Search Results (184)

NiTi Shape Memory Alloys (SMAs) display notable thermomechanical properties such as superelasticity and the elastocaloric effect, which makes them of interest for emerging solid-state cooling and thermal management applications. It is recognized that a considerable amount of work has been recently conducted to improve the understanding of the uniaxial tensile and compressive response of Ni-Ti SMAs; however, there has been limited work on the response to bending, which is an important operational mode in the practical designs of devices. This work consists of an experimental study of the thermomechanical response of Ni-Ti cantilever beams to cyclic bending. Nitinol samples (100 mm × 20 mm × 1 mm) were shape-set at 550 °C for 30 min and tested at 1800 rpm. The sample surface temperature change was monitored with infrared thermography data and analyzed with the Profile Mono Segment and Area Rectangle methods. The findings show that there was a measurable elastocaloric temperature change of approximately 4–5 °C, and temperature change increased by 21–25% as bending deflection increased from 31 mm to 33 mm. This was further shown to be nonlinear with the applied strain amplitude, reinforcing the strong coupling between mechanical and thermal response. The results demonstrate that Ni-Ti cantilever beams have significant potential for compact, sustainable solid-state cooling and energy storage applications, with thermal energy transfer strongly dependent on strain and energy transfer optimization. Full article

Spaceflight has become more accessible than ever due to increased launch reliability and significant advances in electronics. Among these advancements are small-sized PocketQubes, which are small satellites (5 × 5 × 5 cm for 1P) that can be built using commercial off-the-shelf components. A critical subsystem in these satellites is the communication system, which requires compact and deployable antennas. This work focuses on the design of deployable antennas for TU Delft’s upcoming Delfi-Twin PocketQube mission, operating in the 10 m and 6 m amateur bands. The Shape Memory Alloy (SMA) nitinol was selected as the antenna material due to its favorable mechanical and deployment characteristics. However, its high electrical resistivity limits antenna efficiency. This study investigates multiple conductive coating techniques for nitinol antenna wires, aiming to improve electrical performance while maintaining mechanical flexibility. The coatings are evaluated through electrical resistance measurements and mechanical bending tests. Among them, a DuPont ME164 ink showed the most promising performance, significantly reducing wire resistance compared to bare nitinol while preserving mechanical integrity. These results address a novel conductive coating for efficient SMA-based antennas and demonstrate a valid approach for improving deployable antennas in small-satellite applications. Full article

(1) Background: Endovascular therapy is widely used for lower limb peripheral artery disease (PAD), yet device performance varies across vascular territories due to anatomical and biomechanical differences. This study evaluated territory- and lesion-specific outcomes following contemporary endovascular strategies in a real-world cohort. (2) Methods: This retrospective single-center study included consecutive patients undergoing endovascular revascularization of the iliac, superficial femoral (SFA), or popliteal arteries between 2010 and 2023. The primary endpoint was 12-month binary restenosis (≥50% diameter loss) assessed by duplex ultrasonography, CT angiography, or invasive angiography. Secondary outcomes included target lesion revascularization and procedural complications. Kaplan–Meier analysis was used to evaluate restenosis-free survival. Multivariable Cox models were constructed separately for each vascular territory, adjusting for relevant clinical and anatomical covariates. (3) Results: A total of 283 lesions were included (iliac n = 135; SFA n = 145; popliteal n = 102). At 12 months, restenosis rates differed substantially by treatment modality and arterial territory. In the iliac segment, covered stents demonstrated the lowest restenosis (12.8%), whereas in the SFA, interwoven nitinol stents yielded the most favorable profile (15.4%). In the popliteal artery, drug-coated balloons were associated with the lowest restenosis rate (16.7%). In multivariable analysis, covered stents (iliac), interwoven nitinol stents (SFA), and drug-coated balloons (popliteal) were independently associated with lower restenosis risk. Procedural success was high and complication rates were low. (4) Conclusions: Endovascular device performance is strongly influenced by arterial territory and lesion characteristics. Tailoring the treatment strategy to vessel biomechanics and lesion morphology may optimize mid-term patency in lower limb PAD. Larger prospective studies are warranted to validate these findings. Full article

