping materials that are applied in numerous fields. But IPNs will gradually appear to fatigue microcracks and fracture when long‐term in the energy absorption and dissipation. So, the ability for IPNs to recover from damage is necessary that can considerably prolong their service life. Based on polyurethane elastomer and cross‐linked epoxy, several innovative self‐healing IPNs are designed and prepared in this research. The IPNs containing dynamic disulfide bond exhibit favorable damping and self‐healing properties. In detail, the loss factor of IPN‐80/20 is beyond 0.3 at temperatures between −0.8 and 65.5 °C that covers the operating temperature range at room temperature. What is more, The PU/EP IPNs also have excellent shape memory properties, self‐healing ability, and thermal stability.

3D-printing of biomass furan-based polyesters with robust mechanical performance and shape memory property

3D-printing provides a feasible technique for realizing new materials into structural and intelligent parts. In this work, biomass furan-based polyesters poly (ethylene furanoate) (PEF), poly (trimethylene furanoate) (PTF), and poly (butylene furanoate) (PBF) were successfully synthesized in a 5 L reactor through the melt polycondensation process and fabricated into 3D-printing feedstocks. It was demonstrated that the three furan-based polyesters were additively-manufactured into complicated structures. Besides, the mechanical and thermal properties of furan-based polyesters could be tailored by the chain length of diol monomer. The mechanical performance of 3D-printed PEF, PTF and PBF were characterized and compared with commercial filaments. The tensile strength of PEF and PTF could reach 74.6 and 63.8 MPa respectively, which exhibited superior tensile property to poly(ether-ether-ketone) (PEEK), polyamide (PA) and polylactic acid (PLA). Meanwhile, the compression results demonstrated that the PEF and PTF possessed comparable energy absorption capacity with PEEK and PLA respectively, which indicated excellent mechanical properties of furan-based polyesters. It was interesting to find that the 3D-printed structures including solid cube, bionic flower and lattice structures were employed to prove that the PTF possessed excellent shape memory properties. Therefore, the proposed biomass furan-based polymers would offer more freedom in the field of 3D-printing.

Photo‐activated shape memory polymer with chiral twisting based on anisotropic bilayer thin sheets

AbstractThe remotely controlled shape memory behaviors of a two‐dimensional (2D) sheet to controlled helix structure upon external stimuli is of great significance in the field of smart materials. Herein, we devise a strategy to fabricate a series of shape memory polycaprolactone/W18O49 nanowire film via highly efficient UV‐triggered thiol‐acrylate click chemistry. The resultant polymer composites exhibited desirable photothermal transfer efficiency and can enable rapid temperature increase over the melting temperature of polymeric matrix, thus remotely actuating shape transformation within 8 s. Owing to the well‐defined architecture of the polymer network, the fabricated elastic composite film exhibited a high degree of crystallinity and showed excellent shape memory properties with Rf of 93.12% and Rr of 95.32%. Remarkably, under a 160 mW/cm2 simulated sunlight illumination, the transformation of flat 2D film into 3D chiral actuators is driven by designing anisotropic bilayer thin sheet, and it yields right‐ and left‐handed helix. This work will pave the way for designing biomimetic flexible actuators toward multifunctional shape‐shifting devices.Highlights Shape memory polycaprolactone/W18O49 nanowires composite film is fabricated via UV‐triggered thiol‐ene click chemistry. Polymer composites exhibit light‐activated shape memory behaviors. The composite films show excellent shape fixity and shape recovery ratio based on the well‐defined network. The shape morphing behaviors of a flexible 2D bilayer strip into 3D chiral actuators are achieved.

Influence of subsequent thermomechanical cycles on shape memory behavior of 4D printed PEKK

The current study identifies and investigates the shape memory response of poly ether ketone ketone (PEKK) for the first time. 4D printed PEKK are subjected to annealing, crystalline behavior, and shape memory studies under susquent thermomechanical cycles. Scanning electron microscopy (SEM) revealed seamless bonding between the printed layers, confirming the suitability of the chosen printing parameters. Differential scanning calorimetry (DSC) results showed higher Tg (161.20 °C) and Tm (339.03 °C). Shape fixity ratio (Rf) is observed to be lower in the higher cycles (∼10% lower in cycle 8 compared to cycle 1), while the shape recovery ratio (Rr) is noted to be decreasing in each cycle ( 20% decreased in cycle 8 compared to cycle 1) due to reduction in storage modulus. The 4D printed PEKK exhibited excellent shape memory properties as compared to PEEK, making them potential materials in automotive and aerospace applications.