Severe Mechanical Deformations Research Articles

Mechanically Robust and Linearly Sensitive Soft Piezoresistive Pressure Sensor for a Wearable Human-Robot Interaction System.

Soft piezoresistive pressure sensors play an underpinning role in enabling a plethora of future Internet of Things (IoT) applications such as human-robot interaction (HRI) technologies, wearable devices, and metaverse ecosystems. Despite significant attempts to enhance the performance of these sensors, existing sensors still fall short of achieving high strain tolerance and linearity simultaneously. Herein, we present a low-cost, facile, and scalable approach to fabricating a highly strain-tolerant and linearly sensitive soft piezoresistive pressure sensor. Our design utilizes thin nanocracked gold films (NC-GFs) deposited on poly(dimethylsiloxane) (PDMS) as electrodes of the sensor. The large mismatch stress between gold (Au) and PDMS induces the formation of secondary wrinkles along the pyramidal-structured electrode under pressure; these wrinkles function as protuberances on the electrode and enable exceptional linear sensitivity of 4.2 kPa-1 over a wide pressure range. Additionally, our pressure sensor can maintain its performance even after severe mechanical deformations, including repeated stretching up to 30% strain, due to the outstanding strain tolerance of NC-GF. Our sensor's impressive sensing performance and mechanical robustness make it suitable for diverse IoT applications, as demonstrated by its use in wearable pulse monitoring devices and human-robot interaction systems.

A zinc-ion battery-type self-powered strain sensing system by using a high-performance ionic hydrogel.

Flexible strain sensors based on conductive hydrogels have profound implications for wearable electronics and health-monitoring systems. However, such sensors still need to integrate with energy providing devices to drive their functions. Herein, we develop a soaking-free polyacrylamide/carboxymethyl cellulose/tannic acid (PAAM/CMC/TA) hydrogel containing 2 M ZnSO4 + 0.1 M MnSO4 electrolyte for a novel zinc-ion battery-type self-powered strain sensing system. The synthesized hydrogel possesses desirable stretchability (tensile strain/stress of 622%/132 kPa), self-healing and self-adhesive properties, as well as good ionic conductivity (0.76 ± 0.04 S m-1). A mechanically durable Zn-MnO2 battery is developed using the PAAM/CMC/TA hydrogel and it can deliver a high specific capacity (223.0 mA h g-1) and maintain stable energy outputs under severe mechanical deformations. The electrochemical behavior of the battery can recover even after several self-healing cycles. Due to the excellent strain and pressure sensing properties of the PAAM/CMC/TA hydrogel, the battery combined with a fixed resistor served as a self-powered wearable sensing device, which could translate different human movements into distinguishable electrical signals without an external power supply. Our work provides guidance for the development of next-generation self-powered sensors.

