Excellent Shape Memory Effect Research Articles

Mechanically robust enzymatically degradable shape memory polyurethane urea with a rapid recovery response induced by NIR.

Biodegradable shape memory polymers have great potential for use in minimally invasive surgical procedures. Herein, a series of shape memory polyurethanes (SMPUs) containing a chymotrypsin-inspired chain extender with adjustable mechanical properties and excellent shape memory effect (SME) was prepared successfully. The chemical structure, mechanical properties, SME and in vitro degradation of the PUs were systematically characterized by proton nuclear magnetic resonance spectroscopy, tensile testing, dynamic mechanical analysis under controlled force mode, and scanning electronic microscopy. By increasing the molecular weight of poly(ε-caprolactone) (PCL) and hard segment content, a PCL4000-based SMPU with a modulus value of 115 MPa was obtained, which is three times that of a PCL2000-based sample. Further, the modulus of the PCL4000-based SMPU was increased by 50% while that of the PCL2000-based SMPU was significantly reduced when temperature increased from 23 °C to 37 °C. In addition, the PCL4000-based SMPU exhibited excellent SME with the shape fixity ratio and recovery ratio almost reaching 100%. Gold nanorods were further incorporated into the PU matrix, endowing the materials with a fast near-infrared (NIR) response in 23 s for shape recovery (NIR wavelength of 808 nm, 1.5 W). Combined with enzymatic degradability, these PU/gold-nanorod composites exhibit great potential to be used in biodegradable shape memory expanding stents.

Corrosion Behaviors of Sputtered NiTiCu Shape Memory Films

For NiTiCu SMA, the Ni atoms are substituted by Cu atoms, which not only greatly reduce the alloy cost, but also have excellent shape memory effect. Four kinds of shape memory alloy films (Ni49.6Ti50.4, Ni48.2Ti50.4Cu1.4, Ni45.6Ti50.4Cu4, Ni42.7Ti50.4Cu6.9) were prepared using magnetron sputtering. Corrosion behaviors of the four films in phosphate buffered saline (PBS) solutions at 37°C were examined using electrochemical impedance spectroscopy (EIS) method. It was found that the corrosion resistance of the NiTi film is superior to the three NiTiCu films. The EIS data were fitted using a parallel resistance-capacitance (as a constant phase element) circuit associated with the surface oxide film. The thickness of the surface oxide layer of the three NiTiCu films increases with applied potential till 0.8 V, while that of the NiTi film can reach to 1.2 V.

A novel strategy to construct co-continuous PLA/NBR thermoplastic vulcanizates: Metal-ligand coordination-induced dynamic vulcanization, balanced stiffness-toughness and shape memory effect

In the field of dynamic vulcanization, irreversible covalent bonds are utilized to fabricate thermoplastic vulcanizates (TPVs) generally. In this work, a new strategy, metal-ligand coordination-induced dynamic vulcanization, is presented to design polylactide (PLA)/butadiene acrylonitrile rubber (NBR)/cupric sulfate (CuSO4) TPVs with balanced stiffness-toughness and shape memory property. During dynamic vulcanization, the micron-sized CuSO4 particles have been transformed into nanoparticles by the process of “dissolution-reaction-redissolution-reaction” and then distributed in the continuous NBR phase. CuSO4 nanoparticles cross-link NBR through the coordination interaction between nitrile groups and copper ions, and simultaneously reinforce the NBR phase. This endows the TPVs with balanced stiffness-toughness properties: notched Izod impact strength of 152.88 kJ/m2 and tensile strength of 22.30 MPa. Furthermore, the fabricated TPVs exhibit co-continuous morphology which resulted in excellent shape memory effect of obtaining shape recovery ratio of 92.30%. We present a novel approach to toughen and enhance PLA-based shape memory materials simultaneously, and it may expand the research scope of dynamic vulcanization.

Preparation of Non-Planar-Ring Epoxy Thermosets Combining Ultra-Strong Shape Memory Effects and High Performance

Non-planar-ring epoxies together with non-planar-ring hardeners could achieve thermosets combining ultra-high shape recovery speed and excellent thermal properties. High shape recovery speed reflected high efficiency, and could decrease the energy consumption and the harmful effect of external stimuli on the materials, while it often conflicts with the thermal properties of shape memory polymers. In this paper, for the first time, epoxy resins with the super-short shape recovery time within 3 s were developed from non-planar-ring epoxies and hardeners, and their glass transition temperature (Tg) were ~127 °C much higher than their benzene ring analogues. The effects of non-planar-ring structures of the epoxies and hardeners on the curing behavior, thermal properties as well as the shape memory properties of the thermosets were systematically investigated; the structure-property relationships were disclosed with the help of computational simulation of structure parameters and ESP maps. The faster shape recovery speed of the non-planar-ring epoxy thermosets is from their higher molecular mobility contributed by the conformational transition of non-planar-rings as well as their higher recovery force compared with benzene ring analogs. Their higher Tgs are from the steric hindrance by the larger molecular volume of the non-planar-rings than benzene ring. This work will provide an effective method to produce shape memory polymers with excellent shape memory effects and high performance.

