The problem lies in how the international standard, EN ISO 5361:2023, asks manufacturers to evaluate tracheal seals. Under the current protocol, an endotracheal tube is inserted into a transparent rigid cylinder, the cuff is inflated to a preset pressure, a five-centimetre column of water is poured above it, and the volume of water leaking past the cuff in ten minutes is recorded. It is a simple, repeatable test, but it bears little resemblance to the inside of a living patient. A real trachea is not a rigid acrylic pipe; it is a compliant, layered structure of soft mucosa and springy cartilage that flexes with every breath. Nor does a real patient lie still on a bench. The airway pressure rises and falls with each mechanical breath, and over days of intubation the cuff slowly loses pressure as gas diffuses through its walls. None of these dynamics appear in the standard test, which means a tube that performs beautifully in the laboratory may behave very differently in a patient’s chest.

To close that gap, the Nottingham group, led by Delu Zheng and Tamaralayefa B. Agbiki and supervised by Stephen P. Morgan, constructed a benchtop phantom system that brings the clinic into the laboratory. At its heart is a bio-inspired tracheal model with a 22-millimetre internal diameter, fabricated using published ex vivo biomechanical data for human tracheal tissue. The cartilaginous portions of the model replicate reported Young’s modulus values of 3.2 to 23 megapascals and Shore hardness values of 59.6 to 91 ShA, while the mucosal membrane mimics far softer tissue, with moduli of 4 to 18 kilopascals. The result is a heterogeneous artificial airway whose compliant walls deform against the cuff much as living tissue would. Around this tracheal model, the researchers assembled a complete respiratory circuit: a ventilator delivering bilevel pressure ventilation with an inspiratory pressure of 20 centimetres of water and a positive end-expiratory pressure of 4, a two-litre test lung acting as the patient, and an Arduino-controlled automatic cuff inflation system that continuously regulates intracuff pressure using a proportional-integral-derivative control algorithm.

The phantom was designed to run in three modes, each isolating a different aspect of the clinical environment. Standard Mode reproduces the static conditions of the ISO test, with no ventilator and manual cuff inflation. Ventilation Mode adds the ventilator and test lung, introducing the rhythmic pressure swings of mechanical breathing while the cuff remains manually inflated. Auto-inflation Mode completes the picture, adding the automated pressure controller, which uses a miniature pneumatic pump, a solenoid valve and a relay to hold the cuff at its target pressure throughout every ventilation cycle. In all three modes, the researchers followed the ISO protocol’s core logic: the cuff was inflated to 27 centimetres of water, distilled water warmed to 37 degrees Celsius was maintained at a five-centimetre height above the cuff, and a precision balance with 0.01-gram resolution captured every drop that escaped past the seal over one hour.

The team tested two cuff materials that dominate clinical practice: five high-volume low-pressure polyvinyl chloride tubes and five polyurethane-cuffed tubes, all with a 7.0-millimetre internal diameter. The differences were striking. For the PVC tubes, the rigid cylinder phantom reported leakage rates far higher than the bio-inspired model did, with the compliant trachea showing roughly 30 percent less leakage under static conditions, about 50 percent less under ventilation, and approximately 58 percent less with automatic cuff inflation. All comparisons were statistically significant at p less than 0.001, with paired effect sizes ranging from 5.22 to 16.05, indicating enormous differences. In absolute terms, PVC leakage fell from 328.60 millilitres per hour in the cylinder under static conditions to just 81.14 millilitres per hour in the bio-inspired phantom with automatic inflation. The compliant airway, in other words, does not merely refine the numbers; it transforms the apparent performance of the same tube.

The polyurethane cuffs told an even more revealing story. In the rigid cylinder, these tubes showed no measurable leakage at all under any condition, which would seem to certify them as perfect seals. Yet in the bio-inspired phantom under static conditions, a small but measurable leak of 19.67 millilitres per hour appeared, invisible to the standard test but detectable once the airway could flex against the cuff. This finding underscores the central argument of the paper: rigid cylinder testing can mask subtle sealing behaviours that matter clinically. Polyurethane cuffs owe their advantage to physics at the micrometre scale. PVC cuff walls are roughly 50 to 70 micrometres thick and relatively stiff, so when inflated they buckle into large longitudinal folds that form microchannels along the cuff-trachea interface. Polyurethane walls are only about 7 to 10 micrometres thick and far more flexible, allowing the cuff to drape smoothly over the airway surface, shrinking and eliminating those leakage pathways.

Perhaps the most clinically consequential result came from the long-term experiments. The researchers placed inflated cuffs in an oven at 37 degrees Celsius, body temperature, and monitored them continuously for 48 hours. Both materials bled pressure steadily: PVC cuffs lost an average of 12.24 centimetres of water, and polyurethane cuffs lost 9.06, with some individual PVC tubes falling from around 28 centimetres of water to below 15. Since clinical guidelines recommend keeping cuff pressure above roughly 20 centimetres of water to maintain the seal, this silent decay means that a cuff inflated correctly on day one may drift into the danger zone within two days, opening the door to microaspiration without any visible warning. The pressure drop is attributed to gas diffusion through the cuff material and viscoelastic relaxation, processes that accelerate at body temperature and that no static bench test currently accounts for.

The ventilation experiments also produced a counterintuitive insight: mechanical breathing actually reduced fluid leakage. In the bio-inspired phantom, PVC leakage under ventilation was about 48 percent lower than in static mode, and automatic inflation cut it further, by roughly 65 percent relative to baseline. The researchers observed air bubbles travelling proximally through the cuff folds during the inspiratory phase, suggesting that positive airway pressure distal to the cuff generates an outward airflow that transiently opposes liquid ingress. Meanwhile, the automatic inflation system, tuned with controller coefficients of P equal to 3, I equal to 5 and D equal to 0, eliminated measurable cuff deflation entirely across all conditions, stabilising the seal in a way that manual inflation cannot. This aligns with clinical trials suggesting that continuous cuff pressure control may help reduce ventilator-associated pneumonia rates.

