Memory Properties Research Articles

4D printing of biobased shape memory sandwich structures

Lightweight sandwich structures already have many applications in the aerospace, automotive, and construction sectors due to their high strength-to-weight ratio, enhanced stiffness and rigidity, and high energy and shock absorption capabilities. Additive manufacturing (AM) can provide great freedom and flexibility in the fabrication of complex sandwich structures that cannot be made by other conventional processes. The application of smart materials, like shape memory polymers (SMP), can offer the capability of dynamic transformation so that the deformed structure can recover its original shape using external stimuli, such as temperature. This study exploits the potential of this technology in the design and manufacturing of biobased smart sandwich structures with energy absorption capability and shape recovery performance. For that, a combination of recycled poly(lactic acid) (PLA)/poly(butylene succinate) (PBS) biopolymers are developed as printing filaments with shape memory properties. The designed sandwich samples are fabricated by Fused Filament Fabrication (FFF) technology. The mechanical and functional properties of the printed samples are also evaluated. The results show PLA/PBS filaments have good printability and the fabricated parts have acceptable dimensional accuracy, mechanical strength, and functional performance.

4D-Printed MXene-Based Artificial Nerve Guidance Conduit for Enhanced Regeneration of Peripheral Nerve Injuries.

Repairing larger defects (>5mm) in peripheral nerve injuries (PNIs) remains a significant challenge when using traditional artificial nerve guidance conduits (NGCs). A novel approach that combines 4D printing technology with poly(L-lactide-co-trimethylene carbonate) (PLATMC) and Ti3C2Tx MXene nanosheets is proposed, thereby imparting shape memory properties to the NGCs. Upon body temperature activation, the printed sheet-like structure can quickly self-roll into a conduit-like structure, enabling optimal wrapping around nerve stumps. This design enhances nerve fixation and simplifies surgical procedures. Moreover, the integration of microchannel expertly crafted through 4D printing, along with the incorporation of MXene nanosheets, introduces electrical conductivity. This feature facilitates the guided and directional migration of nerve cells, rapidly accelerating the healing of the PNI. By leveraging these advanced technologies, the developed NGCs demonstrate remarkable potential in promoting peripheral nerve regeneration, leading to substantial improvements in muscle morphology and restored sciatic nerve function, comparable to outcomes achieved through autogenous nerve transplantation.

Effect of curing agents n‐octylamine and m‐xylene diamine on the mechanical and memory properties of E51 epoxy resin

AbstractThe effects of curing agents n‐octylamine (OA) and m‐xylene diamine (MXDA) on the mechanical and memory properties of E51 epoxy resin (EP) are investigated in this work. The curing mechanism and thermal stability of OA and MXDA with EP are also investigated via Fourier‐transform infrared spectroscopy and thermogravimetric analysis, the influence of curing agent ratios on the thermo‐dynamic mechanical properties of EP are investigated through dynamic thermo‐mechanical analysis, and the relationship between the storage modulus, the hysteresis phase angle and the temperature are constructed. Moreover, the cross‐linking densities of the EP with different curing agent ratios are calculated using Archimedes's method. Besides, the effects of different proportions of curing agents on the mechanical properties of EP are studied. The results show that with the increases of MXDA ratio, the phase transition temperature, crosslink density, recovery temperature, recovery rate, the tensile strength, tensile modulus, strain strength, and strain modulus are enhanced, however, the hysteresis phase angle MXDA ratio and the tenacity decrease. Finally, the shape memory mechanism of E51 is discussed.

Study of chemically deposited magnetic materials of NiTi memory alloys and their magnetothermal properties

Abstract NiTi alloy has good mechanical properties and biocompatibility, as well as unique shape memory properties. Therefore, it is commonly used to make metal stents in clinical practice. In this study, the substrate used is a NiTi memory alloy, which has been coated with CoNiFeP magnetic material through an electroless plating. The morphology, composition, and magnetic properties of the coating were analyzed using SEM, XRD, and VSM. The magneto-thermal properties were studied by high-frequency alternating magnetic field (AMF) induction equipment. The results showed that after determining a reasonable plating application process, the prepared coatings had certain soft magnetic properties and could exceed 43°C in a short time at different field intensities (Happl×fappl=M×109 Aꞏm−1ꞏs−1, M=1.0, 2.0, 3.0, 4.0, and 5.0) to reach the temperature required for tumor ablation, which can be used to prepare magnetic scaffolds for magnetothermal therapy.

