Repetitive Deformation Research Articles

Stabilizing Metal Coating on Flexible Devices by Ultrathin Protein Nanofilms.

The significant modulus difference between a metal coating and a polymer substrate leads to interface mismatches, seriously affecting the stability of flexible devices. Therefore, enhancing the adhesion stability of a metal layer on an inert polymer substrate to prevent delamination becomes a key challenge. Herein, an ultrathin protein nanofilm (UPN), synthesized by disulfide-bond-reducing protein aggregation, is proposed as a strong adhesive layer to enhance adhesion between polymer substrate and metal coating. Unlike traditional biopolymer adhesives with micrometer-scale thicknesses, the UPN layer is minimized to nanometer/single-molecular scale. Such UPN thereby effectively enhances the interfacial adhesive strength and reduces the cohesion contribution in the entire adhesion system by directly connecting two interfaces with a nearly single-molecular thickness. Using UPN as the adhesive layer, a multifunctional metal coating could be reliably adhered on flexible polymer substrates by ion sputtering, delivering unprecedented adhesion stability even under repetitive mechanical deformation. Applications of this design include reversible transparency control, tension-responsive encryption, reusable optical sensing, and wearable capacitive touch sensors. This work highlights UPN's potential to create strong bonding strength between flexible polymers and metal coatings, offering a biocompatible solution with high surface activity and low cohesion, facilitating the development of hybrid devices with stable metal nano-coating.

Ultraflexible Vertical Corbino Organic Electrochemical Transistors for Epidermal Signal Monitoring.

Skin-conformal organic electrochemical transistors (OECTs) have attracted significant attention for real-time physiological signal monitoring and are vital for health diagnostics and treatments. However, mechanical harmonization amid the inherent dynamic nature of the skin surface and the acquisition of intrinsic physiological signals are significant challenges that hinder the integration of the ultimate skin interface. Thus, this study proposes a novel 4-terminal (4-T) vertical Corbino OECT, exhibiting high transconductance (>400 mS) and offering remarkable resilience and operational stability at an extremely low voltage of 10mV (1.9% of minimal current change after 104 biasing cycles and endurance up to 103 cycles of repetitive deformation with a 5µm bending radius). Consequently, ultralow-power, motion-resistant epidermal electrocardiogram, electromyogram, and electrooculogram sensors are developed with an exceptional signal-to-noise ratio of 40.1dB. The results of this study present a significant stride in non-invasive, skin-interfaced health-monitoring technologies and herald a new era in integrative health technologies.

Bilayer piezoionic sensors for enhanced detection of dynamic, static, and directional forces with self-healing capabilities

Electronic skin (e-skin) aims to replicate the tactile feedback mechanism of natural skin, offering great potential across robotics, healthcare monitoring, and human-machine interfaces. Traditional e-skin systems utilize electron-based sensing through capacitance and piezoresistivity for static forces, and piezoelectricity and triboelectricity for dynamic forces. However, the former group struggles with dynamic stimuli and external power dependencies, while the latter excels in self-powering but fails in static detection. Addressing these gaps, iontronics emerges as a versatile solution, providing innovative avenues for energy harvesting, sensing, and actuation through ion redistribution in response to varied stimuli, but shows limitations in output signals and response times. We report herein the development of bilayerstructured piezoionic materials with significantly enhanced output signal and response time. The piezoionic bilayer structure not only harnesses an ion accumulation interface, leading to amplified output signals and fast response times, but also exhibits an ion-dipole interactive self-healing property. Our sensor generates a signal output of 95 mV and features a quick response time of 30 ms, with an impressive self-healing capability of ∼100%. It demonstrates the ability to accurately detect both static and dynamic forces, including specific movements like bending and vibrations, maintaining its robustness through 8000 cycles of repetitive deformation. Its utility is further proven in a practical setting with a braille reader device, highlighting its potential for incorporation into a wide array of soft, autonomous iontronic systems that require enhanced sensitivity, rapid detection capabilities, and self-sustainability.