The Nottingham team is candid about the limitations of their platform. The phantom uses a single tracheal diameter and fixed ventilator settings, and it cannot reproduce tissue perfusion, mucosal secretions, muscle tone or the anatomical variability of real patients. Only five tubes of each type were tested, and no in vivo validation was performed. Even so, the system, funded by the Medical Research Council, offers something the current standard cannot: a repeatable benchtop model in which cuff materials, tube designs and pressure management strategies can be compared under dynamic, physiologically realistic conditions. As the authors conclude, static pressure retention alone is insufficient to characterise cuff performance, and their bio-inspired phantom reveals sealing behaviours that rigid cylinders simply cannot see. For a device whose failure feeds one of intensive care’s most stubborn infections, that is a meaningful step toward testing tubes the way patients actually experience them.

Subject of Research: A bio-inspired benchtop phantom system for testing endotracheal tube cuff seal performance under mechanical ventilation

Article Title: Phantom system for endotracheal tube cuff seal testing during mechanical ventilation

Article References: Zheng, D., Agbiki, T. B., Correia, R., He, C., Korposh, S., Erdody, S., Hayes-Gill, B. R., Hewson, D. W., Norris, A. M., & Morgan, S. P. (2026). Phantom system for endotracheal tube cuff seal testing during mechanical ventilation. Medical & Biological Engineering & Computing. https://doi.org/10.1007/s11517-026-03691-0

Image Credits: AI Generated

DOI: 10.1007/s11517-026-03691-0

Keywords: endotracheal tube, cuff seal, ventilator-associated pneumonia, mechanical ventilation, bio-inspired phantom, tracheal model, cuff pressure, polyurethane, polyvinyl chloride, microaspiration, EN ISO 5361, medical engineering

Jakob Ilsted Bech and Jamie Engelhardt Simon, writing in the journal Wind Energy Science, argue that the dominant failure mode in modern leading-edge protection systems is not the gradual, uniform wearing-away that conventional models assume, but rather fatigue cracking: the initiation and growth of discrete cracks driven by the cyclic pulse loading of successive droplet impacts. Their X-ray computed tomography images of rain-eroded samples reveal locally occurring cracks surrounded by virtually undamaged material, a signature that looks far more like classical fatigue fracture than like progressive surface loss. For soft, tough, visco-elastic elastomers, the polyurethanes and similar polymers increasingly used to shield blade tips, this distinction matters enormously, because the old stress-based damage models simply do not capture how these materials fail.

The physics of a droplet impact is violent and fast. Numerical studies predict local strains of up to 80 percent and strain rates between 1,000 and 1,000,000 per second during the microseconds of contact. The resulting stress patterns depend on impact velocity, droplet size, and the hyper-visco-elastic properties of the surface. Classic experiments dating back to Bowden and Brunton in 1961 showed that a single high-speed water jet can fracture a polymer, and the crack patterns differ by material type: hard elastic polymers develop ring-shaped surface cracks that propagate conically into the depth, while soft rubbers nucleate cracks inside the bulk, beneath the impact center, which then spread in star-shaped patterns. On a real blade, where droplets strike at random positions, cracks may initiate at randomly distributed defects and inhomogeneities, making the damage harder to predict but no less governed by the laws of fracture mechanics.

Bech and Simon’s central contribution is to bring the established tools of experimental fracture mechanics to bear on this problem for the first time. The key quantity is the tearing energy, T, the energy per unit area released as a crack advances, a concept that traces back to Rivlin and Thomas’s foundational 1953 work on rubber rupture. To measure it, the researchers employed a plane strain tensile test with two slits, often called the pure shear test, in which a thin polymer sheet is clamped at its edges and pre-cut cracks grow under cyclic loading. Because the geometry produces a uniform plane-strain zone between the crack tips and a stress-free zone behind them, the tearing energy can be computed from a remarkably simple energy balance. Their novel analysis technique tracks the evolution of strain energy with crack length throughout the test, comparing the work required to stretch the specimen at successive cycle intervals, so that the energy released per unit of new crack area emerges directly from the measured load-displacement loops.

Testing soft elastomer sheets posed its own engineering challenge. Rubber-like materials are notoriously difficult to grip because they contract in the thickness direction under tension and slip out of conventional flat-jaw grips. The team designed a new test fixture with partially circular grip faces, a 90-degree concave cylinder that wraps around the specimen and compresses it progressively, maintaining grip even at high strains. A prototype was 3D printed in PLA plastic and mounted in an electro-pulse test machine, with specimens cut from sheet material into rectangles of 80 by 46 millimeters. A digital camera recorded the crack tips at peak displacement throughout each test, allowing crack lengths to be tracked by image analysis with a resolution of about 0.02 millimeters per pixel.

Crucially, the loading scheme was designed to mimic the rhythm of rain. Each cycle consists of a short sinusoidal displacement pulse followed by a dwell time before the next pulse, representing the interval between successive droplet impacts. Two dwell times were tested, 0.1 and 1 second, chosen from computed impact frequencies for realistic rain fields, although the researchers note that characteristic impact periods in the field can range from 1 to 100 seconds. This dwell-time dependence turned out to be one of the most revealing aspects of the study, because the material exhibits pronounced visco-elastic behavior, including the Mullins effect, a cyclic stress softening in which stiffness and energy uptake decline over repeated cycles before stabilizing.

The softening behavior was dramatic. With a dwell time of 0.1 seconds, the maximum load in an uncracked specimen fell from about 221 newtons in the first cycle to 126 newtons by cycle 2,000, and the strain energy dropped from 0.28 to 0.15 joules. After a 10-minute recovery period, the same specimen tested with a 1-second dwell time nearly regained its initial state, reaching 215 newtons and 0.27 joules before softening again to 171 newtons and 0.22 joules. With a 10-second dwell time, the material almost fully recovered between cycles, ending at 211 newtons and 0.27 joules after 2,000 cycles. Shorter dwell times also required more cycles to reach stable, repeatable stress-strain loops, meaning that any meaningful crack growth measurement demands a run-in period of potentially several hundred cycles before the material settles into a steady state.

When the crack growth rate per cycle was plotted against maximum strain, the results appeared dwell-time dependent: cracks grew faster at the longer 1-second dwell time, and the strain threshold between slow and fast growth differed by roughly 27 percent between the two regimes. Longer dwell times allow greater recovery between pulses, so the material resumes each cycle at higher stiffness and can absorb more strain energy for a given peak strain, delivering a larger tearing energy to the crack tip. But here lies the study’s most elegant finding: when the same data were plotted against tearing energy rather than strain, the curves for both dwell times collapsed onto a single master curve, differing by only about 10 percent in threshold. Above the threshold, the data follow a power law relating growth rate to tearing energy with an exponent of about 2.2. Tearing energy, not strain, is the governing parameter, independent of how fast the impacts arrive, at least for the dwell times tested.

