Shape Recovery Process Research Articles

Dual effects of pre-deformation and shape recovery process on martensitic transformation behavior in NiTi-Nb composite wire

The martensitic transformation behavior of NiTi-Nb composite wire following the pre-deformation and shape recovery (PD&SR) process was investigated. The wire drawing process significantly decreased the martensitic transformation start temperature (Ms) of NiTiNb alloy. Interestingly, the PD&SR process exhibited dual effects on the initial Ms temperature, depending on the annealing temperature. When the composite wire was annealed at higher temperature, the PD&SR process decreased the Ms temperature. In contrast, when the composite wire was annealed at lower temperature, the PD&SR process raised the Ms temperature. These dual effects can be attributed to the competition between the hindering effect of deformation dislocation and the promoting effect of stress coupling near the interface between the β-Nb phase and the NiTi matrix. At lower annealing temperature, the stress coupling generated by the β-Nb nanowires and the NiTi matrix is stronger, leading to an increase in the Ms temperature. Furthermore, the pre-deformation strain and shape recovery temperature influenced the dislocation density and the strength of stress coupling, thereby regulating the Ms temperature within a certain range.

Origami inspired dual matrix intelligent shape memory polymer composite folds for deployable structures

Abstract It remains a challenge to develop an intelligent, programmable multifunctional material system capable of recovering shape, withstanding high loads, and detecting folding extent remotely for self-deployable structures used in aerospace, robotics, and medical devices. In this work, our objective is to develop intelligent shape memory polymer composite (iSMPC) folds embedded with reduced graphene oxide (rGO)-coated self-sensing fabric. This will enable remote sensing of the fold state based on resistance changes and achieve higher strength and modulus. Firstly, we demonstrate the ability to sense the extent of folding and establish the relationship between piezoresistivity and fold state change by conducting cyclic compression analysis on folds with different gap sizes (6mm, 9mm, and 12mm) at temperatures of 25°C, 35°C, and 45°C. The iSMPC fold with a 6mm gap exhibited the highest bending stiffness (650.3Nmm-1) and curvature (0.55mm-1), resulting in a higher change in fractional change in resistance (FCR). Subsequently, the shape memory cycles of the 6mm iSMPC fold were demonstrated through localized controlled heating. Its shape recovery process exhibited repeatable behavior with a high recovery ratio of 95%. Lastly, a two-fold iSMPC structure was developed, and its performance was analyzed during a complete shape memory cycle. The piezoresistive response during higher-temperature cyclic loading resembled that of the single fold, exhibiting an FCR range between -9% and 5%, thereby demonstrating the repeatability of the iSMPC fold response.

Constitutive model for shape memory polymer and its thermodynamic responses in finite element analysis.

As a new intelligent polymer material, shape memory polymer (SMP) was a potential orthodontic appliance material. This study aimed to investigate the thermodynamic responses of SMP under different loads via finite element analysis (FEA). FEA specimens with a specification of 0.1 × 0.1 × 1 mm were designed. One end of the specimen was fixed, and the other was subjected to displacement load. Different loading, cooling, and heating rates were separately exerted on the specimen in its shape recovery process and used to observe the responses of the SMP constitutive model. Furthermore, specimens with various tensile elongation and sectional areas were simulated and used to elucidate their effect on shape recovering force. The specimens obtained a similar stress of 0.5, 0.44, and 1.07 Mpa for different loading, cooling, and heating rates after a long time. The shape recovering force of specimen increased from 0.0102 to 0.0315 N when the elongation improved from 10% to 40% and to 0.0408 N when the sectional areas were expanded to 0.2 × 0.2 mm. The stiffness of SMP was small at a high temperature but large at a low temperature. The effects of the loading, cooling, and heating rates on SMP can be eliminated after a long time. Furthermore, it was possible to increase the recovering force by increasing the elongation or expanding the sectional area of the specimen. The force was quadratically dependent on the elongation ratio.