3D-Printed Soft Temperature Sensors Based on Thermoelectric Effects for Fast Mapping of Localized Temperature Distributions.

We propose a novel design of thermoelectric (TE) effect-based soft temperature sensors for directly monitoring localized subtle temperature stimuli. This design integrates rheology-engineered three-dimensional (3D) printing of high-performance carbon-based TE materials and polymer-based viscoelastic materials with low thermal conductivity. Rheological engineering of carbon nanotube (CNT) TE inks ensures the 3D printing of highly sensitive TE sensing units on directly written 3D soft platforms. Additionally, we pre-dope CNT inks with p- and n-type organic dopants to achieve high sensitivity and a fast response to temperature changes. The introduced 3D soft platforms with low thermal conductivity lead to an efficient thermal gradient on TE sensing units in the out-of-plane direction. Furthermore, encapsulating the temperature sensor array with the same polymer-based materials as the 3D soft platforms facilitates independent detection of localized temperature stimuli by minimizing thermal interaction between sensing units, resulting in precise temperature mapping by localized detection. Our 3D-printed soft temperature sensors exhibit high sensitivity to relatively small temperature changes, with a minimum sensing resolution of 0.1 K within tens of milliseconds. Moreover, the temperature sensor array not only detects localized temperature stimuli by imaging the temperature distribution but also demonstrates remarkable mechanical reliability against repetitive deformation with high accuracy.

Polymeric Conductive Adhesive-Based Ultrathin Epidermal Electrodes for Long-Term Monitoring of Electrophysiological Signals.

Electrophysiology, exploring vital electrical phenomena in living organisms, anticipates broader integration into daily life through wearable devices and epidermal electrodes. However, addressing the challenges of the electrode durability and motion artifacts is essential to enable continuous and long-term biopotential signal monitoring, presenting a hurdle for its seamless implementation in daily life. To address these challenges, an ultrathin polymeric conductive adhesive,poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)/polyvinyl alcohol/d-sorbitol (PPd) electrode with enhanced adhesion, stretchability, and skin conformability, is presented. The skin conformability and stability of electrodes is designed by theoretical criteria obtained by mechanical analysis.Thus, impedance stability is obtained over 1-week of daily life, and the PPd electrode addresses the challenges related to durability during prolonged usage. Proving stability in electromyography (EMG) signals during high-intensity exercise, the wireless PPd measurement system exhibits high signal-to-noise ratio (SNR) signals even in situations involving significant and repetitive skin deformation. Throughout continuous 1 week-long electrocardiogram (ECG) monitoring in daily life, the system consistently preserves signal quality, underscoring the heightened durability and applicability of the PPd measurement system.

Development of Composite-film-based Flexible Energy Harvester using Lead-free BCTZ Piezoelectric Nanomaterials

Composite-based piezoelectric devices are extensively studied to develop sustainable power supply and selfpowered devices owing to their excellent mechanical durability and output performance. In this study, we design a leadfree piezoelectric nanocomposite utilizing (Ba<sub>0.85</sub>Ca<sub>0.15</sub>)(Ti<sub>0.9</sub>Zr<sub>0.1</sub>)O<sub>3</sub> (BCTZ) nanomaterials for realizing highly flexible energy harvesters. To improve the output performance of the devices, we incorporate porous BCTZ nanowires (NWs) into the nanoparticle (NP)-based piezoelectric nanocomposite. BCTZ NPs and NWs are synthesized through the solidstate reaction and sol-gel-based electrospinning, respectively; subsequently, they are dispersed inside a polyimide matrix. The output performance of the energy harvesters is measured using an optimized measurement system during repetitive mechanical deformation by varying the composition of the NPs and NWs. A nanocomposite-based energy harvester with 4:1 weight ratio generates the maximum open-circuit voltage and short-circuit current of 0.83 V and 0.28 A, respectively. In this study, self-powered devices are constructed with enhanced output performance by using piezoelectric energy harvesting for application in flexible and wearable devices.

