The research team, led by Jinrong Cao of the Geological Carbon Dioxide Storage Technology Research Association and the Research Institute of Innovative Technology for the Earth in Japan, combined three observational streams in a single experiment: distributed fiber-optic strain sensing, time-lapse X-ray computed tomography, and coupled numerical modeling of two-phase flow and poroelastic deformation. Their specimen was a cylindrical tuffaceous sandstone core, 34.83 millimeters in diameter and 179.50 millimeters long, drilled from the Sarukawa oil field in Oga, Akita Prefecture, an area selected for a Japanese advanced carbon storage program targeted to begin operations by 2030. The rock had a porosity of 25.06 percent and an intrinsic permeability of 5.41 millidarcys, with a mineral framework dominated by the zeolite clinoptilolite at roughly 63 percent, alongside quartz, albite, anorthite, and heulandite.

The sensing element was a single-mode silica fiber bonded to the core surface with epoxy at an optimized wrap angle of 80 degrees relative to the core axis. This helical geometry converts one continuous fiber into a dense array of quasi-independent strain sensors, resolving circumferential, or hoop, strain at one-centimeter spatial resolution along the full specimen length. The interrogator, a Neubrex 7020 unit, works by measuring Rayleigh frequency shifts in backscattered laser light using a tunable wavelength coherent optical time-domain reflectometer. Because strain and temperature both shift the Rayleigh spectrum, the team held the experiment at a stable 40 degrees Celsius and applied a calibrated strain coefficient of minus 0.153 gigahertz per microstrain, yielding a strain resolution of about half a microstrain for comparable measurements, far finer than the tens to roughly one hundred microstrains observed during injection.

Before introducing carbon dioxide, the researchers ran a single-phase water flow test to pin down permeability and validate their poroelastic model. When upstream pressure reached 10.5 megapascals, circumferential strain near the inlet jumped to approximately 75 microstrains within a single sampling interval of 36 seconds or less, while the downstream end of the core registered only a few microstrains. Numerical simulations showed that the sub-second initial response could not be resolved experimentally, but by roughly half a second to one second the simulated strain gradient matched the first measured profile, and a steady inlet-to-outlet strain gradient established itself within about one second. This close agreement between measurement and model confirmed that, in fully water-saturated rock, deformation is governed by pore water pressure gradients acting through Biot-style poroelastic coupling.

The main event was the supercritical carbon dioxide flood. Time-lapse CT scans, taken at 60 seconds per volume using an iodide-rich contrast solution to sharpen fluid-rock contrast, tracked the drainage process in detail. During the first 1.6 minutes, corresponding to 0.036 injected pore volumes, carbon dioxide accumulated mainly near the inlet. By 2.67 minutes the saturation field had become spatially nonuniform, reflecting variability in pore accessibility and capillary entry conditions across the zeolite-rich framework. At 4.27 minutes the front reached the specimen midpoint, and breakthrough occurred at 8.0 minutes, when average carbon dioxide saturation hit 19.4 percent. Differential pressure during drainage held steady between 0.45 and 0.48 megapascals at a flow rate near one milliliter per minute.

The striking result was how differently the strain field evolved from the saturation field. At the onset of injection, a pronounced strain gradient appeared immediately: strain near the inlet climbed to roughly 80 microstrains, while even the outlet showed a small but detectable response. The strain front was far more spatially diffuse than the comparatively sharp saturation front imaged by CT. By breakthrough, strain had reached about 100 microstrains near the inlet and 20 microstrains near the outlet. Most tellingly, at a position 0.09 meters from the inlet, a distinct strain increase appeared near the very start of injection, while local carbon dioxide saturation remained at zero for the first four minutes. The delay between strain onset and saturation onset grew with distance from the inlet, exactly the pattern expected if pressure disturbances propagate through the connected aqueous phase faster than the capillary-controlled gas front advances.

