Shape Memory Ability Research Articles

Shape Memory Polyurethane Foams With Tunable Mechanical Properties and Radiation Tolerance for Breast Repair and Reconstruction.

This study developed a shape memory polyurethane foam (SM-PUF) with tunable mechanical properties and exceptional radiation tolerance for potentially implanting tissue defects after mastectomy. The PUFs were synthesized via an insitu foaming strategy using water as a foaming agent, incorporating 4,4'-diphenylmethane diisocyanate (MDI) as the rigid segment and both polyoxytetramethylene glycol and polycaprolactone as the soft segment. The resultant PUFs possess an open-cell structure with a pore size of 30 ~ 800 μm, which achieves a compressive stress of 0.04 MPa under 70% compression strain and a tensile elongation of 667.9%. PUFs exhibit body temperature (37°C)-responsive softening and shape memory abilities, with recovery and fixation ratios reaching 88% and 98%, respectively. It was verified that PUFs can resist 40 Gy radiotherapy without changing their mechanical properties and biocompatibility. This study introduces an innovative approach to produce customizable foam for the reconstruction of implant prostheses for the breast.

Sustainable synthesis of PVA@ZnO:Ga3+ nanocomposite films for UV shielding, food preservation, shape memory and anti-counterfeiting applications

Herein, we successfully fabricated transparent and highly flexible polyvinyl alcohol@ZnO:Ga3+ (PVA@ZnO:Ga3+) nanocomposites (NCs) films by simple solution casting method. Upon excitation at 266 nm, both the ZnO:Ga3+ nanoparticles (NPs) and the PVA@ZnO:Ga3+ NCs exhibit a prominent peak at 385 nm and a broad peak around 550 nm. The optimized PVA@ZnO:Ga3+ NCs demonstrated the most effective ultra violet (UV) blockage across the UV-A (99.99 %), UV-B (100 %) and UV-C (100 %) and high energy blue light HEBL (94.63 %). However, PVA alone absorbed <25 % of the light in all UV regions. Packaging of fresh cherry fruit with PVA@ZnO:Ga3+ (0.1 wt%) NCs enhanced the shelf-life up-to 15 days of storage under room temperature. These innovative NCs packaging films could provide a green, environment-friendly and antimicrobial system to combat the shorter shelf life of cherry fruit. The optimized NCs exhibited excellent shape recovery under pH conditions of 1, 7 and 13 and at a temperature of 70 °C, returning to its original shape within 120, 150, 160 and 6 sec, respectively. This emphasizes the NCs remarkable water-induced shape memory ability. Further, PVA@ZnO:Ga3+ NCs security ink offers strong anti-counterfeiting (AC) properties with UV luminescence and stability against UV exposure, aging and temperature effect. It adheres well to various substrates, ensuring long-term durability and resistance to replication. Overall, the results clearly show that ZnO:Ga3+ NPs hold great promise for applications in AC technology, UV blocking and the food packaging industry, thanks to their low cost, biocompatibility, flexibility and transparency.

Hofmeister effect driven dynamic-bond cross-linked dialdehyde xylan hydrogels with rapid response and robust mechanical properties for expanding stent

The biomedical field urgently needs for programmable stent materials with nontoxic, autonomous self-healing, injectability, and suitable mechanical strength, especially self-expanding characteristics. However, such materials are still lacking. Herein, based on gelatin and dialdehyde-functionalized xylan, we synthesized 3D-printable, autonomous, self-healing, and mechanically robust hydrogels with a reversible Schiff base crosslink network. The hydrogels exhibited excellent mechanical properties and automatic healing properties at room temperature. The solid mechanical properties originate from the Schiff base, hydrogen bonding interactions, and xylan nanoparticle reinforcement of the polymer networks. As a proof of concept, the Hofmeister effect enabled the hydrogel to contract in highly concentrated salt solutions. In contrast, the same hydrogel expanded and relaxed in dilute salt solutions (quick response within 10 s), showing ionic stimulus-response and excellent shape memory characteristics, which demonstrated that the prepared hydrogel could be used as self-expanding artificial vascular stents. In particular, good biocompatibility was confirmed by cytotoxicity and compatibility tests, and ex vivo arterial experiments further indicated the feasibility of these artificial vascular scaffolds (the expansion force reached 1.51 N). Combined with its ionic stimuli-responsive shape memory ability, the strong mechanical, self-healing, 3D-printable, and biocompatibility properties make this hydrogel a promising material for artificial stents in various biomedical applications.