(Digital Presentation) A Shape-Adjustable, Flexible Lithium Battery

Integrating stimuli-responsive materials into energy storage technologies opens a new approach to introduce novel functionalities as well as addressing some of the crucial and unresolved issues. As an example, current flexible lithium-ion batteries (LIBs) still suffer from a fragile or susceptible nature and limited electrochemical performance recovery against severe or repeated mechanical deformations. Thus, integrating a stimuli-responsive material with strong ability to recover from severe and repeated mechanical deformations into the flexible LIBs can be an effective approach to address the shape and performance recovery issue concerning the flexible LIBs [1-3].Herein, we design and synthesize a solid polymer electrolyte (SPE) based on a shape memory polymer (SMP) to integrate into flexible lithium batteries for smart applications, for example, shape recovery from severe mechanical deformation. SMPs are attractive class of programmable, stimuli-responsive polymer materials demonstrating shape-memory behavior. A SMP has the ability to memorize its original or permanent shape; deform, fix into a temporary or secondary shape; and recover its original form via applying an external stimulus, for example, heat, magnetic or electrical field,light [3]. In fact, when mechanical deformation occurs, batteries typically suffer from reduced power, efficiency, capacity and recovery from the deformation without sacrificing the electrochemical performance would be highly desirable. The shape-memory SPE is made based on a cross-linkable polyethylene oxide (PEO) with controlled crystallinity and the ability to indue shape memory behavior above the melting point. PEO is chosen as a model shape-memory polymer due to its unique properties including low-cost, high dielectric constant and Li+-ion solvating ability, high electrochemical and mechanical stability, semi-crystalline nature, and ability to introduce cross-linkable functionalities. In response to a temperature exceeding the melting point of the polymer matrix (~70 oC), the engineered shape memory SPE can recover its original shape and size from mechanical deformations, for example, bending and folding. The all-solid-state shape-memory SPEs also show excellent electrochemical performance in Li/Li and Li/LFP cells at ambient temperature. The Li/LFP cell made using the shape memory SPE delivers a specific capacity ~140 mAh g‒1 with ~92% capacity retention after 100 cycles at 0.2C charge/discharge rate and ~99.85% Coulombic efficiency. Besides excellent electrochemical performance, we demonstrate that a flexible Li based battery made using the shape memory SPE can recover from severe mechanical deformations, for example, bending and folding, upon applying heat. This proof-of-concept study opens up a new approach to design and integrate smart functionalities into energy storage technologies. Reference [1] Z. Fang, J. Wang, H. Wu, Q. Li, S. Fan, J. Wang, J. Power Sources 454, 227932 (2020).[2] M. Koo, K. Park, S. H. Lee, M. Suh, D. Y. Jeon, J. W. Choi, K. Kang, K. J. Lee, Nano Lett. 12, 4810–4816 (2012).[3] V. Jabbari, V. Yurkiv, M. G. Rasul, M. Cheng, P. Griffin, F. Mashayek, R. Shahbazian-Yassar, Small 2021, 2102666, DOI: 10.1002/smll.202102666.

Wearable, freezing-tolerant, and self-powered electroluminescence system for long-term cold-resistant displays

Tremendous efforts in wearable optoelectronics have recently harnessed considerable advances in intrinsically stretchable electroluminescence (EL) devices. However, developing wearable optoelectronics that maintain long-term stability in harsh cold environments is still challenging. Here, a wearable, freezing-tolerant, and self-powered EL system is developed based on organohydrogel-based EL (OH-EL) device integrated with liquid electrolyte-based single-electrode triboelectric nanogenerator (LE-TENG), in which the OH-EL device based on self-healing and highly conductive organohydrogel electrodes can be directly lit by the LE-TENG. The stretchable OH-EL device demonstrates a bright and uniform light emission under 140% tension stretching as well as severe mechanical deformations of bending, rolling, and twisting. Moreover, the optical performances of the OH-EL device exhibit excellent repeatability and durability after continuous 2000 cycles. More importantly, bright blue-green light emission of the self-powered EL system stored at 253 K can maintain for six months, demonstrating extremely long-term freezing-tolerant capability. Furthermore, while harvesting the biomechanical energy of hand slapping and knee/elbow bending, the self-powered EL system worn on different parts of human body can achieve real-time visualized displays. Consequently, the simple fabrication and unique operation of the self-powered EL system demonstrate potential application in cold-resistant displays, wearable self-powered photoelectric devices, soft robotics, and other fields.

A Smart Lithium Battery with Shape Memory Function.

Rapidly growing flexible and wearable electronics highly demand the development of flexible energy storage devices. Yet, these devices are susceptible to extreme, repeated mechanical deformations under working circumstances. Herein, the design and fabrication of a smart, flexible Li-ion battery with shape memory function, which has the ability to restore its shape against severe mechanical deformations, bending, twisting, rolling or elongation, is reported. The shape memory function is induced by the integration of a shape-adjustable solid polymer electrolyte. This Li-ion battery delivers a specific discharge capacity of ≈140mAhg-1 at 0.2 C charge/discharge rate with ≈92% capacity retention after 100 cycles and ≈99.85% Coulombic efficiency, at 20 °C. Besides recovery from mechanical deformations, it is visually demonstrated that the shape of this smart battery can be programmed to adjust itself in response to an internal/external heat stimulus for task-specific and advanced applications. Considering the vast range of available shape memory polymers with tunable chemistry, physical, and mechanical characteristics, this study offers a promising approach for engineering smart batteries responsive to unfavorable internal or external stimulus, with potential to have a broad impact on other energy storage technologies in different sizes and shapes.

