Abstract Although highly integrated probe technologies, three-dimensional (3D) vertical stacking of thin-film devices partially alleviates density constraints but at the cost of increased thickness and fabrication complexity1 (Fig. 1a). One-dimensional (1D) thermally drawn fiber-based devices, as well as injectable or deployable patch platforms, have also been proposed, however, they remain limited in their ability to preserve the high-density monolithic integration intrinsic to 2D patch devices and to maintain robust connectivity with external data acquisition systems2 (Fig. 1b). In parallel, deterministic rolling and wrapping strategies have been developed to transform planar soft electronic sheets into tubular or helical one-dimensional architectures, providing mechanically compliant formats for interfacing with cylindrical and deep tissues3. Although these approaches represent important advances in form-factor engineering, they often rely on external mandrels or shape-memory effects, which complicate fabrication and limit scalability, integration density, and long-term electrical robustness. More fundamentally, such transformations primarily reconfigure device geometry without preserving the monolithic, high-density electronic integration enabled by planar microfabrication. As a result, a central challenge in bioelectronics remains unresolved–how to reconcile the high-density, monolithic integration afforded by conventional microfabrication while satisfying the geometric and mechanical constraints required for minimally invasive implantation into deep or anatomically constrained tissues.
A recent study reported an in situ shape-shifting strategy that circumvents these constraints by mechanically transforming a high-density, fully integrated 2D bioelectronic platform into a 1D geometry without degradation of electrical performance4 (Fig. 1c). In other words, rather than constructing electronics directly in a fiber format, the fully integrated 2D bioelectronic circuit incorporating lithographically defined electrodes and interconnects that are mechanically invisible under repetitive deformation was subsequently reconfigured into a high-density, multifunctional fiber with minimal invasiveness, termed “Spiral-NeuroString”, through a rolled-up process with controlled spiral orientation.

Investigating the effect of VED and lattice strut diameter on the shape memory effect of nitinol actuators

Effect of thermal-hydro-mechanical (THM) on wood shape memory effect and its mechanism

Micromechanisms for coupled effects of W addition and aging on phase transformation and shape memory effect of NiTiHf ultra-high temperature shape memory alloy

Nickel-titanium (NiTi) alloys are attractive for functional and biomedical applications due to their shape memory effect, superelasticity, and favorable corrosion resistance and biocompatibility. In this work, the influence of strut size on the compressive response of laser-based powder bed fusion (PBF-LB/M) fabricated NiTi ortho-octahedral porous scaffolds was systematically investigated using combined experiments and finite element simulations. Four scaffold designs with identical unit-cell size (2 mm) but different strut sizes (280, 320, 360, and 400 μm) were fabricated, and their forming quality and deformation behaviors were examined. The as-built scaffolds exhibited high geometric fidelity to the CAD models and stable manufacturability across the investigated parameter range. Quasi-static compression tests revealed a typical three-stage response (linear-elastic regime, plateau/collapse regime, and densification), with both elastic modulus and compressive strength increasing markedly with strut size. Specifically, the modulus increased from 1.17 to 4.28 GPa and the compressive strength increased from 155 to 564 MPa as the strut size increased from 280 to 400 μm. A pronounced oscillatory plateau was observed for the 280 μm scaffolds, indicating progressive layer-by-layer collapse, whereas larger struts promoted a shear-band-dominated failure mode characterized by an approximately 45° fracture zone. Explicit quasi-static simulations reproduced the experimentally observed collapse sequence and demonstrated that stress preferentially concentrates at nodal junctions, with load transfer dominated by struts aligned with the loading direction. The agreement between experiments and simulations confirms the predictive capability of the proposed modeling framework and provides mechanistic insights into geometry-controlled failure. These findings establish a structure-property-failure relationship for PBF-LB/M-fabricated NiTi octahedral scaffolds and offer practical guidance for tailoring stiffness, strength, and collapse mode through strut-size design.