High‐performance shape memory characteristics by integrating urea linkages into the polyurethane elastomer

AbstractShape memory polymers have been widely researched to develop multifunctional materials that respond smartly to external stimulations and programmed signals. Among them, shape memory polyurethane (SMPU) is drawing great attention owing to its highly tunable properties and ease of integrating new functions. However, the effect of urea bonds on SMPU elastomers has rarely been investigated because of the extreme reactivity of amine crosslinkers. In this study, we used diethanolamine (DEOA), which contains a secondary amine, as the crosslinker for SMPU synthesis. Unlike other crosslinkers containing primary amines, they can form urea bonds in a more gentle manner. The urea bonds reinforce the intermolecular interactions between the hard segments with strong hydrogen bonding, thus increasing the phase separation and degree of crystallization. Consequently, the urea‐containing SMPU exhibits improved mechanical strength and shape memory abilities for both fixing and recovery. Moreover, the transcarbamoylation reaction, which enables the reconfiguration of the original shape, is observed. The introduction of the urea bonds into the SMPU elastomer can be beneficial in achieving flawless shape memory performances in various sensitive applications.

Durable semi-interpenetrating polymer network containing dynamic boroxine bonds for multi-shape manipulated deformation

Shape-shifting materials with multiple shape manipulation, integrated with durability, shape reconfiguration, shape memory, and reversible deformation, are in high demand for applications in soft robotics, electrical devices, and other fields, but remain a significant technical challenge. In this study, we present a straightforward approach to develop a semi-interpenetrating polymer network (named PVP-VPBA-PEGDMA) crosslinked with dynamic boroxine bonds to address these challenges. The typical PVP-VPBA2-PEGDMA0.2 exhibits high mechanical strength of 38.5 MPa, exceptional self-healing capability (with up to 89.4 % efficiency), and recyclability, ensuring remarkable durability during shape-changing process. Notably, the PVP-VPBA-PEGDMA can be programmatically transformed from 2D sheets into a variety of 3D shapes using humidity-induced solid-state plasticity, which is facilitated by humidity-sensitive dynamic boroxine bonds. The PVP-VPBA-PEGDMA can be folded like paper through origami techniques, and maintain permanent shape configurations, highly suitable for complex shape morphing applications. Moreover, the PVP-VPBA-PEGDMA, in their temporary geometries, can power a model car using shape memory, demonstrating substantial actuation ability and mechanical performance. Leveraging the asymmetric humidity-triggered behavior of the PVP-VPBA-PEGDMA, various functional humidity-responsive devices have been developed, including a crawling robot, a hat, and a conveyor belt with wet sorting capability. Given the programmable shape reconfiguration, shape memory and reversible shape-changing ability of PVP-VPBA-PEGDMA, it opens up numerous potential applications in soft robotics, flexible electronic devices, and intelligent sensors.

Thermally-Activated Shape Memory Behavior of Biodegradable Blends Based on Plasticized PLA and Thermoplastic Starch.

Biodegradable blends based on plasticized poly(lactic acid) PLA and thermoplastic starch (TPS) have been obtained. The influence of the PLA plasticizer as a compatibility agent has been studied by using two different plasticizers such as neat oligomeric lactic acid (OLA) and functionalized with maleic acid (mOLA). In particular, the morphological, thermal, and mechanical properties have been studied as well as the shape memory ability of the melt-processed materials. Therefore, the influence of the interaction between different plasticizers and the PLA matrix as well as the compatibility between the two polymeric phases on the thermally-activated shape memory properties have been studied. It is very interesting to use the same additive able to act as both plasticizer and compatibilizer, decreasing the glass transition temperature of PLA to a temperature close to the physiological one, obtaining a material suitable for potential biomedical applications. In particular, we obtain that OLA-plasticized blend (oPLA/TPS) show very good thermally-activated capability at 45 °C and 50% deformation, while the blend obtained by using maleic OLA (moPLA/TPS) did not show shape memory behavior at 45 °C and 50% deformation. This fact is due to their morphological changes and the loss of two well-distinguished phases, one acting as fixed phase and the other one acting as switching phase to typically obtain shape memory response. Therefore, the thermally-activated shape memory results show that it is very important to make a balance between plasticizer and compatibilizer, considering the need of two well-established phases to obtain shape memory response.

