Excellent Memory Research Articles

High-Performance Triple-Network Hydrogels Derived from Chrome Leather Scraps: Ultrahigh Compressive Strength, Adhesion, and Self-Recovery.

The development of engineered hydrogels with high strength, self-recovery, and adhesion is essential for applications requiring resistance to large deformations and cyclic loading. Herein, a triple-network (TN) hydrogel with ultrahigh compressive strength, strong adhesion, and good self-recovery was constructed by using tannic acid-modified chrome leather scrap hydrolysate as the first network, polyacrylamide as the second network, and poly-2-propenamide-2-methylpropanesulfonic acid as the third network. The ultrahigh (70 MPa compressive strength and 95% compression deformation) TN hydrogels were effectively created, which is attributed to the synergy of the three networks. The TN hydrogels display adhesion (adhesion strength > 20 kPa) ascribed to the introduction of phenolic hydroxyl groups in tannic acid. Intriguingly, the TN hydrogels exhibit excellent self-recovery performance (93.6% dissipated energy recovery at 70 °C) and shape memory performance (restored to the original shape in 20 s). These properties are essential for the development of high-performance hydrogels and promote the resource utilization of leather waste.

Flexible and durable shape memory EVA/MXene/EVA fiber membrane for programmable EMI shielding

Flexible and lightweight electromagnetic interference (EMI) shielding materials are currently the focus of electromagnetic protection material research. By applying shape memory polymers to the field of electromagnetic shielding, intelligent electromagnetic shielding composites with programmable shielding performance can be prepared. In this study, a flexible EVA/MXene/EVA electromagnetic shielding composite membrane with programmable shielding effectiveness was prepared using electrospinning, vacuum filtration, and hot pressing techniques. Even with a low MXene content, the EMI shielding effectiveness in the X-band still achieved 40.5 dB, and the specific EMI shielding effectiveness was as high as 6.23 × 103 dB cm2 g−1. The composite membrane exhibited excellent shape memory performance, with a shape fixation rate (Rf) of 93.8 % and a shape recovery rate (Rr) of 92.1 %, achieving a programmable shielding effectiveness of 14.1–40.5 dB under 0–30 % tensile strain. Additionally, the composite membrane could serve as a switch for electromagnetic shielding, controlling the reception and shielding of electromagnetic waves. Simultaneously, the composite membrane exhibits excellent hydrophobicity, electrothermal conversion capability, and durability. Importantly, it retains almost the same shielding effectiveness even after undergoing 500 cycles of bending and folding, as well as prolonged exposure to strong acids and alkalis. This work not only offers new insights into the development of multifunctional and intelligent electromagnetic shielding composites suitable for harsh environments but also expands the application scope of shape memory smart materials.

Doping- and capacitor-less 1T-DRAM cell using reconfigurable feedback mechanism

In this paper, we propose a doping- and capacitor-less 1T-DRAM cell, which achieved virtual doping by leveraging charge plasma and bias-induced electrostatic doping (bias-ED) techniques in a 5 nm-thick intrinsic silicon body, thereby eliminating doping processes. Platinum was in contact with the drain, while aluminum was in contact with the source, enabling virtual doping of the silicon body into ap*-i-n* configuration via the charge-plasma technique. Two coupled polarity gates and one control gate are positioned above the intrinsic channel region. The intrinsic channel region is virtually doped through the bias-ED by applying voltages to the gates, forming potential wells inside the channel. The voltage applied to the two coupled polarity gates determines whether the device operates in thep- orn-channel mode, whereas the control gate governs the flow of charge carriers. Charge carriers are stored and released in the potential wells inside the channel by adjusting the gate, effectively replacing the capacitor. In this device, the placement of polarity gates on either side of the control gate enables the observation of the reconfigurable characteristics. Moreover, the proposed device utilizes a feedback mechanism, enabling excellent memory characteristics such as a high on/off current ratio of ∼109, steep switching behavior of ∼0.2µV dec-1, short write time of 10 ns, long hold retention of over 100 s, and long read retention of over 600 s.

