Shape Recovery Characteristics Research Articles

Additive-free Absorbable Keratin Sponge With Procoagulant Activity for Noncompressible Hemostasis.

The development of a natural, additive-free, absorbable sponge with procoagulant activity for noncompressible hemostasis remains a challenging task. In this study, we extracted high molecular weight keratin (HK) from human hair and transformed it into a hemostatic sponge with a well-interconnected pore structure using a foaming technique, freeze-drying, and oxidation cross-linking. By controlling the cross-linking degree, the resulting sponge demonstrated excellent liquid absorption ability, shape recovery characteristics, and robust mechanical properties. The HK10 sponge exhibited rapid liquid absorption, expanding up to 600% within 5 s. Moreover, the HK sponge showed superior platelet activation and blood cell adhesion capabilities. In SD rat liver defect models, the sponges demonstrated excellent hemostatic performance by sealing the wound and expediting coagulation, reducing the hemostatic time from 825 to 297 s. Furthermore, HK sponges have excellent biosafety, positioning them as a promising absorbable sponge with the potential for the treatment of noncompressible hemostasis.

4D printing of lattice structures to test their behavior by repetitive shape processing cycles

This study thoroughly investigated the shape memory effects of 4D printed lattice structures influenced by repetitive shape processing cycles and materials variability. The structures were fabricated by an amorphous and semicrystalline type shape memory material (SMP) and subjected to time-temperature-based thermomechanical memory cycles. Shape programming and recovery characteristics for 4D printing were done inside an environmental chamber at a loading rate of 2 mm. min−1. The shape memory effects driven by SMP’s viscoelastic behavior and performance factors were studied by stress-free strain recovery experiments upon the interaction of thermal stimuli. The stress-free strain recovery analysis expressed, that the influence of repetitive cycles was exceptional and significant for both materials. Extensive investigation on shape memory reactive strain components (i.e., programming strain, residual strain, and thermal strain) reflected, with the increasing number of cycles, the shape recovery ratios of the first to fourth cycles increased from 82 → 100% of amorphous and 79 → 95% of semicrystalline SMP and then tend to stable thereafter. Contrarily, the shape fixity ratios of semicrystalline structures have shown a decreased tendency during the consecutive cycles from 100 → 80%. The successful execution of data-oriented shape processing cycles enhanced the potential of SMP-based lattice structures for their monotonous applications as intelligent devices. The time and temperature-dependent shape memory characteristics of repetitive cycles presented in this study are advantageous to model the viscoelastic behavior of such artful structures.

4D Printing of novel poly(ethylene-vinyl acetate) / poly(butyl methacrylate-co-isobutyl methacrylate) shape memory polymer blends

4D printing is a technology that combines additive manufacturing with shape memory polymers, aiming to enhance the functionality of 3D printed structures. Filaments made from thermoplastic polymers are commonly used in Fused Deposition Modeling (FDM), which is one of the most prevalent types of 3D printing. Here, novel heat-responsive shape memory polymer blends were produced from ethylene-vinyl acetate copolymer (EVA) and poly(butyl methacrylate-co-isobutyl metacrylate) polymers. The effect of blend composition on the morphological, thermal, mechanical, and shape memory properties was investigated. The blend (60E-40B) containing 60 % by weight EVA and 40 % by weight BMA-co-iBMA exhibited optimum shape memory performance with a shape fixing (Rf) of 94.1 % and a shape recovery (Rr) of 94.5 % at a shape transition temperature (Ttrans) of 55 °C. Filament for the 60E-40B blend was produced for FDM type 3D printers, and 4D parts for various applications were printed using this filament. These 4D printed parts, designed for robotic grippers, self-assemble rivets, movable cog-wheel teeth, surface traps, and finger splints, displayed shape recovery characteristics in both hot oven and hot water environments.

Impact of CoFe2O4 Magnetic Nanoparticles on the Physical and Mechanical Properties and Shape Memory Effect of Polylactide

The acceleration in advancements of smart materials and non-contact controlled devices in the field of 4D printing is facilitated by the use of magnetically responsive shape memory polymer (SMP) composites. This study is dedicated to the development of promising shape memory materials based on polylactic acid (PLA) and cobalt ferrite (CoFe2O4) nanoparticles. The activation of the shape memory effect (SME) in magnetic nanoparticle composites was achieved by applying a high-frequency alternating magnetic field (HFAMF). The PLA/CoFe2O4 composites exhibited a remarkable shape recovery ratio (>84%) and underwent rapid heating when exposed to HFAMF. The interaction of these composites with mouse adipose-derived mesenchymal stem cells demonstrated adequate cytocompatibility. The rapid magnetosensitive behavior and high shape recovery characteristics of PLA/CoFe2O4 composites make them promising candidates for biomedical 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.