A novel strategy for the design of cooperatively reinforced, shape-memory, recyclable ESO-based carbon fiber composites

To improve the poor performance of epoxidized soybean oil (ESO) thermosetting materials in preparing high-performance carbon fiber composites, we synthesized novel bio-based epoxy monomers using naringin (EN) as an epoxy monomer. EN's hydrogen bonding and benzopyrenone structure enhanced the crosslinking density, rigidity, bond shear strength, glass transition temperature (Tg), tensile and lap shear strength, and shape memory ability of ESO/MeHHPA/EN. The resulting carbon fiber composites had high tensile strength (349 MPa) and could be fully recovered using ethanolamine, with the recovered fibers maintaining almost 100% of the mechanical properties of the original sample. This study provides a new approach for fabricating multifunctional, high-performance, and recyclable ESO-based carbon fiber reinforced composites.

Selective near-infrared laser programming for shape-memory polymer–carbon nanotube composite material 4D printing

Abstract Light stimulation can realise the remote control of the deformation of the specific position of 4D printing structure. Shape-memory polymer–carbon nanotube (CNT) composite materials, with outstanding near-infrared photothermal conversion rate and shape-memory ability, is one type of the most popular light responsive smart materials. However, current studies focused on the photothermal effect and shape-memory applications of light-responsive shape-memory polymer composite (SMPC) sheet structures, and there is no research on the photothermal effect in the depth direction of light-responsive SMPC three-dimensional structures. Here, we prepared a UV curable, mechanically robust, and highly deformable shape-memory polymer (IBBA) as the matrix of light responsive SMPC. CNTs were added as photothermal conversion materials. We explore the photothermal effect of near-infrared laser on the surface and depth of IBBA–CNT composites cube. Shape-memory experiments show that different folded shapes can be obtained by selective near-infrared laser programming. Selective near-infrared laser programming three-dimensional movable type plate shows a programming application in depth direction of three-dimensional light-responsive intelligent structure. This research extends the application of near-infrared laser in 4D printing to the depth direction of intelligent structures, which will bring more complex and interesting 4D printing structures in the future.

Exchangeable disulfide bond containing highly flexible epoxy vitrimers with shape‐memory, self‐healing, and UV shielding attributes

AbstractWith the rise in momentous resource wastage and severe environmental pollution, a viable path for sustainability is through the use of reprocessable and recyclable materials like vitrimers. Herein, we demonstrated the synthesis of dynamic disulfide‐containing epoxy resin by condensing an amide derivative of 2,2′‐dithiodibenzoic acid with epichlorohydrin. The aforementioned epoxy resin was cured utilizing the two bio‐based curing agents poly(amido amine) and cystamine to produce three distinct epoxy vitrimers. The use of reactive diluent reduced the generation of volatile organic compounds during the curing process. The existence of disulfide bond and aliphatic moiety in the epoxy vitrimers established high elongation at break with good tensile strength. Owing to the dynamic bond, the vitrimers exhibited self‐healing properties with a healing efficiency of 71.48% along with good shape memory abilities. Additionally, the disulfide bond dynamic exchange reaction allowed the polymer chain architecture to topologically reorganize, making them reprocessable and degradable. Moreover, these epoxy vitrimers have the ability to shield ultraviolet radiation as well as inhibits oxidation, and have good chemical resistance properties. The investigated epoxy thermoset thus provides a lot of potential for application as a durable thin film material.