The measured crack growth rates spanned a striking range. Below a tearing energy threshold estimated at approximately 2,100 joules per square meter, with a standard deviation of about 200, cracks grew at only 3 to 6 nanometers per cycle, effectively negligible. Above the threshold, rates jumped to between 0.6 and 10 micrometers per cycle, three orders of magnitude faster. Some tests revealed intriguing anomalies: one crack sat dormant for nearly 570,000 cycles before abruptly accelerating, suggesting the threshold had been marginally crossed; another crack paused at an apparent tough inhomogeneity before finding a path around it and resuming its original rate. These observations reinforce the picture of a sharp fatigue limit, analogous to the mechanical fatigue limit long established for rubber, below which a component could theoretically endure impacts indefinitely.

The implications reach well beyond the laboratory. The authors propose that crack growth resistance could become a key parameter in material standards, in the systematic development of new protective coatings, and even in operational strategy. In so-called erosion-safe operation, the tearing energy threshold could serve as a curtailment criterion, with rotor speed limited during extreme precipitation so that the energy delivered to cracks stays below the propagation threshold, a function of protection material properties and meteorological conditions such as droplet size and liquid water content. The fracture mechanics approach also offers a mechanistic basis for evaluating materials before costly whirling-arm rain erosion testing, and the authors call for future work on ultra-high strain rates, possibly using low temperatures and time-temperature superposition to mimic impact conditions, and on rain erosion tests with controlled defects to link laboratory fracture data directly to field performance. If successful, this paradigm shift could finally give the wind industry a rigorous, physics-based route to eliminating one of its most persistent and expensive failure modes.

Subject of Research: Fatigue crack growth characterization of elastomeric leading-edge protection materials for wind turbine blades using experimental fracture mechanics

Article Title: Fatigue crack growth in elastomers for leading-edge erosion protection of wind turbine blades

Article References: Bech, J. I., & Simon, J. E. (2026). Fatigue crack growth in elastomers for leading-edge erosion protection of wind turbine blades. Wind Energy Science, 11(10), 3803-3821. https://doi.org/10.5194/wes-11-3803-2026

Image Credits: AI Generated

DOI: 10.5194/wes-11-3803-2026

Keywords: wind energy, leading-edge erosion, fatigue crack growth, elastomers, fracture mechanics, tearing energy, polyurethane, rain erosion, Mullins effect, wind turbine blades, materials testing, visco-elasticity

The study, led by JinLin Han, ChouJung Tsao, HungTa Wu, and KuanLiang Liu, focuses on a class of materials known as interpenetrating polymer networks, or IPNs. In an IPN, two different polymer networks are formed within the same volume, each threading through the other without being chemically bonded together in the conventional sense. The result is a material that combines the best traits of both components. In this case, the researchers paired epoxy resin, prized for its stiffness and chemical resistance, with polyurethane, which contributes elasticity and toughness. The combination is well known in polymer science, dating back to foundational work on polyurethane-epoxy graft networks in the early 1990s, but the Taiwanese team asked a more specific question: how do the molecular weight of the polyurethane and the surface treatment of the reinforcing fibers shape the final material?

To answer it, the researchers systematically varied three variables. They used two polyurethane prepolymers built from polypropylene glycol of different chain lengths, designated PPG450 and PPG1000, where the numbers refer to the approximate molecular weight of the soft segment. Shorter chains produce a stiffer, more tightly crosslinked network, while longer chains introduce more flexible, mobile segments that can absorb energy and deform without fracturing. They also varied the amount of polyurethane blended into the epoxy matrix, and they adjusted the loading of sugarcane fiber from moderate to very high levels, reaching 50 percent by weight in the strongest formulations.

The fiber treatment proved to be the decisive factor in tensile performance. Raw sugarcane fiber is covered in waxes, lignin, and hemicellulose that make it hydrophilic and poorly matched to the hydrophobic polymer matrix. The team compared fibers cleaned with ethanol alone against fibers additionally treated with 3-glycidoxypropyltrimethoxysilane, a silane coupling agent abbreviated GPS. Silanes are molecular intermediaries: one end of the molecule reacts with hydroxyl groups on the fiber surface, while the other end carries epoxy groups that can participate in the curing chemistry of the surrounding resin. When the fibers were treated with GPS, the tensile strength of the composites climbed to a maximum of 39.3 megapascals, a clear demonstration that covalent bridges between fiber and matrix allow stress to transfer efficiently across the interface instead of concentrating at defects.

Flexural behavior told a complementary story. The highest flexural strength recorded was 62 megapascals, achieved in composites containing 50 percent sugarcane fiber by weight. Bending loads engage both compression and tension through the thickness of a specimen, so flexural strength is sensitive not only to interfacial bonding but also to how densely the fibers pack and how well the matrix wets them. The fact that the best bending performance came at the highest fiber loading suggests that, once the interface is properly engineered, the fibers themselves carry a large share of the load, effectively acting as a reinforcing skeleton within the IPN. This is a significant result for waste-derived fibers, which often underperform glass or carbon reinforcements precisely because their surfaces resist adhesion.

Dynamic mechanical analysis added a thermal dimension to the picture. In DMA, a specimen is subjected to a small oscillating deformation while temperature is swept, revealing how much elastic energy the material stores and how it softens as molecular motion increases. The researchers found that increasing the sugarcane fiber content raised the storage modulus, meaning the composites became progressively stiffer under dynamic loading. The fibers also improved thermal stability, an effect the authors attribute to reinforced interfacial interactions and reduced mobility of the polymer chains near the fiber surfaces. Rigid fiber surfaces constrain the segments of the surrounding network, delaying the onset of large-scale molecular motion and helping the material hold its shape at elevated temperatures.