Analysing the shape memory behaviour of GnP-enhanced nanocomposites: a comparative study between experimental and finite element analysis

Shape memory polymers (SMPs) are capable of enduring significant deformations and returning to their original form upon activation by certain external stimuli. However, their restricted mechanical and thermal capabilities have limited their broader application in engineering fields. To address this, the integration of graphene nanoplatelets (GnPs) with SMPs has proven effective in enhancing their mechanical and thermal properties while maintaining inherent shape memory functions. The study evaluated shape memory nanocomposites (SMNCs) using dynamic mechanical, thermogravimetric, and static tensile, flexural, and shape memory tests, along with scanning electron microscopy to analyse tensile fractures. The results indicate that the optimal content of GnP is 0.6 wt%, resulting in excellent shape memory, thermal, and mechanical properties. Specifically, this composition demonstrates a shape recovery ratio of 94.02%, a storage modulus of 4580.07 MPa, a tensile strength of 61.42 MPa, and a flexural strength of 116.37 MPa. Additionally, the incorporation of GnPs into epoxy reduces recovery times by up to 52% at the 0.6 wt% concentration. While there is a slight decrease in the shape fixity ratio from 98.77% to 93.02%, the shape recoverability remains consistently high across all samples. Current finite element (FE) models often necessitate complex, problem-specific user subroutines, which can impede the straightforward application of research findings in real-world settings. To address this, the current study introduces an innovative finite element simulation method using the widely used ABAQUS software to model the thermomechanical behaviour of SMNCs, importantly incorporating the time-dependent viscoelastic behaviour of the material. The effectiveness of this new approach was tested by comparing experimental results from bending test of SMNCs cantilever beam with outcomes derived from FE simulations. The strong agreement between the experimental data and simulation results confirmed the precision and reliability of this novel technique.

Mechanical and biological properties of current materials of clear aligner

With the development of new materials related to clear aligners, the physical properties are improving, and the clinical performance of the devices is expected to improve. Clear aligners require constant, controlled force on the teeth to achieve the desired tooth movement. However, unlike superelastic wires for orthodontic treatment, clear aligner materials are characterized by significant short-term or long-term stress relaxation after installation of the device. In addition, clear aligners are a complex manufacturing process that requires creating a tooth model and trimming the aligners, and various degrees of shrinkage and expansion may occur during the thermoforming process or direct printing of device. These changes can affect the thickness or fit of each tooth area and make it difficult to achieve the clinical treatment goals of clear aligner.Recently, multi-layered clear orthodontic products with improved physical properties have been introduced to increase the predictability of aligner treatment, and with the recent introduction of direct printing materials, innovative manufacturing methods for clear orthodontic devices have become possible. As shape memory properties have been reported among direct printing materials, interest in related materials is increasing. In this issue, we will introduce the latest materials related to clear aligners and explain the physical and biological properties that clinicians need to know for proper use.

Effect of dual dispersion of carbon fiber and silica nanoparticles on recovery performance of shape memory epoxy