Co-continuous structure enhanced magnetic responsive shape memory PLLA/TPU blend fabricated by 4D printing

ABSTRACT Combining poly (L-lactic acid) (PLLA) with thermoplastic polyurethane elastomer (TPU) can integrate the advantages of excellent biocompatibility and intrinsic shape memory ability of PLLA and high elasticity and excellent shape memory properties of TPU in the application of minimally invasive surgery for bone tissue engineering. However, TPU easily forms a sea-island-like structure in PLLA matrix, decreasing shape memory properties. In this study, a co-continuous structure of TPU phase in PLLA matrix was constructed by adding Fe3O4 nanoparticles due to the changed interfacial tension and flow behavior of TPU, which endowed the TPU/PLLA/Fe3O4 blend fabricated via selective laser sintering (SLS) with excellent shape memory properties. As a result, the morphology of TPU in the blend changed from sea-island-like structure to complete co-continuous structure with increasing Fe3O4 content (0 to 10wt%), and shape recovery ratios in 50 °C water increased from 66.67 to 95.92%. The introduction of Fe3O4 endowed the blend with magnetic responsive shape memory in alternating magnetic field because Fe3O4 could heat it by generating heat from relative friction and particle collisions. Besides, the tensile modulus and hardness of the specimen with 10wt% Fe3O4 nanoparticles increased. In addition, the blend demonstrated excellent biocompatibility by promoting cell adhesion, spreading, and proliferation.

Preshaped 4D Photocurable Ultratough Organogel Microcoils for Personalized Endovascular Embolization.

Endovascular embolization using microcoils can be an effective technique to treat artery aneurysms. However, microcoils with fixed designs are difficult to adapt to all aneurysm types. In this paper, a photocurable ultratough shape memory organogel with a curing time of only 2 s and megapascal-level mechanical properties is proposed. Then, it is used to manufacture the personalized 4D microcoil with a wire diameter of only 0.3mm. The improved mechanical modulus (511.63MPa) can reduce the possibility of microcoils' fracture during embolization. Besides, the fast body-temperature-triggering shape memory ability makes the 4D microcoil applicable in vivo. These 4D microcoils are finally delivered into the rabbit, and successfully blocked the blood flow inside different aneurysms, with neoendothelial cells and collagen fibers growing on the microcoil surface snugly, indicating full aneurysm recovery. This 4D organogel microcoil can potentially be used in personalized clinical translation on human beings.

UV-assisted direct ink writing 4D printing of benzoxazine/epoxy thermosets

Benzoxazine is employed in an increasing number of domains due to its exceptional thermal stability, but it is difficult to apply for 4D printing due to its high brittleness and lack of photo-curable groups. Herein, dual-cure DIW 4D printing inks (BZs) consisting mainly of a commercial benzoxazine and a synthesized diglycidyl ether bisphenol A monoacrylate (DGEBAMA) were formed. In the dual-cure ink, photo-curable groups were cross-linked to rapidly prototype complex structures. After thermal curing, 4D-printing structures with isotropic properties were obtained. The ether bonds provided by the copolymerization of epoxy groups and oxazine rings and the soft segment of DGEBAMA increased the material's toughness. The highest overall performance was obtained by BZ50, which displayed higher glass transition temperature (188 °C), tensile strength (92.13 MPa), elongation at break (9.34 %), and good shape-memory ability. This work provides a straightforward method for enabling the 4D printing of benzoxazine/epoxy-based materials with good toughness, excellent thermal properties, and shape-memory abilities, expanding the potential application of benzoxazine/epoxy-based materials in advanced fields.

Preparation of a Zn/hydroxyapatite/chitosan composite coating with an antibacterial ability and cytocompatibility on a NiTi alloy

Zn has been extensively used to prevent microbial infections in orthopedic implants; however, high amounts of Zn inhibit cell proliferation. This study investigated the ability to decrease the cytotoxicity of Zn-doped coatings on NiTi shape memory alloys (NiTi SMAs) while maintaining their antibacterial activity. The Zn3(PO4)2 distributed in the chitosan coating, annotated as ZHAP, was obtained by electrophoretic deposition in a chitosan solution with Zn acetate acid and hydroxyapatite particles. The ZHAP inhibited bacterial growth and exhibited a good antibacterial activity (86 %) against Staphylococcus aureus. In addition, the MG63-cell adhesion and cytocompatibility with ZHAP were better than those with the Zn-doped coating due to the precipitation of Zn3(PO4)2 which decreased the release of Zn2+ ions from the chitosan matrix. The coatings did not affect neither the superelasticity (< 0.5 % residual strain) nor the shape memory ability (100 % recovery rate) of the NiTi SMAs.