Scanning electron microscopy confirmed the mechanistic interpretation. Micrographs of the fracture surfaces showed that silane-treated fibers were well wetted by the matrix, with polymer adhering to the fiber surfaces and fewer clean pull-out channels, the telltale signature of weak adhesion. In poorly bonded samples, fibers slid out of the matrix during fracture, leaving smooth voids and indicating that load transfer had failed at the interface. The combination of mechanical testing, thermal analysis, and microscopy allowed the team to connect macroscopic properties directly to interfacial structure, the kind of structure-property correlation that guides practical formulation.

The polyurethane molecular weight emerged as a second, independent lever. Composites based on the shorter PPG450 soft segments produced harder, more rigid networks, while the longer PPG1000 chains imparted greater flexibility and altered how the two polymer networks distributed themselves through the material. In IPN chemistry, the degree of phase separation between the two networks depends on chain length, crosslink density, and the kinetics of network formation. Longer polyurethane chains can phase-separate into soft domains that act as energy-absorbing regions, toughening the composite at the cost of some stiffness. By selecting the molecular weight, a materials designer can tune the balance between rigidity and resilience for a given application, whether that is a stiff panel or a component that must survive repeated impact.

The broader significance of the work lies in its convergence of sustainability and performance. Sugarcane bagasse is generated in enormous quantities in tropical agricultural economies, and finding value-added uses for it reduces both waste disposal burdens and reliance on petroleum-derived fillers. At the same time, natural fibers bring drawbacks, including moisture sensitivity and variability from crop to crop, that interfacial chemistry must overcome. The Taiwanese study demonstrates that a single, commercially available silane treatment can transform an agricultural byproduct into an effective reinforcement for a sophisticated dual-network polymer system, achieving tensile and flexural properties suitable for structural and functional applications ranging from automotive interior panels to construction materials.

The researchers, who report no external funding for the study, emphasize that their findings provide practical guidance for optimizing natural fiber-reinforced IPN composites: choose the fiber treatment to maximize interfacial adhesion, select the polyurethane molecular weight to dial in flexibility, and push fiber loading high enough to exploit the reinforcing skeleton without compromising wetting. As industries seek lighter, greener composites, the lesson from this work is that the answer may lie as much in the chemistry of a fiber’s surface as in the fiber itself, and that the fibrous residue of a sugar mill could become the raw material for the next generation of engineered plastics.

Subject of Research: Mechanical properties of silane-modified sugarcane fiber-reinforced polyurethane-epoxy interpenetrating polymer network composites

Article Title: Mechanical properties of sugarcane fiber/polyurethane–epoxy IPN composites: effects of PU molecular weight and fiber interfacial modification

Article References: Han, J., Tsao, C., Wu, H., & Liu, K. (2026). Mechanical properties of sugarcane fiber/polyurethane–epoxy IPN composites: effects of PU molecular weight and fiber interfacial modification. Polymer Bulletin, 83(12), Article 669. https://doi.org/10.1007/s00289-026-06711-z

Image Credits: AI Generated

DOI: 10.1007/s00289-026-06711-z

Keywords: sugarcane fiber, polyurethane, epoxy, interpenetrating polymer network, silane coupling agent, natural fiber composites, tensile strength, flexural strength, dynamic mechanical analysis, fiber surface modification, bagasse, thermal stability

The design philosophy starts with an observation about biology. Human skin is not a uniform material; its sensory structures are distributed asymmetrically through its thickness, which is part of why a fingertip can distinguish pressure from shear and bending from stretching with such precision. The research team replicated this asymmetry artificially using a gravity-driven self-assembly strategy. MXene nanosheets—atomically thin two-dimensional carbides prized for their metallic conductivity—were modified with tannic acid and then dispersed in a polyurethane matrix. As the mixture settled, gravity arranged the nanosheets into a gradient through the film’s thickness, producing what materials scientists call a Janus structure: two faces with different compositions and therefore different responses to mechanical stimuli.

The resulting composite achieved a combination of properties that flexible electronics researchers usually have to trade off against one another. The film could stretch to 114 percent of its original length before fracturing, while maintaining a tensile strength of 7.56 megapascals and an electrical conductivity of 9.2 × 10⁻³ siemens per centimeter. In practical terms, the material is tough and stretchy enough to survive repeated deformation on a moving joint, yet conductive enough that small mechanical distortions produce measurable changes in its electrical response. The asymmetric distribution of MXene through the thickness is what makes those responses selective: because the nanosheet density varies along the film’s cross-section, bending in one direction compresses a different portion of the conductive network than bending in the opposite direction, allowing a single sensor to discriminate between bending direction, applied pressure, and tensile strain.

Perhaps the most chemically interesting element of the design is the mechanism that lets the material heal itself. The researchers introduced a host-guest supramolecular interaction between cyclodextrin, a ring-shaped sugar molecule that acts as the host, and adamantane, a rigid cage-shaped hydrocarbon that acts as the guest. Cyclodextrin’s interior cavity is just the right size and chemical environment to capture adamantane, and the pair locks together reversibly in water-rich environments. By building these host-guest pairs into the polyurethane as physical cross-links, the team created a network in which the connections between polymer chains can break and reform dynamically rather than permanently. When the film is cut or damaged, bringing the surfaces back into contact allows the reversible cross-links to re-engage, stitching the material back together without heat, catalysts, or external agents.

This dynamic cross-linking network delivered a self-healing efficiency of 77.8 percent, meaning the material recovered more than three-quarters of its original mechanical and electrical performance after damage. The authors emphasize that this property is not merely a laboratory curiosity: it is what allows the sensor to maintain structural integrity and stable electrical response under the constant, dynamic deformation of real-world use. A wearable device attached to a wrist or finger is flexed thousands of times per day, and microscopic damage accumulates quickly in conventional elastomers. A material that continuously repairs its own conductive network can keep delivering reliable signals long after a static composite would have degraded.

Where the study moves from materials chemistry to applied intelligence is in its fusion with deep learning. A single flexible sensor produces a complicated, sometimes ambiguous electrical signal when attached to a moving body part—the same gesture performed at slightly different speeds or angles produces waveforms that differ in ways that would defeat simple threshold-based readout. The researchers trained machine learning algorithms on the sensor’s output streams and found that the system could reliably classify the signals into discrete categories. In one demonstration, the sensor was used as an input device for digital recognition: a user writing or gesturing digits produced characteristic signal signatures, and the trained algorithm identified which numeral had been traced with high adaptability across repeated trials.

