Full Shape Recovery Research Articles

Effectiveness of Starch Nanocrystals on Mechanical and Shape Memory Behaviour of Smart Rubber

Shape memory rubber (SMR) is a type of smart rubber that can undergo reversible changes when exposed to external stimuli such as temperature, solvent, pH, light, magnetic field and oxidation. Lightly crosslinked rubber demonstrated shape memory behaviour without any initial heat treatment. However, the strength of lightly crosslinked natural rubber latex (NRL) film cured by sulphur is relatively low. With the concept of sustainability in mind, the idea of fabricating green smart material for continuous development has motivated researchers to explore the realms of sustainable materials. This research aims to investigate the mechanical behaviour of starch nanocrystals (SNC) reinforced rubber composite films. To this end, the emphasis is laid on evaluating the effectiveness of SNC on shape memory effect (SME) of rubber nanocomposite films. In the current work, up to 8 wt% of SNC synthesized by acid hydrolysis was incorporated into NRL and the mixture was cast to form rubber nanocomposite films. SNC effectively increased the modulus and energy-storing potential of the rubber nanocomposite films. Moreover, the shape memory behaviour of the rubber nanocomposite films improved significantly with SNC content, leading to increased shape fixity (Sf) and full shape recovery (Sr).

Investigating the impact of infill patterns on shape memory effect in material extrusion

Extensive research has been conducted on Shape Memory Polymers (SMPs) for their potential application in additive manufacturing. The Shape Memory Effect (SME), a key attribute of SMPs, enables 3D-printed objects to alter their shape in response to external stimuli. Several methods for programming SMEs have been explored, such as modifying printing parameters like infill patterns or density. However, incorporating SMPs as substitutes for conventional functional components has been challenging due to grafting difficulties and the limited reliability of SMEs. In this research, the influence of internal structures on SMEs is examined by comparing the full shape recovery period. This investigation has revealed the impact of different infill structures on SMEs and uncovered a complex shape recovery pattern termed multi-phased SME. This occurs when straight infill structures are nearly parallel along the length of a cuboid specimen that has been programmed to form a 90° curve. This finding enhances the creation of complex shape recovery behaviours by simply modifying printing parameters and is applicable to a variety of SMPs.

Nanucellulose from Tofu Production Waste for Wastewater Treatment

Solid waste from tofu production, also known as okara, has numerous applications and can produce high-value-added products. However, the utilization of okara in Indonesia is not yet significant. This written work proposes okara as a source of nanocellulose to produce wastewater adsorbents in freshwater by fabricating it as aerogels and hydrogels. Wastewater is highly hazardous to the environment and living organisms as it can contain saturated salts, heavy metals, organic compounds, oil emulsions, dyes, and even microbes as pollutants that can lead to various diseases or death. Therefore, research on biosorbents is always a hot topic. Biosorption is the process of binding metal ions into the cellular structure of biological materials. Lignocellulosic biosorbents have high adsorption properties due to their ion exchange capability. Okara biosorbent can increase the absorption capacity of Pb2+ ions by up to 20% compared to conventional absorbents. The soybean skin component could also remove contaminated textile dyes from water. Additionally, the low lignin content in okara makes it easier to utilize than other lignocellulosic materials. This research study also shows that okara-based nanocellulose aerogels can maintain their shape or exhibit full shape recovery properties even after being used repeatedly.

Three-Dimensional Printing of Shape Memory Liquid Crystalline Thermoplastic Elastomeric Composites Using Fused Filament Fabrication.

Liquid crystalline elastomers (LCEs) are stimuli-responsive materials utilised in shape memory applications. The processability of these materials via advanced manufacturing is being paid increasing attention to advance their volume production on an industrial scale. Fused filament fabrication (FFF) is an extrusion-based additive manufacturing (AM) technique that offers the potential to address this. The critical challenge, however, is the rheological characteristics of LCEs that need to be tuned to achieve a facile processability through the extrusion-based method. In this work, new filaments of liquid crystalline thermoplastic elastomer (LCTPE) and its composites with lignin were made by the ternary system of LCE, thermoplastic polyurethane (TPU), and lignin. The results showed that TPU improves the melt flow index of the LCTPE system to approximately 10.01 g/10 min, while adding lignin further enhances the value of this index for the composites up to 21.82 g/10 min. The microstructural analysis indicated that the effective distribution of lignin and reduced domain size of the LCEs in the ternary blend contribute to the enhanced flowability of this filament through 3D printing. Samples of 3D-printed LCTPE and LCTPE/lignin composites maintained their shape memory characteristics via thermomechanical activation. Full shape recovery of the new LCTPE matrix and its composites with lignin was achieved in 39 s and 32 s at 130 °C, followed by 28 s and 24 s at 160 °C, respectively. The successful fabrication of LCTPE and LCTPE/lignin composite samples through 3D printing demonstrates a potential procedure for processing these shape memory materials using the FFF technique, and lignin offers a sustainable and cost-effective material solution that enhances the properties of this composite material.