A multifunctional partially bio-based epoxy resin by renewable chitosan as reaction raw material: Shape memory effect, bonding property, excellent degradability, and toughening performance

To expand the variety of partially bio-based epoxy resins with superior performance and improve the efficiency of utilizing renewable raw materials, a chitosan-based bisphenol A epoxy resin (CBE) was successfully synthesized. With PA651 as the curing agent, the strain energy CBE/PA651 reached 15.11 MJ m−3, which was higher than those of many typical ductile epoxy resins in comparative literature. The shape fixity and shape recovery rate of CBE/PA651 were 94.72 % and 98.74 %, respectively, demonstrating excellent shape memory effects. When CBE was used as wood adhesives, it exhibited a relatively high bonding strength and excellent water resistance, and the dry and boiling bond strength can exceed 4.08 MPa and 1.91 MPa, respectively. Simultaneously, CBE/PA651 can be completely degraded within 8 h at 90 °C, exhibiting excellent degradability. In addition, CBE was employed as a toughening agent for DGEBA/DDM. It was found that when the CBE content was 20 wt%, the elongation at break, the impact strength, and KIC of CBE/DGEBA/DDM reached their peak values of 8.55 %, 17.62 kJ m−2 and 1.75 MPa m1/2 respectively, representing a significant increase of 101.65 %, 43.6 %, and 78.57 % compared to DGEBA/DDM. The toughening mechanism was revealed by SEM and crosslinking simulation networks.

Nickel–titanium alloy porous scaffolds based on a dominant cellular structure manufactured by laser powder bed fusion have satisfactory osteogenic efficacy

Nickel–titanium (NiTi) alloy is a widely utilized medical shape memory alloy (SMA) known for its excellent shape memory effect and superelasticity. Here, laser powder bed fusion (LPBF) technology was employed to fabricate a porous NiTi alloy scaffold featuring a topologically optimized dominant cellular structure that demonstrates favorable physical and superior biological properties. Utilizing a porous structure topology optimization method informed by the stress state of human bones, two types of cellular structures—compression and torsion—were designed, and porous scaffolds were produced via LPBF. The physical properties of the porous NiTi alloy scaffolds were evaluated to confirm their biocompatibility, while their osteogenic efficacy was investigated through both in vivo and in vitro experiments, with comparisons made against a traditional octahedral unit cell structure. NiTi alloy porous scaffolds can be nearly net-shaped via LPBF and exhibit favorable physical properties, including a low elastic modulus, high hydrophilicity, a specific linear expansion rate, as well as superelastic and shape memory effects. These scaffolds demonstrate excellent biocompatibility, support in vitro osteogenesis, and possess significant in vivo bone ingrowth capabilities. When compared to titanium alloys, NiTi alloys show comparable osteogenic properties in vitro but superior bone ingrowth properties in vivo. Additionally, among octahedral-type, torsion-type, and topologically optimized compression-type porous scaffolds, the latter demonstrates enhanced bone ingrowth properties. LPBF technology is effective for manufacturing porous NiTi alloy scaffolds with fine pore structures and excellent mechanical properties. The scaffolds based on topologically optimized dominant cellular structures facilitate satisfactory and efficient bone formation.

Smart and Sustainable 3D-Printed Nanocellulose-Based Sensors for Food Freshness Monitoring.

Annually, about one-third of the food produced around the world is wasted due to spoilage. Food contamination and spoilage, along with the use and disposal of nondegradable packaging materials, impact human health and have huge economic and sustainability implications. Achieving sustainability within the food system requires innovative solutions to reduce the environmental footprint. Herein, we describe the formulation, scalable manufacturing, and characterization of three-dimensional (3D)-printed sensors prepared from a mixture of edible biopolymer hydrogels, 8% alginate, and 10% gelatin and nanocellulose (CNC) as a reinforcement filler. We demonstrate that incorporating CNC improves the overall mechanical performance of the printed film and enables the stabilization of pH-responsive dyes for monitoring the release of total volatile basic nitrogen (TVB-N), an indicator of food freshness. Mechanical performance enhancement includes increases of 43% in load-depth indentation, 28.2% in hardness, and 17.4% in elastic modulus. This enhancement facilitates its use as a smart label technology, enabling the visual assessment of spoilage when placed inside packaging over a period of 3 days at room temperature. The 3D-printed film exhibits excellent durability, flexibility, shape memory, and robustness, along with pH responsiveness, showing distinctive color changes over the pH range of 2 to 13. These performances are demonstrated in packaged meat and fish, enabling monitoring over several days and illustrating potential as a real-time freshness indicator. The material formulations developed in this work are biodegradable, eco-friendly, and inexpensive, making them suitable candidates for smart and sustainable food packaging.