Interconnecting 3D Conductive Networks with Nanostructured Iron/Iron Oxide Enables a High-Performance Flexible Battery.

Aqueous Ni/Fe alkaline batteries with features of low cost and high safety show great potential for application in portable and wearable electronics. However, the poor kinetics of the Fe-based anode greatly limits the large-scale applications of Ni/Fe batteries. Herein, we report an interconnected 3D conductive network with carbon-coated nanostructured iron/iron oxide (3D-Fe/Fe2O3@C) as an efficient anode for a flexible Ni/Fe battery. A hydrogel precursor is used to molecularly link and confine Fe3+ to spatial networks, resulting in a uniform dispersion of Fe/Fe2O3-heterostructured nanoparticles. Theoretical investigations reveal regulated potential loss and improved delocalized carrier density as a result of carbon coating and the mixed metal/metal oxide structure. In addition to these merits, due to the regulated wettability and electroactive surface areas, the 3D-Fe/Fe2O3@C anode with a high mass loading delivers an extraordinary areal capacity of 3.07 mA h cm-2, as well as the boosted rate capability and Coulombic efficiency. When coupled with the NiCo2O4 cathode, the flexible quasi-solid-state Ni/Fe battery exhibits an admirable energy density of 15.53 mW h cm-3 and a maximum power density of 761.91 W h cm-3. The good stability after 20,000 cycles and severe mechanical deformations of the as-fabricated Ni/Fe battery imply it as a promising flexible energy storage device for practical applications.

Printed Stretchable Single-Nanofiber Interconnections for Individually-Addressable Highly-Integrated Transparent Stretchable Field Effect Transistor Array.

Stretchable electronics have been spotlighted as promising next-generation electronics. In order to drive a specific unit device in an integrated stretchable device, the interconnection of the device should be placed in a desired position and addressed individually. In addition, practical stretchable interconnection requires reliable stretchability, high conductivity, optical transparency, high resolution, and fast and large-scale production. This study proposes an approach to meet these requirements. We print the single wavy polymer nanofibers (NFs) in a desired position and convert them into metal NF interconnections. The nanoscale diameter and the wavy cylindrical shape of the metal NFs are the main reasons for the reliable stretchability and the excellent transparency. Using the stretchable metal NFs and the stretchable organic semiconductor NFs, an array of all-stretchable transparent NF-field effect transistors (NF-FETs) is demonstrated. The highly integrated NF-FET array (10 FETs/mm2) shows uniform performance and good stability under repeated severe mechanical deformations.

Super Stretchable and Durable Electroluminescent Devices Based on Double-Network Ionogels.

Ionogels are good candidates for flexible electronics owing to their excellent mechanical and electrical properties, including stretchability, high conductivity, and stability. In this study, conducting ionogels comprising a double network (DN) of poly(N-isopropylacrylamide-co-N,N'-diethylacrylamide)/chitosan which are further reinforced by the ionic and covalent crosslinking of the chitosan network by tripolyphosphate and glutaraldehyde, respectively, are prepared. Based on their excellent mechanical properties and high conductivity, the developed DN ionogels are envisioned as stretchable ionic conductors for extremely stretchable alternating-current electroluminescent (ACEL) devices. The ACEL device fabricated with the developed ionogel exhibits stable working operation under an ultrahigh elongation of over 1200% as well as severe mechanical deformations such as bending, rolling, and twisting. Furthermore, the developed ACEL devices also display stable luminescence over 1000 stretch/release cycles or at temperatures as harsh as 200 °C.

Neuroprosthetics: Durable and Fatigue‐Resistant Soft Peripheral Neuroprosthetics for In Vivo Bidirectional Signaling (Adv. Mater. 20/2021)

In article number 2007346, Dae-Hyeong Kim, Taeghwan Hyeon, Donghee Son, and co-workers develop a durable and fatigue-resistant soft bidirectional neuroprosthetic device composed of a biocompatible nanocomposite of gold-nanoshell-coated silver flakes dispersed in a tough, stretchable, and self-healing polymer. The electrical conductivity of our neuroprosthetics spontaneously recovers even after repetitive degradations by irregular and severe mechanical deformations.