Development of Multiwalled Carbon Nanotubes/Halloysite Nanotubes Reinforced Thermal Responsive Shape Memory Polymer Nanocomposites for Enhanced Mechanical and Shape Recovery Characteristics in 4D Printing Applications.

The mechanical and shape-recovery characteristics of 4D-printed thermally responsive shape-memory polyurethane (SMPU) reinforced with two types of reinforcements, multiwalled carbon nanotubes (MWCNTs) and Halloysite nanotubes (HNTs), are investigated in the present study. Three weight percentages of reinforcements (0, 0.5, and 1) in the SMPU matrix are considered, and the required composite specimens are obtained with 3D printing. Further, for the first time, the present study investigates the flexural test for multiple cycles to understand the 4D-printed specimens' flexural behavior variation after shape recovery. The 1 wt% HNTS-reinforced specimen yielded higher tensile, flexural, and impact strengths. On the other hand, 1 wt% MWCNT-reinforced specimens exhibited quick shape recovery. Overall, enhanced mechanical properties were observed with HNT reinforcements, and a faster shape recovery was observed with MWCNT reinforcements. Further, the results are promising for the use of 4D-printed shape-memory polymer nanocomposites for repeated cycles even after a large bending deformation.

Mechanical and Shape Recovery Characterization of MWCNTs/HNTs-Reinforced Thermal-Responsive Shape-Memory Polymer Nanocomposites.

Mechanical and shape recovery characteristics of thermal-responsive shape-memory polyurethane (SMPU) reinforced with two types of reinforcements, multiwalled carbon nanotubes (MWCNTs) and halloysite nanotubes (HNTs), were studied in the present research work. Three weight percentages of reinforcement (0, 0.5 and 1%) in the SMPU matrix were considered, and the required composite specimens were obtained through injection moulding. Tensile, flexural, impact and shape recovery behaviours were studied experimentally. Further, flexural tests were performed for multiple cycles to understand the specimens' flexural strength variation after shape recovery. The concentration of both reinforcements (MWCNTs and HNTs) considered in the present study significantly improved mechanical properties and shape recovery.

On stress- and strain-temperature behavior of titanium nickelide with various grain/subgrain size

• The effect of grain/subgrain size of TiNi alloy on martensitic transformation and stress-temperature behavior is revealed. • The effect of the grain size on plasticity is ambiguous and depends on test temperature. • The phenomena of a two-stage shape recovery under heating is revealed. • Variation of pre-strain value permits the precise control of the finish temperature of shape recovery in a wide range. The effect of grain/subgrain size in the range of 0.13−9.0 μm on mechanical and shape recovery characteristics of Ti−50.8 at.%Ni alloy was studied at test temperatures from 77 K to 373 K using tensile and bending modes. The revealed regularities can be used for the precise control of the studied properties including applied tasks.

Thermoforming Characteristics of PLA/TPU Multi-Material Specimens Fabricated with Fused Deposition Modelling under Different Temperatures.

Multi-material products are required in fused deposition modelling (FDM) to meet a desired specification such as a rigid structure with soft material for impact protection. This paper focuses on the thermoformability and shape recovery characteristics of three-dimensional (3D)-printed multi-material specimens under different thermoforming temperatures. The multi-material specimens consist of polylactic acid (PLA) and thermoplastic polyurethane (TPU). The PLA/TPU specimens were prepared by depositing the TPU component on top of the PLA component using a fused deposition modelling (FDM) machine. Simple thermoforming tests were proposed, where the specimens were bent under load and molded into a circular shape at different thermoforming temperatures. The bent specimens were then reheated at 60 °C to evaluate their shape memory ability. The test results were quantified into apparent bending modulus and shape recovery percentage. The PLA/TPU specimens showed a better apparent bending modulus of 143 MPa than a PLA specimen at a temperature between 60 °C to 90 °C. However, only the PLA/TPU specimens being thermoformed into a circular shape at 100 °C or greater showed good shape retention accuracy and interfacial surface bonding. The PLA/TPU specimens that were thermoformed at 60 °C to 90 °C showed reasonable shape memory of about 60% recovery when reheated. Finally, suitable thermoforming temperatures for thermoforming PLA/TPU specimens were suggested based on design needs.

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.

NIR Photothermal-Responsive Shape Memory Polyurethane with Protein-Inspired Aggregated Chymotrypsin-Sensitive Degradable Domains.