The second, and more visually striking, demonstration involved table tennis. Return posture in table tennis is a fast, fine-grained motor behavior: the angle of the wrist, the orientation of the forearm, and the timing of the swing all determine whether the ball comes back as a loop, a chop, a drive, or a block. The team attached their flexible sensors to a player and recorded the electrical signals generated during return strokes, then used the integrated deep learning pipeline to perform dynamic pose analysis and ball return determination. The system could distinguish among return postures during live scoring conditions, verifying that the sensor-algorithm combination was feasible for capturing fine motion and recognizing complex, multi-joint movement behaviors—not just slow, deliberate gestures.

The significance of the work lies in how three separate design layers reinforce one another. The biomimetic Janus architecture provides multi-modal sensitivity, so one sensor element can distinguish several kinds of mechanical stimulus without additional hardware. The supramolecular host-guest cross-linking provides durability and self-repair, so the sensitivity survives prolonged use. And the machine learning layer provides interpretive power, converting noisy analog waveforms into discrete, actionable classifications. Each layer addresses a known failure mode of wearable sensors: single-mode devices that cannot disambiguate stimuli, brittle composites that fail under repeated strain, and raw signal outputs that require human experts to interpret. The authors describe the combination as a new theoretical basis and implementation path for high-performance flexible sensors built on biomimetic structural design, supramolecular dynamic regulation, and intelligent algorithm fusion.

The broader context is the rapid growth of flexible and wearable electronics for health monitoring, human-machine interfaces, and sports science. MXene-based composites have become a leading platform for such devices because of their exceptional conductivity and processability, but issues of oxidation, mechanical brittleness in dense films, and signal ambiguity under complex deformation have limited real-world deployment. Strategies like tannic acid modification, which can both stabilize MXene nanosheets and promote interfacial bonding with polymer matrices, and gravity-driven gradient assembly, which requires no expensive patterning equipment, point toward manufacturing routes that could scale. Meanwhile, the demonstration that a deep learning model can extract meaningful behavioral categories—down to the classification of an athlete’s stroke—from a minimal sensor array suggests a future in which lightweight wearable patches, rather than camera systems or instrumented gloves, provide motion analytics for training, rehabilitation, and gesture-based computing.

The study was supported by the Zhejiang Provincial Natural Science Foundation of China and the Zhejiang Sci-Tech University Fund, and it is published open access, making the full technical details available to researchers worldwide. For now, the image of a table tennis player’s wrist wrapped in a self-healing electronic skin that knows the difference between a loop and a chop stands as a vivid illustration of where the field is heading: materials that mimic biology in structure, repair themselves like living tissue, and lean on artificial intelligence to make sense of what they feel.

Subject of Research: A biomimetic Janus-structured MXene-polyurethane flexible sensor with host-guest self-healing cross-links integrated with deep learning for motion recognition

Article Title: Host-guest interaction viscoelastic polyurethane composite MXene flexible sensor: Integrated deep learning for digital recognition and table tennis return posture monitoring

Article References: Ao, Q., Wang, T., Liu, Y., Jiang, L., & Zhang, X. (2026). Host-guest interaction viscoelastic polyurethane composite MXene flexible sensor: Integrated deep learning for digital recognition and table tennis return posture monitoring. Advanced Composites and Hybrid Materials. https://doi.org/10.1007/s42114-026-02054-5

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02054-5

Keywords: flexible sensor, MXene, polyurethane, host-guest interaction, cyclodextrin, adamantane, self-healing materials, Janus structure, deep learning, wearable electronics, motion capture, table tennis

The motivation came from a very concrete engineering problem. In the 125-millimeter cannon system considered by the team, the space available for an energy absorber is severely constrained: although the cannon’s outer diameter is 125 millimeters, the designated installation region offers only 85 millimeters of diameter and a mere 12 millimeters of axial height. Protecting sensitive testing and electronic components inside such a platform requires not just high energy absorption but stable, predictable crushing under extreme loads. Many previously reported foam-filled absorbers stand 25 millimeters or taller, which rules them out for this kind of application outright. The researchers, led by Peng Zhang and Yu’nan Chen of North University of China along with colleagues, set out to see how much performance could be squeezed into that tiny envelope.

Their answer was a multi-cell thin-walled structure, or MTS, machined from 5052-H14 aluminum alloy. The geometry consists of an outer ring 70 millimeters in diameter, an inner ring 35 millimeters across, and four radial connecting ribs, together dividing the interior into a central cylindrical cell and several fan-shaped cells. Multi-cell designs are prized in crash engineering because subdividing the cross-section creates many potential plastic hinges, encouraging a stable, progressive folding mode under axial compression rather than sudden, catastrophic buckling. Earlier work by Chen and Wierzbicki and others showed that partitioning a tube into multiple cells can raise mean crushing force substantially; one classic study found that a 3-by-3 grid of cells could improve energy absorption efficiency by up to 50 percent over a single-cell tube of the same weight.

But geometry alone was not enough for the team’s purposes, because the energy dissipation of an empty thin-walled structure still depends entirely on the deformation of its walls. So the researchers turned to fillers. They used spherical open-cell aluminum foam, a metallic honeycomb-like material with spherical pores 4 to 6 millimeters across, an average density of about 900 kilograms per cubic meter, and a porosity of roughly 67 percent. Into the interconnected pore network they infiltrated a commercially available GF-5 polyurethane using a straightforward vacuum process: the foam was cleaned in ethanol and ultrasonically bathed, mixed polyurethane components were poured into a mold holding the foam and frame, a vacuum defoaming machine drew the polymer into the accessible pores for ten minutes, and the assembly cured at 90 degrees Celsius for ten hours. Gravimetric measurements showed the polyurethane filled about 67 percent of the foam’s volume, closely matching the foam’s porosity, and scanning electron microscopy and micro-computed tomography confirmed close interfacial contact between the polymer, the foam skeleton, and the aluminum walls.

