Possess Shape Memory Research Articles

Full shape memory effect of Cu-13.5Al-4Ni-6Fe shape memory martensite single crystal

The Cu−13.5Al−4Ni−6Fe centimeter-leveled martensite single crystals with full shape memory effect were prepared through simply annealing the cast alloy. The microstructure, reversible martensitic transformation, shape memory effect of this single crystal were investigated using optical microscopy, transmission electron microscope, differential scanning calorimeter, thermal mechanical analysis and compression test. The results show that Cu−13.5Al−4Ni−6Fe single crystal consists of 18R and 2H martensite, as well as rich-Fe bcc nanoprecipitate. The starting temperatures and the finishing temperatures of the forward and reverse martensitic transformations are 387, 397, 365 and 432 K, respectively. When the pre-strain is 6%, 7%, and 8%, this single crystal exhibits full shape memory effect of 4.4%, 4.7% and 5.2%, respectively. The obtained Cu−13.5Al−4Ni−6Fe martensite single crystal possesses shape memory properties that can be comparable to those of traditional shape memory alloys.

Lightweight and geometrically complex ceramics derived from 4D printed shape memory precursor with reconfigurability and programmability for sensing and actuation applications

There is growing interest in additive manufacturing (AM) of ceramics due to the feasibility of achieving geometrically complex shapes for various engineering applications. Polymer-derived ceramics (PDCs), pyrolyzed from polymeric ceramic precursors, act as a competitive material for ceramic AM with advantages such as easy processability, flexible designability, and relatively low sintering temperature. However, the functionality of preceramic polymers is far from being fully exploited, thus restricting the development and applications of 3D printed ceramics. Herein, a novel multifunctional preceramic polymer composite with reconfigurability and shape memory effect is synthesized. By tuning the material compositions, the precursor inks suitable for 4D printing are pyrolyzed into lightweight self-shaping ceramics, allowing complex geometries to be fabricated. The preceramic polymers undergo a stepwise partial-to-full crosslinking process to form interpenetrating polymer networks, resulting in reconfigurability where the as-printed parts can be transformed into shapes with higher complexity. Unlike traditional precursors with static shapes, the precursor here possesses shape memory capability (Tg ∼ 95 °C). During the sintering process, the 3D printed precursor could successively undergo programmable active shape transformation with a high recovery ratio (∼100 %) and pyrolysis conversion into lightweight ceramics (1.05 g/cm3). By exploring the semiconducting behavior of resulting ceramics, temperature sensors leveraging the advantages of reshaping are designed to detect the surface over a wide range (25–750 °C) with good conformability. The development of 4D printed reconfigurable and programmable precursors for the construction of complex ceramics enriches both the complexity and self-shaping capability of ceramics, allowing them to be applied as smart thermistors and deployable structures.

Flexibility and shape memory of phase change material capable of rapid electric heating function for wearable thermotherapy

Thermotherapy is often preferable to medication and surgery because of its mild side effects and noninvasiveness. However, current research methods are unable to improve the efficiency of pre-treatment resulting in unportable use, and poor room temperature flexibility has become its critical limitation. Herein, a novel conductive flexible composite phase-change material (CPCM) was prepared for high-performance thermotherapy. Styrene ethylene butylene styrene (SEBS) and expanded graphite (EG) absorb paraffin (PA) and silicone oil onto a three-dimensional network. The CPCM possesses a high energy storage density (100.8–164.5 J/g) and sufficient volume conductivity (383.76 S·m−1) and can improve the thermal conductivity to 1600 % relative to pure PA. Moreover, it is flexible and possesses shape memory at both room temperature and the phase change temperature (44 ℃). The hardness of the material is 44.5 HA at room temperature and can be reduced to 2.0 HA after phase transition. When heated electrically, it heated threefold faster than when heated by hot air. The material was tested by volunteers and was found to maintain a temperature above 40 °C for more than 30 min. The utilization of this CPCM in thermotherapy is a promising low-cost and environmentally friendly strategy.

Shape Memory Behaviour of PMMA-Coated NiTi Alloy under Thermal Cycle.

Both poly(methyl methacrylate) (PMMA) and NiTi possess shape memory and biocompatibility behavior. The macroscale properties of PMMA–NiTi composites depend immensely on the quality of the interaction between two components. NiTi shape memory alloy (SMA) and superelastic (SE) sheets were spin coated on one side with PMMA. The composite was prepared by the spin coating method with an alloy-to-polymer-thickness ratio of 1:3. The bending stiffness and radius of curvature were calculated by using numerical and experimental methods during thermal cycles. The experimental radius curvatures in actuation have good agreement with the model. The change in shape results from the difference in coefficients of thermal expansion between PMMA and NiTi. Actuation temperatures were between 0 and 100 °C for the SMA–PMMA composite with a change in curvature from 10 to 120 mm with fixed Young’s modulus of PMMA at 3 GPa, and a change in Young’s modulus of NiTi from 30 to 70 GPa. PMMA–NiTi composites are useful as actuators and sensor elements.