The object of the study is a permanent joint of thin wires made of nitinol alloy. The problem of ensuring the formation of a joint of wires made of nitinol alloy was solved based on minimising changes in the structure of the welded joint material relative to the materials being joined. The properties of the welded joint material of the nitinol were studied using scanning electron microscopy and micro-X-ray spectral analysis. The studied permanent joint was obtained by TIG, microplasma (PAW) and capacitor discharge (CDW) welding. It was found that TIG welding can ensure the proximity of the microstructures of the wire and welded joint materials under conditions of sufficient protection in an argon atmosphere. Such TiNi welded joints have a welded joint material that retains its superelastic properties (within the limits of the shape memory effect). Capacitor discharge welding allows the joint to be brought closer to the required level of microstructure of the weld material. The results of mechanical tests demonstrated the limited capabilities of joints made of thin nitinol wires. At the same time, the appearance of only newly formed TiNi + TiNi₃ eutectics in the weld material and a sufficient level of restoration of the welded joint shape give reason to consider capacitor discharge welding promising for joining thin nitinol wires. PAW leads to the formation of a significant amount of oxides in the weld and an increase in the number of Ti₂Ni inclusions, which leads to brittle fracture of the welded joint even at low degrees of deformation. The results of the study can be used, in particular, for the manufacture of nitinol wire joints in medical devices. Full article

Objectives: Transcatheter aortic valve implantation (TAVI) has become the standard of care for severe aortic stenosis across all surgical risk categories. Continuous innovation in prosthesis technology necessitates a comprehensive and clinically oriented analysis of contemporary TAVI systems to guide device selection and understand evolving trends. This review aims to provide a practical, device-specific decision-making framework for TAVI prosthesis selection, synthesizing the latest evidence (2023–2025) to address the challenge of individualized choice in an era of device proliferation. We conducted a detailed review of current TAVI models from leading manufacturers (Medtronic, Abbott, Boston Scientific, Biotronik, etc.), examining their technical specifications, design innovations, and data from recent international clinical trials and registries. A comparative analysis was performed based on key parameters: delivery profile, resheathability/repositionability, sealing mechanisms, hemodynamic performance, and complication rates. Modern TAVI prostheses demonstrate significant advancements. Self-expanding nitinol frames offer superior adaptability and lower profiles (as low as 14 Fr). Innovations in sealing technology have drastically reduced the incidence of moderate-to-severe paravalvular leak (PVL) to below 2–3%. Supra-annular leaflet designs provide superior hemodynamics. Clinical outcomes show excellent 30-day mortality rates (1.1–2.0%) and durability estimates of 10–15 years. Variation exists between devices in rates of permanent pacemaker implantation and coronary access. The current generation of TAVI prostheses represents a mature technology offering high safety and efficacy. The key development vectors are focused on further device miniaturization, enhancing long-term durability, and expanding indications. This analysis provides a novel, clinically oriented comparison that moves beyond technical specifications to guide optimal device selection based on specific patient anatomy and clinical characteristics. Full article

Shape memory alloys are key to sustainable technology and future industries, with one of the most remarkable materials at present being Nitinol (NiTi), which is known to have unique driving properties and applications, working in extreme conditions and capable of being applied in specific actuation tasks. In this context, this work presents an actuator prototype using versatile springs composed of nickel–titanium to produce angular displacements, beginning with contextual findings on the latest trends and opportunities for solutions in the field of Nitinol (NiTi) devices. Considering the research and industry concerns regarding shape memory materials and the need for research, design, and innovation in the development and investigation of various prototypes of Nitinol-based (NiTi) actuators, the functionalities, physical design, and static/dynamic performance of this newly proposed angular actuator offer strong potential. This work also presents and discusses the results of both experimental model testing and an analytical model simulation within MATLAB and Simulink R2022b. Full article