From these ingredients the team built five structural configurations: an empty multi-cell frame; frames partially filled with plain aluminum foam or foam-polyurethane composite in the fan-shaped cells; and fully filled versions that also packed the central cylinder. Each configuration was tested at three wall thicknesses of 0.8, 1.0, and 1.2 millimeters, yielding fifteen specimen groups evaluated under both slow quasi-static compression and dynamic drop-hammer impact at 1176 joules. The results were striking. Under quasi-static loading, the best configuration, a partially foam-polyurethane-filled structure with 1.2-millimeter walls, absorbed 895.41 joules, nearly double the 448.47 joules of its unfilled counterpart. Under dynamic impact, the same design reached 984.40 joules, a 115.65 percent improvement over the empty frame.

Perhaps the most counterintuitive finding was that filling everything was not the best strategy. The fully filled structures generated higher mean crushing forces, but the central filler restricted the inward folding of the inner ring and shortened the effective crushing stroke, the distance over which the structure can deform before densifying. At the 1.0- and 1.2-millimeter wall thicknesses, complete filling raised the mean crushing force by roughly 15 percent but cut the effective stroke by about 17 percent, so total energy absorption actually fell below that of the partially filled design. Energy absorbed is the product of force and stroke, and the partially filled configuration struck the better balance: it left the central cell open as deformation space while the fan-shaped composite fillers braced the walls. The researchers are careful to note this balance is specific to their geometry rather than a universal rule, but within their design space the partial fill won decisively at every wall thickness.

The polyurethane infiltration itself proved remarkably effective in the partially filled topology. Compared with structures filled with plain aluminum foam, the polymer-infiltrated versions showed mean crushing forces 23 to 27 percent higher and energy absorption 35 to 49 percent higher under quasi-static loading, with similar gains of 39 to 52 percent under dynamic impact. Post-crushing microscopy revealed why: the polyurethane had fractured and torn during compression, indicating substantial polymer deformation, while the aluminum foam skeleton showed cell-wall cracking, and the polymer remained bonded to both the foam and the frame. The three phases did not deform independently; the foam provided lateral support, the polyurethane constrained local collapse and stretched as it failed, and the interfaces transferred stress between them, extending the region of the structure participating in plastic work.

To understand and predict this behavior, the team combined finite element simulation in LS-DYNA with an analytical model built on the simplified super-folding element theory. The theory treats the frame’s energy dissipation as the sum of plastic hinge bending and membrane stretching, deriving an optimal folding half-wavelength and a theoretical mean crushing force. Predictions agreed with quasi-static experiments within roughly 4 to 8 percent across all configurations, respectable accuracy for an engineering approximation. The validated simulations showed that the thin-walled frame contributed about 65 percent of the energy absorption in the partially filled design, with the fan-shaped composite fillers supplying the remaining 35 percent, and that dynamic loading amplified mean crushing forces by 4 to 20 percent through inertia, rate-dependent polymer response, and frame-filler interaction.

The headline number for compact applications is volumetric specific energy absorption. Because installation volume, not mass, is the binding constraint in the cannon platform, the researchers emphasized energy absorbed per unit volume. Their best structure achieved 21.32 joules per cubic centimeter with a crushing force efficiency of 0.84, all within a 12-millimeter height. Compared against previously reported absorbers, including aluminum honeycombs filled with polyurethane foam, 3D-printed lattices, and foam-filled CFRP tubes, the new design offers one of the best combinations of compactness, volumetric efficiency, and load stability. Simulations of a harsh acceleration pulse, a half-sine input peaking at 40,000 g over 200 microseconds, suggested the structure could cut the transmitted peak acceleration on a protected object by roughly 75 percent, holding the response below 10,000 g.

The authors are candid about limitations. They did not independently characterize the polyurethane’s modulus, strength, or strain-rate dependence, did not quantify pore-size distributions in the foam, and could not fully separate the energy contributions of the foam skeleton, the polymer, and their interfaces. The finite element model was validated against only one configuration, and dynamic testing covered a single impact condition. Environmental durability, fatigue, and temperature effects remain unexamined. Still, the core message stands: by pairing a multi-cell aluminum frame with a cheap, commercially available polyurethane infiltrated into open-cell foam, and by deliberately leaving part of the structure empty to preserve crushing stroke, the team has shown that extreme miniaturization and high energy absorption need not be enemies. For anyone packing electronics into missiles, satellites, or other cramped, high-g environments, that 12-millimeter slab of crumpling aluminum, foam, and polymer may be exactly the cushion they have been looking for.

Subject of Research: Energy absorption of compact polyurethane-infiltrated aluminum foam-filled multi-cell thin-walled structures under quasi-static and dynamic crushing

Article Title: Energy absorption of multicell thin walled structures filled with polyurethane infiltrated open cell aluminum foam

Article References: Zhang, P., Chen, Y., Shi, Y., Zhao, R., Guo, T., Guo, H., Chen, L., & Yu, P. (2026). Energy absorption of multicell thin walled structures filled with polyurethane infiltrated open cell aluminum foam. iScience, 29(10), Article 117716. https://doi.org/10.1016/j.isci.2026.117716

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117716

Keywords: energy absorption, thin-walled structures, aluminum foam, polyurethane, multi-cell tubes, impact protection, crashworthiness, progressive folding, finite element analysis, drop hammer test, specific energy absorption, hybrid materials

The challenge the researchers set out to solve is a familiar one in the field of thermoplasmonics. Gold nanostructures absorb light most efficiently at their localized surface plasmon resonance, the collective oscillation of conduction electrons that turns a gold nanoparticle into a tiny optical antenna. Most temperature-measurement techniques exploit that same resonance, relying on the strong absorption or fluorescence shifts that occur when the laser matches the plasmon peak. But many practical applications, including the self-healing polymer coatings that motivated this study, require heating at wavelengths where the gold is a comparatively weak absorber. At those off-resonance wavelengths, conventional absorption-based thermometry loses sensitivity, and engineers are left guessing at the thermal landscape inside their devices.

The Ningxia team, led by Yanru Xu and Yupeng Qi of the School of Mechanical Engineering, together with Yanqing Wang of the School of Materials and New Energy, turned to a different kind of probe altogether. Rather than measuring absorption, they measured the Raman spectrum of silicon nanoparticles scattered across the surface of their gold nanoarrays. Raman scattering is famously sensitive to temperature: as a crystal warms, its optical phonon peak shifts and broadens in a predictable way. The silicon nanoparticles used here displayed a remarkably stable temperature coefficient of minus 0.023 plus or minus 0.002 wavenumbers per kelvin, and crucially, that coefficient held constant across particle sizes ranging from 20 to 150 nanometers. That size independence means the probes can be deployed without worrying that variations in particle dimensions will corrupt the calibration.