4D printing of Nd-Fe-B composites with both shape memory and permanent magnet excitation deformation

Novel composite filaments are developed by mixing PLA, TPU, and Nd-Fe-B components and utilizing melt extrusion for 4D printing. The results reveal that the Nd-Fe-B magnetic particles are uniformly dispersed in the PLA/TPU polymer matrix, and the composite filaments meet the requirements of high-precision printing. Increasing the proportion of Nd-Fe-B magnetic particles in the composite contributes to higher remanence, coercivity, and magnetic energy product for the printed magnets. Under the 70 °C thermal stimulus, it has a high shape fixed ratio (>99 %), a high shape recovery ratio (>90 %), and a rapid response time (≤6.55 s). The magnetic particles accelerate the shape recovery process. Moreover, the petal-like structure and the hollow ball structure are designed and printed. After deformation, each structure can nearly fully recover its initial shape. This recovery is achieved through a non-contact stimulus response based on ’thermal-magnetic’ coupling. The grippers printed by the developed composite show comprehensive properties of shape memory and magnetically controlled smart gripping.

Thermo-Structural Coupled Finite Element Analysis of Repair Process for Steam Turbine Blade Using Laser-Directed Energy Deposition Method

This study presents a numerical additive manufacturing simulation aimed at simulating the shape recovery process of a steam turbine blade damaged by corrosion, using laser-directed energy deposition (LDED). The simulation integrates the finite element (FE) method with heat conduction and thermo-elastoplastic constitutive equations, incorporating phase transformation. The additive manufacturing process by LDED was modeled using the death-birth algorithm, wherein a deposition layer is defined as a virtual element. Its stiffness and thermal properties activated when the laser irradiation regions overlapped. In this study, the shape of the virtual element was determined based on the cross-sectional shape of the deposition layer manufactured under various laser conditions. To validate the numerical simulation results, additive manufacturing was conducted for one pass deposition in the width direction at the center of a cantilever-supported plate made of SUS304 steel, and the changes in displacement at the free edges with respect to the process time were compared. The obtained FE results are in good agreement with the experimental results. Finally, an FE simulation was performed for the shape recovery of a steam turbine blade thinned due to corrosion damage. The results revealed that the residual stress component becomes more compressive as the laser output decreases and scanning speed increases, which is advantageous for improving the fatigue strength of steam turbine blades.

A novel polymer based on ethylene-methyl acrylate copolymer/chloroprene rubber thermoplastic vulcanizates with rapid thermo-responsive shape memory property

A simple and effective strategy for preparing thermo-responsive shape memory polymers (TSMPs) can be designed where the novel TSMPs based on ethylene-methyl acrylate copolymer (EMA) and chlorinated polyethylene rubber (CR) thermoplastic vulcanizates (TPVs) were prepared using dynamic vulcanization. The morphology of the EMA/CR TPVs exhibited a sea-island structure obviously; moreover, the EMA served as the continuous phase and mainly provided the shape fixation (SF) capability of the blend, while the highly elastic CR was acted as the dispersed phase and provided the primary driving force during the shape recovery (SR) process. The SF and SR behaviors of the EMA/CR TPVs can be effectively controlled by varying the weight ratio of EMA/CR blends. Increasing the weight ratio of EMA/CR, the SF% of the EMA/CR TPVs was enhanced while the SR% was decreased remarkably. The shape memory behaviors of EMA/CR TPVs were significantly influenced by temperature. Notably, when the fixation and recovery temperatures were all set at 95°C, both the SF% and SR% of the EMA/CR TPVs with a weight ratio of 80/20 exceeded 95%, and the SR time was 15∼20s, demonstrating the excellent shape memory property.