3D-Printed Shape Memory and Piezoelectric Bifunctional Thermoplastic Polyurethane/Polyvinylidene Fluoride Porous Composite Scaffold for Bone Regeneration.

Physical stimulations such as mechanical and electric stimulation can continuously work on bone defect locations to maintain and enhance cell activity, and it has become a hotspot for research in the field of bone repair. Herein, bifunctional porous composite scaffolds with shape memory and piezoelectric functions were fabricated using thermoplastic polyurethane (TPU) and poly(vinylidene fluoride) through triply periodic minimal surfaces design and selective laser sintering technology. Thereinto, the shape fixity ratio and recovery ratio of the composite scaffold reached 98.6% and 81.2%, respectively, showing excellent shape memory functions. More importantly, its piezoelectric coefficient (d33 = 2.47 pC/N) is close to the piezoelectric constant of bone tissue (d33 = 0.7-2.3 pC/N), and the voltage released during the compression process can reach 0.5 V. Furthermore, cyclic compression experiments showed that the strength of composite scaffold was up to 8.3 times compared with the TPU scaffold. Besides, the composite scaffold showed excellent cytocompatibility. In conclusion, the composite scaffold is expected to continuously generate mechanical and electric stimulation due to shape memory and piezoelectric function, respectively, which provide an effective strategy for bone repair.

Crosslinking of polyurethane with boronic ester bonds: An impact of B–N coordination

In this contribution, we reported a new approach to crosslink linear polyurethane (PU) with dynamic boronic ester bonds. First, a linear PU was synthesized, which carries a plethora of 1,3-diol structural units. Second, two structurally similar diboronic acids were designed and synthesized, which contained amino and amido groups, respectively. Thereafter, the crosslinking between the linear PU and the diboronic acids was carried out via the generation of boronic ester bonds. Thanks to the crosslinking, the PU networks significantly displayed improved thermomechanical properties, contingent on types of crosslinkers. More importantly, the excellent reprocessing and shape memory properties were imparted to the PU networks, which were implemented by dynamic boronic ester bonds between 1,3-diol moieties of the linear PU and boronic acids of the crosslinkers. The dynamic exchange of boronic ester bonds is responsible for the reprocessing properties. For the shape memory properties, the PU networks featured the reprogramming behavior of original shapes via the dynamic exchange of boronic ester bonds. More importantly, the shape memory properties were also dependent on types of diphenylboronic acids, which was reflected with the difference in dynamicity of boronic ester bonds. For the PU networks with amino-containing crosslinker, the boronic ester bonds featured the B–N coordination. As a result, the boronic ester bonds had the increased dynamicity, which significantly affected the reprocessing properties.

Shape memory and shape recovery characterization of thermoplastic urethane

ABSTRACT Polyurethane shape memory polymer, as a smart material, has been becoming more and more popular due to its greater multifunctionality in various industrial and biomedical applications. Here, the authors reported the characterization, and comprehensive methodology and acquired the results of thermoplastic urethane (SMTPU) as a shape memory polymer, with 35°C as the glass transition temperature, by examining its creep. This smart polymer exhibits excellent shape memory behaviour due to its steady, chemically cross-linked network. Such behaviour of shape memory polymer determines its usability in various functional applications. Furthermore, the activation temperature range of SMPTPU is close to body temperature and room temperature as well, so it can be employed in more demanding industrial applications. Thus, it becomes essential to investigate the shape-changing/memory behaviour of commercial SMTPU. A quantitative analysis was done to determine the effects of programming temperature, maximum uniaxial strain, and compressive strain on shape memory characteristics viz. the shape recovery ratios and shape fixity ratios. Along with the excellent shape memory effect, this material also exhibits high creep and elasticity at room temperature, indicating that it may be used for various industrial and biomedical applications.