A novel thermoplastic elastomer from double CO2-Route oligomers

As carbon dioxide (CO 2 ) is an inexpensive, abundant, sustainable and green carbonyl resource, its utilization to produce value-added chemicals and polymeric materials has attracted much more attention. In this work, a novel CO 2 route polyurea (PUa) was synthesized. The chemical composition, molecular structure, and aggregation structure of polyurea has been confirmed by 1 H-NMR, HMBC-NMR, DSC, TG, MALDI-TOF MS and POM. The result from POM shows that polyurea gives out a spherulitic morphology, exhibited a typical black cross pattern formed by many concentric circles with different light and shade. Moreover, shape memory polymers of polyurea-multiblock-poly(propylene carbonate) (PUa- mb -PPCs) with a M n nearly 4.72 × 10 4 Da and a polydispersity index (PDI) of 1.51–1.64 were synthesized by chain extension of the polyurea with CO 2 derived poly(propylene carbonate) diols (PPC-OH). The PUa- mb -PPCs possess high strength and elasticity because the crystallinity formed by polyurea and amorphous region from PPC. Notably, excellent shape memory effect (SME) is observed in shape thermomechanical testing. The present work provides a simple and renewable process for the synthesis of CO 2 -copolymer with multiblock structure, opening a new route for preparation of functional polymeric materials from carbon dioxide conversion.

Development of the Snoek Anelastic Relaxation Correlated with Oxygen in β-Ti Alloys

The β-Ti alloys exhibit excellent shape memory effect and superelastic properties. The interstitial atoms in the alloys have important effect on their physical and mechanical properties. For the interstitial atoms, the internal friction technique can be used to detect their distributions and status in the alloys. The anelastic relaxation in β-Ti alloys is discussed in this paper. β-Ti alloys possesses bcc (body center body) structure. The oxygen (O) atoms in in the alloys is difficult to be removed. The O atoms located at the octahedral sites in the alloys will produce relaxation under cycle stress. In addition, the interaction between the interstitial atoms and substitute atoms, e.g., Nb-O,Ti-O can also produce relaxation. Therefore, the observed relaxational internal friction peak during the measuring of internal friction is widened. The widened multiple relaxation peak can be revolved into Debye,s elemental peaks in Ti-based alloys. The relaxation peak is associated with oxygen movements in lattices under the application of cycle stress and the interactions of oxygen-substitute atoms in metastable β phase (βM) phase for the water-cooled specimens and in the stable β (βS) phase for the as-sintered specimens. The damping peak height is not only associated with the interstitial oxygen, but also the stability and number of βM in the alloys.

Self-healing high temperature shape memory polymer

Self-healing can improve reliability and extend service lifetime of materials while shape memory polymers (SMPs) have potential in many smart applications, and here self-healing shape memory polyimide (SHSMPI) that can heal damages at high temperature is fabricated for the first time. SHSMPI is synthesized by incorporating fusible thermoplastic polystyrene (PS) at 8% weight content into shape memory polyimide (SMPI) matrix, and it exhibits excellent shape memory effect. SHSMPI can self-heal crack, pierced hole, and cut effectively at heal-temperature of 243 °C. Self-healing mechanism of SHSMPI is discussed, and SMPI matrix produces spatial proximity through shape memory effect while PS acts as healing agent to heal the damages. SHSMPI can produce stored energy of 0.105 J g−1 at the efficiency of 33.1% upon triggering. The designing of SHSMPI at macroscale makes it suitable for mass production, and the self-healing performance will greatly expand application areas of SMPI.