An origami-inspired design of highly efficient cellular cushion materials

Current architectured cellular cushion materials rely mainly on damage and/or unpredictable collapse of their unit cells to absorb and dissipate energy under impact. This prevents shape recovery and produces undesirable force fluctuations that limit reusability and reduce energy absorption efficiency. Here, we propose to combine advanced manufacturing technologies with Origami principles to create a new class of architectured cellular viscoelastic cushion material which combines low weight and high energy absorption efficiency with damage resistance and full behavior customization. Each unit cell in the proposed material is inspired by the Kresling Origami topology, which absorbs impact energy by gracefully folding the different interfaces forming the cell to create axial and rotational motions. A large part of the absorbed energy is then dissipated through viscoelasticity and friction between the interfaces. The result is a nearly ideal cushion material exhibiting high energy absorbing efficiency (∼ 70%) combined with high energy dissipation (94% of the absorbed energy). The material is also tunable for optimal performance, reliable despite successive impact events, and achieves full shape recovery.

Modelling, simulation, and experiments of 4D printed twisting actuator

Since its introduction, 4D (4 Dimensional) printing has sparked a lot of attention and applications in various fields. Unlike 3D (3 Dimensional) printing, 4D printing allows the printed item to alter shape and function over time when environmental variables change, such as temperature, light, electricity, and water. 4D printing technologies and materials have advanced rapidly in the last few years. As per market reports, the 4D printing sector will be worth about USD 313.1 million by 2025. The report attributes this exponential rise in the market to the high demand for 4D materials in the military, defense, aerospace, and healthcare industries. This study introduces the design and manufacturing method of a 4D printed twisting actuator with Shape Memory Alloy (SMA) integrated with the static 3D printed flexible matrices. Test models were printed with an SMA called Nitinol embedded in the experimental part. Numerical simulation (ANSYS) was carried out to analyze the shape recovery rate of the twisted actuator. Subsequently, numerical results were validated with experimental results. Our investigation reveals that this twisting wrist actuator is lightweight, shows good repeatability, and is capable of full shape recovery in about 4 s with an input current supply of 28 Amp. With its unique twisting ability, this embedding mechanism can be leveraged in industrial production to make robotic arms more dynamic and versatile.

Electrothermally Actuated Semitransparent Shape Memory Polymer Composite with Application as a Wearable Touch Sensor.

A semitransparent shape memory polymer (SMP):silver nanowire (AgNW) composite is demonstrated to be capable of low-temperature actuation, thus making it attractive for wearable electronics applications that require intimate contact with the human body. We demonstrate that the SMP:AgNW composite has tunable electrical and optical transparency through variation of the AgNW loading and that the AgNW loading did not significantly change the mechanical behavior of the SMP. The SMP composite is also capable of electrical actuation through Joule heating, where applying a 4 V bias across the AgNWs resulted in full shape recovery. The SMP was found to have high strain sensitivity at both small (<1%) and large (over 10%) applied strain. The SMP could sense strains as low as 0.6% with a gauge factor of 8.2. The SMP composite was then utilized as a touch sensor, able to sense and differentiate tapping and pressing. Finally, the composite was applied as a wearable ring that was thermally actuated to conformably fit onto a finger as a touch sensor. The ring sensor was able to sense finger tapping, pressing, and bending with high signal-to-noise ratios. These results demonstrate that SMP:AgNW composites are a promising design approach for application in wearable electronics.

Evolution of electrical conductivity in semi‐interpenetrating polymer network of shape memory polyvinyl chloride and polyaniline

AbstractElectrically conductive semi‐interpenetrating polymer network (IPN) from shape memory polyvinyl chloride (PVC) and polyaniline (PANI) is realized. The mechanical properties and shape memory performance of semi‐IPN are slightly different from the original PVC. The distribution of PANI within PVC is found to be non‐uniform in the thickness direction. The electrical conductivity of the as‐fabricated sample at room temperature is around 4.5 × 10−2 S/cm. However, after heating, thermal strain results in significant drop in electrical conductivity. Programming remarkably reduces the electrical conductivity as well. A higher programming temperature and higher programming strain result in more reduction. Subsequent heating for shape recovery causes further reduction in electrical conductivity, despite nearly full shape recovery is achieved. Doping (dedoping and redoping) is confirmed not the major player, but microgaps/fracture in PANI chains during stretching in programming and heating for shape recovery.