Shape Memory Polymer Bioglass Composite Scaffolds Designed to Heal Complex Bone Defects.

An off-the-shelf scaffold with requisite properties could enable the viable treatment of irregular craniomaxillofacial bone defects. Notably, the scaffold should be conformally fitting, innately bioactive, and bioresorbable. In prior work, we developed a series of shape memory polymer (SMP) scaffolds based on cross-linked poly(ε-caprolactone) (PCL). These were capable of "self-fitting" into complex bone defects when exposed to temperatures above the melt transition of the constituent PCL, either linear-PCL-diacrylate (linear-PCL-DA, Tm ∼55 °C) or star-PCL-tetraacrylate (star-PCL-TA, Tm ∼45 °C) for the potential to improve tissue safety. To achieve favorably increased degradation rates versus PCL-only scaffolds, semi-interpenetrating networks (semi-IPNs) were formed by including linear- or star-poly(l-lactic acid) (PLLA). A potential limitation of these self-fitting scaffolds is the lack of bioactivity, which is essential to osteoinductivity and osseointegration. Herein, analogous composite scaffolds were formed with 45S5 bioglass (BG) to impart bioactivity. The solvent-cast particulate leaching fabrication method was adapted to introduce BG to the fused salt template, resulting in composites with BG concentrated on the pore wall surfaces rather than within pore struts. Composite scaffolds with good pore wall integrity were produced with 2.5, 5, and 10 wt % BG. All composite scaffolds exhibited non-brittle behavior and did not fracture with 85% strain. For semi-IPN composite scaffolds, PLLA crystallinity was lost, and mechanical properties were not appreciably altered versus the non-BG controls. Sufficient retention of PCL crystallinity led to excellent shape memory behavior. The inclusion of 5 and 10 wt % BG led to hydroxyapatite mineralization after 1 day of exposure to simulated body fluid, as well as increased rates of in vitro degradation.

Effects of fluorine atom numbers on electrochromic properties of the benzothiadiazole-based D-A polymers

In this work, two fluorinated D-π-A-π-D type monomers, F-EDOT and FF-EDOT, were facilely synthesized by donor-acceptor-donor method via Stille coupling reaction, with monofluorinated benzothiadiazole and difluorinated benzothiadiazole as the acceptor units and 3,4-ethylenedioxythiophene (EDOT) as the donor units. The electrochemical polymerization behavior of the fluorinated monomers, electrochemical and electrochromic properties of the corresponding fluorinated D-A polymers were compared to study the effects of different fluorine atom numbers on the optoelectronic properties of the monomers and their resultant D-A polymers. The results show that the introduction of more F atoms into the conjugated backbone increases the oxidation potential of monomers, both of them have low initial oxidation potential (0.65 V/0.70 V). As in the case of monomers, the substitution of more F atoms also leads to the decreased HOMO energy level of the polymers, thus leading to the increased band gap energy of P(FF-EDOT) (1.39 eV). This result can be attributed to the deviation of planarity and the reduced effective conjugate length. As prepared fluorinated D-A polymers also have good adhesion on the electrode surface, favorable redox activity, and outstanding redox stability (the redox activity of P(F-EDOT) remains 99 % after 1000 cycles). At the same time, the fluorinated D-A polymers also show distinguish electrochromic properties under various external potentials; both the optical contrast and coloration efficiency decreased with the increase of F atom numbers, and the corresponding response time increased. As a result, both the fluorinated D-A polymers show light green in the neutral state, P(F-EDOT) shows more obvious electrochromic performance in the near infrared region (optical contrast: 35.02 %, coloration efficiency: 159.94 cm2 C−1, and quick response time: 0.2 s), accompanied with excellent discoloration stability and optical memory effect. The study of novel fluorinated-based electrochromic materials further expands the selection of acceptor units and the application prospect of electrochromic materials.