The coupled numerical model, a two-dimensional axisymmetric finite-element representation of the full specimen, provided the physics-based bridge between the observable strain and the unmeasured internal pressure. The team calibrated two-phase flow parameters exclusively against the CT-derived saturation profiles, then compared the predicted strain against the fiber measurements as an independent test. Simulated pore gas and pore water pressures evolved concurrently but with different spatial patterns, related through capillary pressure, and the modeled strain reproduced both the magnitude and the timing of the measured response. Because the sandstone’s apparent drained bulk modulus of roughly one to two gigapascals makes it relatively compliant, a given pressure perturbation produces a large, measurable strain. The authors are careful to stress that the fiber does not measure pressure directly; the strain signal is a model-constrained poroelastic proxy for the evolving pressure footprint, not a standalone pressure gauge.

The engineering implications reach well beyond the laboratory. Operational surveillance of storage sites typically relies on wellhead and bottomhole pressure, flow rates, sparse downhole gauges, and episodic plume imaging, none of which uniquely constrains the internal pressure field. Distributed strain sensing adds a spatially continuous constraint that can be folded into coupled flow and geomechanical models, helping to characterize uncertain formation properties and to evaluate deformation relevant to reservoir, caprock, and wellbore integrity. Field deployments already hint at feasibility: distributed fiber sensing has been demonstrated under field-scale injection conditions at the CO2CRC Otway site in Australia, a pumping test at Mobara in Japan captured pressure-related reservoir deformation, and behind-casing water-injection measurements show that injection-induced strain is detectable through a casing-cement-formation system.

The authors are equally candid about the limitations that separate their benchtop result from routine field practice. The adhesive layer bonding the fiber to the core was not independently calibrated, so perfect strain transfer was assumed. Field fibers are usually installed axially behind casing, where recorded amplitude depends on cable orientation, completion design, cement properties, gauge length, and strain-transfer efficiency, and axial strain is not generally equivalent to the hoop strain measured here. Stiffer formations or rocks with a lower Biot-Willis coefficient would produce smaller strains that may fall below detection thresholds, meaning an absent strain signal cannot be read as absent pressure communication. The homogeneous axisymmetric model also cannot capture localized effects of bedding, fractures, or anisotropic permeability, and longer-term chemical interactions between carbon dioxide, brine, and reactive minerals may gradually alter rock stiffness and fracture behavior.

Even with those caveats, the study delivers a compelling proof of concept: the mechanical consequences of injection arrive before the plume does, and a helically wound strand of glass can watch them happen. Future priorities include experiments on rocks with contrasting stiffness and capillary behavior, direct internal pressure measurements, three-dimensional models that explicitly represent the helical fiber geometry, and field studies that integrate distributed strain with pressure gauges, time-lapse geophysics, distributed acoustic and temperature sensing, and surface deformation observations. As global net-zero pathways call for roughly ten gigatons of carbon dioxide storage per year by 2050, tools that convert invisible pressure transients into measurable, interpretable strain signals could become an essential part of the monitoring toolkit, giving operators and regulators earlier and more defensible warnings about where the subsurface is being mechanically stressed.

Subject of Research: Distributed fiber-optic sensing of poroelastic strain precursors during supercritical CO2 core flooding in sandstone

Article Title: Poroelastic strain precursors during laboratory carbon dioxide core flooding revealed by helically bonded fiber sensing

Article References: Cao, J., Park, H., Xue, Z., Nakajima, T., Amer, R., & Ouchi, W. (2026). Poroelastic strain precursors during laboratory carbon dioxide core flooding revealed by helically bonded fiber sensing. Communications Engineering, 5(1), Article 164. https://doi.org/10.1038/s44172-026-00783-5

Image Credits: AI Generated

DOI: 10.1038/s44172-026-00783-5

Keywords: carbon capture and storage, distributed fiber-optic sensing, poroelasticity, CO2 core flooding, X-ray computed tomography, pore pressure, geomechanics, sandstone, capillary pressure, geological storage, strain sensing, two-phase flow

The core insight behind the design is elegantly simple once spelled out. When a soft elastic material is stretched in one direction, it narrows in the perpendicular directions—the familiar Poisson effect that causes a rubber band to thin as you pull it. Conventional fluidic strain sensors exploit this indirectly, measuring resistance changes as a stretched channel lengthens and its cross-section shrinks. The Xi’an Jiaotong team realized that a carefully shaped cavity could weaponize this effect. Their drum-shaped microstructures sit along the microchannel network like a string of tiny barrels, and as the material is strained, the transverse contraction of each drum drives its top and bottom walls toward one another. At a critical strain the gap between them closes, constricting the fluidic channel underneath in a sudden, dramatic gating event.