Shape memory polymer lattice structures with programmable thermal recovery time

Shape memory polymer (SMP) lattice structures have garnered considerable attention due to their intrinsic capability for self-recovery and mechanical reconfiguration. The temporal path, encompassing aspects such as recovery time and deployment sequence, of the shape recovery process in SMP lattice structures holds paramount significance across various domains, including but not limited to medical devices and space deployable structures. Nonetheless, the programming of shape recovery time or deployment sequences in SMP lattice structures, particularly in scenarios devoid of external controllers, remains a challenge. In addressing these challenges, this study presents a novel class of SMP structures endowed with customizable thermal recovery times and programmable deployment sequences, leveraging the influence of structural geometry. Notably, the programmable recovery time and serialized deployment behavior of the proposed SMP lattice structure are achieved within a constant temperature environment, obviating the need for external time-varying stimuli. Finite element simulations and experimental validations corroborate that the proposed SMP structures can be programmed to exhibit recovery times spanning from mere seconds to several hundred seconds. Moreover, a three-stage sequential recovery behavior is attained without necessitating prior local configuration programming. Furthermore, exploiting the distinctive sequential reversibility inherent in a constant high-temperature environment, the designed lattice structure showcases the ability to transition to multiple distinct stable configurations by modulating the duration of high-temperature exposure. The proposed recovery time programmable SMP lattice structure thus presents a viable avenue for realizing intricate multistage controllable shape-shifting structures devoid of external control equipment.

Nucleation, Development and Healing of Micro-Cracks in Shape Memory Polyurethane Subjected to Subsequent Tension Cycles.

Thermoresponsive shape memory polymers (SMPs) have garnered increasing interest for their exceptional ability to retain a temporary shape and recover the original configuration through temperature changes, making them promising in various applications. The SMP shape change and recovery that happen due to a combination of mechanical loading and appropriate temperatures are related to its particular microstructure. The deformation process leads to the formation and growth of micro-cracks in the SMP structure, whereas the subsequent heating over its glass transition temperature Tg leads to the recovery of its original shape and properties. These processes also affect the SMP microstructure. In addition to the observed macroscopic shape recovery, the healing of micro-crazes and micro-cracks that have nucleated and developed during the loading occurs. Therefore, our study delves into the microscopic aspect, specifically addressing the healing of micro-cracks in the cyclic loading process. The proposed research concerns a thermoplastic polyurethane shape memory polymer (PU-SMP) MM4520 with a Tg of 45 °C. The objective of the study is to investigate the effect of the number of tensile loading-unloading cycles and thermal shape recovery on the evolution of the PU-SMP microstructure. To this end, comprehensive research starting from structural characterization of the initial state and at various stages of the PU-SMP mechanical loading was conducted. Dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS) and scanning electron microscopy (SEM) were used. Moreover, the shape memory behavior in the thermomechanical loading program was investigated. The obtained average shape fixity value was 99%, while the shape recovery was 92%, which confirmed good shape memory properties of the PU-SMP. Our findings reveal that even during a single loading-unloading tension cycle, crazes and cracks nucleate on the surface of the PU-SMP specimen, whereas the subsequent temperature-induced shape recovery process carried out at the temperature above Tg enables the healing of micro-cracks. Interestingly, the surface of the specimen after three and five loading-unloading cycles did not exhibit crazes and cracks, although some traces of cracks were visible. The traces disappeared after exposing the material to heating at Tg + 20 °C (65 °C) for 30 min. The crack closure phenomenon during deformation, even without heating over Tg, occurred within three and five subsequent cycles of loading-unloading. Notably, in the case of eight loading-unloading cycles, cracks appeared on the surface of the PU-SMP and were healed only after thermal recovery at the particular temperature over Tg. Upon reaching a critical number of cycles, the proper amount of energy required for crack propagation was attained, resulting in wide-open cracks on the material's surface. It is worth noting that WAXS analysis did not indicate strong signs of typical highly ordered structures in the PU-SMP specimens in their initial state and after the loading history; however, some orientation after the cyclic deformation was observed.