Abstract Shape setting is a crucial step in the production of NiTi shape memory alloys (SMAs) elements for tuning their functional performances. The laser technology can be successfully implemented for fast shape setting of thin, cold-worked NiTi wires, promoting optimal thermo-mechanical response. In this work, Ti-rich NiTi wires were subjected to laser scanning at different power values for inducing shape memory effect (SME). Differential scanning calorimetry and strain recovery testing allowed to characterize the transformation temperatures and the functional response of the laser-annealed wires. Moreover, transmission electron microscopy was carried out for evaluating the precipitation and the evolution of the microstructure at varying the laser process conditions. Reference wires, in straight-annealed condition, from which cold-worked wires were manufactured, were compared for selecting the most suitable laser condition. It was found that optimal functional properties can be achieved by selecting the correct laser power; the corresponding TEM observations indicate the presence of both equiaxial and elongated grains, containing a high degree of defects, due to the previous plastic deformation. These characteristics give the laser-treated wire functional properties that are comparable to, or even superior to, those of commercially available wires. These achievements can drive novel applications, in which regions offering different performances of SME can be tuned depending on the incident laser power.

In this study, nonmagnetic and bioresorbable iron alloy foam was fabricated for bomedical implant applications. Mn and Si were included in order to obtain shape memory effect. Ti was included in order to enhance biocompatibility. Mg and Zn wre included in order to increase biodegradation rate. C was included in order to prevent ferromagnetic properties. Mg alloys biodegrade too fast with H2 evolution. Zn alloys show biodegradation rates in the middle of Mg and Fe alloys, but the Zn alloys are very brittle. Zn also shows low strength and low plastic deformation. Fe alloys show strength and radio-opaqueness, which is important in the coronary stents. Fe alloy specimens with open porous structure were fabricated by space holder method. Carbamide was used as a space holder. Biodegradation rate was investigated by weight loss measurements. Microstructure was investigated by using optical microscope and scanning electron microscope. Young’s modulus values of the porous Fe-4Mn-4Si-2Ti-5Mg-5Zn-0.5C alloy specimens were deceased from 4.6 GPa to 4.2 GPa with immersion time. Weight change value of the Fe-4Mn-4Si-2Ti-5Mg-5Zn-0.5C alloy was 7.9 % for 21 days immersion period in SBF solution, which is a suitable period for temporary implants. Fe-4Mn-4Si-2Ti-5Mg-5Zn-0.5C alloy does not have a cytotoxic potential on the cells according to neutral red uptake assay. As a result, Fe-4Mn-4Si-2Ti-5Mg-5Zn-0.5C alloy has showed mechanical properties and biodegradation rate suitable for temporary implant material in biomedical applications.

ABSTRACT This work presents a fully thermomechanically coupled material model for shape memory alloys (SMAs), capable of predicting shape memory effect, superelasticity, stress and strain recovery, and martensite reorientation. Formulated within the Generalized Standard Material (GSM) framework, the model employs a rate potential, whose variations yield the governing equations, including linear momentum balance, energy balance, and evolution of internal variables. A potential‐based line search method integrated with a Newton–Raphson scheme enhances the robustness and convergence of the solution algorithm. Extending the Sedlák [14] model's energy and dissipation formulations, we apply the proposed framework to an SMA‐based out‐of‐plane bistable microactuator design. The actuator features two antagonistically coupled SMA microbridges and exhibits bistable behavior, snapping between stable states under thermomechanical loading and using constrained recovery forces to perform work. Results demonstrate the model's efficiency and accuracy in capturing the complex thermomechanical response of SMA devices, highlighting its potential for advanced bistable actuator design.

Supramolecular network-modified pyrolytically recycled carbon fiber composites with recyclability, shape-memory effects, and flame retardation

In this study, different shape memory polyurethane (SMPU)-based electrospun nanofibers containing Fe3O4 magnetic nanoparticles (MNPs) were prepared. The shape-memory behavior of these scaffolds enables minimally invasive applications within biological systems, while their magnetic properties enhance the growth, proliferation, and differentiation of the bone cells. SMPU was synthesized via a two-step pre-polymerization method. The effects of MNPs on hydrogen bonding, crystallinity, thermal properties, hydrophilicity, water absorption, and mechanical and shape memory properties of SMPU were investigated. The results revealed that MNPs restricted the hydrogen bonds formation and promoted microphase separation in SMPU hard and soft segments. Moreover, a reduction in the degree of crystallinity of oft segments in the SMPU nanocomposites was observed by the addition of MNPs. Scanning electron microscopy was employed to determine the average diameters and size distributions of the SMPU nanofibers. In addition, the results showed that the prepared electrospun nanofibrous mats have adequate mechanical and shape memory properties for practical biomedical applications. Bioactivity studies indicated that the presence of MNPs could enhance the In-vitro cell cultivation of MG63 bone cells on the nanofibers. These results indicated that the prepared electrospun nanofibers could be utilized as a potential candidate for shape memory-assisted smart wound healing applications.