Shape memory polymers are utilized in diverse fields, including deployable structures and components, owing to their advantageous properties like low density, cost-effectiveness, and ease of processing. The current study investigates the effect of dual dispersion of carbon fibers (CF) and silica nanoparticles (SN) on the recovery performance of shape memory epoxy composites. CF (0.25 wt.%) reinforced epoxy composite, SN (0.25 wt.%) reinforced epoxy composite, and dual (CF and SN 0.25 wt.% each) dispersed epoxy composite were developed using magnetic stirring and ultrasonic mixing to study the mechanical properties and shape memory behaviour. Flexural strength, tensile strength and fracture toughness of pristine epoxy was found to be 134.38, 52.15 MPa and 1.91 MPa∙m1/2, respectively. The addition of CF resulted in a flexural strength of 135.70 MPa and a tensile strength of 53.01 MPa, while the incorporation of SN led to a flexural and tensile strength of 138.40 and 53.69 MPa, respectively. The fracture toughness of composites after adding CF and SN was found to be 2.22 and 2.39 MPa∙m1/2, respectively. With dual dispersion, the flexural strength of 139.82 MPa, tensile strength of 54.64 MPa, and fracture toughness of 2.75 MPa∙m1/2 were achieved. Dual dispersion has shown improved mechanical properties compared to single dispersion. The introduction of CF slightly decreased the shape fixity ratio (Rf ) and shape recovery ratio (Rr ) of the pristine epoxy from 98.67% and 96.62% to 96.67% and 95.15%, respectively. Similarly, the addition of SN further reduced these ratios to 98.00% and 91.83%, respectively. With a dual dispersion approach Rf and Rr were observed to be about 97.33% and 93.83%, respectively. The addition of fillers led to a reduction in Rf and Rr due to inhibition of polymeric chains, resulting in partial shape recovery. However, recovery time improved from 28 to 23 and 26 s with addition of CF and SN, respectively, in epoxy. With dual dispersion, a speedy recovery was achieved with a recovery time of 21 s. The findings of this study demonstrate the potential of dual dispersed fillers to improve the mechanical and shape memory properties of epoxy, which could find applications in the smart materials and structural engineering.

Manufacture and use of In-house clear aligners using digital technology

With the development of digital technology, in-house manufacturing of clear aligners is increasing. As a result, it has become possible to create more elaborate and precise aligners compared to the manual manufacturing method. In addition, along with the technology to print clear aligners directly from a 3D printer, a material with completely different properties were also created. Since this new material with shape memory properties is created through a chemical reaction into the aligners with properties appropriate for tooth movement, only through the right processes and procedures can a safe aligner without harmful effects and excellent properties be completed. Thanks to the unique properties of this aligners, there is a possibility of overcoming the limitations of existing clear aligners. The author explained the process of manufacturing a clear aligners using digital technology in your clinic, and summarized the things you need to know when manufacturing a new aligners using shape memory polymer.

Zr and V-doped effect on Martensitic transformations and magnetic properties of NiMnIn shape memory alloy

In this study, the elements vanadium (V) and zirconium (Zr) were doped separately as a fourth element to the ternary NiMnIn Heusler magnetic shape memory alloy and the alloys were produced as ingots by arc-melting method. The shape memory properties, microstructures, magnetic and microstructural changes of these new alloys were investigated in detail. The vanadium (V) and zirconium (Zr) elements doped into the alloy caused a decrease in the transformation temperature values of the alloy, but did not cause a significant change in its magnetic properties. The master sample, which has low hysteresis, undergoes a phase transition from the martensite phase to the austenite phase due to an increase in the nucleation of austenite phases at the twinning boundaries. Here, the vanadium and zirconium doping of the alloy caused an increase in the strength and ductility values of the alloy and this caused the formation of the second phase. Due to the increase of this phase formation in the alloy, it can be said that there is a slight decrease in the shape retention of the alloy.

Shape Memory Materials Based on a NiMnSb Alloy and Polylactic Acid/Polyhydroxyalkanoate: Evaluation of The Chemical And Physical Properties

AbstractIn this study, NiMnSb alloy and PLA/PHA blend composite films with shape memory properties, which exhibit magnetic, elastic, and smart properties at the same time, were prepared by solution casting method. After the magnetic shape memory alloy (MSMA) used in different ratios was doped into the polymer, its effect on the characteristic functional groups of PLA and PHA was examined by attenuated total reflectance‐infrared spectroscopy (ATR‐IR). When the thermal data were examined, it was determined that as the NiMnSb ratio increased, the percentage residue amount increased and the highest residue amount at 500 °C was in the PLA/PHA blend composite film containing 20 % alloy. In X‐ray diffraction (XRD), it was observed that the characteristic signal of the NiMnSb alloy in polymer blend composite films became evident with increasing concentration at 2θ=45° (222). VSM results showed that when a ferromagnetic material such as NiMnSb was doped into the diamagnetic PLA/PHA blend film, the resulting composite now showed ferromagnetic properties. In addition, it has been determined that MSMA further improves this feature of the PLA/PHA blend, which has a shape memory effect.