Friction Blisters of the Feet: A New Paradigm to Explain Causation.

Friction blisters on the feet commonly occur when individuals engage in active pursuits such as running, hiking, and military training. The high prevalence of blisters in active individuals underscores the fact that the pathomechanics of this condition are not fully understood. The traditional blister causation paradigm revolves around heat, moisture, and friction. In reality, foot friction blisters are caused by repetitive shear deformation. The 3 fundamental elements of blister-inducing shear deformation are (1) motion of bone, (2) high friction force, and (3) repetition of the resulting shear events. Rubbing at the skin surface is not a mechanism for friction blister formation. To that end, prevention of the friction blister continues to be an elusive quest for both the patient and the treating clinician. In this article, we aimed to highlight the limitations of the long-held blister-causation paradigm and offer a new explanation.

Magnetic non-destructive monitoring of a ship's propeller blade after long-term operation

This study examines the potential of magnetic non-destructive techniques for monitoring surface damage to ship propeller blades made of stainless steel. The propeller considered in this investigation operated for 35 years in the Danube river. Sheet and vortex cavitations, as well as random mechanical impacts on the trailing and leading edges, were detected as the major mechanisms of damage to the blade. Non-destructive monitoring of this damage was based on the Barkhausen noise and Helmholtz feritscope techniques. The blades investigated here had a composite structure in which the ferrite stainless body was mixed with the deposition of austenite on the trailing and especially the leading edges. Damage to the ferritic phase was mostly associated with sheet cavitation and a decreasing magnitude of Barkhausen noise as a result of repetitive plastic deformation. Conversely, vortex cavitation and random impacts to the edges in the austenite regions were associated with increasing Barkhausen noise due to strain-induced martensite transformation, a result that was also confirmed by data obtained from a Helmholtz feritscope. Information about plastic deformation and the fraction of strain-induced transformation was also confirmed by X-ray and electron backscatter diffraction techniques.

A flexible supercapacitor with high energy density and wide range of temperature tolerance using a high-concentration aqueous gel electrolyte

As the demand for a wide range of wearable devices increases, extensive effort is devoted to developing high-performance flexible energy storage devices such as batteries and supercapacitors. Of particular interest, flexible supercapacitors using aqueous electrolytes have high application potential owing to their many advantages including low cost, harmlessness to the human, and environmental safety compared to others using electrolytes such as ionic liquids and organic electrolytes. However, poor temperature tolerance and narrow operation voltage window have hindered the practical application of aqueous supercapacitors. In this study, we report on a wide temperature-tolerant flexible aqueous supercapacitor featuring high electrochemical performance designed by a deliberate selection of electrode materials and electrolytes. As a flexible electrode, three-dimensional microporous graphene foam coated with conducting polymer Polypyrrole (PPy) is used to enhance capacitance up -to 90.0 F/g by increasing the surface area and inducing the pseudo-capacitance of PPy. As a gel-type electrolyte, a high-concentration NaClO4 is mixed with Polyvinyl alcohol to enlarge the voltage window to 1.8 V and a stable temperature range from -25 to 80°C, even under repetitive bending deformation. The fabricated supercapacitor exhibits a superior energy density of 37.4 Wh kg−1 and maintains 92.0% of initial capacitance at room temperature after three repeated cycles of cooling/heating across a wide temperature range over 100°C. This work suggests a high potential application of the fabricated supercapacitor as an eco-friendly and stable energy storage system for powering diverse wearable devices under various conditions.

Tough Interfacial Adhesion Enabled Extremely Durable Flexible Supercapacitors.