An end-capping strategy for shape memory phthalonitrile resins via annealing enables conductivity and wave-absorption

Shape memory polymers (SMPs) with elevated switching temperatures and enduring thermal properties are highly desirable yet challenging in certain aerospace applications. In this study, high-temperature shape memory phthalonitrile resins (SMPNs) were developed using an end-capping strategy with the uniphthalonitrile (UPN) as the end-capping reagent to modulate the density of the cross-linked network. The resultant SMPNs exhibit a glass transition temperature (Tg) at approximately 300 °C, with a shape fixation rate of about 98 % and a shape recovery rate around 97 %. Importantly, these SMPNs also demonstrated exceptional thermal stability, with a thermal decomposition temperature exceeding 445 °C. Additionally, an oxyacetylene ablative test revealed the SMPNs' robust ablative resistance, as the linear ablation rate remained below 0.1 mm/s and the mass ablation rate was less than 0.1 g/s. The commendable shape memory performance and superior high-temperature resistance allowed the SMPNs to successfully undergo the shape recovery process when subjected to a butane flame. Furthermore, after a high-temperature annealing process, the SMPNs exhibited electrical conductivity due to graphitization, even possessing wave-absorbing properties within a specific frequency range. It is foreseeable that these multifunctional SMPNs will have extensive applications in the aerospace sector, given the advancement of smart structures.

Hydration Programmable, Shape Memorable Artificial Muscles for Antagonistic Movements

AbstractShape memory polymers (SMPs) capable of generating various deformations from anisotropic temporary shapes to permanent shapes have been emerging as soft robots. However, traditional SMPs cannot imitate the antagonistic movement of human skeletal muscles due to their modulus limitations in shape programming and recovery process. Herein, hydration programmable shape memory polymer (HP‐SMP)‐based fibers that can undergo reversible actuation by assembling antagonistic pairs are reported, where the shape programming of the antagonist muscle relies on the contraction of agonist muscle. HP‐SMP fibers are composed of tunicate cellulose nanocrystals (TCNCs) reinforced semi‐interpenetrating polymer networks. Leveraging their distinctive structure and hydration programmability, the HP‐SMP fibers exhibit large actuation strain (−60%) and high work capacity (751 J kg−1), allowing for reversible actuation under constant stress. Most significantly, the continuous antagonistic movements of HP‐SMP fibers assembled into artificial limbs are demonstrated to realize humanoid motion. This work provides new possibilities for replicating a series of lifelike human movements through the biomimetic design of antagonistic pairs of artificial muscles, utilizing renewable and sustainable biosourced materials.

Research on the forming and demolding process of shape memory self-demolding mold

The molding method is highly anticipated in engineering fields and has been preliminarily applied. However, traditional demolding methods introduce subtle deviations in demolding direction, leading to demolding defects and reduced forming accuracy. To address this, we developed an innovative Shape Memory Polymer (SMP) mold. Through finite element simulation, we extensively investigated the effects of diaminodiphenylmethane (DDM) addition, temperature, and load on the template forming and shape recovery processes. Finally, we experimentally verified the feasibility of the self-demolding of the template. The findings demonstrate that as the amount of DDM added increases, the glass transition temperature of SMP progressively elevates. This can be attributed to the enhanced crosslinking triggered by the addition of DDM. Consequently, during the stage of preserving shape in mold formation, SMP exhibits a heightened storage modulus and diminished shape recovery. Notably, when 1.5 g of DDM is added, the shape memory template exhibits the least shape recovery, with a shape retention rate of 78.2%. Conversely, employing 1.6 g of DDM generates the highest shape recovery but only achieves a shape retention rate of 59.5%. Augmenting the amount of DDM is advantageous in accomplishing template demolding. Higher temperatures expedite the initiation of the shape recovery process, facilitating template demolding during the shape recovery stage. Moreover, increasing the load can minimize template rebound and enhance the precision of mold formation. However, it also intensifies the complexity of self-demolding. Consequently, it is imperative to sensibly determine and implement suitable process parameters in applications.