Strengthening-Durable Trade-Off and Self-Healing, Recyclable Shape Memory Polyurethanes Enabled by Dynamic Boron-Urethane Bonds.

Addressing the demand for integrating strength and durability reinforcement in shape memory polyurethane (SMPU) for diverse applications remains a significant challenge. Here a series of SMPUs with ultra-high strength, self-healing and recyclability, and excellent shape memory properties through introducing dynamic boron-urethane bonds are synthesized. The introducing of boric acid (BA) to polyurethane leading to the formation of dynamic covalent bonds (DCB) boron-urethane, that confer a robust cross-linking structure on the SMPUs led to the formation of ordered stable hydrogen-bonding network within the SMPUs. The flexible crosslinking with DCB represents a novel strategy for balancing the trade-off between strength and durability, with their strengths reaching up to 82.2MPa while also addressing the issue of durability in prolonged usage through the provision of self-healing and recyclability. The self-healing and recyclability of SMPU are demonstrated through rapid dynamic exchange reaction of boron-urethane bonds, systematically investigated by dynamic mechanical analysis (DMA). This study sheds light on the essential role of such PU with self-healing and recyclability, contributing to the extension of the PU's service life. The findings of this work provide a general strategy for overcoming traditional trade-offs in preparing SMPUs with both high strength and good durability.

Controlled pathways and sequential information processing in serially coupled mechanical hysterons

The complex sequential response of frustrated materials results from the interactions between material bits called hysterons. Hence, a central challenge is to understand and control these interactions, so that materials with targeted pathways and functionalities can be realized. Here, we show that hysterons in serial configurations experience geometrically controllable antiferromagnetic-like interactions. We create hysteron-based metamaterials that leverage these interactions to realize targeted pathways, including those that break the return point memory property, characteristic of independent or weakly interacting hysterons. We uncover that the complex response to sequential driving of such strongly interacting hysteron-based materials can be described by finite state machines. We realize information processing operations such as string parsing in materia, and outline a general framework to uncover and characterize the FSMs for a given physical system. Our work provides a general strategy to understand and control hysteron interactions, and opens a broad avenue toward material-based information processing.

Programmable Retention Characteristics in MoS2-Based Atomristors for Neuromorphic and Reservoir Computing Systems.

In this study, we investigate the coexistence of short- and long-term memory effects owing to the programmable retention characteristics of a two-dimensional Au/MoS2/Au atomristor device and determine the impact of these effects on synaptic properties. This device is constructed using bilayer MoS2 in a crossbar structure. The presence of both short- and long-term memory characteristics is proposed by using a filament model within the bilayer transition-metal dichalcogenide. Short- and long-term properties are validated based on programmable multilevel retention tests. Moreover, we confirm various synaptic characteristics of the device, demonstrating its potential use as a synaptic device in a neuromorphic system. Excitatory postsynaptic current, paired-pulse facilitation, spike-rate-dependent plasticity, and spike-number-dependent plasticity synaptic applications are implemented by operating the device at a low-conductance level. Furthermore, long-term potentiation and depression exhibit symmetrical properties at high-conductance levels. Synaptic learning and forgetting characteristics are emulated using programmable retention properties and composite synaptic plasticity. The learning process of artificial neural networks is used to achieve high pattern recognition accuracy, thereby demonstrating the suitability of the use of the device in a neuromorphic system. Finally, the device is used as a physical reservoir with time-dependent inputs to realize reservoir computing by using short-term memory properties. Our study reveals that the proposed device can be applied in artificial intelligence-based computing applications by utilizing its programmable retention properties.