The interfacial void and delamination between the hydrogel electrolyte and flexible electrode caused by the inconformal contact and weak adhesion lead to serious performance degradation of solid-state-sandwiched supercapacitors (SCs) upon repetitive deformation. Herein, we propose a hydrogel polymer electrolyte (HPE) engineering strategy for enhancing the interfacial adhesion (Γ) to achieve extremely durable SCs via the soft, tough, and self-adhesive HPE. Using a self-cross-linked poly(N-hydroxyethyl acrylamide)/H3PO4 (PHEAA/H3PO4) HPE as the model, the interfacial adhesion between HPE and polyaniline (PANI)-modified carbon cloth (CC) electrode (CC/PANI) reaches up to 556 J/m2, leading to excellent durability of electrochemical performance under long-term repetitive deformations. The as-assembled sandwiched SC retains 94.14 and 93.62% of initial capacitance after 180° bending and twisting for 100,000 cycles, respectively. Furthermore, benefiting from the addition of H3PO4, the flexible sandwiched SC displays excellent tolerance to low temperatures and delivers a capacitance retention of 98.03% after 180° bending for 10,000 cycles at -20 °C. This work highlights the importance of interfacial adhesion engineering for the design of extremely deformation-tolerable SCs.

Selective Cell-Cell Adhesion Regulation via Cyclic Mechanical Deformation Induced by Ultrafast Nanovibrations.

The adoption of dynamic mechanomodulation to regulate cellular behavior is an alternative to the use of chemical drugs, allowing spatiotemporal control. However, cell-selective targeting of mechanical stimuli is challenging due to the lack of strategies with which to convert macroscopic mechanical movements to different cellular responses. Here, we designed a nanoscale vibrating surface that controls cell behavior via selective repetitive cell deformation based on a poroelastic cell model. The vibrating indentations induce repetitive water redistribution in the cells with water redistribution rates faster than the vibrating rate; however, in the opposite case, cells perceive the vibrations as a one-time stimulus. The selective regulation of cell-cell adhesion through adjusting the frequency of nanovibration was demonstrated by suppression of cadherin expression in smooth muscle cells (fast water redistribution rate) with no change in vascular endothelial cells (slow water redistribution rate). This technique may provide a new strategy for cell-type-specific mechanical stimulation.

Cyclic strain of poly (methyl methacrylate) surfaces triggered the pathogenicity of Candida albicans

Candida albicans is an opportunistic yeast and the primary etiological factor in oral candidiasis and denture stomatitis. The pathogenesis of C. albicans could be triggered by several variables, including environmental, nutritional, and biomaterial surface cues. Specifically, biomaterial interactions are driven by different surface properties, including wettability, stiffness, and roughness. Dental biomaterials experience repetitive (cyclic) stresses from chewing and biomechanical movements. Pathogenic biofilms are formed over these biomaterial surfaces under cyclic strain. This study investigated the effect of the cyclic strain (deformation) of biomaterial surfaces on the virulence of Candida albicans. Candida biofilms were grown over Poly (methyl methacrylate) (PMMA) surfaces subjected to static (no strain) and cyclic strain with different levels (ε˜x=0.1 and 0.2%). To evaluate the biomaterial-biofilm interactions, the biofilm characteristics, yeast-to-hyphae transition, and the expression of virulent genes were measured. Results showed the biofilm biomass and metabolic activity to be significantly higher when Candida adhered to surfaces subjected to cyclic strain compared to static surfaces. Examination of the yeast-to-hyphae transition showed pseudo-hyphae cells (pathogenic) in cyclically strained biomaterial surfaces, whereas static surfaces showed spherical yeast cells (commensal). RNA sequencing was used to determine and compare the transcriptome profiles of cyclically strained and static surfaces. Genes and transcription factors associated with cell adhesion (CSH1, PGA10, and RBT5), biofilm formation (EFG1), and secretion of extracellular matrix (ECM) (CRH1, ADH5, GCA1, and GCA2) were significantly upregulated in the cyclically strained biomaterial surfaces compared to static ones. Genes and transcription factors associated with virulence (UME6 and HGC1) and the secretion of extracellular enzymes (LIP, PLB, and SAP families) were also significantly upregulated in the cyclically strained biomaterial surfaces compared to static. For the first time, this study reveals a biomaterial surface factor triggering the pathogenesis of Candida albicans, which is essential for understanding, controlling, and preventing oral infections. Statement of significanceFungal infections produced by Candida albicans are a significant contributor to various health conditions. Candida becomes pathogenic when certain environmental conditions change, including temperature, pH, nutrients, and CO2 levels. In addition, surface properties, including wettability, stiffness, and roughness, drive the interactions between Candida and biomaterials. Clinically, Candida adheres to biomaterials that are under repetitive deformation due to body movements. In this work, we revealed that when Candida adhered to biomaterial surfaces subjected to repetitive deformation, the microorganism becomes pathogenic by increasing the formation of biofilms and the expression of virulent factors related to hyphae formation and secretion of enzymes. Findings from this work could aid the development of new strategies for treating fungal infections in medical devices or implanted biomaterials.