Textile-based wearable solid-contact flexible fluoride sensor: Toward biodetection of G-type nerve agents

Rising global concerns posed by chemical and biological threat agents highlight the critical need to develop reliable strategies for the real-time detection of such threats. While wearable sensing technology is well suited to fulfill this task, the use of on-body devices for rapid and selective field identification of chemical agents is relatively a new area. This work describes a flexible printed textile-based solid-contact potentiometric sensor for the selective detection of fluoride anions liberated by the biocatalytic hydrolysis of fluorine-containing G-type nerve agents (such as sarin or soman). The newly developed solid-contact textile fluoride sensor relies on a fluoride-selective bis(fluorodioctylstannyl)methane ionophore to provide attractive analytical performance with near-Nernstian sensitivity and effective discrimination against common anions, along with excellent reversibility and repeatability for dynamically changing fluoride concentrations. By using stress-enduring printed inks and serpentine structures along with stretchable textile substrates, the resulting textile-based fluoride sensor exhibits robust mechanical resiliency under severe mechanical strains. Such realization of an effective textile-based fluoride-selective electrode allowed biosensing of the nerve-agent simulant diisopropyl fluorophosphate (DFP), in connection to immobilized organophosphorus acid anhydrolylase (OPAA) or organophosphorus hydrolase (OPH) enzymes. A user-friendly portable electronic module transmits data from the new textile-based potentiometric biosensor wirelessly to a nearby smartphone for alerting the wearer instantaneously about potential chemical threats. While expanding the scope of wearable solid-contact anion sensors, such a textile-based potentiometric fluoride electrode transducer offers particular promise for effective discrimination of G-type neurotoxins from organophosphate (OP) pesticides, toward specific field detection of these agents in diverse defense settings.

Organism epidermis/plant-root inspired ultra-stable supercapacitor for large-scale wearable energy storage applications

Wearable energy storage system must maintain robust electrochemical performance under severe mechanical and chemical deformations. Here, we demonstrate wearable supercapacitor system assembled with electrodes composed of one-step carbonized plant epidermis and gelatin based hydrogel electrolyte which possesses high electrochemical performance and superior reliability under ambient condition. The carbonized mulberry paper (MP) was used as an electrode to achieve improved volumetric energy density as well as mechanical-chemical reliability (e.g. mechanical toughness and acid resistance). Rationally designed active materials composed of vertically grown WO 3 NRs and reduced graphene oxide (rGO) anchored on MP, were employed for developing organism epidermis based supercapacitor. Such electrode exhibits high volumetric energy and power densities of 30.28 mWh cm −3 and 7.67 W cm −3 , retaining the volumetric capacitance of 96.0% even after 110,000 charge-discharge cycles. As the final step, we employed the gelatin based electrolyte with high ionic conductivity to solve evaporation and leakage problems of conventional electrolytes. Organism epidermis based supercapacitor integrated with hydrogel electrolyte showed high electrochemical performance and long-term stability under ambient condition even after exposure to acid, demonstrating its gareat suitability as a large-scale wearable energy storage system. We demonstrate wearable supercapacitor system assembled with electrodes composed of one-step carbonized plant epidermis and gelatin based hydrogel electrolyte which possesses high electrochemical performance and superior reliability under ambient condition. Organism epidermis based supercapacitor integrated with hydrogel electrolyte showed high electrochemical performance and long-term stability under ambient condition even after exposure to acid, demonstrating its great suitability as a large-scale wearable energy storage system. • We maximized areal and volumetric electrochemical performance (energy & power densities) and mechanical/chemical toughness through carbonized mulberry paper integrated with reduced graphene oxide (rGO) layer. Mulberry fibers inherently show excellent mechanical flexibility and acid resistance, since they have lower portion of lignin cellulose (~40%) compared with conventional paper fiber. However, electrochemically inactive mulberry fiber exhibits still low areal/volumetric energy densities and electrochemical reliability. Thus, we used carbonized mulberry paper as a substrate and electrode in this study, which was maximized for volumetric energy/power densities and mechanical/chemical toughness. • We have designed the plant-root inspired active materials structure with excellent electrochemical reliability and performances. Inspired from plant-root, we synthesized active materials structure by one-step reduction heat treatment, where WO 3 nanorods (NRs) vertically grow within the spaces of rGO and are anchored as strongly as plant-root on the carbonized mulberry fibers. The anchored structure can effectively maintain electrochemical performance and flexibility of carbonized paper by preventing delamination of WO 3 NRs even without protection layer. WO 3 NRs anchored carbonized mulberry paper (thickness 110 µm) with rGO layer exhibits volumetric capacitance retention of 96% for 110,000 cycles. In addition, maximum volumetric energy and power densities were increased to 30.28 mWh cm −3 and 7.67 W cm −3 (improvement of 220%). • Conventional liquid and gel-type electrolyte have critical issues including evaporation under ambient condition and leakage under mechanical bending-twisting deformation. Such problems are main causes of rapid electrochemical performance degradation. In our work, gelatin based hydrogel electrolyte extracted from porcine skin was integrated with electrode, in order to fabricate wearable energy storage system that is capable of operating in ambient conditions. The gelatin based hydrogel electrolyte can retain water contents and high ionic conductivity under ambient condition over 2 weeks. Ionic conductivity maintained 90.3% (228 mS cm −1 ) after two weeks of exposure to ambient condition, and the moisture content was maintained 98.0%. • We further extended organism epidermis based supercapacitor to large-scale application capable of operation in ambient condition. High hydrophilicity of mulberry paper enables the uniform deposition of precursor material for growth of WO 3 , i.e, WO 3 precursor, that is dispersed in the aqueous solution. As a result, GO and WO 3 precursor were uniformly deposited on large-area electrode with 9, 25, 49 cm 2 followed by carbonization, resulting in the fabrication of large-scale organism epidermis based supercapacitor.