4D Optical fibers based on shape-memory polymers

Adaptative objects based on shape-memory materials are expected to significantly impact numerous technological sectors including optics and photonics. In this work, we demonstrate the manufacturing of shape-memory optical fibers from the thermal stretching of additively manufactured preforms. First, we show how standard commercially-available thermoplastics can be used to produce long continuously-structured microfilaments with shape-memory abilities. Shape recovery as well as programmability performances of such elongated objects are assessed. Next, we open the way for light-guiding multicomponent fiber architectures that are able to switch from temporary configurations back to user-defined programmed shapes. In particular, we show that distinct designs of fabricated optical fibers can maintain efficient light transmission upon completion of multiple temperature-triggered bending/straightening cycles. Such fibers are also programmed into more complex shapes including coils or near 180 ° curvatures for delivering laser light around obstacles. Finally, a shape-memory exposed-core fiber is employed in fiber evanescent wave spectroscopy experiments to optimize the performance of the sensing scheme. We strongly expect that such actuatable fibers with light-guiding abilities will trigger exciting progress of unprecedented smart devices in the areas of photonics, electronics, or robotics.

A crosslinked waterborne poly(vinyl acetate) for greenhouse gas fixation with improved elastomeric properties, shape-memory ability, and recyclability

The development of raw materials from methane and carbon dioxide holds significant potential to cut greenhouse gas (GHG) emissions and reduce the global carbon footprint. As an important monomer, vinyl acetate (VAc) can be produced by the consumption of acetic acid, which will potentially contribute to the reduction of GHGs emission. However, polymers based on VAc are usually prepared from emulsion polymerization in water which brings about the challenges of using modification processes to improve their properties. Here, a newly developed crosslink was able to establish covalently adaptable networks directly in water, enabling the formation of a poly(vinyl acetate) (PVAc) composite. As a result, PVAc emulsions using a monomer of 100% VAc could be transformed from a soft and weak adhesive polymer into an elastomeric polymer composite network with an elongation (775%) at break and flexibility. With the enhanced rubbery modulus, the polymer possesses characteristics for shape-memory material applications with 93% shape fixity and 99% shape recovery after repeated deformation and shape fixity for three times. The recyclability of the PVAc thermosets was demonstrated after granulating and remolding three times, representing an opportunity for designing a greenhouse gas fixing material.

Aldehyde modified cellulose-based dual stimuli responsive multiple cross-linked network ionic hydrogel toward ionic skin and aquatic environment communication sensors

Recently, materials with complicated environmentally-sensitive abilities, high stretchability and excellent conductive sensitivity are interesting actuators in future applications. Herein, we fabricated a versatile and facile polyvinyl alcohol/polyacrylic acid/dialdehyde cellulose nanofibrils-Fe3+ hydrogel integrated with programmable dual-shape memory properties, high mechanical strength, good recoverability, and heat-induced self-healing capability. Benefiting from the synergistic effect of hydrogen bonds and dual metal coordination bonds of cellulose-based dialdehyde and carboxyl with Fe3+and then heating-freeze-thawing cycle treatment, the obtained hydrogel exhibited dual shape memory abilities, high tensile strain (up to 600 %), good self-recovery, and anti-fatigue properties. Moreover, the resultant hydrogel sensors showed revealed high strain sensitivity (gauge factor = 2.95) and satisfactory electrochemical performance; and such hydrogel-based sensor could be used as ionic skin to detect various human motions in real-time and barrier-free communication in the aquatic environment. The composite hydrogel with superior and versatile performances reported in this study could offer a great promise to be applied under extreme conditions as multifunctional sensors.

Shape optimization of thermal shape memory epoxy resin and its mechanism for improving the self-healing of asphalt mixtures