Flexible Transparent Planar Heater Comprising ZnO/Cu/Al2O3

In this study, we fabricated transparent heaters composed of an ultrathin Cu-layer heating element sandwiched between a ZnO underlayer and an Al2O3 overlayer. With the Cu layer thickness fixed at 8.5 nm, the thicknesses of the ZnO and Al2O3 layers were independently varied to reach the optimum antireflecting condition (maximum transmittance of 88.3% and average visible light transmittance of 79.8% were achieved). The sheet resistances for the ZnO/Cu/Al2O3 heaters can be varied by simply modulating the Cu layer thicknesses. In order to assess the flexibility of the transparent heaters, we constructed a ZnO/Cu/Al2O3 structure on flexible polyimide substrates, and the thermal, electrical, optical and mechanical characteristics were evaluated. Because of the planar heating element of the Cu layer, the thermal response was found to be extremely high, i.e., less than 10 s were required to reach 90% of the target temperatures. Once the target temperatures were reached, the heater temperatures were highly stable with no degradation of electrical and optical properties. Furthermore, the heating capability was maintained under severe mechanical deformation, e.g., at a bending radius of 4 mm. The structure also exhibited highly sustainable optoelectronic properties under repetitive mechanical deformation, confirming the potential for commercialization. Finally, we demonstrated that ZnO/Cu/Al2O3 rolled around a human finger exhibited highly uniform heating characteristics, rendering the heaters suitable for wearable, healthcare electronics.

All Direct Ink Writing of 3D Compliant Carbon Thermoelectric Generators for High‐Energy Conversion Efficiency

AbstractCompliant thermoelectric generators (TEGs) can fully exploit their energy conversion efficiency by establishing conformal interfaces on arbitrarily shaped 3D heat sources. Although additive manufacturing processes allow scalable fabrication with flexibility and customizability, most printable TEGs are fabricated as planar‐type devices that harvest heat only in the in‐plane direction. Herein, 3D‐compliant TEGs fabricated solely using direct ink writing, which enables thermal‐transfer optimization for efficient through‐plane heat‐to‐electricity conversion owing to the out‐of‐plane printing of viscoelastic thermoelectric (TE) inks and unique device design is proposed. The rheological properties of carbon nanotube (CNT) TE inks are engineered to ensure conformal printing along directly written vertical thermal insulators. The ink TE properties are enhanced by the fine‐tuned incorporation of p‐ and n‐type dopants, where the electrical conductivity is further facilitated by nozzle‐induced CNT packing to achieve high‐power factors. To minimize the parasitic thermal loss from heat sources, an ultra‐thin bottom substrate is directly printed with polydimethylsiloxane, thereby realizing compliant 3D TEGs for heat harvesting in the out‐of‐plane direction. The TEG exhibits the highest normalized open‐circuit voltage (0.28 mV K−1 cm−2) among the additively manufactured TEGs and retains remarkable mechanical reliability against repetitive deformation, promising its potential as body heat harvesters or temperature sensors.