There is a clever twist in how the technique achieves its sensitivity. Although the 785-nanometer excitation laser used in the experiments sits away from the gold nanoarrays’ plasmon resonance, the plasmon still does useful work. The near-field enhancement generated by the localized surface plasmon resonance amplifies the Raman signal from any silicon nanoparticle sitting close to the gold surface, making even subtle temperature-induced spectral shifts detectable. In effect, the gold nanoarray serves double duty: it is both the heat source being studied and the signal amplifier that makes the measurement possible. This plasmon-enhanced Raman thermometry therefore works precisely in the regime where absorption-based methods falter, giving researchers a non-contact, label-free alternative to fluorescence thermometry that requires no dye molecules or genetic tags.

The headline result is a quantitative map of photothermal heating under non-resonant conditions. When the team illuminated their silicon-on-gold-on-silica samples, they measured a temperature rise coefficient of 0.505 plus or minus 0.038 kelvin per milliwatt of laser power, a fourfold enhancement over control samples lacking the gold nanoarrays. At a laser intensity of 5.1 times ten to the seventh watts per square meter, the probes registered a temperature rise of 202 plus or minus 15 kelvin. Those are substantial numbers, hot enough to soften and flow thermoplastic polymers, and they demonstrate that meaningful photothermal conversion does not require driving the plasmon at its resonance peak.

Perhaps the most scientifically interesting part of the study is the mechanistic accounting of where the heat actually comes from. By comparing samples with and without the gold nanoarrays, the researchers decomposed the total heating into two contributions. Roughly 72 percent of the measured temperature rise originates from the non-radiative decay of localized surface plasmons in the gold itself, the process by which the collective electron oscillation relaxes into lattice vibrations and dumps its energy as heat. The remaining 28 percent comes from the plasmon-enhanced intrinsic absorption of the silicon nanoparticles, whose own absorption is boosted by the intensified near field around the gold structures. This kind of quantitative partitioning is rare, and it gives designers a clear rule of thumb for how much heating they can attribute to the metal versus the surrounding materials.

To prove the technique is more than a laboratory curiosity, the team validated it in a practical setting: the photothermal self-healing of polyurethane. Thermoplastic coatings can repair scratches and microcracks if they can be heated locally above their glass transition or flow temperature, allowing the polymer chains to migrate and re-fuse the damaged region. Gold nanoarrays embedded in such coatings act as remotely triggered heaters, and the new Raman thermometry provides the thermal benchmarks needed to design those triggers with precision. Knowing that a given laser intensity produces a given local temperature rise means coating engineers can specify light doses that heal damage without thermally degrading the surrounding material.

The implications extend well beyond self-healing coatings. Plasmonic heating is the engine behind photothermal catalysis, solar-driven water distillation, optical trapping, nanoscale actuation, and biomedical ablation, and in nearly all of these fields the local temperature is the quantity that actually controls performance, yet it is notoriously hard to measure. Techniques such as anti-Stokes luminescence thermometry, photothermal microscopy, and interferometric scattering each have their strengths, but many require resonant excitation, fluorescent labels, or single-particle isolation. The silicon nanoparticle approach is comparatively simple: it uses chemically robust, optically stable probes whose Raman signature is unaffected by photobleaching, and it can be implemented on a standard confocal Raman microscope. Because the probes are non-invasive and label-free, they can be scattered onto virtually any plasmonic substrate without altering its optical properties.

The work also speaks to a broader debate in the plasmonics community about how heat and hot electrons partition after plasmon excitation. Recent studies have examined whether interband or intraband excitation pathways dominate the steady-state population of hot electrons in gold, and how quickly the absorbed energy thermalizes into the lattice. By working at an off-resonance wavelength and quantifying the non-radiative decay contribution directly, the Ningxia measurements add a useful data point: even far from resonance, the plasmon-mediated channel remains the dominant heat source, accounting for nearly three quarters of the observed warming in these nanoarrays. That finding should inform models of photothermal conversion in ordered nanoparticle arrays, where interparticle coupling and substrate effects both shape the absorption profile.

For now, the technique establishes silicon-nanoparticle Raman thermometry as a versatile platform for spatially resolved thermal profiling of plasmonic systems, and the authors suggest it could become a standard benchmarking tool for anyone designing precision photothermal triggers. As smart coatings, thermoplasmonic actuators, and light-driven chemical reactors move from the laboratory toward commercial deployment, the ability to measure, rather than merely estimate, the temperature at the nanoscale may prove to be one of the field’s most valuable enabling technologies. What began as a question about how hot a gold nanoarray gets under the wrong color of laser light has ended with a general-purpose thermometer built from one of the most abundant materials on Earth.

Subject of Research: In situ Raman thermometry using silicon nanoparticle probes to quantify non-resonant photothermal conversion in gold nanoarrays

Article Title: Quantifying non-resonant photothermal conversion in gold nanoarrays via in situ Raman thermometry with silicon nanoparticle probes

Article References: Quantifying non-resonant photothermal conversion in gold nanoarrays via in situ Raman thermometry with silicon nanoparticle probes. (n.d.). https://doi.org/10.1007/s11051-026-06751-6

Image Credits: AI Generated

DOI: 10.1007/s11051-026-06751-6

Keywords: Raman thermometry, silicon nanoparticles, gold nanoarrays, plasmonic heating, photothermal conversion, localized surface plasmon resonance, non-resonant excitation, self-healing coatings, polyurethane, nanoscale thermometry, thermoplasmonics, Journal of Nanoparticle Research

The research team set out to answer a deceptively simple question: what exactly is floating in and settling out of the air inside the buildings where people work and live? To find out, they collected settled indoor dust from three contrasting urban microenvironments in Tiruchirappalli, a major city in the southern Indian state of Tamil Nadu. The sampling sites included an academic office, a residential dwelling located near a busy traffic corridor, and a second residence situated close to a small-scale industrial area with comparatively lighter traffic. By choosing locations that differed in both their surrounding land use and their internal activity patterns, the researchers could probe whether outdoor pollution sources or indoor behaviors dominate the microplastic burden that people actually breathe and swallow.