In this investigation, Ni_50.9Ti_49.1 wires cold rolled to 40% and straight annealed at 480 °C, 510 °C, and 550 °C, respectively, were heat treated to shape set these wires as helical springs and enhance their SME for use as electro-mechanical actuators. These spring actuators were heat treated at 350 °C, 400 °C, and 450 °C for 30, 60, and 90 min. The wires’ performance as actuators was assessed on a custom-built testing rig, which measured both the stroke and actuation time for each wire. Additionally, the wires were characterised experimentally by DSC, XRD, and nanoindentation. The final resulting properties of the R-phase transformation helical spring actuator are controlled by the competing mechanisms of dislocation annihilation, and precipitation of Ni₄Ti₃, as well as the prior thermomechanical treatment. The optimum conditions for actuator response in Ni_50.9Ti_49.1 40% cold-worked wires were a straight annealing temperature of 480 °C and shape-setting aging conditions of 450 °C for 60 min. These parameters result in the optimum combination of defect annihilation and density of precipitates, resulting in a high-stroke (56 mm), low-hysteresis (2.68 °C) actuator with an actuation time of 6 s. Full article

Patent foramen ovale (PFO) is implicated in cryptogenic stroke and other clinical syndromes, with transcatheter closure demonstrating superiority over medical therapy in selected patients. Most closure devices are composed of nitinol, a nickel–titanium alloy, raising concerns in individuals with nickel hypersensitivity, one of the most prevalent contact allergies worldwide. Although typically manifesting as localized dermatitis, nickel allergy has been associated with systemic reactions after device implantation, including chest pain, palpitations, migraines, dyspnea, and cutaneous eruptions. Recent evidence indicates that nickel-sensitive patients experience a significantly higher incidence of post-procedural device-related symptoms. Nevertheless, severe reactions remain rare, and the benefits of PFO closure generally outweigh the risks. The predictive value of pre-implantation patch testing remains uncertain, and the lack of nickel-free alternatives constrains device selection. Management strategies are empirical, relying on symptomatic treatment with corticosteroids, antihistamines, or device explantation in refractory cases. Future research should focus on elucidating the pathophysiology of nickel-induced hypersensitivity in cardiovascular implants, improving diagnostic algorithms, and developing biocompatible, nickel-free devices. A multidisciplinary approach involving cardiologists, dermatologists, and allergists is essential to optimize outcomes in this complex subset of patients. Full article

Background: Stapes prostheses represent one of the earliest and most widely applied “biomedical actuators” designed to restore hearing in patients with otosclerosis. Unlike conventional actuators, which convert energy into motion, stapes prostheses function as passive or smart micro-actuators, transmitting and modulating acoustic energy through the ossicular chain. Objective: This paper provides a comprehensive analysis of stapes prostheses from an engineering and biomedical perspective, emphasizing design principles, materials science, and recent innovations in smart actuators based on shape-memory alloys combined with surgical applicability. Methods: A narrative review of the evolution of stapes prostheses was consolidated by institutional surgical experience. Comparative evaluation focused on materials (Teflon, Fluoroplastic, Titanium, Nitinol) and design solutions (manual crimping, clip-on, heat-activated prostheses). Special attention was given to endoscopic stapes surgery, which highlights the ergonomic and functional requirements of new device designs. Results: Traditional fluoroplastic and titanium pistons provide reliable sound conduction but require manual crimping, with a higher risk of incus necrosis and displacement. Innovative prostheses, particularly those manufactured from nitinol, act as self-crimping actuators activated by heat, improving coupling precision and reducing surgical trauma. Emerging designs, including bucket-handle and malleus pistons, expand applicability to complex or revision cases. Advances in additive manufacturing and middle ear cement fixation offer opportunities for customized, patient-specific actuators. Conclusions: Stapes prostheses have evolved from simple passive pistons to innovative biomedical actuators exploiting shape-memory and biocompatible materials. Future developments in stapes prosthesis design are closely linked to 3D printing technologies. These developments have the potential to enhance acoustic performance, durability, and patient outcomes, thereby bridging the gap between otologic surgery and biomedical engineering. Full article