Multifunctional double network hydrogel with multi-directional actuation and high-precision sensing

Conductive hydrogels have gained great attention for applications in flexible electronics, electronic skins, and as human-machine interfaces. However, poor environmental tolerance of traditional hydrogels and defects in hydrogel actuator make them unfit for use in certain environments. Herein, a small natural molecule, proline (ZP), was introduced into the PAA/CS dual network system to prepare multifunctional hydrogel materials with high concentration of physically crosslinked metal coordination points. The elongation at break and mechanical strength of the hydrogel with optimized structure were 1277 % and 202 kPa, respectively. The effect of ZP on the destruction of hydrogen bonds of free water in the hydrogel provided the hydrogel with excellent temperature resistance. Multiple reversible interactions endowed the PAA/CS/Al0.5/ZP8 hydrogel with excellent self-healing properties at room temperature and even at −40 ℃. The PAA/CS/Al0.5/ZP8 hydrogel sensor with excellent comprehensive performance could be applied for the monitoring of a variety of human motions, small shape changes of flexible objects, and detection of vibrations in rigid pipes. The interactions between Fe3+, ascorbic acid, and -COOH groups on the hydrogel surface were used to record information and erase it repeatedly at low temperature and showed excellent shape memory. Based on the self-healing property, the hydrogel with gradients of swelling rates and water loss rates was assembled into a double-layer actuator, which could complete the actuation process in opposite directions in air and also underwater. This work provides a new idea for the design of soft robots and intelligent switches.

Hofmeister effect driven dynamic-bond cross-linked dialdehyde xylan hydrogels with rapid response and robust mechanical properties for expanding stent

The biomedical field urgently needs for programmable stent materials with nontoxic, autonomous self-healing, injectability, and suitable mechanical strength, especially self-expanding characteristics. However, such materials are still lacking. Herein, based on gelatin and dialdehyde-functionalized xylan, we synthesized 3D-printable, autonomous, self-healing, and mechanically robust hydrogels with a reversible Schiff base crosslink network. The hydrogels exhibited excellent mechanical properties and automatic healing properties at room temperature. The solid mechanical properties originate from the Schiff base, hydrogen bonding interactions, and xylan nanoparticle reinforcement of the polymer networks. As a proof of concept, the Hofmeister effect enabled the hydrogel to contract in highly concentrated salt solutions. In contrast, the same hydrogel expanded and relaxed in dilute salt solutions (quick response within 10 s), showing ionic stimulus-response and excellent shape memory characteristics, which demonstrated that the prepared hydrogel could be used as self-expanding artificial vascular stents. In particular, good biocompatibility was confirmed by cytotoxicity and compatibility tests, and ex vivo arterial experiments further indicated the feasibility of these artificial vascular scaffolds (the expansion force reached 1.51 N). Combined with its ionic stimuli-responsive shape memory ability, the strong mechanical, self-healing, 3D-printable, and biocompatibility properties make this hydrogel a promising material for artificial stents in various biomedical applications.

Nanocomposites of Poly(n-Butyl Acrylate) with Fe3O4: Crosslinking with Hindered Urea Bonds, Reprocessing and Related Functional Properties.

In this contribution, we reported the synthesis of the nanocomposites of poly(n-butyl acrylate) with Fe3O4 nanoparticles (NPs) via dynamic crosslinking of poly(n-butyl acrylate)-grafted Fe3O4 NPs with hindered urea bonds (HUBs). Towards this end, the surfaces of Fe3O4 NPs were grafted with poly(n-butyl acrylate-ran-2-(3-tert-butyl-3-ethylureido)ethyl acrylate) chains [denoted as Fe3O4-g-P(BA-r-TBEA)] via living radical polymerization. Thereafter, 1,2-bis(tert-butyl)ethylenediamine was used as a crosslinker to afford the organic-inorganic networks with variable contents of Fe3O4 NPs and crosslinking densities. It was found that the fine dispersion of Fe3O4 NPs in the matrix of poly(n-butyl acrylate) was achieved. The nanocomposites exhibited excellent reprocessing properties, attributed to the introduction of HUBs. Owing to the crosslinking, the nanocomposites displayed excellent shape memory properties. Further, the nanocomposites possessed photo- and magnetic-thermal properties, which were inherited from Fe3O4 NPs. These functional properties allow triggering the shape shifting of the nanocomposites in an uncontacted fashion.