Improvement of synaptic property of GeSe based CBRAM by engineering the deposition condition of switching matrix

A study of effect of deposition condition of germanium selenide (GeSe) switching layer to Conductive bridging random access memory (CBRAM) device property was conducted to enhance memory property and synaptic property. The devices deposited under the varied deposition conditions were analyzed by current distribution of each state (Low-resistance state [LRS], High-resistance state [HRS]), conduction mechanism analysis, chemical analysis, and synaptic analysis according to pulse conditions. When we deposited switching layer at lowest power (40 W), more Ag ions move to the switching matrix and make lower operation voltage. But there were some disadvantages, which were worst distribution and higher HRS current, less memory window, nonlinear and rapid increase of potentiation process. Conversely, although the device deposited at high voltage increased the operating voltage, but there are improvements, such as the highest memory window and improved linearity of potentiation. The best sample was conducted the synaptic property measurement, and the device successfully mimicked the biological synaptic property with the good linearity of potentiation and depression, spike-rate dependent plasticity (SRDP) and spike-timing dependent plasticity (STDP) properties.

Exploring the role of nanoparticles in enhancing thermal performance of fractional Carreau fluid flow under magnetic field and hall current

Nanofluids garner significant scientific interest due to their exceptional heat-conducting abilities and potential to enhance heat transfer efficiency. This manuscript investigates the behavior of a two-dimensional fractional Carreau fluid model on a stretched sheet over time, incorporating convection, magnetic fields, nanoparticles, diffusion, and thermal radiations. The model elucidates viscoelastic nanofluids’ memory and inheritance properties, employing non-integer Caputo fractional derivatives innovatively. Fundamental equations are transformed into dimensionless form and solved using an explicit finite difference approach. Essential parameters like Skin friction coefficient, Nusselt number, and Sherwood number are accurately determined. Rigorous stability and convergence criteria ensure effective solution convergence. Visual representations demonstrate the significant impact of each parameter on fluid flow. It is noted that temperature gradient increases 49.38% with the increase of fractional exponent α while it decreases 13.39% with the increase of magnetic parameter M. Moreover, concentration gradient increases 66.48% with the increase of thermophoresis parameter Nt and 94.71% with the increase of pedesis parameter Nb.

Towards a Sustainable Laser Powder Bed Fusion Process via the Characterisation of Additively Manufactured Nitinol Parts

Is additive manufacturing (AM) a sustainable process? Can the process be optimised to produce sustainable AM parts and production techniques? Additive manufacturing offers the production of parts made of different types of materials in addition to the complex geometry that is difficult or impossible to produce by using the traditional subtractive methods. This study is focused on the optimisation of laser powder bed fusion (L-PBF), one of the most common technologies used in additive manufacturing and 3D printing. This research was carried out by modulating the build layer thickness of the deposited metal powder and the input volumetric energy density. The aim of the proposed strategy is to save the build time by maximizing the applied layer thickness of nitinol powder while retrieving the different AM part properties. The saving in the process time has a direct effect on the total cost of the produced part as a result of several components like electric energy, inert gas consumption, and labour. Nickel-rich nitinol (52.39 Ni at.%) was selected for investigation in this study due to its extremely high superplastic and shape memory properties in addition to the wide application in various industries like aerospace, biomedical, and automotive. The results obtained show that significant energy and material consumption can be found by producing near full dens AM parts with limited or no alteration in chemical and mechanical properties.

Hofmeister-Effect-Driven Hybrid Glycerogels for Perfect Wide-Temperature Shape Fixity and Shape Recovery in Soft Robotics Applications.

Shape memory gels have emerged as crucial elements in soft robotics, actuators, and biomedical devices; however, several problems persist, like the trade-off between shape fixity and shape recovery, and the limited temperature range for their application. This article introduces a new class of shape memory hybrid glycerogels (GGs) designed to address these limitations. The well-modulated internal structure of the GGs, facilitated by the Hofmeister salting-out effect, strategically incorporates a higher crystallite content, abundant crosslinking points, and a high elastic modulus. Unlike reported shape memory gels, the GG exhibits a perfect triple-step shape memory behavior in air with 100% shape fixity in a wide programming temperature range (75-135°C) and simultaneously achieves 100% shape recoverability. The gel recovers its shape at -40°C under near-infrared light across a wide programming temperature range (25-135°C), showing unexpected initiation even at subzero temperatures. Inspired by the mechanics of composite structures, a method is proposed to integrate the GG seamlessly with a shape memory alloy, which further expands the temperature range that yields perfect shape memory properties. Finally, two light-controlled fluttering and crawling soft robot prototypes are engineered to illustrate the versatility and potential applications of the composite gel in soft robotics.