Microstructure, martensitic transformation and excellent shape memory effect of Ga-alloyed Cu–Al–Mn–Fe shape-memory single crystal

A Cu–10Al–6Mn–3Fe–4Ga (wt.%) single crystal was simply prepared, and its microstructure, reversible martensitic transformation, mechanical and SME properties were investigated. The results show that this single crystal consists of dominant 2H martensite retained L2 1 parent and fine Fe-rich nanoparticles. Its reversible martensitic transformation temperatures are respectively 313 K ( M s ), 299 K ( M f ), 339 K ( A s ), and 354 K ( A f ), which are suitable for practical applications. A large stress platform with a strain of approximately 8% was associated with the reorientation of existing martensite and stabilization of stress-induced martensite. Furthermore, full shape recovery characteristics are obtained all the time while changing the pre-strains from 6% to 11%. The maximum shape memory effect is up to 9.2% with a 100% shape recovery rate.

Molecular movements of trehalose inside a single network enabling a rapidly-recoverable tough hydrogel

ABSTRACT It remains a challenge to achieve rapidly recoverable hydrogels by molecular hydrogen-bonding interaction because of its slow interaction kinetics. This work for the first time reports a trehalose (Tre)-based molecular movement mechanism inside a single network of polyacrylamide (PAM) that accelerates the kinetics of hydrogen-bonding interaction, and thereby endows the hydrogel with high toughness and rapid shape and mechanical recoverability. The resultant PAM@Tre hydrogel is capable of full shape recovery after 10,000 loading/unloading cycles at a strain of 500%. Even after being stretched at a strain of 2500%, it can recover to its original shape within 10 seconds. Moreover, the molecular movement of trehalose also endows the PAM@Tre hydrogel with fracture energy and toughness as high as ~9000 J m–2 and ~1600 kJ m–3, respectively, leading to strong resistance to both static and dynamic piercing. The PAM@Tre hydrogel is thus believed to have enormous potentials in protection devices, bionic skin, soft actuator, and stretchable electronics.

Facile template preparation of novel electroactive scaffold composed of polypyrrole-coated poly(glycerol-sebacate-urethane) for tissue engineering applications

• Porous poly(glycerol sebacate urethane)-based scaffolds prepared. • Loading of ZnO nanoparticles and in-situ polymerization of pyrrole in the scaffolds performed. • Electrical conductivity (4 ∼ 7 × 10 -2 S/cm) was obtained for pyrrole containing scaffolds. • ZnO particles could effectively suppress bacterial growth. • The scaffolds were elastic with full shape-retention ability under cyclic loading. Poly(glycerol-sebacate-urethane) (PGS-U) is an attractive candidate as a super-elastic and biocompatible scaffold for inserting nanoparticles and polymers with a straightforward synthesis. Herein, a series of PGS-U scaffolds with various crosslink densities was prepared for subsequent polypyrrole (PPy) polymerization. The in-situ polymerization of PPy was employed to deposit the PPy particles throughout the scaffolds, and the continuous electrically conductive pathways were built within the scaffolds. Moreover, due to their favorable mechanical and anti-bacterial properties, zinc oxide (ZnO) nanoparticles were embedded within the scaffold. The composition of the scaffolds was confirmed by different characterization techniques, including FTIR, FE-SEM, and EDX. Static and cyclic compression tests were conducted to evaluate the mechanical performance of scaffolds under dry and hydrated conditions. All scaffolds presented high structural stability and full shape recovery after releasing the load. They were thermally stable up to at least 200 °C. The addition of PPy boosted the electrical conductivity, and the inclusion of ZnO particles improved the surface hydrophilicity and anti-bacterial behavior of the scaffolds. Altogether, this study suggests the further developments of these nanocomposites as satisfactory electrically conductive scaffolds for tissue engineering applications.