A Nitinol rod-driven discrete continuum robot with two sections and eight units was developed to support clinicians in performing transoral surgery. The robot measures 120 mm in length, with each unit having a diameter of 15 mm and a height of 20 mm. The distal and proximal sections are designed to bend independently, each with two degrees of freedom (DOF) actuated by four Nitinol rods. To validate the independent controllability of the two sections, two-dimensional bending tests and ANSYS simulations were conducted. For the assessment of clinical feasibility, head and neck CT images from ten patients were manually segmented to reconstruct three-dimensional oral cavity models. Ten fictitious reference passages were generated from the lips to the oropharynx, and planar path-planning simulations were performed using these passages. Verification experiments were carried out on three reference passages employing experimentally derived inverse kinematics. The simulation results demonstrated an average reference path-following error within a root mean square (RMS) of 1.9705 mm at maximum insertion length. Experimental path-planning results showed average absolute angular differences of 5.6 degrees in the distal section and 4.1 degrees in the proximal section when compared with the simulations. Full article

Purpose: Transcatheter heart valve replacements (TVR) are typically designed in a closed shape with initial leaflet coaptation. However, recent studies suggest a semi-closed geometry without a predefined coaptation zone, relying on diastolic pressure and clinical oversizing of 10–20 % for closure. This approach may minimize pinwheeling, a phenomenon linked to early valve degeneration. Method: Seven valve geometries were assessed: one closed design (G0) and six semi-closed variations (G1–G6). The semi-closed designs differed in free edge shape (linear, concave, convex) and opening degree, defined as the relative distance from the leaflet to the valve center in the unloaded state. The opening degree was systematically increased across G1–G6, with G6 exhibiting the highest value. 30 mm valves were fabricated using porcine pericardium and self-expanding nitinol stents. Performance was assessed in a pulse duplicator system, evaluating transvalvular pressure gradient (TPG), effective orifice area (EOA), regurgitation fraction (RF) and a novel pinwheeling index (PI) which was validated by finite element simulations. Results: Finite element simulations demonstrated that semi-closed geometries achieve valve closure at a diameter reduction of >5%. In vitro tests confirmed these findings with more homogeneous coaptation and reduced pinwheeling. With increased opening degree the RF reduced significantly (RF_G0 = 18.54 ± 8.05%; RF_G6 = 8.22 ± 1.27%; p < 0.0001), while valve opening remained comparable (p = 0.4519). Conclusions: A semi-closed leaflet geometry enhances valve closure, reducing regurgitation and pinwheeling while preserving effective opening. With clinical oversizing, a higher opening degree improves coaptation and may enhance durability by mitigating structural deterioration, ultimately improving the long-term performance and lifespan of transcatheter valve replacements. Full article

Shape memory alloy (SMA) materials are valued for their shape memory effect, superelasticity, and biocompatibility, making them an ideal choice for applications in biomedical, aerospace, and actuator fields. Nickel–titanium (NiTi) SMA is a promising biomedical material. It is widely used in the manufacture of biomedical instruments, devices, implants, and surgical tools. However, its complex thermo-mechanical behavior and poor machinability pose challenges for conventional machining. To manufacture high-quality nitinol parts, traditional machining processes are being replaced by advanced machining technologies. Electric discharge machining (EDM) is an advanced machining technique whose mechanism of material removal involves erosion caused by plasma formation and spark generation. It has proven effective for processing difficult-to-machine materials. This review summarizes EDM and its variants, including hybrid EDM, with a focus on machining NiTi-SMA materials for biomedical, aerospace, microelectromechanical systems, and automotive applications, and systematically explores key factors such as process parameters, material removal mechanisms, surface integrity, tool wear, and optimization strategies. This review begins with an introduction to nitinol (i.e., NiTi-SMA) and its variants, followed by an in-depth discussion of plasma formation, spark generation mechanisms, and other key aspects of EDM. It then provides a detailed analysis of notable past research on the machining of NiTi SMA materials using EDM and its variants. This paper concludes with insights into future research directions, aiming to advance EDM-based machining of SMA materials and serve as a valuable resource for researchers and engineers in the field. Full article