4D printing of shape memory polymer with continuous carbon fiber

Shape memory polymer composites (SMPCs) have gained attention for their shape memory effects and wide-ranging applications. Understanding the bending shape recovery characteristics of 3D printed SMPCs is crucial for optimizing their performance. This study focuses on investigating the influence of different fiber orientations of continuous carbon fiber (CCF) in thermally stimulated SMPC. By controlling printing parameters and fiber orientation during the 3D printing process, we fabricate tailor-made rectangular composite test specimens. These specimens are subjected to controlled bending above the glass transition temperature of the polymer, inducing temporary deformation. The subsequent shape recovery process is carefully captured through high-speed video. Precise measurements of the bending curvature over time are obtained using the row-by-row image processing technique and analyzed. The shape recovery rate, shape recovery ratio, and shape fixity ratio of the test specimens were evaluated as a function of three CCF layout arrangements as well as fiber infill density embedded in Shape Memory Polymer (SMP) test specimens. The results revealed that the addition of CCF in the polymer matrix has a significant impact on shape memory behavior. Vertically aligned CCF in the SMP matrix improves the shape recovery ratio (92.97% compared to 78.77% of the pure SMP sample), while horizontal alignment of CCF ensures maximum shape fixity ratio (91.78% compared to 66.22% of the pure SMP sample). The cross-aligned CCF sample provides good recovery as well as fixity values. Further, it was observed that the horizontal alignment of CCF yields the fastest recovery performance. The outcome confirms that optimizing the fiber orientation enhances shape memory performance. Also, 40% of fiber infill density had greater shape fixity and overall recovery performance when compared to 30% and 50%. These findings have implications for tailored and high-performance SMPCs in biomedical devices, aerospace components, and robotics. Understanding temporal curvature behavior enables optimizing the design of materials with precise control over shape recovery. This research contributes to the design and optimization of SMPCs for diverse applications.

Four-Dimensionally Printed Continuous Carbon Fiber-Reinforced Shape Memory Polymer Composites with Diverse Deformation Based on an Inhomogeneous Temperature Field.

Four-dimensionally printed continuous carbon fiber-reinforced shape memory polymer composite (CFSMPC) is a smart material with the ability to bear loads and undergo deformation. The deformation of CFSMPC can be driven by the electrothermal effect of carbon fibers. In this study, the effect of temperature on the shape memory recovery performance of polylactic acid (PLA) was first studied experimentally. Continuous carbon fibers were incorporated into PLA to design CFSMPCs with thickness gradients and hand-shaped structures, respectively. The distribution strategy of the carbon fibers was determined based on simulations of the electrically driven shape recovery process of the aforementioned structures. Both the simulations and experiments demonstrated that the electrification of the CFSMPC structures resulted in an inhomogeneous temperature field, leading to distinct deformation recovery processes. Eventually, a precise unfolding was achieved for the thickness gradient structure and the five fingers in the hand-shaped structure by utilizing a safe voltage of 6 V. This demonstrates that the 4D-printed CFSMPC with diverse deformations based on an inhomogeneous temperature field has potential applications in actuators, reconfigurable devices, and other fields.

Regulation of electrically responsive shape recovery behavior of 4D printed polymers for application in actuators

Four-dimensional (4D) printing, an additive manufacturing technology for intelligent materials and structures, has received increasing scholarly attention for its ability to achieve variable shapes, properties and functions. However, recent research has primarily focused on developing new materials and structures, neglecting the regulation of deformation behavior. We hereby propose a novel photocuring 4D printing strategy for electrically responsive shape memory polymers (E-SMPs) actuators embedded with a dual-layered electrothermal layer (ETL) and channel. One way to achieve tunable shape recovery behavior in E-SMPs is to regulate the heat generation behavior of ETL by introducing a coolant into the channel. The electric heating and water cooling were sequentially and simultaneously activated to achieve suspension of the shape recovery process and reduction in the shape recovery rate, respectively. E-SMPs embedded with single and double ETLs were utilized to evaluate their electrically-induced heating behavior, electrically responsive shape recovery behavior, and shape recovery force. Additionally, sequential shape recovery behavior was achieved by serially interconnecting three (3) ETLs with varying thicknesses. Furthermore, the channel integrated within the SMPs were employed to realize remote thermally responsive shape recovery (T-SMPs), for which the shape recovery rate was regulated by adjusting the flow rate of hot water and channel dimensions. This strategy was successfully demonstrated for manufacturing E-SMPs actuators with adjustable shape recovery rate, sequential recovery behavior, and high-load deformation capability.