Multi-shape-changing interpenetrating networks with shape memory effect and adaptive plastic deformations

Shape-changing materials with precisely programmable configurations, each having its own functional regime, provide a wide range of applications in engineering and biomedical fields. Polymers with dynamic reversible covalent/non-covalent bonding feature the potential of having remarkable plasticity, which endows them with the capability of undergoing significant and sophisticated shape changes. Here we report a facile method to build an interpenetrating network (IPN) structure with plastic deformation and shape memory properties. The IPN is consisting of Poly(vinyl Alcohol) (PVA) with slight chemical covalent crosslinking and poly(UPyMA-AAc) with two potential dynamic reversible non-covalent bonding (quadruple hydrogen-bonding and ferric coordination bonding). This IPN structure not only has the capability of thermal plasticity and metal-coordinated plasticity, but also possesses shape memory properties similar to typical shape memory polymers. Hence, the polymers with this structure can undergo programmable shape changes through sequential adaptive plastic deformations triggered by a variety of stimuli.

Bioinspired four-dimensional polymeric aerogel with programmable temporal-spatial multiscale structure and functionality

The original four-dimensional (4D) polymeric aerogel design introduces a concept of programmable temporal-spatial multiscale structure, in which the fourth dimension is time. The novel aerogel possesses shape memory properties, which can fix temporary state and recover permanent state by releasing frozen stress under stimulus without any sophisticated electro-mechanical equipment in the programmable manner. Its structure can be tailored by precrosslinked ice template method to obtain high permeable multiscale structure. Its functionalities and performances can be customized and optimized by adjusting porous framework, matrix, functional groups, and self-adaptivity based on application demands. Comparing with traditional aerogels, the emerging 4D aerogel has many unique properties, including excellent self-adaptivity, high permeable multiscale structure, flexible preprogrammed ability, customized functional groups, low cost, and environmental friendliness. Its exploration and development could draw much attention due to various promising potential applications including water treatment, intelligent structure, and sensor. These high-value applications would further promote the development of the intelligent aerogels and the reliable preparation technologies. As an interesting field, the 4D aerogel idea is revolutionary for traditional aerogels and expected to provide new perspective and practical approach to realize the integration of material, structure, and functionality.

Highly thermally conductive phase change composites for thermal energy storage featuring shape memory

Highly thermally conductive form-stable phase change materials (PCMs) possessing shape memory are designed based on covalent-noncovalent interpenetrating polymer network and boron nitride. The matrix network relies on the composition of two functional species, cured mesogenic epoxy (EO) and polyethylene glycol (PEG). It is demonstrated that the covalent network of EO can trap PEG by forming hydrogen bond with PEG chains. On the basis of EO/PEG networks, by incorporating boron nitride, the thermally conductivity of the PCMs can reach to 2.962 W m−1 K−1. The prepared composites show satisfied thermal energy storage capability and good shape stability when undergo long time heating at 80 °C. In addition, the prepared composite exhibits excellent shape memory function. Diverse functions of the PCMs might produce new applications in thermal energy storage or thermal management fields.

Multifunctional light-responsive graphene-based polyurethane composites with shape memory, self-healing, and flame retardancy properties

It is a challenge to manufacture light responsive polymer composite that possesses shape memory, self-healing, and flame retardancy capacities. Herein, multi-functionalized graphene oxide (mfGO) wrapped with nitrogen-, phosphorus-, and silicon- containing units was prepared via in-situ polymerization and subsequently was incorporated into a diselenide-containing polyurethane (dPTD) matrix to fabricate composite. The successful functionalization of mfGO was initially confirmed by a series of measurements. Taking advantage of the crystallization-induced and photo-thermal effects of mfGO as well as the dynamic exchange characteristic of diselenide bonds, the dPTD-mfGO2 composite containing 2 wt% of mfGO exhibited admirable shape memory and self-healing behaviors under visible-near infrared light within 3 min, and its shape memory characteristics and healing efficiencies were kept above 90% and 76% after three cycles, respectively. Further combustion experiments demonstrated that dPTD-mfGO2 composite showed superior LOI (24.9%) and UL-94 rating (V-2) without flaming drips, owing to the synergistic catalyzing carbonization and barrier effect of mfGO. Additionally, the dPTD-mfGO2 composite possessed an improved water contact angle of 109.5°. These findings suggest that the introduction of 2 wt% mfGO to the dPTD matrix can synergistically improve the toughness, shape memory, self-healing, flame retardancy, and water resistance as compared with the neat dPTD. This work provides a promising pathway to fabricate stimulus-responsive composite materials with versatile functions.