Work hardening influencing on shape memory effect of NiTi alloy by varying milling speeds

Nickel-titanium (NiTi) shape memory alloys (SMA) are widely being used as medical implants due to their excellent shape memory effect (SME) and super-elasticity (SE). The medical implants such as artificial knee joint are usually fabricated by mechanical milling operations. However, the work hardening generated during milling process affects the SME of NiTi alloy. There is requirement to study the effect of milling on the SME of NiTi alloy. The influence of milling parameters on SME of NiTi alloy is investigated by analyzing the effect of milling speed on work hardening in this research. It is found that work hardening decreases before 200 m min−1 cutting speed, but increases rapidly after 200 m min−1. And the change tendency of SME is contrary to that of work hardening. SME is reflected by the recovery rate of residual strain, and the difference of residual strain recovery rate is distinct under various milling speeds. Most of all the recovery rate of 200 m min−1 is obviously higher than those of other milling speeds. The plastic deformation in milling process is serious which weakens the SME when the work hardening becomes larger. Considering the comprehensive influence of milling speed on SME and work hardening induced by machining process, the 200 m min−1 milling speed should be selected.

Transparent, High Glass-Transition Temperature, Shape Memory Hybrid Polyimides Based on Polyhedral Oligomeric Silsesquioxane

Optically transparent polyimides with excellent thermal stability and shape memory effect have potential applications in optoelectronic devices and aerospace industries. A series of optically transparent shape memory polyimide hybrid films are synthesized from 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2′-bis-(trifluoromethyl)biphenyl-4,4′-diamine (TFMB) with various polyhedral oligomeric silsesquioxane (POSS) contents and then subjected to thermal imidization. The hybrid films show good optical transparency (>80% at 400 nm and >95% at 500 nm) with cutoff wavelengths ranging from 318 to 336 nm. Following the incorporation of the inorganic POSS structure, the hybrid films exhibit excellent thermal stability with glass transition temperature (Tg) ranging from 351 to 372 °C. The hybrid films possess the highest Tg compared with the previously-reported shape memory polymers. These findings show that POSS is successfully utilized to develop transparent polyimides with excellent thermal stability and shape memory effect.

Large superelastic recovery and elastocaloric effect in as-deposited additive manufactured Ni50.8Ti49.2 alloy

A Ni50.8Ti49.2 alloy is fabricated by the Laser Solid Forming (LSF) technique by using prealloyed powder in this work. Characterization of the microstructure, phase transformation, and shape recovery of the as-deposited alloy are explored. Columnar grains with ⟨110⟩ preferred orientation are well aligned with the building direction, and the martensitic transformation (MT) behavior shows spatial distribution characteristics. With the increase in the deposited height, MT varies from the two-stage B2 →R→ B19′ transformation to the one-stage B2 → B19′ transformation. Shape recovery properties are studied by compression tests. The as-deposited material without any further heat treatment shows a remarkably large superelastic recovery strain of 9.2% at room temperature, which is the largest value in the additive manufactured NiTi alloy. A negative adiabatic temperature change of –18.6 K induced by the elastocaloric effect during the unloading process is obtained. The shape memory effect (SME) of the as-deposited LSF Ni50.8Ti49.2 alloy is not only dependent on the detwinning of martensite but also associated with the partial superelasticity of the parent phase in the present work, demonstrating a unique two-stage yielding behavior. A residual strain up to 6% is recovered while heating, indicating an excellent SME.

Biocompatible shape‐memory poly(vinyl chloride) with a tunable switching temperature via a plasticization effect

ABSTRACTBiocompatible shape‐memory poly(vinyl chloride) (PVC) with a tunable switching temperature (Ts) was fabricated via the incorporation of an environmentally friendly plasticizer of 1,2‐cyclohexane dicarboxylic acid diisononyl (DINCH). It was revealed that both of the shape‐memory effect (SME) and Ts were significantly influenced by the plasticization effect. With the addition of DINCH, the shape‐fixing ratio (Rf) showed a slight reduction, whereas the shape‐recovering ratio (Rr) was greatly enhanced, and Ts was decreased from 90 to 47 °C. PVC with 40 phr plasticizer realized an excellent SME with an Rf of 97.0% and a Rr of 90.1%; this resulted from the formation of an efficient shape‐memory network via the physical crosslinking of the amorphous chains with crystals and rigid chain entanglements. In addition, the blood compatibility of the DINCH‐plasticized PVC was evaluated, and the results indicate that it was of great potential for biomedical applications. Therefore, in this study, we successfully developed a new shape‐memory polymer and provided a promising strategy for achieving SME with tunable Ts. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47992.