Incorporating Nitinol (NiTi) shape memory alloy (SMA) into concrete structures has gained significant attention in recent years due to its ability to enhance the properties of concrete. This review paper illustrates the history of NiTi SMA and its use in various civil engineering structural applications. A detailed analysis of the existing literature and case studies offers perspectives on the possible applications, benefits, and prospects of utilizing NiTi SMA to reinforce and strengthen elements in concrete structures. The study examined publications on the internal usage of NiTi SMA in concrete and cement-based matrices as an embedded element, including fibers, bars, cables, wires, powder, and strands. In addition, superelastic and shape memory forms of NiTi were considered. It was concluded that the superelasticity of NiTi aided in energy dissipation from impact or seismic events. It also improved the re-centering performance and deformation capacity and reduced residual stresses, strains, and cracks. Conversely, the SMA effect of NiTi helped bridge cracks, recover the original shape, and induced prestressing forces under thermal activation. Full article

Background/Objectives: Lower urinary tract symptoms (LUTSs) due to benign prostatic obstruction (BPO) represent a common condition affecting aging men. Transurethral resection of the prostate represents the gold standard surgical treatment but is not without complications such as retrograde ejaculation, bleeding and urinary retention. The temporary implantable nitinol device (iTIND) is considered a minimally invasive surgical technique, designed to treat LUTS while preserving erectile and ejaculatory function. Herein we report the results of a multi-center, real-world assessment of the iTIND procedure. Methods: Data from five international centers treating LUTS with the iTIND device were collected. We recorded changes through an International Prostatic Symptom Score (IPSS) questionnaire with Quality of Life (QoL), International Index of Erectile Function (IIEF5) questionnaire, antegrade ejaculatory function, maximum flow (QMax), post voiding residual volume (PVR) and freedom from repeat intervention. Results: A total of 74 subjects were enrolled; median follow-up was 12 months. IPSS and QoL changed from a median of 23 and 4 points at baseline to 11 and 2 points, respectively, at the last follow-up. A mean improvement in Qmax and PVR from 9 mL/s and 56 mL at baseline to 13 mL/s and 40 mL was noticed at the last follow-up. Total median operative time was 10 min, and the median time of iTIND indwell time was 7 days. The median device removal time was 5 min. There were no changes in IIEF5 scores and antegrade ejaculation rate. No intraoperative complications were reported, and non-serious postoperative complications occurred in six patients (two urinary retention, two mild haematuria, two urinary tract infection). Finally, four patients underwent reoperation during the follow-up period. All procedures were performed as outpatient day cases. Conclusions: Our results confirms that treatment with the iTIND is effective and safe in terms of improving urinary symptoms and quality of life without impacting sexual function. Longer follow-up is required to better define the durability of this minimally invasive procedure. Full article

Thoracic endovascular aortic repair (TEVAR) for cardiovascular diseases often encounters complications that are closely linked to the mechanical properties of stent-grafts. Both the design and material properties influence device performance, but the specific impacts of material properties remain underexplored and poorly understood. This study aims to fill this gap by systematically investigating how material science can modulate stent-graft mechanics. Four types of bare nitinol stents combined with expanded polytetrafluoroethylene (e-PTFE) or polyethylene terephthalate (PET) grafts were modeled via finite element analysis, creating eight stent-graft configurations. Key mechanical properties—flexibility, crimpability, and fatigue performance—were evaluated to dissect material effects. The results revealed that nitinol’s properties significantly influenced all performance metrics, while PET grafts notably enhanced flexibility and fatigue life. No significant differences in equivalent stress were found between PET and e-PTFE grafts, and both had minimal impacts on radial force. This work underscores the potential of material science-driven optimization to enhance stent-graft performance for improved clinical outcomes. Full article