4D Printing of Recyclable Lightweight Architectures Using High Recovery Stress Shape Memory Polymer

High-performance lightweight architectures, such as metallic microlattices with excellent mechanical properties have been 3D printed, but they do not possess shape memory effect (SME), limiting their usages for advanced engineering structures, such as serving as a core in multifunctional lightweight sandwich structures. 3D printable self-healing shape memory polymer (SMP) microlattices could be a solution. However, existing 3D printable thermoset SMPs are limited to either low strength, poor stress memory, or non-recyclability. To address this issue, a new thermoset polymer, integrated with high strength, high recovery stress, perfect shape recovery, good recyclability, and 3D printability using direct light printing, has been developed in this study. Lightweight microlattices with various unit cells and length scales were printed and tested. The results show that the cubic microlattice has mechanical strength comparable to or even greater than that of metallic microlattices, good SME, decent recovery stress, and recyclability, making it the first multifunctional lightweight architecture (MLA) for potential multifunctional lightweight load carrying structural applications.

Polydiacetylene-Polyurethane Crisscross Elastomer as an Intrinsic Shape Memory Conductive Polymer.

Owing to the high phase transition temperature and incompatibility with thermoplastic elastomers, conjugated polymers are hardly formulated as shape memory materials. This work presents a crisscross polymer composed of polyurethane and polydiacetylene. Phase separation is completely avoided based on the photoinduced polymerization of polydiacetylene from polyurethane chains. The two backbones are intercrossed and covalently linked to each other. Particularly, polyurethane acts as a soft segment to provide elastic performance, and the rigid polydiacetylene provides conductive pathways. Such a crisscross topology, combined with soft and rigid compositions, renders the possibility to serve the polymer as an intrinsically elastic conductive polymer. Intriguingly, the polymer possesses shape memory performance, meanwhile retaining the reliable conductivity. Electrical tests demonstrate that the shape memory conductive polymer is one attractive candidate for exploiting shape-customized strain sensors.

Shape memory effect of mycologically destroyed wood

Wood is a natural smart material which possesses shape memory effect (SME). The paper deals with SME behaviour of sound and mycologically destroyed wood and shows the influence of cellulose, hemicelluloses, and lignin content on the wood ability to remember the temporary and to recover the permanent shapes. The research was carried out on sliced veneer samples (beech Fagus sylvatica L. and pine Pinus sylvestris L.) and rotten samples (pocket rot, brown rot) to reveal the influence of on the deformative conversions and quantities of SME. Results of research are shown that at moisture drop the higher values of strain fixity rate for all wood species and types of rot are noted (0.82 – 0.97). The more remarkable difference for sound and rotten wood is observed for strain recovery rate at temperature change. Despite the change of chemical composition for pocket rot the speed of recovery of permanent shape was almost the same as for sound wood. Results of this research can be used for the developing of new biocomposite materials based on wood.

Effect of carbon nanotubes reinforcement on the polyvinyl alcohol – polyethylene glycol double-network hydrogel composites: A general approach to shape memory and printability

The developing polyethylene glycol (PEG) and polyvinyl alcohol (PVA) double network (DN) hydrogel are promising to utilize as matrix composites due to their unique characteristics such as shape memory. The DN hydrogel are hydrophilic smart materials that possess shape memory phenomenon by thermal stimuli-responsive. Scientifically, the DN hydrogel can describe as a combination of polymers with two different sets of properties. In particular, the PEG play as a minor network of a stiff framework and the PVA play as a major network of an elastic matter. In addition, the use of carbon nanotubes (CNTs) become reinforcement has emerged as one of the most promising to bring new conceptual paradigm for DN hydrogel, due to their advantages have well-established in the polymer matrix. The development of DN hydrogel composite becomes high novelty with approaching attributes on general studies about shape memory and printability. The result shows that the CNTs additional are capable to maintain the shape memory effect of hydrogels and improve the viscoelasticity for printability, respectively.