Repeatable compressive functionality of 3D printed shape-memory thin-walled corrugated structures

This work aimed to investigate the compressive and shape recovery performance of the 3D printed shape-memory corrugated tubes (SMCTs). The structures were manufactured by fused deposition modeling technique and made from the shape memory polymer. The effects of corrugation number and amplitude on crushing and shape recovery behaviors were studied by shape memory experiment. Compression experimental results indicated that the mode transition of diamond-mixed-ring occurred with the corrugation number and amplitude increasing. After induced by thermal actuation, all structures could complete the shape recovery process with the shape recovery ratio above 98% within 20 s. Ten consecutive shape memory (compressive and recovery) cycles were carried out to analyze the repeatable compression functionality. The specific energy absorption of corrugated tubes presented the significant convergent tendency, while straight tubes showed a continuous decrease. The repeatable compressive and recovery characteristics with stable mechanical properties were achieved by applying the corrugation design. The theoretical model was developed to predict the mean crushing force of SMCTs in each cycle. Considering the shape memory cycling effect, the attenuation coefficient was introduced into the model. The prediction data for SMCTs were well agreed to the experimental results. The finding of this study offered a promising design concept for developing the advanced reversible energy absorber and implementing in multi-functional applications.

Preparation and Properties of Shape Memory PEG/IEM Resin and Its Composite Designed for Ureter Stent.

In this paper, isocyanoethyl methacrylate (IEM) is used to functionalize the two ends of poly(ethylene glycol)(PEG) diol with acrylic acid groups through an urethanisation reaction. The synthesized PEG/IEM resin is then photo-cured with a 405nm ultraviolet lamp. Ttrans of the PEG/IEM resin can be regulated by the different molecular weights of PEG and the use of plasticizer Triacetin to reach 44°C, which is closer to the human body temperature. Cytotoxicity assay and DMA shape memory cycling testing show that the PEG/IEM resin has excellent biocompatibility and shape memory properties. The flower structure is prepared and its shape recovery process is demonstrated. The performance of 10wt% nano Fe3 O4 /PEG4000/IEM resin and its composite spring stent structure satisfy the requirement of the stent properties in vivo, and can quickly recover to the original shape under magneticallydriven. This work provides a material option for developing new biological application devices such as ureter stents. This article is protected by copyright. All rights reserved.

4D printing of continuous fiber-reinforced electroactive smart composites by coaxial additive manufacturing

In this study, a coaxial additive manufacturing process was developed for four-dimensional (4D) printing with continuous carbon fiber-reinforced shape memory polymers (SMPs). These materials have potential applications in the aerospace, automotive, and biomedical industries due to their high strength-to-weight ratio and shape memory properties. The mechanical and thermal properties of the SMPs were evaluated and the effects of printing parameters on printability and carbon fiber volume fraction were analyzed to determine optimal printing conditions. It was found that even a small amount of carbon fiber significantly improved the mechanical properties of the 4D printed samples. The shape memory properties of the printed samples were also examined, and it was found that the structure was able to recover the original shape quickly at low-temperature programming, making it suitable for load-bearing structures. At high-temperature programming, the structure retained the programmed shape well, but recovery of the original shape was slower and incomplete. The use of continuous carbon fiber reinforced SMPs also allows for Joule heating to be used for shape recovery, with the applied voltage able to control the shape recovery process. A high level of deformation recovery (95%) was also achieved in highly deformed structures.