Microstructural Evolutions During the ECMAP Process Using the Die with Optimum Geometrical Parameters

Various severe plastic deformation methods have been considered by numerous researchers with the purpose of making fine-grained parts with a high strength-to-weight ratio by applying severe mechanical deformations without changing the chemical composition of the material. The die of equal channel multiangular pressing (ECMAP) process was used here to exert repetitive severe plastic deformation on Al-3%Mg strip-type samples. In this work, the ECMAP die was made considering optimal geometric values that had been obtained in the previous studies by the grey optimization method, and then the microstructural evolution of output parts were studied carefully. Grain size distribution in various channels and channels curvature was extracted. The results showed that the average grain size obtained after the initial annealing operation is 39.48 μm, after passing through the first channel; the value reduces to 19.57 μm, and after passing through the second and third channels, the average grain size decreases to 9.74 and 6.66 μm, respectively.

Intertwined Nanosponge Solid-State Polymer Electrolyte for Rollable and Foldable Lithium-Ion Batteries.

Herein, we report a straigthforward procedure to prepare an excellent intertwined nanosponge solid-state polymer electrolyte (INSPE) for highly bendable, rollable, and foldable lithium-ion batteries (LIBs). The mechanically reliable and electrochemically superior INSPE is conjugated with intertwined nanosponge (IN) poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) and ion-conducting polymer electrolyte (PE) containing poly(ethylene glycol) diacrylate (PEGDA), succinonitrile (SCN) plasticizer, and lithium bis(trifluoromethanesilfonyl)imide (LiTFSI). The conjugated INSPE has both high strength with great flexibility (tensile strength of 2.1 MPa, elongation of 36.7%), and excellent ionic conductivity (1.04 × 10-3 S·cm-1, similar to the values of liquid electrolytes). As a result of such special combination, the as-prepared INSPE retains almost 100% of its ionic conductivity when subjected to many types of severe mechanical deformations. Therefore, the INSPE is successfully applied to bendable, rollable, and foldable LIBs that show excellent energy storage performance despite the intense mechanical deformations.