A Biocompatible, Biodegradable, and Functionalizable Copolyester and Its Application in Water-Responsive Shape Memory Scaffold

Shape memory polymers are of great interest for biomedical applications. However, most stimuli used to trigger shape memory processes, including heat, light, electricity, magnetism, and pH are inconvenient and maybe harmful to the body. Here, we designed and fabricated a new shape memory porous scaffold using biocompatible and readily available water as the trigger. This scaffold was based on poly(fumaricacid-co-1,7-octadiene diepoxide-co-terephthalic acid) (PFOT) synthesized via epoxide ring-opening polymerization in one step. The PFOT scaffold promoted the adhesion, spreading, proliferation and function of cardiomyoblast H9C2 cells in a manner comparable to that for the poly(lactic-co-glycolic acid) scaffold. It exhibited an excellent water-responsive shape memory effect with a fixity and recovery ratio >97% and a shape-recovery process of several minutes, suitable for surgery. In addition, the PFOT scaffold presented good in vitro biodegradation. More importantly, PFOT contains extensive free hydroxyl ...

Atomic Layer Deposited Al2O3 Films on NiTi Shape Memory Alloys for Biomedical Applications

NiTi shape memory alloys (SMAs) have been widely applied in biomedical fields owing to their excellent shape memory effect, super-elasticity, biomedical properties and fatigue performance. These applications include the cardiovascular stent, guidewire, stone extractors used in the cystic duct, artificial heart valve and orthodontic wire, etc. However, NiTi alloys might release out the Ni atoms in the physiological environment, which will induce the serious problems of allergic reaction, poisoning and causing cancer. This study employs the atomic layer deposition (ALD) technique to deposit Al2O3 films on the surfaces of NiTi SMAs. Experimental results show that the chemical compositions of ALD-Al2O3 films are well homogeneous. The ALD-Al2O3 films exhibit a fair adhesion with the NiTi substrates and sustain a suitable deformation strain. The ALD-Al2O3 films can also effectively inhibit the release out of Ni atoms from the NiTi SMAs. Meanwhile, the corrosion resistance of NiTi SMAs can be improved by the ALD-Al2O3 films.

Tunable Large Recovery Strain and Wide Response Temperature with Near-Zero Response Interval in Cu-Al-Mn-Fe Single Crystals

Shape memory alloys can recover the deformed shape due to their superelasticity or shape memory effect. Generally, in one shape memory alloy either the superelasticity or shape memory effect can be displayed under a certain temperature, depending on the relationship between the martensitic transformation and deformation temperature. Here we report novel Cu-Al-Mn-Fe shape memory material simultaneously showing excellent superelasticity and shape memory effect at room temperature, as well as tunably wide response temperature range with near-zero interval of reverse phase transformation by deformation. When deforming one single crystal at room temperature, it not only possesses full superelasticity of 7%, but also tunable shape memory effects up to 8.8%. The full shape recovery during heating exhibits near-zero response interval and tunably wide response temperature range of 166 K depending on the deformation. The functional characteristics of the alloys result from the controllable reverse phase transformation hinging on the stabilization of stress-induced martensite induced by completely coherent nanoparticles during deformation. This class of Cu-Al-Mn-Fe alloys may be used as both superelastic materials, and shape memory materials with wide working temperature range as high-sensitive detector, driver or sensor.

Synthesis and Performance Evaluation of Epoxy Resin–Modified Shape Memory Polyurethane Sealant

Abstract To evaluate the effects of epoxy resin (EP) on different properties of shape memory polyurethane (SMPU) when used as a sealant with a tailored thermal transition temperature (Tt) for concrete pavement joints, the thermal and dynamic mechanical performances were discussed to determine the shape memory switching temperature of EP-modified SMPU, and then the compatibility between EP and SMPU, microscopic morphology, shape memory effect, and tensile property were also characterized. The results indicate that the tailored Tt of EP-modified SMPU can be used as the shape memory switching temperature to match its working temperature. EP and SMPU show considerable compatibility. EP inhibits the crystallization of soft phase content and increases the hard phase content. Both hydroxyl and epoxy groups participate in chemical reactions. The ring-opening reactions occur between fractional benzenes and SMPU. EP was successfully grafted onto the main chains of SMPU. Additionally, the peak load, tensile strength, and elongation at break of SMPU are first increased and then decreased when the EP content increase. An EP content of 10 % improves the tensile properties of SMPU, but excessive EP content leads to a decrease in the tensile strength and elongation at break. Finally, it is found that a small amount of EP has little influence on the shape memory properties of SMPU, but EP can improve the tensile properties of SMPU. EP-modified SMPU shows excellent shape memory effects. The prepared EP-modified SMPU with the specially tailored Tt can meet the requirements of practical engineering when used as a sealant for concrete pavement joints.