A finding of four-way shape memory effect in Ni51Ti49 alloy by constraint-aging within a transitional zone

Manipulating multi-dimensional crystal defects for ultra-high superelastic stress and excellent shape memory effect in additively manufactured NiTiFe shape memory alloys

The paper continues the authors’ efforts to characterize and control the shape memory effect (SME) occurring in 3D printed specimens of recycled polyethylene terephthalate (rPET) and polyethylene terephthalate glycol (rPETG). Lamellar and “dog-bone” configuration specimens were 3D printed in the form of stratified composites with five different rPET/rPETG ratios, 100:0, 60:40, 50:50, 40:60, and 0:100, and two different angles between the specimen’s axis and the deposition direction, 0° and 45°. The lamellar specimens were used for: (i) free-recovery SME-investigating experiments, which monitored the variation of the displacement, of the free end of specimens which were bent at room temperature (RT), vs. temperature, during heating, (ii) differential scanning calorimetry (DSC), which emphasized heat flow variation vs. temperature, during glass transition and (iii) dynamic mechanical analysis (DMA), which recorded storage modulus vs. temperature in the glass transition interval. Dog-bone specimens were subjected to tensile failure and loading-unloading tests, performed at RT. The broken gauges were metallized with an Au layer and analyzed by scanning electron microscopy (SEM). The results showed that the specimens printed with 0° raster developed larger free-recovery SME strokes, the largest one corresponding to the specimen with rPET/rPETG = 40:60, which experienced the highest storage modulus increase, 872 MPa, and maximum value, 1818 MPa, during heating. The straight lamellar composite specimens experienced a supplementary shape recovery when bent at RT and heated, in such a way that their upper surface became concave, at the end of heating. Most of the specimens 3D printed at 0° raster developed stress failure plateaus, which were associated with the formation of delamination areas on SEM fractographs, while the specimens printed with 45° raster angle experienced necking failures, associated with the formation of crazing areas. The results suggested that 3D printed stratified rPET-rPETG composites, with dedicated spatial configurations, have the potential to serve as executive elements of light actuators for low-temperature operation.

Despite the considerable promise of flexible Zn-I2 batteries for next-generation electronics, their development remains constrained by the polyiodide shuttle effect that severely compromises electrochemical stability and a lack of intrinsic shape adaptability. To address these challenges, this study successfully constructs a Zn-I2 battery with both high electrochemical stability and excellent shape-memory functionality through the approach of "shape-memory skeleton, corrosion-resistant coating, and fibrous architecture". The in situ formed inert fluorinated coating (FeF2/ZnF2) shows a good barrier effect for polyiodides, and the fiber Zn-I2 battery demonstrates high electrochemical stability, maintaining a capacity retention of over 96% after 250 cycles. Furthermore, due to the excellent shape-memory effect of the NiTi skeleton, combined with the flexibility of the fibrous structure, the battery achieves rapid (within 2 s) and stable (recovery rate above 70%) shape restoration. This work facilitates the development of flexible and shape-memory batteries.

ABSTRACT Soft actuators that combine compactness, rapid response, and high output power are critical for advancing high-performance soft robotic systems. Although bistable architectures can amplify speed through elastic instability, their combination with functional materials often sacrifices compactness or lacks tunability. Here, we report a Venus flytrap-inspired shape memory alloy – embedded snapping actuator (SMA-ESA) that achieves compact and tunable actuation by structurally integrating pre-shaped SMA wires within a double-tilted elastomeric matrix. The SMA skeleton not only triggers snap-through via its thermal shape memory effect but also regulates performance. Combined experimental and finite element studies reveal that the actuation performance – characterized by energy storage capacity as well as the rate and efficiency of energy release – is tunable through both geometric parameters and input power. As a proof of concept, the SMA-ESA is demonstrated in a flytrap-inspired capture device that selectively responds to external stimuli. These results establish a generalizable strategy for embedding high-power-density materials into bistable soft structures, offering new opportunities for compact, responsive, and bio-inspired soft robotics.