Flexible and Photo-responsive superwetting surfaces based on porous materials coated with Mussel-Inspired Azo-Copolymer

The decoration of porous materials with stimulus-responsive polymers is an efficient strategy for the fabrication of superwetting surfaces; however, the weak interfacial interaction between the polymers and the substrates limits their application. Herein, inspired by the molecular structure of the mussel foot protein, a series of catechol-functionalized azobenzene-containing copolymers with diverse chain structures are synthesized via solution radical polymerization and used for the preparation of smart superwetting surfaces. After dip-coating with the mussel-inspired azo-copolymers, the modified cotton fabrics and melamine sponges possessed smart surfaces with photo-switchable wettability. These as-prepared flexible smart surfaces exhibited rapid wettability transition between high hydrophobicity and superhydrophilicity with alternating ultraviolet (UV) and visible light irradiation. Meanwhile, these superwetting surfaces were also experimentally found to be robust without apparent degradation in their photo-responsiveness, even after being soaked in acid/base solutions and subjected to repetitive mechanical deformation. Especially, the functionalized melamine sponges as bulk superwetting materials have excellent mechanical stability, which can tolerate harsh abrasion cycles and repetitive compressive deformations. More importantly, it was also confirmed that the mussel-inspired azo-copolymers exhibited excellent adhesion properties at the interface of various substrates. This bioinspired strategy and developed functional copolymers paves the way for facile and large-scale fabrication of superwetting surfaces, which may find a wide range of advanced potential applications in microfluidic devices, biomedicine and sensors.

Highly Air-Stable, Flexible, and Water-Resistive 2D Titanium Carbide MXene-Based RGB Organic Light-Emitting Diode Displays for Transparent Free-Form Electronics.

Flexible see-through displays are considered to be the next generation smart display, providing improved information flow, safety, situational awareness, and overall user experience in smart windows, automotive displays, glass-form biomedical displays, and augmented reality systems. 2D titanium carbides (MXenes) are promising material as electrodes of the transparent and flexible displays due to their high transparency, metallic conductivity, and flexibility. However, current MXene-based devices have insufficient air stability and lack engineering schemes to develop matrix-addressable display forms with sufficient pixels to display information. Here, we develop an ultraflexible and environmentally stable MXene-based organic light-emitting diode (OLED) display by combining high performance MXene electrodes, flexible OLEDs, and ultrathin and functional encapsulation systems. The MXene material was synthesized and used to fabricate a highly reliable MXene-based OLED that can stably operate in air condition for over 2000 h, endure repetitive bending deformation of 1.5 mm radius, and maintain environmental stability for 6 h when exposed to wet surroundings. The RGB MXene-based OLEDs were fabricated, (1691 cd m-2 at 40.4 mA cm-2 for red, 1377 cd m-2 at 4.26 mA cm-2 for green, and 1475 cd m-2 at 18.6 mA cm-2 for blue) and a matrix-addressable transparent OLED display was demonstrated that could display letters and shapes.

Pulvinar slits: Cellulose-deficient and de-methyl-esterified pectin-rich structures in a legume motor cell.

The cortical motor cells (CMCs) in a legume pulvinus execute the reversible deformation in leaf movement that is driven by changes in turgor pressure. In contrast to the underlying osmotic regulation property, the cell wall structure of CMCs that contributes to the movement has yet to be characterized in detail. Here, we report that the cell wall of CMCs has circumferential slits with low levels of cellulose deposition, which are widely conserved among legume species. This structure is unique and distinct from that of any other primary cell walls reported so far; thus, we named them "pulvinar slits." Notably, we predominantly detected de-methyl-esterified homogalacturonan inside pulvinar slits, with a low deposition of highly methyl-esterified homogalacturonan, as with cellulose. In addition, Fourier transform infrared spectroscopy analysis indicated that the cell wall composition of pulvini is different from that of other axial organs, such as petioles or stems. Moreover, monosaccharide analysis showed that pulvini are pectin-rich organs like developing stems and that the amount of galacturonic acid in pulvini is greater than in developing stems. Computer modeling suggested that pulvinar slits facilitate anisotropic extension in the direction perpendicular to the slits in the presence of turgor pressure. When tissue slices of CMCs were transferred to different extracellular osmotic conditions, pulvinar slits altered their opening width, indicating their deformability. In this study, we thus characterized a distinctive cell wall structure of CMCs, adding to our knowledge of repetitive and reversible organ deformation as well as the structural diversity and function of the plant cell wall.