Analysing the shape memory behaviour of MWCNT-enhanced nanocomposites: a comparative study between experimental and finite element analysis

Shape memory polymers (SMPs) are known for their unique ability to withstand large deformations and revert to their original shape under specific external stimuli. However, their broader application in biomedical and structural applications is restricted by limited mechanical and thermal properties. Introducing multi-walled carbon nanotubes (MWCNTs) into SMPs has proven to significantly enhance these characteristics without affecting their inherent shape memory features. This study investigates shape memory nanocomposites (SMNCs) through dynamic and thermogravimetric analyses, along with tensile, flexural, and shape memory testing, and explores fracture interfaces using scanning electron microscopy. Findings indicate optimal shape memory, thermal, and mechanical properties with 0.6 wt% MWCNT content, showcasing a shape recovery ratio of 93.11%, storage modulus of 4127.63 MPa, tensile strength of 55 MPa, and flexural strength of 107.94 MPa. Moreover, incorporating MWCNTs into epoxy demonstrated a reduction in recovery times by up to 50% at 0.6 wt% concentration. Despite a slight decrease in shape fixity ratio from 98.77% to 92.11%, shape recoverability remained nearly consistent across all samples. The study also introduces a novel finite element (FE) method in ABAQUS for modeling the thermomechanical behavior of SMNCs, incorporating viscoelasticity, validated by matching experimental results with FE simulations, highlighting its accuracy and practical applicability in engineering.

Water‐Assisted Reprocessing and Shape Programming of Epoxy Vitrimer

AbstractVitrimers are reprocessing and recycling thermosetting plastics. They possess reconfigurable polymer networks that allow for unlimited transformation in shape in principle. However, current strategies to reshape the vitrimers typically involve heat or light, which often induces undesirable oxidation and decomposition. To address this issue, here a water‐assisted approach is proposed for programming epoxy vitrimers’ shapes. In this design, water molecules are utilized to reversibly dissociate the hydrogen bonds in epoxy vitrimers to enable the polymer segments to move flexibly. The hydrated epoxy vitrimers can then be reprogrammed and retained into different temporary shapes by removing the water. Such samples would be recovered to their original shapes by rehydration, exhibiting water‐induced shape memory property. More than temporary deformation, the permanent figures of the hydrated vitrimers can also be permanently changed at room temperature (rt) or elevated temperatures in the presence of transesterification catalysts. Combing the shape memory and high temperature plasticity or utilizing rt plasticity, sophisticated shapes such as spiral shapes are demonstrated. It is envisioned that this water‐assisted methodology can be useful in programming cross‐linked polymers into diverse 3D structures, which has wide practical applications in soft robots, deployable devices, aerospace materials, etc.

Experimental investigations of temperature-sensitive shape memory polymer composites for 4D printing

Shape memory polymers (SMPs) and their composites (SMPCs) have emerged as popular materials in a variety of industries due to their unique properties of shape-changing behavior in response to external stimuli. The inclusion of reinforcement may modify the SMPs to enhance their thermal and shape memory properties. Different types of bio ceramics have already been used to alter the thermal and shape memory behavior of SMPs. However, using bioactive glass (BG) as filler to modify these properties has not yet been explored. Despite the significant advantages that shape-memory polymers (SMPs) offer when combined with 3D/4D printing technology, their potential in 3D printing has been explored only to a limited extent. This work created a solvent-based 4D-printed temperature-sensitive shape memory polymer composites (SMPCs) system using polylactic acid (PLA) and bioactive glass (BG). The influence of BG on the thermal as well as shape-memory capabilities of composites was further examined. An increase in the degree of crystallinity and viscoelastic characteristics of PLA/BG composites led to improved shape memory properties, like shape fixity and shape recovery. These findings suggest the potential for using the developed SMPC printed through 4D printing technology, to develop complex shapes for self-foldable structures and smart biomedical devices in the future.