Self-healing thermoplastic polyurethane (TPU)/polycaprolactone (PCL) /multi-wall carbon nanotubes (MWCNTs) blend as shape-memory composites

Polymer blends with self-healing capability when damaged have received increasing interests and have been developing rapidly because of their many potential applications. Here, the polymer blend comprising of thermoplastic polyurethane (TPU) and polycaprolactone (PCL) as shape memory matrix was initially prepared by melting blending, and then the multiwalled carbon nanotubes (MWCNTs) were incorporated to endow the blend with excellent self-healing property in the presence of near infrared (NIR) irradiation (808 nm, 0.14 W). Compared with the traditional heat-induced self-healing shape memory composites, NIR irradiation could not only reduce the healing time, but also can selectively repair the exposed damaged regions without distinct interference to the performance of surrounding parts. As revealed, these composites presented superior shape memory and self-healing behavior in the presence of NIR irradiation. Specifically, the blend containing 50% TPU, 50% PCL and 3 MWCNTs (U1C1-3) possesses shape memory properties as manifested by a ca. 96.8% shape fixing ratio (Rf) and ca. 63.9% shape recovery ratio (Rr). The surface crack and scratches can be completely recovered in 3 min NIR irradiation. And moreover, this NIR stimulated self-healing could performed repeatedly for at least 4 times, with healing efficiency of ca. 96%. All these observations could be attributed to the hybrid crystalline and amorphous regions of PCL and TPU, as well as the well distribution of MWCNTs in the polymeric matrix. The superior shape memory and self-healing properties, along with the easy and scalable process of fabrication, make these blends ideal candidates for an ensemble of applications, including biomedical, packing and microelectronics.

Stereolithographic 4D Bioprinting of Multiresponsive Architectures for Neural Engineering.

4D printing represents one of the most advanced fabrication techniques for prospective applications in tissue engineering, biomedical devices, and soft robotics, among others. In this study, a novel multiresponsive architecture is developed through stereolithography-based 4D printing, where a universal concept of stress-induced shape transformation is applied to achieve the 4D reprogramming. The light-induced graded internal stress followed by a subsequent solvent-induced relaxation, driving an autonomous and reversible change of the programmed configuration after printing, is employed and investigated in depth and details. Moreover, the fabricated construct possesses shape memory property, offering a characteristic of multiple shape change. Using this novel multiple responsive 4D technique, a proof-of-concept smart nerve guidance conduit is demonstrated on a graphene hybrid 4D construct providing outstanding multifunctional characteristics for nerve regeneration including physical guidance, chemical cues, dynamic self-entubulation, and seamless integration. By employing this fabrication technique, creating multiresponsive smart architectures, as well as demonstrating application potential, this work paves the way for truly initiation of 4D printing in various high-value research fields.

Deep Drawing of a Ni-Ti Shape Memory Alloy Sheet

This study is aimed to investigate the properties of Ni-rich Ni-Ti shape memory alloy sheet parts during and after deep drawing process at room temperature, in which the metal is under plane tension-compression stress state. After annealing at different elevated temperature, shape memory alloy sheet is formed at room temperature by a circular cylindrical punch in different forming depths. Thereafter the deep drawn sheet part is subjected to aging for shape memory treatment. A free shape recovery test is further conducted onto the deep drawn shape memory alloy sheet part. As a result, the sheet metal has austenitic phase at room temperature, which shows superelasticity. Too small forming amount causes severe springback and the form of the deep drawn sheet part is very hard to detect with the naked eye. Only if a forming amount greater than or equal to 4 mm is applied, a form can be achieved on to the sheet part. The subsequent aging shape memory treatment can induce further springback of the deep drawn sheet part. The higher the temperature of the previous annealing, the less the springback by aging. The free shape recovery test shows that the deep drawn sheet part only undergoing annealing without shape memory treatment still possesses shape memory effect. Nevertheless, the deep drawn sheet part aged for shape memory can show a better shape recovery.

An Investigation of the Micro-Electrical Discharge Machining of Nickel-Titanium Shape Memory Alloy Using Grey Relations Coupled with Principal Component Analysis