Feasibility of wear reduction for soft nanostructured thin film through enhanced elastic recoverability and contact stress relief

This work shows that a soft, thin film comprising randomly aligned carbon nanotubes (CNTs) can reduce surface wear more effectively than a homogeneous thin film because of enhanced elastic recoverability and contact stress relief originating from its mesh structure. To investigate the wear characteristics of the mesh structure compared to those of the homogeneous thin film, multi-walled CNTs (MWCNTs) and diamond-like carbon (DLC) thin films were prepared to conduct nanoscale tribological experiments using the atomic force microscopy (AFM). The MWCNT thin film showed unmeasurably low wear compared with the DLC thin film under a certain range of normal load. To demonstrate the wear reduction mechanism of the MWCNT thin film, its indentation and frictional behaviors were assessed. The indentation behavior of the MWCNT thin film revealed repetitive elastic deformation with a wide strain range and a significantly lower elastic modulus than that of the DLC thin film. The permanent deformation of the MWCNT thin film was observed through frictional experiments under relatively high normal load conditions. These results are expected to provide insights into the design of highly wear-resistant surfaces using nanostructures.

High frame rate deformation analysis of knee cartilage by spiral dualMRI and relaxation mapping.

Daily activities including walking impose high-frequency cyclic forces on cartilage and repetitive compressive deformation. Analyzing cartilage deformation during walking would provide spatial maps of displacement and strain and enable viscoelastic characterization, which may serve as imaging biomarkers for early cartilage degeneration when the damage is still reversible. However, the time-dependent biomechanics of cartilage is not well described, and how defects in the joint impact the viscoelastic response is unclear. We used spiral acquisition with displacement-encoding MRI to quantify displacement and strain maps at a high frame rate (25 frames/s) in tibiofemoral joints. We also employed relaxometry methods (T1 , T1ρ , T2 , T2 *) on the cartilage. Normal and shear strains were concentrated on the bovine tibiofemoral contact area during loading, and the defected joint exhibited larger compressive strains. We also determined a positive correlation between the change of T1ρ in cartilage after cyclic loading and increased compressive strain on the defected joint. Viscoelastic behavior was quantified by the time-dependent displacement, where the damaged joint showed increased creep behavior compared to the intact joint. This technique was also successfully demonstrated on an in vivo human knee showing the gradual change of displacement during varus load. Our results indicate that spiral scanning with displacement encoding can quantitatively differentiate the damaged from intact joint using the strain and creep response. The viscoelastic response identified with this methodology could serve as biomarkers to detect defects in joints in vivo and facilitate the early diagnosis of joint diseases such as osteoarthritis.

Dynamic observation of a damping material using micro X-ray computed tomography coupled with a phase-locked loop

As rubber materials are used for damping, clarifying the relationship between the loss factor and microstructure would help develop high-performance damping materials. Although nondestructive observations using X-ray computed tomography (CT) under repetitive deformation have been reported, no observations have been reported at the submicron order that capture low-strain deformation, such as vibration exposure. The internal deformation behavior of materials with different loss factors has not yet been evaluated. This study proposes a dynamic X-ray CT method for specimens under tensile amplitudes, directly evaluating the internal deformation behavior of materials under dynamic conditions. The proposed 4D-CT has an excitation of 1 Hz and a spatial resolution of 0.5 μm. The local strain was obtained from X-ray CT at each phase, and the deformation behavior was evaluated. The results revealed that the peak of the local strain amplitude distribution curve decreased and the distribution widened as fine particles were mixed.