Design of flexible polyethylene glycol-based phase change materials by crystal structure regulation

The design of flexible phase change materials (FPCMs) with polyethylene glycol (PEG) as phase change components remains a great challenge due to high crystalline structure makes for high thermal energy storage ability yet deteriorates mechanical toughness. Herein, the preparation strategy of FPCMs was developed by introducing crystal structure regulators (CSRs) in PEG-based FPCM networks in a form of covalent linkages. The hydroquinone CSR had the strongest ability of crystal structure regulation over FPCMs compared to the three other used CSRs. The FPCMs had tuneable phase change temperatures (−2.0 °C–49.7 °C) and enthalpies (40.7 J g−1 to 109.3 J g−1) depending on the number-average molecular weight (Mn = 4000 Da, 6000 Da) of PEGs used as well as the content and type of CSRs, further enabling tuneable mechanical stress (0.59–15.61 MPa) and strain (5.74%–505.86 %). Compared with the pristine PEGs, the FPCMs yielded excellent shape stability, thermal stability and thermal reliability. The flexibility and phase change properties endowed the FPCMs with excellent self-adaptability and shape memory function. The innovative strategy towards FPCMs highlights the application potential on individual wearable temperature-controlled devices.

Self-Healable, Transparent, Biodegradable, and Shape Memorable Polyurethanes Derived from Carbon Dioxide-Based Diols.

A series of CO2-based thermoplastic polyurethanes (TPUs) were prepared using CO2-based poly(polycarbonate) diol (PPCDL), 4,4'-methylenebis (cyclohexyl isocyanate) (HMDI), and polypropylene glycol (PPG and 1,4-butanediol (BDO) as the raw materials. The mechanical, thermal, optical, and barrier properties shape memory behaviors, while biocompatibility and degradation behaviors of the CO2-based TPUs are also systematically investigated. All the synthesized TPUs are highly transparent amorphous polymers, with one glass transition temperature at ~15-45 °C varying with hard segment content and soft segment composition. When PPG is incorporated into the soft segments, the resultant TPUs exhibit excellent self-healing and shape memory performances with the average shape fixity ratio and shape recovery ratio as high as 98.9% and 88.3%, respectively. Furthermore, the CO2-based TPUs also show superior water vapor permeability resistance, good biocompatibility, and good biodegradation properties, demonstrating their pretty competitive potential in the polyurethane industry applications.

4D printing and optimization of biocompatible poly lactic acid/poly methyl methacrylate blends for enhanced shape memory and mechanical properties

This study introduces a novel approach to 4D printing of biocompatible Poly lactic acid (PLA)/poly methyl methacrylate (PMMA) blends using Artificial Neural Network (ANN) and Response Surface Methodology (RSM). The goal is to optimize PMMA content, nozzle temperature, raster angle, and printing speed to enhance shape memory properties and mechanical strength. The materials, PLA and PMMA, are melt-blended and 4D printed using a pellet-based 3D printer. Differential Scanning Calorimetry (DSC) and Dynamic Mechanical Thermal Analysis (DMTA) assess the thermal behavior and compatibility of the blends. The ANN model demonstrates superior prediction accuracy and generalization capability compared to the RSM model. Experimental results show a shape recovery ratio of 100% and an ultimate tensile strength of 65.2 MPa, significantly higher than pure PLA. A bio-screw, 4D printed with optimized parameters, demonstrates excellent mechanical properties and shape memory behavior, suitable for biomedical applications such as orthopaedics and dental implants. This research presents an innovative method for 4D printing PLA/PMMA blends, highlighting their potential in creating advanced, high-performance biocompatible materials for medical use.