Wood as a hydrothermally stimulated shape-memory material: mechanisms of shape-memory effect and molecular assembly structure networks

Abstract This study aimed to evaluate the shape-memory effect (SME) of wood (Populus x beijingensis W. Y. Hsu) and identify the net-points and switches in its molecular and morphological structures. During several cycles of deformation and subsequent recovery, a high shape recovery rate and ratio were maintained. The transverse compression tests of wet and dry wood reveal that the hydrothermal coupling stimulation can considerably reduce the strength of wood. The X-ray diffraction characterization of wood under hydrothermal stimulation shows that the role of network nodes in the SME of wood is influenced by temperature. The wavenumber shifting and changes in the intensity ratio of the characteristic Fourier transform infrared peaks showed that hydrogen bonds acted as switches for the water-stimulated shape-memory behavior. By taking into account viscoelastic relaxation, a kinetic model derived from nonequilibrium thermodynamic fluctuation theory was used to describe the shape recovery process. The effects of hydration on recovery kinetics, activation, and dynamic mechanical behaviors were also studied. To explain the shape-memory mechanism of wood under hydrothermal stimulation, a hybrid-structure network model based on a single three-dimensional switch network was proposed in this study.

Study of Correlation between Structure and Shape-Memory Effect/Drug-Release Profile of Polyurethane/Hydroxyapatite Composites for Antibacterial Implants.

The effectiveness of multifunctional composites that combine a shape-memory polyurethane (PU) matrix with hydroxyapatite (HA) as a bioactive agent and antibiotics molecules results from a specific composite structure. In this study, structure-function correlations of PU-based composites consisting of 3, 5, and 10 (wt%) of HA and (5 wt%) of gentamicin sulfate (GeS) as a model drug were investigated. The performed analysis revealed that increasing HA content up to 5 wt% enhanced hydrogen-bonding interaction within the soft segments of the PU. Differential-scanning-calorimetry (DSC) analysis confirmed the semi-crystalline structure of the composites. Hydroxyapatite enhanced thermal stability was confirmed by thermogravimetric analysis (TGA), and the water contact angle evaluated hydrophilicity. The shape-recovery coefficient (Rr) measured in water, decreased from 94% for the PU to 86% for the PU/GeS sample and to 88-91% for the PU/HA/GeS composites. These values were positively correlated with hydrogen-bond interactions evaluated using the Fourier-transform-infrared (FTIR) spectroscopy. Additionally, it was found that the shape-recovery process initiates drug release. After shape recovery, the drug concentration in water was 17 μg/mL for the PU/GeS sample and 33-47 μg/mL for the PU HA GeS composites. Antibacterial properties of developed composites were confirmed by the agar-diffusion test against Escherichia coli and Staphylococcus epidermidis.

Electro-activated shape memory behavior of a three-dimensional lightweight knitted tubular composite

Electro-activated shape memory polymer composites (SMPCs) are usually fabricated with adding conductive nanoparticles and conductive fibers into shape memory polymeric matrix. The current researches of electro-activated SMPCs mainly focus on two-dimensional rectangular panels and they have the disadvantages of large mass and long recovery time. Here a knitted-net shape memory tubular composite was developed and the experimental and numerical studies of electro-activated shape memory behavior subjected to compressive loading were conducted. The effects of component ratios and voltages on the electrical property, shape recovery behavior, recovery force and mechanical property of the tubular composites were investigated. The results show that the bulk density of knitted-net lightweight tubular composite is only 0.50 g/cm3. The shape fixity ratio and the shape recovery ratio are over 99%, and the recoverable compressive strain is up to 60%. The electro-activated shape recovery time of the tubular composites with DC voltage of 20 V is short to 12 s. The maximum recovery force can reach 3.19 N. An electricity-heat-deformation coupled finite element model was built and simulated the temperature variation and shape-changing in the shape recovery process. The knowledge gained in this work will be beneficial to the future development of remotely controlled fast-responsive actuators.