The result is a sensor whose response is anything but linear and gentle. As the drum gaps approach closure, the electrical resistance of the conductive fluid inside the channels changes precipitously, yielding a peak gauge factor—a standard measure of relative signal change per unit strain—exceeding 43,200. For context, that is a four-order-of-magnitude enhancement over unstructured fluidic channels, which typically produce modest, smoothly varying signals. The steep near-closure regime acts as an internal amplifier: minute strains around the gating threshold produce enormous fractional changes in resistance, allowing the device to discriminate strain magnitudes that would be invisible to a conventional architecture. This is precisely the kind of mechanical gain that biological mechanoreceptors achieve through their own gating proteins, which open and close ion channels in response to membrane tension.

Directional sensing, the second half of the challenge, comes from the orthogonal geometry of the channel network. The device contains two families of channels arranged at right angles to one another, and the Poisson effect guarantees that they respond in opposition. When the sensor is stretched along the longitudinal axis, the longitudinal channels elongate and narrow while the transverse channels simultaneously shorten and widen. When the stretch direction rotates, the roles reverse. Because the two channel families are embedded in a single monolithic elastic body rather than stacked as separate layers, there are no interfacial stress concentrations to cause signal drift—a failure mode that plagues layered sensor architectures subjected to complex, multi-axial deformations. The cross-coupled opposition between the two channel sets provides intrinsic directional selectivity, with a measured near-axial average selectivity of 15.42, meaning the response along the loading axis dominates the cross-axis response by more than an order of magnitude.

To convert raw two-channel signals into a full picture of arbitrary strain orientation, the researchers turned to machine learning. Trained on the paired resistance responses of the orthogonal channels, the algorithm achieves quadrant-resolved strain sensing with sub-2-degree angular resolution across a strain range of up to 80 percent, provided the general loading quadrant is known. That combination of range and angular precision is notable because most strain sensors must trade stretchability against sensitivity: highly sensitive solid-state materials such as cracked metal films or carbon nanotube networks tend to fail or drift at large deformations, while robust elastomeric conductors produce weak, noisy signals. The fluidic transduction mechanism sidesteps this trade-off entirely, because the conductive liquid inside the channels has no fixed microstructure to fatigue, crack, or delaminate. The elastomer surrounding it deforms reversibly, and the liquid simply redistributes.

Durability figures bear this out. The sensor withstood 100,000 loading cycles with exceptional stability, a figure that speaks to the elimination of the mechanical fatigue inherent in solid-state sensing materials. Where a metallic nanowire network might slowly lose percolation pathways under repeated strain, and a layered device might accumulate interfacial damage, the drum-gated fluidic architecture returns to its baseline resistance cycle after cycle. For wearables intended to live on joints, fingertips, or athletic equipment—environments defined by millions of deformation events over a product’s lifetime—this kind of endurance is arguably as important as raw sensitivity.

The team validated the technology in a scenario that rewards exactly this combination of traits: table tennis stroke recognition. Fastened to a player’s equipment or limb, the sensor captured the rapid, multidirectional deformations associated with different strokes, and a machine-learning classifier trained on the resulting signals identified the stroke types with greater than 95 percent accuracy. The demonstration points toward closed-loop athletic training systems in which a coach or an application receives real-time, quantitative feedback on technique—stroke by stroke, rep by rep—rather than relying on video review or subjective assessment. The same sensing principles could extend naturally to resilient human-machine interfaces, where robots and prosthetics must interpret rich, multidirectional contact information from soft, deformable surfaces.

What makes the work resonate beyond its immediate application is the design philosophy. Rather than stacking more materials or engineering ever-finer conductive networks, the researchers reshaped the sensor’s mechanical geometry to make physics do the amplification. The Poisson effect is free—it comes with every stretchable solid—and by sculpting drum-shaped cavities the team converted a modest, linear geometric side-effect into a nonlinear gating event with enormous signal gain. The bioinspired framing is not merely rhetorical: tactile sensory cells in skin also transduce mechanical stimuli through gating mechanisms in which small displacements produce large, abrupt changes in electrical output. The artificial analogue here trades ion channels for liquid-filled microchannels, but the underlying strategy—amplify by gating rather than by gradual deformation—reads the same.