Microwave-induced shape-memory poly(vinyl alcohol)/poly(acrylic acid) interpenetrating polymer networks chemically linked to SiC nanoparticles

Microwave (MW)-induced shape-memory poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) interpenetrating polymer networks (SMP-IPNs) were prepared through in situ polymerization. Silicon carbide (SiC) nanoparticles were modified by 3-(methacryloyloxy) propyltrimethoxysilane (KH570). 3-(Methacryloyloxy) propyltrimethoxysilane was covalently bonded on the surface of SiC through the reaction of silanol and the methoxy groups. The polymerization of acrylic acid (AA) using N,N′-methylenebis (2-propenamide) (MBA) as cross-linker in PVA solution was initiated through the double bonds of KH-570 grafted on SiC, leading to a PAA polymer network cross-linked with MBA. The PVA molecular chains run through the PAA cross-linking network and form an IPN structure. Therefore, SiC as a strong MW absorbing material could be chemically cross-linked into polymer matrix. The effect of composition on the properties of SMP-IPN was studied using dynamic mechanical analysis, dielectric properties and shape memory effect (SME) test. The results showed that the introduction of SiC in IPNs not only provided samples with excellent MW-induced shape memory effect (SME), but also caused a higher equilibrium temperature under MW irradiation. Moreover, both SiC content and applied MW power affected the shape recovery properties of PVA/PAA interpenetrating composites. MW-induced SMPs offered great advantages such as fast recovery, high recovery rate, and remote actuation. This study provides the potential applications of the fast and environmentally friendly SMPs used as MW-responsive sensors, implantable devices, etc.

Enhanced dual-responsive shape memory nanocomposites with rapid and efficient self-healing capability

High-strength nanocomposites were prepared by in situ polymerization of 2-methoxyethyl acrylate and N,N′-dimethylacrylamide with the existence of TiO2 nanoparticles. Based on the reversible hydrogen bond network, the resultant materials showed enhanced mechanical strength, excellent shape memory effect, and superior self-healing capability. To accomplish the goal of rapid and efficient self-healing for the materials, the elevated temperature was chosen as the healing temperature, and the fracture sample could be completely repaired within 10 min with the fracture strength of 13.56 MPa and high healing efficiency of ~ 100% (MD50-T5). Combining the high strain and water-absorbing nature of materials, the recovery of the complex shape of helix structure and self-lacing process in water under physiological temperature could be programmed and finished. Thus, the dual functional elastomers could be used in coating, suturing, and possess the wide application prospects in bioengineering and smart devices.

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

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

Light-actuated reversible shape memory effect of a polymer composite

In the current study, a novel polymer composite with excellent light-actuated two-way shape memory effect (2W-SME) was fabricated using poly (ethylene-co-vinyl acetate) (EVA) as matrix and p-aminodiphenylimide (p-AP) as both light-absorber and heat source (EVA/p-AP). Unlike traditional thermally-driven two-way reversible shape memory polymers, in our concept, the EVA/p-AP featured remotely controlled and light-manipulatable reversible two-way shape memory behaviors. Utilizing the distinct light-responsive behavior of p-AP in the irradiation of 365 nm ultraviolet (UV) light, the EVA/p-AP composite exhibited excellent light-actuated reversible 2W-SME by a light-manipulated procedure. The results from this study indicated that the composite material could have greatly potential applications in soft reversible drivers.

Synthesis and Evaluation of Fracture Behaviour of Cu-Al-Be-Mn Quaternary Shape Memory Alloy

Cu-based quaternary SMA’s are less expensive, easy to prepare and exhibits excellent shape memory effect. In this paper, Cu-Al-Be-Mn quaternary alloys taken in the range of 11-14 wt% of Al, 0.2-0.4 wt % of Mn, 0.47 wt% of Be and rest is copper were synthesized through ingot melting method in the inert atmosphere and also conducted bend test to demonstrate the shape memory property after step quenching process at room temperature. Beryllium kept constant and manganese concentration in the alloy was varied to evaluate the fracture toughness of each alloy specimens by taking stress intensity factor (KIC) into account. In the current study modified single edge cracked plate tension specimen was prepared by using wire EDM. Fracture toughness of shape memory alloys is determined by testing the alloy specimens on uniaxial tensile testing machine, which are initially tested under low fatigue tensile loading to create a pre crack and then subjected to a uniaxial tensile loading until fracture. After fracture maximum load was noted down and stress intensity factor (KIC) can be evaluated for all the alloy samples. The fractured surface of the specimens was studied under scanning electron microscope (SEM) and examined the effect of composition and notch configuration on the fracture behaviour of SMA. An experimental result shows that the alloys exhibits good fracture toughness with KIC values up to 41 MPa m ^ 0.5 and stress intensity factor (KIC) increases with the increase in wt % of manganese