Bending fatigue damage reduction in indium tin oxide (ITO) by polyimide and ethylene vinyl acetate encapsulation for flexible solar cells

Hybrid organic-inorganic perovskites hold tremendous promise for next-generation portable power source applications. However, the device reliability under severe mechanical deformations is limited due to the use of brittle indium tin oxide (ITO). In the current study, we have attempted to enhance the bendability of the device by employing an encapsulation on the ITO coated polyethylene terephthalate (PET) substrate. The aim of this encapsulant buffer layer is to shift the location of the maximum bending stresses away from the ITO as well as provide barrier properties against the environment. Ethylene-vinyl acetate (EVA), as well as Polyimide (PI) films, have been used as encapsulating materials with the aim to shift the location of the neutral axis to the ITO. Finite element analysis has been done to evaluate the principal stresses generated in ITO during monotonic bending under different modes of bending, the thickness of encapsulant layers as well as radii of bending. The effect of the number of bending cycles, mode of bending as well as the bending radii on the conductivity of the ITO have been studied experimentally. A large change in resistance of ITO film has been used as a metric to determine the failure of the ITO film. Samples encapsulated with an optimum thickness of PI shows a significant reduction in percentage change in resistance as compared to raw samples for both cases of bending, while EVA encapsulated samples hardly show any improvement. Moreover, both the modulus and thickness of an encapsulant play an important role in enhancing the bendability.

Vapor dealloying of ultra-thin films: a promising concept for the fabrication of highly flexible transparent conductive metal nanomesh electrodes

The booming market of flexible electronic displays has urged the development of highly flexible transparent conductive electrodes (FTCE)1–3 with the ability to replace indium tin oxide (ITO) thin films routinely used as transparent conductive electrodes in photoelectronic devices. The high cost of indium and the poor mechanical stability of ITO under deformation are the main driving forces behind the development of this research area.4 The use of metal nanomeshes as FTCE is a promising concept with a real potential to substitute ITO in photoelectronic devices.5,6 However, the development of a low-cost fabrication approach allowing producing metal nanomesh electrodes with competitive prices and a high performance remains a real bottleneck for the photoelectronic industry. In this paper, we report on a robust approach very easy to implement allowing producing highly flexible metal nanomesh electrodes with high performance at a very low cost. This approach lies on a concept consisting in applying dealloying process to ultra-thin Au-Cu alloy thin films using acidic vapors instead of a liquid phase as routinely done in the literature. Using an appropriate procedure, the nanomeshes can be transferred to any planar or curved support where they can serve as a FTCE. As a proof of concept, we demonstrate that using this approach, one can easily fabricate gold nanomesh electrodes transferred onto polyethylene terephthalate (PET) film surface with 79% of transmittance and a sheet resistance as low as 44 Ω □−1 while maintaining exceptional stability under severe mechanical deformations.

Cross-sectional pinching in human femoropopliteal arteries due to limb flexion, and stent design optimization for maximum cross-sectional opening and minimum intramural stresses.

High failure rates of femoropopliteal artery (FPA) interventions are often attributed to severe mechanical deformations that occur with limb flexion. One of these deformations, cross-sectional pinching, has a direct effect on blood flow, but is poorly characterized. Intra-arterial markers were deployed into n = 50 in situ cadaveric FPAs (80 ± 12 years old, 14F/11M), and limbs were imaged in standing, walking, sitting and gardening postures. Image analysis was used to measure marker openings and calculate FPA pinching. Parametric finite element analysis on a stent section was used to determine the optimal combination of stent strut amplitude, thickness and the number of struts per section to maximize cross-sectional opening and minimize intramural mechanical stress and low wall shear stress. Pinching was higher distally and increased with increasing limb flexion. In the walking, sitting and gardening postures, it was 1.16-1.24, 1.17-1.26 and 1.19-1.35, respectively. Stent strut amplitude and thickness had strong effects on both intramural stresses and pinching. Stents with a strut amplitude of 3 mm, thickness of 175 µm and 20 struts per section produced pinching and intramural stresses typical for a non-stented FPA, while also minimizing low wall shear stress areas, and ensuring a stent lifespan of at least 107 cycles. These results can help guide the development of improved devices and materials to treat peripheral arterial disease.