Thermal shape memory epoxy resin (T-SMER) is a novel smart material. The shape memory effect of T-SMER is stimulated by sensing and responding to temperature changes in the asphalt mixtures. The shape memory effect of T-SMER can be used to repair initial cracks in the asphalt mixtures. T-SMER’s shape can influence its shape memory effect and ability to improve the self-healing property of the asphalt mixtures. It also affects the performance of asphalt and asphalt mixtures. Therefore, granular T-SMER and filamentous T-SMER were prepared in this study, and their basic properties were examined. To determine the T-SMER shape with better shape memory effect, the three major indicators and elastic recovery performance of asphalt with granular T-SMER were tested, AC-5 asphalt mixture and AC-10 asphalt mixture with granular T-SMER were formed. Although the granular T-SMER improved the self-healing property of asphalt, its compatibility with asphalt was poor, and there existed a swelling phenomenon in AC-5 and AC-10 asphalt mixture. The adhesiveness between the asphalt and filamentous T-SMER, Marshall indexes, and preliminary study on self-healing property of the asphalt mixtures with the filamentous T-SMER were also investigated. The addition of the filamentous T-SMER significantly increased the consistency of asphalt, improving its strength and self-healing. Thus, the filamentous T-SMER was more suitable for application in the asphalt mixtures. To study the mechanism of the filamentous T-SMER for improving the self-healing property of the asphalt mixtures, the visualization of asphalt mixtures with filamentous T-SMER self-healing process by ANSYS were analyzed. The shape memory ability of the T-SMER can be stimulated to enhance the self-healing property of asphalt mixtures.

Cationically photocured epoxy/polycaprolactone materials processed by solution electrospinning, melt electrowriting and 3D printing: Morphology and shape memory properties

Epoxy/polycaprolactone (PCL) blends containing cationic photo-initiator were prepared by both solution and melt blending. These materials were processed by solvent casting, solution electrospinning (SE), melt electrowriting (MEW), and Fused Deposition Modeling (FDM) 3D printing. The final materials were obtained after UV curing at room temperature. FTIR, and gel content measurements showed that all the materials were crosslinked and that the PCL was part of the network. The shape memory abilities (measured by DMA experiments) depended on the processing technique. Thus, the fixity and recovery ratios were optimal for electrospun fibers, while the 3D printed sample was not able to recover any shape, probably because of the poor adhesion between the printed layers. According to AFM images, samples obtained by MEW and 3D printing produced materials with spherulitic morphology, while solution electrospinning rendered fibers with Shish-Kebab-type crystalline morphology. The latter was highly anisotropic, and many chains were oriented along the nanofiber axis interdispersed with amorphous regions where the epoxy resin formed covalent links with the PCL chains. This morphology conferred extraordinary solvent resistance and shape memory properties to the electrospun mats. The latter manifested a very high affinity towards chloroform, and accordingly, they displayed potential applications as chloroform sensors.

Compatibilised and toughened of PLA/PCL blends via modified-chitosan linking amorphous regions: 4D printing and shape memory processes

It is valuable research to improve the compatibility and toughness of PLA/PCL blends while endowing them with shape memory & 4D printing capability. In this work, lactic acid/caprolactone-modified chitosan (mCS) was used to connect the amorphous region of PLA and PCL to achieve compatibilisation, toughening and 4D printing shape memory ability. The effects of different mCS additions on the morphology, crystalline behaviour, and thermal properties of PLA/PCL blends were observed to study the mechanism of compatibilisation and toughening. Adding 0.5 g mCS into 10 g PLA/PCL blends had the best compatibilisation and toughening effect. At the same time, the blends with this addition ratio had the best shape memory performance after 4D printing. The shape fixity and shape memory ratios of the 4D printing model were as high as 100% and 94.5%, respectively. This work provides a new way to fabricate biomedical devices and bionic components with 4D printing.

Tough and biodegradable polyurethane-silica hybrids with a rapid sol-gel transition for bone repair

Inorganic–organic hybrid materials have promising properties for bone repair because of the covalent bonding between their inorganic and organic phases. This desirable interaction allows the limitations of composite materials, such as inhomogeneous biodegradation rates and nonbiointeractive surfaces, to be overcome. In this study, a polycaprolactone (PCL)-based polyurethane (PU) with an organosilane functional group was synthesized for the first time. Thereafter, a biodegradable PU-silica hybrid was produced through the sol-gel process. The PU-silica hybrid was not only flexible and fully biodegradable but also possessed shape memory ability. In addition, allophanate bonding enabled the silane coupling agent to induce increased crosslinking between the polymer and silica network, as well as between polymer and polymer. Accordingly, the sol-to-gel gelation time required to produce the hybrids was very short, which allowed the production of 3D porous hybrid scaffolds through a simple salt-leaching process. A hybrid scaffold with a 30 wt. % silica composition was the most ideal bone regenerative scaffold since it was able to withstand thermal deformation with promising mechanical properties. Moreover, the hybrid scaffold induced osteogenic differentiation and angiogenesis to accelerate bone regeneration.