Thermadapt shape memory AB-copolymer networks exhibiting tunable properties and kinetics of topological rearrangement

Polycaprolactone (PCL) based thermadapt shape memory polymers (SMPs) have exhibited superiority over traditional analogues by allowing shape-editing to reconfigure permanent shapes into more complex geometrical shapes, driven by the pursuit of advanced functionalities for high-value applications. Nevertheless, although transesterification-based PCL networks exhibit impressive shape reconfigurability as prototypical thermadapt SMPs, there are still constraints in terms of the need for significant flexibility in architectural adjustment and property modulation without compromising reconfigurability, which would be relevant for practical applications. Here, we present a simple yet efficient strategy to create PCL-based thermadapt SMPs that possess a highly tunable structure and properties, as well as exceptional reconfigurability. The family of SMPs, called thermadapt shape memory AB copolymer networks (AB-CPNs), was synthesized by UV-initiated free radical polymerization between PCL diacrylate as crosslinker and 4-hydroxybutyl acrylate (HBA) as comonomer. The thermadapt AB-CPNs allow for significant structural alterations with 0 wt% to 70 wt% HBA while maintaining excellent shape memory and shape reconfigurability effects. The insertion of the polymer segment containing free hydroxyls not only promises tunable material properties but also makes network rearrangement easier since dynamic hydroxy-ester bonds are more active than dynamic ester-ester bonds. It is envisioned that the thermadapt shape memory AB-CPNs with widely tunable macroscopic properties will drive progress in the real-world applications of SMP devices with complicated geometric structures.

A Novel TCN-LSTM Hybrid Model for sEMG-Based Continuous Estimation of Wrist Joint Angles.

Surface electromyography (sEMG) offers a novel method in human-machine interactions (HMIs) since it is a distinct physiological electrical signal that conceals human movement intention and muscle information. Unfortunately, the nonlinear and non-smooth features of sEMG signals often make joint angle estimation difficult. This paper proposes a joint angle prediction model for the continuous estimation of wrist motion angle changes based on sEMG signals. The proposed model combines a temporal convolutional network (TCN) with a long short-term memory (LSTM) network, where the TCN can sense local information and mine the deeper information of the sEMG signals, while LSTM, with its excellent temporal memory capability, can make up for the lack of the ability of the TCN to capture the long-term dependence of the sEMG signals, resulting in a better prediction. We validated the proposed method in the publicly available Ninapro DB1 dataset by selecting the first eight subjects and picking three types of wrist-dependent movements: wrist flexion (WF), wrist ulnar deviation (WUD), and wrist extension and closed hand (WECH). Finally, the proposed TCN-LSTM model was compared with the TCN and LSTM models. The proposed TCN-LSTM outperformed the TCN and LSTM models in terms of the root mean square error (RMSE) and average coefficient of determination (R2). The TCN-LSTM model achieved an average RMSE of 0.064, representing a 41% reduction compared to the TCN model and a 52% reduction compared to the LSTM model. The TCN-LSTM also achieved an average R2 of 0.93, indicating an 11% improvement over the TCN model and an 18% improvement over the LSTM model.

Development of shape memory epoxy resin/polyethylene glycol film based on molecular dynamics simulation and performance investigation

AbstractBased on the molecular dynamics (MD) simulation of glass transition temperature (Tg) and hydrogen bonding in the composite system of epoxy resin (Ep) and polyethylene glycol (PEG), this work developed shape memory Ep/PEG (EpP) films with controllable thermal response, recycling and reprocessing functions using melt dispersion and polymerizing‐pressing processes. EpP films with different PEG contents exhibit excellent shape memory performance, among which the shape recovery rate of EpP‐5 film can reach 92.7%, which can recover from complex structures to the initial shape. The PEG in the composite system can effectively regulate the thermal and mechanical properties of EpP, especially increasing the strain at break and reducing the Tg. Compared with EpP‐0 film. The Tg of EpP‐15 film increased by 40°C and the strain at break increased by 18.56%. Furthermore, compared with the EpP‐0 film, the recycling‐reprocessing temperature of EpP‐15 film has been reduced by 75°C. In summary, based on MD simulation, shape memory EpP films with controllable thermal response, recycling, and reprocessing functions have been successfully developed, and have shown considerable application prospects in the field of intelligent materials.