Identifying plastics at the microscopic scale requires more than a good magnifying glass. The team used micro-Fourier transform infrared spectroscopy, or µ-FTIR, a technique that shines infrared light on individual particles and reads the characteristic vibrational fingerprints of the chemical bonds within them. Because every polymer absorbs infrared radiation at a distinctive set of wavelengths, the method allows researchers to distinguish polyethylene terephthalate from nylon, polystyrene, polyethylene, polyurethane, and polyvinyl chloride with high confidence. This chemical specificity matters enormously for risk assessment, because different polymers carry different hazard profiles based on the monomers, additives, and residual catalysts they contain.

The polymer analysis revealed a familiar cast of characters. Polyethylene terephthalate, the plastic of beverage bottles and synthetic textiles; nylon, ubiquitous in carpets, clothing, and furnishings; polystyrene, common in packaging and disposable containers; and polyethylene, the world’s most produced plastic, all appeared consistently in the dust across all three sites. These findings align with what indoor air studies in cities from Tehran to Birmingham to Dhaka have reported, reinforcing the picture of indoor environments as reservoirs of plastic fragments shed from fabrics, furniture, packaging, and countless everyday objects that slowly degrade into inhalable and ingestible particles.

But the numbers told a more surprising story. Microplastic deposition differed significantly among the three sites, a difference confirmed statistically with a Kruskal-Wallis test yielding a p-value of 0.027. The academic office, designated Site A, recorded the highest mean deposition at 241 plus or minus 23 particles per square meter per day. The traffic-adjacent residence, Site C, came in second at 151 plus or minus 24 particles per square meter per day, while the residence near the small-scale industrial zone, Site B, showed by far the lowest deposition at just 54 plus or minus 3 particles per square meter per day. If outdoor sources were the primary driver, one might have expected the industrial-adjacent home to fare worst. Instead, the office dominated, suggesting that occupant activity, source diversity, and cleaning frequency inside a building can outweigh the industrial or traffic influences just beyond its walls.

Particle size added another layer of concern. The size distribution varied significantly among sites, with a p-value below 0.001, and the office again stood out for the wrong reasons. Particles at Site A averaged just 18.9 plus or minus 11.2 micrometers, markedly smaller than the 33 to 36 micrometer particles typical of the two residences. The authors attribute this to greater occupant activity, less frequent cleaning, and a wider diversity of plastic sources in the office environment. The size difference is toxicologically important: smaller particles can penetrate deeper into the respiratory tract, reaching the lower airways more readily, and they also remain suspended in air longer, increasing the chance of inhalation before they ever settle into dust. Children and infants, who play on floors and frequently bring hands to mouths, are considered especially vulnerable to ingesting dust-bound particles.

Perhaps the study’s most consequential finding concerns risk. When the researchers weighted their polymer identifications by hazard scores, drawing on established chemical-composition-based ranking frameworks for plastic polymers, the pattern of danger did not follow the pattern of abundance. Site A, the academic office, recorded the highest potential exposure risk associated with polyurethane and polyvinyl chloride, reaching 1,750 hazard units. Polyurethane appears in foams, coatings, and adhesives, while polyvinyl chloride is notorious for its additive suite, including plasticizers and stabilizers of toxicological concern. Site C, the traffic-side residence, registered a potential polyurethane-associated hazard ranking of 1,500 hazard units. Site B, the industrial-adjacent home, exhibited a negligible polymer-associated potential hazard score despite its proximity to industrial activity.

This inversion carries a blunt message: site classification based on outdoor environment, whether traffic-dominated or industrial-influenced, does not align with actual indoor exposure risk. A building next to a small factory can be safer to breathe in than an ordinary office, if the office harbors more hazardous polymers in its dust. The authors emphasize that mere particle counts cannot determine risk, and that a comprehensive understanding and characterization of indoor microplastic sources is essential for designing targeted mitigation strategies. Counting particles alone, in other words, tells only half the story; knowing whether that count is dominated by relatively benign polyethylene or by additive-laden PVC changes the entire risk calculus.

The study arrives amid a rapidly expanding global literature on airborne microplastics, which have now been documented in indoor air and dust across five megacities in China, in subway stations in Istanbul, in classrooms in Shiraz and Dhaka, in hospitals in India, and in homes from Pakistan to Barcelona. Researchers have also shown, using breathing thermal manikins, that humans inhale measurable quantities of indoor airborne microplastics under ordinary conditions, and that plastic particles can act as vectors, carrying adsorbed contaminants and associated microorganisms into the body. What the Tiruchirappalli study adds is a tropical savanna data point, a region and climate underrepresented in the existing literature, along with a methodological argument that hazard-weighted assessment should become standard practice in exposure studies.

For readers wondering what to do with this information, the findings point toward practical, source-focused interventions. Frequent and thorough cleaning, careful selection of furnishings and textiles, reduced use of plastic packaging indoors, and attention to ventilation all plausibly reduce the reservoir of settled particles that resuspension turns into breathable air. But the deeper lesson is structural. The plastic burden of indoor dust reflects the materials we choose to surround ourselves with, and the polymers that shed from foams, coatings, and synthetic fabrics can be more hazardous than their abundance suggests. As the authors conclude, understanding what the particles are made of, not merely how many there are, is the key to protecting the people who live and work among them.

Subject of Research: Microplastic contamination of indoor dust and associated human health risks in a tropical savanna urban environment

Article Title: Indoor exposure to microplastics in dust: polymeric composition and health risks in a tropical savanna climatic region

Article References: Sibhi M, R., Mohan V, L., & Passi, A. (2026). Indoor exposure to microplastics in dust: polymeric composition and health risks in a tropical savanna climatic region. Air Quality, Atmosphere & Health, 19(10), Article 210. https://doi.org/10.1007/s11869-026-02107-0

Image Credits: AI Generated

DOI: 10.1007/s11869-026-02107-0

Keywords: microplastics, indoor dust, polymer composition, µ-FTIR spectroscopy, inhalation exposure, polyurethane, polyvinyl chloride, PET, health risk assessment, Tiruchirappalli, tropical savanna climate, indoor air quality