Invited commentary

Given that the superficial femoral and popliteal arteries look fairly straight when a patient is lying supine on a fluoroscopy table, the temptation to view this arterial segment as one long biomechanical continuum seems somewhat understandable. However, Poulson et al have adeptly reminded us that this is not necessarily the case. With the use of an innovative system of nitinol markers deployed along the course of cadaveric femoral and popliteal arteries, these authors have depicted the significant deformations that take place during the course of normal daily activities. Poulson et al are not the first to demonstrate that the femoropopliteal arteries shorten, elongate, bend, buckle, and twist. Numerous prior researchers have done that using three-dimensional magnetic resonance angiography, three-dimensional computed tomography angiography, and fluoroscopy, in combination with finite-element analysis.1Ansari F. Pack L.K. Brooks S.S. Morrison T.M. Designed considerations for studies of the biomechanical environment of the femoropopliteal arteries.J Vasc Surg. 2013; 58: 804-813Abstract Full Text Full Text PDF PubMed Scopus (68) Google Scholar, 2Ghriallais R.N. Bruzzi M. Effects of knee flexion on the femoropopliteal artery: a computation of study.Med Eng Phys. 2013; 35: 1620-1628Abstract Full Text Full Text PDF PubMed Scopus (10) Google Scholar, 3Fortier A. Gullapalli V. Mirshams R.A. Review of biomechanical studies of arteries and their effect on stent performance.IJC Heart Vessels. 2014; 4: 12-18Abstract Full Text Full Text PDF Scopus (52) Google Scholar However, the current study does emphasize just how inhomogeneous and severe these strains can be, particularly at sites where arteries are fixed to surrounding structures, such as descending geniculate branches, the adductor canal, and popliteal bifurcation. Although the femoropopliteal arteries in the current study came from older donors, the arteries were relatively free of atherosclerosis. It would be quite interesting to see the effect of calcification, atherosclerotic thickening, and the presence of one or even multiple overlapping stents on the motion of these arteries. Manufacturers have made some progress with regard to stents specifically designed for the femoropopliteal environment. However, we also need to advance our clinical knowledge (eg, the correct stent for the correct segment, the optimal degree of overlap, if any), because there is much room for improvement in the way we use these stents. The opinions or views expressed in this commentary are those of the authors and do not necessarily reflect the opinions or recommendations of the Journal of Vascular Surgery or the Society for Vascular Surgery. Limb flexion-induced axial compression and bending in human femoropopliteal artery segmentsJournal of Vascular SurgeryVol. 67Issue 2PreviewHigh failure rates of femoropopliteal artery (FPA) interventions are often attributed in part to severe mechanical deformations that occur with limb movement. Axial compression and bending of the FPA likely play significant roles in FPA disease development and reconstruction failure, but these deformations are poorly characterized. The goal of this study was to quantify axial compression and bending of human FPAs that are placed in positions commonly assumed during the normal course of daily activities. Full-Text PDF Open Archive

Carbon‐Nanotube‐Templated, Sputter‐Deposited, Flexible Superconducting NbN Nanowire Yarns

Flexible superconducting yarns consisting of sputter‐deposited NbN nanowires on highly aligned carbon nanotube (CNT) array sheets are reported. In the microscopic view, the NbN nanowires are formed on top of individual CNT fibrils, and the superconductivity property of the twist‐spun NbN–CNT yarn system is comparable to that of a typical NbN thin film on a normal solid substrate. Because of its intrinsic porosity, the system exhibits superior mechanical flexibility with a small bending radius. It also remains a superconducting state even when subjected to severe mechanical deformations, primarily due to the proximity superconductivity through carbon nanotube bundles. The results demonstrate the possibility of fabricating flexible superconducting yarns in a conventional thin‐film deposition process, using ultraflexible free‐standing CNT sheets as a template. In addition, preliminary tests on reducing the normal‐state resistance toward superconducting cable applications are presented.