Phase equilibria of Co-V-Ga ternary system and composition dependence of martensitic transformation characteristics in Co2VGa Heusler alloys

The phase equilibria at 1000 °C of the Co-V-Ga ternary system and composition dependence of martensitic transformation characteristics in Co2VGa Heusler alloys are investigated. Firstly, the results show that six three-phase regions and three ternary compounds are identified in the isothermal section. The CoVGa compound is discovered with a composition range of 43.0–46.2 at.% V and 27.3–31.4 at.% Ga. Secondly, according to the obtained phase equilibria, the martensitic transformation characteristics depending on composition for those alloys that locate the Co2VGa Heusler phase region are investigated. The results confirm that the Co2VGa Heusler phase exists in a wide composition range (about 39.7–66.5 at.% Co, 4.8–40.0 at.% V, and 15.0–31.2 at.% Ga). Furthermore, the critical compositions with the martensitic transformation temperature close to room temperature are determined, in which those alloys (50.8–58.5 at.% Co, 20.2–33.0 at.% V, and 15.2–21.5 at.% Ga) show the martensite structure at room temperature. Thirdly, based on the phase equilibria and the composition dependence of martensitic transformation characteristics, a Co55V24Ga21 shape memory alloy is designed. Its microstructure, reversible martensitic transformation, and shape memory effect are investigated. Full shape recovery of about 2.6% is obtained. The present obtained results may provide useful information for composition designation and the estimation of martensitic transformation temperatures of Co-V-Ga Heusler shape memory alloys.

One-step fabrication of chitosan sponge and its potential for rapid hemostasis in deep trauma

In this paper, a facile and efficient preparation strategy for a porous and hydrophilic chitosan sponge is demonstrated, combining a surfactant and a pore-foaming agent. The resulting chitosan sponge possesses an interconnected pore structure and soft texture, exhibits fast water absorption rate and capacity, and the compressed sponge can achieve full shape recovery 5 s after absorbing water. Moreover, our process removes the residual acid commonly found in chitosan sponges prepared by the acid method. In addition, the results demonstrate the useful characteristics of our chitosan sponge, in terms of its contribution to improved blood coagulation, together with its compression strength and biocompatibility. It also demonstrates effective antibacterial properties in relation to both Escherichia coli and Staphylococcus aureus. Further testing via animal experimentation reveals that rapid hemostasis can be achieved within 50 s using our chitosan sponge.

Influence of Silver Addition on Structure, Martensite Transformations and Mechanical Properties of TiNi-Ag Alloy Wires for Biomedical Application.

The microstructural and functional behavior of TiNi-based wires with a silver content of 0–1.5 at.% was evaluated. The concentration range for Ag doping determined for the TiNi wires with potential for the medical industry was 0–0.2 at.%. Microstructure analysis of TiNi wires with different silver contents at room temperature indicated a multiphase structural state. Various internal structures with tangled grain boundaries were formed by intense plastic deformation. The nanocrystalline structure and phase state of wire with the minimum silver content (0.1 at.% Ag) provide full shape recovery, the greatest reversible strain, and optimal strength and ductility. TiNi ingots with a high Ag content (0.5–1.5 at.%) cracked under minimum load due to excess silver that crystallized along the grain boundaries and broke cohesion bonds between the TiNi grains.

Role of β(FeAl) nanoparticles in abnormal grain growth in the annealing of cast Cu-Al-Mn-Fe shape memory alloys

In this study, the low-cost production of Cu-Al-Mn-Fe shape memory alloy single crystals exceeding 46 mm by abnormal grain growth was realized only through annealing their cast alloys. The results show that the misorientation formed during annealing may be responsible for such abnormal grain growth process. It was confirmed that this misorientation resulted from the dissolution of bcc β(FeAl) nanoparticles during heat treatment at a sufficiently temperature of approximately 1173 K. The rate of migration of the abnormal grain boundary was experimentally measured to be approximately 9.3 × 10-5 m s-1 within 2 min of the commencement of abnormal grain growth. Additionally, the range of composition of the alloys that can lead to abnormal grain growth was determined. When the Cu-13.0Al-6.5Mn-3.2Fe single crystal close to the [100] direction was deformed to a pre-strain of 12%, full shape recovery happened without any residual strain. At that time, the superelastic strain was approximately 9%. Such a superelastic characteristic remained nearly constant over 50 cycles, showing excellent fatigue resistance. The superelastic properties of the present Cu-13.0Al-6.5Mn-3.2Fe single crystal are compared to those of commercial Ni-Ti-based shape memory alloys. Therefore, it can be considered as a new kind of superelastic material having practical applications. The obtained results should be of great significance in the development of Cu-based shape memory alloys. Furthermore, it is expected that a similar microstructure can be designed for the production of more metallic single crystals.