Surface microstructures have been widely employed in pressure sensors to enhance sensitivity. However, the microstructures are susceptible to irreversible collapse under prolonged cyclic loading, leading to device failure. This work develops a recyclable ionogel (PUF/IL) with shape memory-assisted healing microstructure for highly sensitive ionotronic pressure sensor. Hydrogen bond units (UPy) and fluorinated chain extenders (OHD) are used to regulate the various properties of PUF/IL. Benefiting from the ion-dipole interactions between OHD and ionic liquids (IL), IL can be firmly stabilized in the ionogel network. PUF/IL exhibits exceptional shape-memory properties, demonstrating fixation and recovery rates of 99% and 86%, respectively. More importantly, when the microstructure is mechanically damaged during long-term use, it can be fully recovered through a shape-memory process. Due to the dynamic interactions, PUF/IL shows remarkable recyclability. The mechanical properties, shape memory performance, and pressure-sensing capabilities of recycled PUF/IL retain over 95% of their initial values. Overall, the strategy of healing collapsed microstructures via the shape-memory effect of PUF/IL, combined with its recyclability, effectively improves the long-term reliability and sustainability of pressure sensors. This work provides a solid foundation and creative design ideas for the development of next-generation durable, sustainable, highly sensitive pressure sensors.

Biocompatible poly(lactic acid) (PLA) was plasticized with poly(ethylene glycol) (PEG) added at concentrations of 10, 15, and 20 wt.% relative to PLA, and then processed into gyroid triply periodic minimal surface (TPMS) scaffolds using fused filament fabrication (FFF) 3D printing. The influence of PEG concentration and gyroid structure (50% infill density) on thermal transitions, crystallinity, and low–temperature shape-memory performance was systematically investigated. The shape-memory effect (SME) of the PLA–based scaffolds was tailored through compositional control and structural design. Shape recovery under thermal activation at 40 °C and 50 °C was examined to reveal the correlation between composition and structure in governing low–temperature shape-memory behavior. The optimal composition (PLA/10 PEG, 50% gyroid infill) achieved shape recovery with a recovery ratio (Rr) of 97 ± 1% at 40 °C within 6 ± 1 min, demonstrating optimal shape-memory activation close to physiological temperature. Structural and morphological changes were characterized using ATR–FTIR, Raman spectroscopy, DSC, XRD, and SEM, providing comprehensive insight into the plasticization of the PLA matrix and its impact on structure–property relationships relevant to bone tissue engineering.

Abstract Soft robotics requires structural systems capable of performing complex and programmable deformations to adapt to unstructured or dynamic environments. Shape memory materials (SMMs) offer a promising solution owing to their shape memory effect and stimulus-responsive adaptability. However, actuators relying on a single type of SMM are often constrained by nonlinear actuation behavior and limited stiffness variation, which restrict their ability to achieve coordinated, multifunctional responses. Addressing these challenges, this study introduces a hybrid programmable morphing structure that integrates a shape memory polymer (SMP) and a shape memory alloy (SMA) to realize cooperative actuation and adaptive stiffness variation within a single unit. In the proposed configuration, the SMA springs act as thermally activated actuators that generate deformation. The SMP cylindrical core employs its shape memory effect to realize reversible shape locking and serves as a thermal switch that enables controlled stiffness variation through temperature regulation. A coupled numerical model was established to describe the cooperative behavior between the SMA and SMP components, and the numerical results were validated through experimental testing. The agreement between simulations and experiments confirms the feasibility and repeatability of the proposed design. The structure achieves a maximum bending angle of 55° under dual-SMA actuation and 42° under single-SMA actuation, while maintaining any intermediate shape during thermal cycling. Furthermore, the hybrid system demonstrates a reversible six-fold increase in stiffness and a motion range extending up to three times its original length, representing a significant improvement over conventional single-material soft actuator. Moreover, the proposed hybrid structure offers a flexible strategy for programmable morphing and demonstrates scalable applicability in practical applications, such as adaptive grasping, reconfigurable locomotion, and environmental exploration. In conclusion, this work provides a feasible and generalizable framework for integrating multiple SMM into programmable morphing structures which can be applied into multifunctional soft robotic systems.

In advanced shape memory-assisted anticounterfeiting polymeric materials, stimuli-induced shape change resulting from the shape memory effect is used as one security mode, while other smart phenomena serve as additional alarm modes. Image of cubic structure generated with AI.

Research on the synergistic enhancement mechanism of shape memory effect and mechanical properties of NiTiNb shape memory alloys by coupling severe cold rolling deformation and electric pulse treatment