The limitations that remain are the usual ones for a new sensor architecture. The sub-2-degree angular resolution currently requires that the loading quadrant be known in advance, so full arbitrary-orientation decoding without prior information would need either additional sensing elements or smarter algorithms. And the steep sensitivity gain concentrated near gap closure means the most valuable part of the response curve occupies a specific strain window, which system designers must account for when matching the sensor to a given application. Still, the reported combination of a gauge factor above 43,200, directional selectivity of 15.42, 80 percent stretchability, 100,000-cycle durability, and 95 percent stroke-classification accuracy marks a substantial step for flexible electronics. It suggests that the next generation of wearable sensors may owe less to exotic materials and more to clever geometry—microscopic drums that snap shut under strain and, in doing so, teach soft machines to feel direction as keenly as they feel magnitude.

Subject of Research: Bioinspired fluidic strain sensing using Poisson-actuated microchannel gating for stretchable, multidirectional wearable sensors

Article Title: Bioinspired Poisson‑actuated gating enabled high-sensitivity and stretchable multidirectional strain sensing

Article References: Bioinspired Poisson‑actuated gating enabled high-sensitivity and stretchable multidirectional strain sensing. (n.d.). https://doi.org/10.1038/s41528-026-00644-3

Image Credits: AI Generated

DOI: 10.1038/s41528-026-00644-3

Keywords: wearable sensors, strain sensing, Poisson effect, flexible electronics, microfluidics, machine learning, gauge factor, directional selectivity, bioinspired design, human-machine interfaces, athletic training, durability

The material at the heart of the study is a double-network hydrogel, a class of soft solids in which two interpenetrating polymer architectures share the same water-rich matrix. The first network in this design is built from chitosan, a naturally derived polysaccharide prized for its biocompatibility and its abundance of chemically active terminal groups. The second is a modified polyethylene glycol network, which contributes elasticity and water retention. Suspended within this paired architecture are graphene nanosheets, the atomically thin carbon layers whose exceptional electrical conductivity makes them a favorite filler for flexible electronics. The logic of the design is straightforward: the polymer networks supply the mechanical toughness and stretchability that a skin-like sensor demands, while the graphene supplies a continuous conductive pathway whose resistance changes predictably when the material is deformed or heated.

Double-network hydrogels earn their reputation through a clever division of labor. When the material is stretched, the more brittle of the two networks sacrificially fractures at the molecular scale, dissipating energy that would otherwise tear the sample apart. The more ductile network survives, holding the structure together and allowing it to recover. This energy-dissipating mechanism is what allows the chitosan and modified polyethylene glycol composite to remain mechanically resilient at strains of up to 350 percent, a stretch ratio far beyond what ordinary rigid sensors can tolerate. In practical terms, the hydrogel can be wrapped around a finger, an elbow, or an ankle and endure the full range of human motion without losing its integrity or its electrical function.

The strain-sensing performance is quantified by the gauge factor, a dimensionless ratio that describes how strongly the electrical resistance responds to deformation. For this hydrogel, the researchers report a gauge factor of 13.8, a high value that indicates sharp sensitivity to even small movements. When the material is attached to the wrist, fingers, elbows, or ankles, it converts bending, stretching, and joint flexion into clean, dynamic changes in relative resistance, denoted ΔR/R₀. Crucially, these signals remain stable during motion, and the sensor maintained cyclic electromechanical stability over more than 500 stretching cycles, an endurance benchmark that matters enormously for any device expected to survive daily wear.

Temperature sensing is where the chitosan-based chemistry reveals an additional advantage. The hydrogel exhibits a thermoresistive response, meaning its electrical resistance changes with temperature, and the researchers measured a linear response across the fever-relevant window of 37.5 to 40 degrees Celsius. That linearity is a genuine asset: it means the sensor output can be translated into a temperature reading with simple calibration rather than complex curve fitting. Even more striking is the temperature coefficient of resistance, which the team reports as an ultrahigh negative 5.62 percent per degree Celsius. In plain terms, a one-degree rise in temperature changes the resistance by more than five percent, a sensitivity that allows the sensor to detect fever-range changes in real time. Most commercial thermistors and resistive temperature detectors operate with coefficients orders of magnitude smaller, so this figure represents a substantial leap in thermal resolution for a soft, wearable format.