Biodegradable shape memory polymers are promising biomaterials for stents used in minimally invasive surgical procedures such as intestinal stents. Herein, a series of biodegradable shape memory polyurethanes (SMPUs) containing a novel phenylalanine-derived chain extender (PHP) are synthesized. Inspired by the fact that the function of biomacromolecules such as proteins is rich and varied because of the multiple combinations of the amino acid in highly evolved biosystems, this study finds that the sequence distribution of PHP in SMPU will also have a great influence on the phase structure and degradation behavior, especially the difference of surface morphology caused by degradation. Considering that the transition temperature (Ttrans ) of SMPU obtained is higher than physiological temperature, oxidized carbon black (OCB) with the ability of photothermal conversion is introduced into SMPU, which can not only endow SMPU with near-infrared response shape recovery characteristics, but also enhance phase separation degree and mechanical properties of them. SMPU/OCB composites show excellent shape memory effect and rapid photothermal response, and they can be degraded by chymotrypsin with an adjustable degradation rate. These SMPU/OCB composites show broad potential for application as intestinal stents.

Magnetron Sputtering of Au-Based Alloys on NiTi Elements: Surface Investigation for New Products in SMA-Based Fashion and Luxury Accessories and Watchmaking

A novel approach for the deposition of Au-based coatings on NiTi components was proposed to give rise to innovative SMA-based products for the fashion, luxury, and watchmaking fields. Different Au-Cu and Au-Ag-Cu alloys (with confidential compositions within the color designations 2N, 4N, and 5N) were deposited by magnetron sputtering on superelastic and shape-memory NiTi ribbons. After preliminary morphological and microstructural characterizations, the influence of the film deposition on the functional, mechanical, and tribological behavior was deeply investigated. The macroscopic mechanical properties, including the damping, superelastic, and shape recovery characteristics, were not affected since the behavior upon both small and severe deformations was unchanged and the coatings were not damaged. Indeed, both the film adhesion and the precious aspect were maintained. Furthermore, a more detailed surface characterization, through nanoindentation, tribocorrosion, and scratch and wear tests, was performed. This experimental investigation evidenced the ductile behavior of the Au-based films and their good adhesion on NiTi substrates. Moreover, the coatings exhibited a good wear resistance, both in dry conditions and simulated body fluids, which proved to be suitable for fashion and watchmaking fields. Despite slight differences being observed within the films’ responses, all of them could be considered suitable and interesting for the design of smart luxury accessories, proving that the chosen deposition process is sound and reliable for these applications.

Comparison of binary, ternary and quaternary shape memory alloys and techniques to enhance their mechanical properties: A focused review

Shape memory alloys (SMAs) are smart materials having an ability to remember the original shape when deformed at the temperatures below martensite finish (Mf), which can be recovered up to certain extent by heating these alloys to temperatures above austenite finish (Af). SMAs find wide applicability in engineering sectors including automotive, aerospace, and biomedical. Prior to fabrication of any sensors and actuators using SMA, it is recommended to have an extensive simulation study that requires material properties as a prime input to the software. Scattered literature on SMA’s material properties make this challenging for new researchers. This paper presents a review of binary, ternary and quaternary alloys exhibit shape memory effect and their comparison in terms of transformation temperatures and mechanical properties. It also comments on effects in their properties due to addition of ternary and quaternary elements. Impact of thermomechanical treatments to enhance the mechanical properties and shape recovery characteristics of SMAs is reviewed. The study concludes with signifying the use of processing techniques in enhancing mechanical properties of SMAs for their utilization in possible sensing applications.

Shape Recovery Characteristics of SMP Lattice Structures Fabricated by FDM

Shape memory polymers (SMPs) have unique properties and can be formed into arbitrary shapes using an FDM 3D printer. In this study, SMP lattice structures simulating foam materials were fabricated using an FDM 3D printer, with the goal of developing SMP lattice structures with recovery equivalent to that of foam materials. The main results obtained are summarized as follows. (1) Specimens at a nozzle temperature of 473 K were more susceptible to significant deformation by heat treatment than by shape recovery testing, and in addition, specimens prepared with an infill rate of 20% were deformed by more than 10% by heat treatment. (2) Increasing the nozzle temperature increases the crystallinity and reduces the deformation rate during heat treatment. However, since molding is insufficient and recovery is small, it is necessary to increase the crystallinity by another method.

Enhancement of Tensile Strength and Shape Recovery Characteristics of Grafted Polyurethane Using Melamine as a Crosslinking Agent

Enhancement of Tensile Strength and Shape Recovery Characteristics of Grafted Polyurethane Using Melamine as a Crosslinking Agent

Microstructure evolution and strain recovery characteristic of proton-irradiated Ti-rich NiTi thin films

The effect of 120 ​keV proton irradiation with different fluences on the phase constitution, microstructure, and shape recovery characteristics of Ni-51.4 ​at.%Ti shape memory alloy thin films was systematically investigated. The results showed that the proton irradiation induced the formation of a multiple-layer structure at the surface of NiTi thin film. Meanwhile, the hybrid defects such as vacancies, dislocations, and nano-scale precipitates were observed in the irradiation layer. The transition temperature and shape recovery strain decreased gradually with the increasing irradiation fluence, which can be attributed to the formation of the multilayer structure and the generation of irradiation-induced defects.