Shape memory alloys (SMAs) are advanced engineering materials which possess shape memory effects and super-elastic properties. Their high strength, high wear-resistance, pseudo plasticity, etc., makes the machining of Ni-Ti based SMAs difficult using traditional techniques. Among all non-conventional processes, micro-electric discharge machining (micro-EDM) is considered one of the leading processes for micro-machining, owing to its high aspect ratio and capability to machine hard-to-cut materials with good surface finish.The selection of the most appropriate input parameter combination to provide the optimum values for various responses is very important in micro-EDM. This article demonstrates the methodology for optimizing multiple quality characteristics (overcut, taper angle and surface roughness) to enhance the quality of micro-holes in Ni-Ti based alloy, using the Grey–Taguchi method. A Taguchi-based grey relational analysis coupled with principal component analysis (Grey-PCA) methodology was implemented to investigate the effect of three important micro-EDM process parameters, namely capacitance, voltage and electrode material.The analysis of the individual responses established the importance of multi-response optimization. The main effects plots for the micro-EDM parameters and Analysis of Variance (ANOVA) indicate that every parameter does not produce same effect on individual responses, and also that the percent contribution of each parameter to individual response is highly varied. As a result, multi-response optimization was implemented using Grey-PCA. Further, this study revealed that the electrode material had the strongest effect on the multi-response parameter, followed by the voltage and capacitance. The main effects plot for the Grey-PCA shows that the micro-EDM parameters “capacitance” at level-2 (i.e., 475 pF), “discharge voltage” at level-1 (i.e., 80 V) and the “electrode material” Cu provided the best multi-response.

Surgical Correction of Child Pectus Excavatum by TiNi-based Materials

This article describes the serious and urgent issue of surgical treatment of congenital child pectus excavatum and the approaches in the surgical correction of this children pathology. The authors propose an original surgical treatment method in applying TiNi-based materials possessing shape memory in OP treatment of pectus excavatum. Plain integral TiNi-based plasty creates supplemental correction force due to the material isoelastic properties, providing stable fixation of corrected chest section throughout the immobilization period.

Shape memory thermoplastic polyurethane (TPU)/poly(ε-caprolactone) (PCL) blends as self-knotting sutures

Thermally responsive shape memory polymers have promising applications in many fields, especially in biomedical areas. In this study, a simple method was purposed to prepare thermoplastic polyurethane (TPU)/poly(ε-caprolactone) (PCL) blends that possess shape memory attributes. TPU and PCL were melt compounded via a twin-screw extruder and injection molded at various ratios. Multiple test methods were used to characterize their shape memory properties and reveal the underling mechanism. The blends containing 25% TPU and 75% PCL possessed the best shape memory properties as indicated by a 98% shape fixing ratio and 90% shape recovery ratio. This was attributed to the hybrid crystalline and amorphous regions of PCL and TPU. We also found that PCL and TPU had good miscibility and that the PCL domain in TPU25% had higher crystallinity than neat PCL. The crystalline region in TPU25% could deform and maintain its temporary shape when stretched, which contributed to its high shape fixing attribute, while the rubbery TPU region assisted in the recovery of the sample upon heating by releasing the deformation energy stored. Moreover, the TPU25% string prepared could knot itself in a hot water bath, indicating a potential for suture applications. Lastly, the 3T3 fibroblast cells cultured on the TPU/PCL blends showed high viability and active substrate–cell interactions.

Influence of partial shape memory deformation on the burst character of its recovery in heated Ni–Fe–Ga–Co alloy crystals

Room-temperature stress–strain curves of Ni49Fe18Ga27Co6 alloy single crystals possessing shape memory (SM) have been studied. Specific features of these diagrams are revealed upon compressive loading of these single crystals in the [110]A direction. The influence of preliminary SM deformation on the process of its recovery during the reverse martensite transformation has been studied. It is established that SM deformation above 4.2% leads to a sharp increase in the shape recovery on heating and the process exhibits a burst character, involving motion of the entire crystal. The experimental data are analyzed and stress–strain curves are simulated in the framework of the theory of diffuse martensitic transitions.

Shape memory fiber supercapacitors

Smart energy storage materials, which not only store electrochemical energy but also exhibit sensitivity to environmental stimuli, can provide novel multi-functionalities. Here, we report a smart shape memory fiber supercapacitor constituted with a highly stretchable shape memory polymer nanocomposite fiber substrate, multi-walled carbon nanotubes (MWCNT) conductive layer and pesudocapacitive polyaniline layer. Using layer by layer (LBL) technology, we first produce a densely packed MWCNT layer that serves as a well-developed conductive current collector network. Then polyaniline, as an active material, was deposited on the surface of the MWCNT layer to further promote the energy storage capability of the fibers. After the infiltration of a polyvinyl alchohol (PVA) based polymer electrolyte into the porous MWCNT and PANI layer, conductivity of ∼50S/cm and stretchability of more than 400% are obtained. The resultant shape memory polymer supercapacitors (SMPFSCs) not only possess shape memory properties, but also exhibit outstanding energy storage performance, with the best pseudo-capacitance exceeding ∼427F/cm3. Such design strategies can also be extended to other polymer substrates, and could open the door to smart (multi-functional) supercapacitor technologies.