SS31 Effects of Different Stent Designs on Limb Flexion-Induced Axial Compression, Bending, and Torsion in Human Femoropopliteal Arteries

Endovascular reconstructions of the femoropopliteal artery (FPA) demonstrate high rates of failure. Poor durability of repair is often attributed to severe mechanical deformations that occur with limb flexion and inability of stent designs to accommodate these deformations. Stent-artery interactions associated with limb flexion-induced FPA deformations may contribute to arterial wall injury and intimal hyperplasia. We measured limb flexion-induced deformations of human cadaveric FPAs before and after stenting with seven different commercially available peripheral artery stents. Retrievable nitinol markers were deployed into 28 in situ FPAs of 14 human cadavers. Limbs were perfused with 37°C fluid, and thin-section computed tomography images were acquired with limbs in the standing (180°), walking (110°), sitting (90°) and gardening (60°) postures. Image segmentation and analysis allowed comparison of relative spatial locations of each intra-arterial marker for determination of baseline FPA axial compression, bending, and torsion. Markers were then retrieved from the arteries, and the FPAs were stented with pre- and post-balloon dilatation. Zilver, Absolute Pro, Innova, Smart Control, SmartFlex, Supera stents, and Viabahn stent grafts were deployed across the adductor hiatus. Four unique limbs received each stent type with only one stent type per artery. After stenting, markers were redeployed in stented FPAs and imaged in the same postures. Comparison of the baseline and stented FPA deformations allowed determination of the influence of specific stent type (Fig). Smart Control, Smart Flex, Zilver, Supera, and Absolute Pro restricted axial compression of the FPA within the stented segment by 56%, 45%, 42%, 26%, and 22%, respectively (P < .05). Smart Flex, Smart Control, and Zilver exacerbated FPA compression distal to the stent by 61% (P < .01), while no differences were observed proximally. Within the stented segment, maximum torsion was restricted by Supera 4° to 12°/cm (P < .05), and exacerbated by Smart Flex 10° to 15°/cm (P < .05). Torsion of the FPA proximal and distal to the stented region was not affected by stenting. Stents reduced bending of the FPA by an average of 42% (P < .01) within the stented segment, but no differences were observed proximally or distally. Different stent designs significantly affect limb flexion-induced deformations of the FPA not only within the stented segment but also distal to it. Stents that better match natural limb flexion-induced FPA deformations may mitigate arterial injury and potentially improve clinical outcomes of endovascular peripheral artery disease treatments. These data can be used to help more rationally select stent designs specific to arterial segments and patient conditions.

Limb flexion-induced axial compression and bending in human femoropopliteal artery segments

BackgroundHigh failure rates of femoropopliteal artery (FPA) interventions are often attributed in part to severe mechanical deformations that occur with limb movement. Axial compression and bending of the FPA likely play significant roles in FPA disease development and reconstruction failure, but these deformations are poorly characterized. The goal of this study was to quantify axial compression and bending of human FPAs that are placed in positions commonly assumed during the normal course of daily activities. MethodsRetrievable nitinol markers were deployed using a custom-made catheter system into 28 in situ FPAs of 14 human cadavers. Contrast-enhanced, thin-section computed tomography images were acquired with each limb in the standing (180 degrees), walking (110 degrees), sitting (90 degrees), and gardening (60 degrees) postures. Image segmentation and analysis allowed relative comparison of spatial locations of each intra-arterial marker to determine axial compression and bending using the arterial centerlines. ResultsAxial compression in the popliteal artery (PA) was greater than in the proximal superficial femoral artery (SFA) or the adductor hiatus (AH) segments in all postures (P = .02). Average compression in the SFA, AH, and PA ranged from 9% to 15%, 11% to 19%, and 13% to 25%, respectively. The FPA experienced significantly more acute bending in the AH and PA segments compared with the proximal SFA (P < .05) in all postures. In the walking, sitting, and gardening postures, average sphere radii in the SFA, AH, and PA ranged from 21 to 27 mm, 10 to 18 mm, and 8 to 19 mm, whereas bending angles ranged from 150 to 157 degrees, 136 to 147 degrees, and 137 to 148 degrees, respectively. ConclusionsThe FPA experiences significant axial compression and bending during limb flexion that occur at even modest limb angles. Moreover, different segments of the FPA appear to undergo significantly different degrees of deformation. Understanding the effects of limb flexion on axial compression and bending might assist with reconstructive device selection for patients requiring peripheral arterial disease intervention and may also help guide the development of devices with improved characteristics that can better adapt to the dynamic environment of the lower extremity vasculature.