Excellent shape recovery characteristics of Cu-Al-Mn-Fe shape memory single crystal

Shape memory alloys can recover the deformed shape due to their superelasticity or shape memory effect. In this study, a novel Cu-Al-Mn-Fe shape memory single crystal is reported. The results show that it has excellent superelasticity and shape memory effect simultaneously when deformed at room temperature, as well as tunably wide response temperature range with near-zero interval of reverse phase transformation. 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. This class of Cu-Al-Mn-Fe alloy may be used as both superelastic materials, and shape memory materials with wide working temperature range as high-sensitive detector, driver or sensor.

Microstructure, martensitic transformation and shape memory effect of polycrystalline Cu-Al-Mn-Fe alloys

In this study, two Cu-Al-Mn-Fe polycrystalline alloys were prepared, and their microstructure, reversible martensitic transformation, mechanical properties and shape memory effects were investigated. The results show that the reversible martensitic transformation temperatures of the studied alloys are between room temperature and 373 K, which are suitable for practical applications. Two typed martensites of 18R and 2H coexist both in two alloys. The bcc β (FeAl) nanoparticles are Fe-rich, Mn-rich and Cu-poor, whereas the martensite is Cu-rich, Fe-poor and Mn-poor. The size of nanoparticles ranges from tens to hundreds of nanometers. Full shape recovery property is displayed in Cu-12.9Al-4.5Mn-2.6Fe alloy all the time while applying different deformation from 5% to 8%. The maximum recoverable strain is up to 4.4% with a recovery rate of 100%.

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.

Additive manufacturing with a flex activated mechanophore for nondestructive assessment of mechanochemical reactivity in complex object geometries

We used digital light processing additive manufacturing (DLP-AM) to produce mechanochemically responsive test specimens from custom photoresin formulations, wherein designer, flex activated mechanophores enable quantitative assessment of the total mechanophore activation in the specimen. The manufactured object geometries included an octet truss unit cell, a gyroid lattice, and an “8D cubic lattice”. The mechanophore activation in each test specimen was measured as a function of uniaxial compressive strain applied to the structure. Full shape recovery after compression was exhibited in all cases. These proof-of-concept results signify the potential to use flex activated mechanophore for nondestructive, quantitative volumetric assessment of mechanochemistry in test specimens with complex geometries. Additionally, the integration of DLP-AM with flex activated mechanophore build materials enabled the creation of customizable, three-dimensional mechanochemically responsive parts that exhibit small molecule release without undergoing irreversible deformation or fracture.

Shape memory polymer composite coatings with enhanced mechanical and antimicrobial properties

PurposeThis paper aims to exploit shape memory polymer (SMP) composite as multifunctional coatings for protecting substrates from surface wear and bacterial. The efficiency of added nano or micro-sized particles in enhancing the properties of SMP was investigated. This study also attempts to use a low-cost and effective spraying approach to fabricate the coatings. The coatings are expected to have good conformability with the substrate and deliver multi-functional performance, such as wrinkle free, wear resistance, thermal stability and antimicrobial property.Design/methodology/approachHigh-performance SMP composite coatings or thin films were fabricated by a home-made continuous spray-deposition system. The morphologies of the coatings were studied using the scanning electron microscope and the transmission electron microscope. The abrasion properties were evaluated by Taber Abraser test, and thermo-gravimetric analysis was carried out to investigate the thermal properties of prepared composites. The antimicrobial property was determined by the inhibition zone method using E. coli. The thermally responsive shape memory effect of the resulting composites was also characterized.FindingsThe morphology analysis indicated that the nanoclay was distributed on the surface of the coating which resulted in a significant improvement of the wear property. The wear resistance of the coatings with nanoclay was improved as much as 40 per cent compared with that of the control sample. The thermo-gravimetric analysis revealed that the weight loss rate of composites with nanoclay was dropped over 40 per cent. The SMP coating with zinc oxide (ZnO) showed excellent antimicrobial effect. The shape recovery effect of SMP/nanoclay and SMP/ZnO composites can be triggered by external heating and the composites can reach a full shape recovery within 60 s.Research limitations/implicationsThis study proposed a continuous spray-deposition fabrication of SMP composite coatings, which provides a new avenue to prepare novel multi-functional coatings with low cost.Originality/valueMost studies have emphasized on the sole property of SMP composites. Herein, a novel SMP composite coating which could deliver multi-functionality such as wrinkle free, wear resistance, thermal stability and antimicrobial property was proposed.