Role of Nickel Content in One-Way and Two-Way Shape Recovery in Binary Ti-Ni Alloys

The shape recovery characteristics of titanium nickelide with an Ni content of 50.0 at % and 50.7 at % were studied in a wide range of structures obtained as a result of cold drawing with an accumulated true strain of e = 0.52 and subsequent annealing in the 250 to 700 °C temperature range. Shape memory effect (SME) inducing was carried out by bending using a non-isothermal loading mode, which made it possible to reveal implementing elastic strain in the equiatomic alloy up to 12% and thereby increase the total shape recovery by a factor of 1.5. The obtained results prove that the Ni content strongly affects the value and specific features of changes of the shape recovery characteristics with loading strain as well as grain/subgrain size. In equiatomic alloy, the total recovery strain manifests its maximum of 13.5–15% and the recovery strain of 9% at a loading strain range of 12 to 14%. In Ni-rich alloy, the total recovery strain manifests its maximum of 20% and the recovery strain of 14% at a loading strain range of 15 to 21%. The maximum two-way SME value correlates with the residual strain in both alloys and reaches its maximum of 3.0% in a material with a recrystallized structure. Varying the loading strain value under bending in the 11 to 21% range allows regulation of the temperature of shape recovery in Ni-rich alloy in the 45 to 80 °C range.

Deformation Behavior, Structure, and Properties of an Aging Ti-Ni Shape Memory Alloy after Compression Deformation in a Wide Temperature Range

The deformation behavior, microstructure, phase composition, and mechanical and functional properties of Ti-50.9 at.%Ni shape memory alloy during uniaxial compression in the temperature range from 25°C to 1000°C have been analyzed and are discussed herein. It was found that the deformation temperature of 300°C marked a boundary for the transition from the low- to high-temperature type of flow curves; achievement of the steady-state deformation stage was observed across a wide range of deformation temperatures. Following comprehensive analysis of the obtained data, the temperature ranges of the dynamic processes of recovery, polygonization, and recrystallization of the Ti-50.9 at.%Ni alloy were determined. Deformation in the range of dynamic polygonization is accompanied by not only the formation of B2-austenite and R-phase, but also the precipitation of fine Ti3Ni4 particles during deformational aging. The highest shape recovery characteristics were obtained after deformation of the Ti-50.9 at.%Ni alloy in the temperature range from 300°C to 600°C.

A relative study of the effect of static and dynamic vulcanization upon shape memory nature of thermally actuated peroxide crosslinked polyolefinic blends

AbstractThermally actuated peroxide crosslinked shape memory polyolefinic blends of EOC and EPDM has been developed. Effect of static and dynamic vulcanization process on the shape memory character has been pursued in detail. Shape memory properties study at 60°C reveals that statically vulcanized blend and dynamically vulcanized blend are superior in terms of shape fixity character and shape recovery behavior, respectively. Breakage of lower percentage of crystalline structure gives higher percentage of shape fixity for the statically vulcanized blend. In a parallel way, statically vulcanized blend shows better stress–strain properties also. On the other hand, higher degree of crosslinked network structure results higher shape recovery percentage for the dynamically vulcanized blend. Similar to shape recovery characteristics, dynamically vulcanized blend shows better thermal stability and higher percentage of gel content.

Biomass-Derived, Water-Induced Self-Recoverable Composite Aerogels with Robust Superwettability for Water Treatment.

Polluted water is a worldwide problem; therefore, effective separation of oil/water and removal of dyes, organic micropollutants, and heavy metals in wastewater are the need of the hour. Herein, hydrophilic β-cyclodextrin-grafted carboxymethyl cellulose, biodegradable polyvinyl alcohol, and chitosan were used as main raw materials to construct a multifunctional aerogel framework by simple sol-gel and directional freeze-drying methods. Featuring intrinsic superamphiphilic wettability in air, robust superoleophobic wettability underwater, and excellent shape-recovery characteristics, the biomass-derived aerogel presents durable oil/water separation even after 10 cycles. The aerogels possess prominent adsorption capacity for methyl blue, 1-naphthylamine, and Cu2+, which was as high as 121.55 mg/g, 33.96 mg/g, and 122.6 mg/g, respectively. In addition, various pollutant mixtures could be effectively adsorbed by the aerogel at the same time with the adsorption capacity of 121.75 mg/g for methyl blue, 0.97 mg/g for bisphenol A, and 20.11 mg/g for Cu2+.