The dual-mode capability raises an obvious engineering question: how does a single sensor distinguish a change in temperature from a change in strain, when both alter its resistance? The answer lies in the very different signatures the two stimuli produce. Strain-induced resistance changes are typically large, transient, and correlated with movement, while temperature changes produce slower, sustained shifts. By separating fast dynamic components from slow baseline drifts in the resistance signal, the sensor can deliver stable pulse waveforms from the wrist even while the wearer moves, and simultaneously flag a rising body temperature. This decoupling is precisely what a tactile healthcare patch would need: continuous pulse monitoring during exercise, for example, alongside early detection of a fever developing underneath the device.

Another practical hurdle for wearable hydrogels has always been adhesion. Soft gels tend to slide off skin or peel away from substrates after a few minutes of wear. The chitosan network in this material solves the problem chemically. Its terminal hydroxyl and amino groups are prolific hydrogen-bond donors and acceptors, allowing the hydrogel to form spontaneous adhesive contacts with a striking variety of surfaces, including plastic, rubber, glass, metal, and human tissue. This self-adhesion eliminates the need for separate tapes or medical adhesives, simplifying device assembly and improving comfort during extended wear on the skin. It also means the sensor conforms intimately to curved body surfaces, which improves both mechanical coupling for strain measurement and thermal contact for temperature measurement.

The implications for wearable healthcare devices are considerable. A single soft patch that tracks joint motion, captures pulse waveforms, and monitors fever-range temperature could serve applications ranging from postoperative recovery monitoring to athletic performance tracking to continuous screening in clinical settings. Because the material is water-rich and built partly from a biocompatible polysaccharide, it sits comfortably within the emerging paradigm of skin-interfaced electronics that prioritize softness and conformity over the rigid silicon packages of conventional devices. The combination of a 350 percent strain tolerance, a gauge factor of 13.8, more than 500 stable cycles, and a temperature coefficient of negative 5.62 percent per degree Celsius in one material is a rare confluence of specifications in the flexible sensor literature.

The work also illustrates a broader trend in materials science: the deliberate fusion of structural and functional design at the nanoscale. Rather than treating a sensor as a rigid chip attached to a flexible substrate, the researchers engineered the sensing function directly into a soft structural material. Graphene, the conductive filler, does double duty as both the electrical transducer and a mechanical reinforcement within the double-network matrix. The chitosan does double duty as a structural polymer and an adhesive. This multifunctional economy, where each component serves multiple roles, is increasingly recognized as the path toward devices that are simultaneously simpler to manufacture, more robust in use, and more comfortable to wear.

Challenges remain before such hydrogels reach the clinic or the consumer market. Long-term dehydration of the gel, biocompatibility over weeks of continuous wear, and scalable manufacturing all require further study, and the published work reports laboratory characterization rather than clinical deployment. Yet the demonstration stands as a compelling proof of concept. By marrying a tough double-network polymer architecture with the conductivity of graphene and the natural adhesivity of chitosan, the Khalifa University-led team has produced a material that behaves less like an electronic component and more like a piece of engineered skin, one that feels the body move and reads its temperature at the same time. As flexible electronics mature, designs of this kind, documented in the open-access literature and available for the wider community to build upon, may well define what the next generation of wearable health monitors looks like.

Subject of Research: A graphene-integrated double-network nanocomposite hydrogel for dual strain and temperature wearable sensing

Article Title: A multifunctional graphene-integrated double-network nanocomposite hydrogel for dual strain-temperature wearable sensing

Article References: A multifunctional graphene-integrated double-network nanocomposite hydrogel for dual strain-temperature wearable sensing. (n.d.). https://doi.org/10.1007/s42114-026-02106-w

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02106-w

Keywords: wearable sensor, hydrogel, graphene, double-network hydrogel, strain sensing, temperature sensing, nanocomposite, chitosan, flexible electronics, healthcare monitoring, soft materials, 2D materials