The research, led by Associate Professor Isao Shitanda of the Department of Pure and Applied Chemistry in the Faculty of Science and Technology at Tokyo University of Science, was published online in ACS Omega on September 21, 2026. Co-authored by second-year master’s student Takuma Fujisawa, the study describes a fully integrated system: screen-printed ion-selective electrodes for sodium and potassium, a printed liquid-junction reference electrode, a fabric-based sample transport layer, and custom digital electronics packaged in a wristwatch form factor that can process, store, and transmit data. The work was supported by JSPS KAKENHI Grant-in-Aid for Scientific Research (B), Grant Number 24K02819.

To understand why this integration matters, it helps to look at how wearable ion sensors actually work. Most of them are potentiometric devices, which means they do not measure a concentration directly. Instead, they measure a voltage that changes predictably with the concentration of a specific ion in the sample touching the electrode. An ion-selective electrode is designed to respond preferentially to one ion species, such as sodium or potassium, generating a potential that tracks that ion’s activity in sweat. But a single electrode cannot give a meaningful reading on its own. Every potentiometric measurement is a comparison against a second, unchanging potential, and that is the job of the reference electrode.

The reference electrode is the quiet workhorse of electrochemistry, and it is also the weak link in many printed wearable sensors. Conventional printed reference electrodes can take considerable time to stabilize before they deliver a steady potential, and until they do, the readings from the ion-selective electrodes are unreliable. For a device meant to be strapped on and used immediately, whether on a factory floor or a running trail, a long pre-adjustment period is a serious practical obstacle. Continuous monitoring in dynamic, real-world contexts demands a reference electrode that is ready almost as soon as the sweat arrives.

The Tokyo University of Science team attacked this problem with a liquid-junction reference electrode built by screen printing. The key ingredient is silica gel embedded in the liquid junction, which facilitates water permeation into the electrolyte layer. That permeation allows the reference electrode to reach rapid initial stabilization, dramatically shortening the time between putting on the device and obtaining trustworthy measurements. Because the electrode is printed rather than assembled from bulky conventional components, it fits naturally into a flat, flexible, low-profile sensor that can sit against the skin on the wrist.

Getting sweat to the electrodes is its own engineering challenge, and the researchers addressed it with a dedicated sample transport layer. This layer consists of fabric and superabsorbent fiber placed over the electrodes. Its job is twofold: it helps wet the sensing area as sweat is produced, and it facilitates transport of the sample through the sensing region so that fresh sweat, carrying up-to-date ion information, continuously reaches the electrodes. Without such a layer, a wearable sensor can sit dry against the skin or read stale, pooled fluid, either of which undermines the goal of real-time monitoring.

The sensing elements alone do not make a wearable device, so the team integrated them with digital electronics in a wristwatch-type package. The custom device processes the signals from the sodium- and potassium-selective electrodes, transmits them wirelessly to a host computer, and simultaneously stores them locally on a micro-SD card. That combination of live transmission and onboard storage is important for field use, where wireless links can drop or where data may need to be reviewed after the fact. The wearer gets continuous monitoring without any interruption to their activity, and the researcher or safety officer gets a complete record.

The most striking demonstration came not in the laboratory but at an active construction site. One construction worker wore the wristwatch device through a normal workday, including breaks, hydration, and meals, while carrying out usual tasks around the site. Over approximately two hours and forty-five minutes, the device acquired sodium- and potassium-responsive signals in real time as the worker moved and worked. The measurements were successfully transmitted wirelessly to a host computer and simultaneously stored on the device, showing that the integrated system could acquire and relay ion-responsive signals under the messy, moving, sweaty conditions of genuine fieldwork rather than the controlled stillness of a lab bench.

Dr. Shitanda emphasized that the breakthrough is one of integration rather than novel materials. According to the researchers, the central achievement of the work lies not in proposing a new electrode material, but in combining a printed electrode, a sample transport mechanism, and a wireless measurement circuit, and demonstrating the feasibility of that combination in a real-world environment. This framing matters for anyone following the wearable-sensor field: elegant chemistry in a paper is common, but a printed, wireless, wrist-worn system that survives a full shift on a construction site is rare, and it is exactly the kind of systems-level proof that turns laboratory concepts into practical technology.

The researchers are careful about what has and has not been proven. Quantitative sweat analysis will require controlled sweating experiments and further validation, so the device should be understood today as a demonstration of field feasibility for an integrated wearable electrolyte-sensing system rather than a finished clinical or occupational health product. Even so, the implications are broad. Because the electrodes can be fabricated using printing technology, the approach lends itself to low-cost manufacturing and large-scale production, which is essential if wearable electrolyte monitors are to move from research demonstrations to devices worn by thousands of workers and athletes. Dr. Shitanda noted that the technology could serve as a foundation for acquiring information about ions contained in sweat without interrupting work or exercise in construction sites, manufacturing plants, sports, and outdoor activities, and that in the future, by combining this information with data such as sweat volume and water intake, it could be applied to health management and hydration support in hot environments. As heat stress grows into an ever more pressing occupational and athletic concern, a printed wristwatch that quietly reads the body’s electrolyte story as it unfolds may prove to be one of the more consequential wearables on the horizon.

Subject of Research: Wearable potentiometric sweat sensors for real-time sodium and potassium monitoring

Article Title: Wristwatch-type wearable sensor enables real-time monitoring of sodium and potassium

Article References: Wristwatch-type wearable sensor enables real-time monitoring of sodium and potassium. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: wearable sensor, sweat analysis, sodium, potassium, ion-selective electrode, reference electrode, screen printing, potentiometry, real-time monitoring, hydration, occupational health, Tokyo University of Science

The research team, led by Teng Li and Yongqiang Hou of Anhui University of Science and Technology, prepared cylindrical specimens from a mixture of crushed coal gangue, Class II fly ash, and ordinary Portland cement in a mass ratio of 5:2:1:2, yielding a slurry with a solid mass concentration of 80 percent. The gangue came from the Xieqiao Coal Mine operated by Huaihe Energy Group and was graded into coarse, medium, and fine aggregate fractions of 35, 35, and 30 percent respectively. After 24 hours of initial setting, the specimens were demoulded and cured for 28 days in a programmable chamber held at 95 percent relative humidity and one of four temperatures: 20, 30, 40, or 50 degrees Celsius. Three parallel specimens were tested per condition to average out experimental scatter.

Under uniaxial compression in a displacement-controlled electronic universal testing machine, every specimen told the same four-part story: an initial compaction stage in which pre-existing pores and microcracks close, an approximately linear elastic stage, a concave-down yield stage where irreversible deformation accumulates, and a post-peak failure stage marked by flaking and blocky spalling. But the numbers behind those stages shifted dramatically with temperature. Compaction stress climbed from 0.4219 megapascals at 20 degrees to 1.4195 megapascals at 40 degrees, an increase of roughly 236.5 percent, before falling back to 0.9605 megapascals at 50 degrees. Peak stress followed the same arc, rising from 1.6645 megapascals at 20 degrees to a maximum of 5.682 megapascals at 40 degrees, then dropping 32.4 percent to 3.841 megapascals at 50 degrees.

The elastic modulus, a measure of the material’s stiffness, traced the same non-monotonic curve with an even tighter fit to a quadratic function. It rose from 239.86 megapascals at 20 degrees to 609.99 megapascals at 40 degrees, a gain of 154.4 percent, then fell 31.2 percent at 50 degrees. Interestingly, stiffness and strength did not respond to temperature in perfect lockstep. The modulus gained less than strength during the warming phase but lost about the same proportion during the overheating phase, suggesting that stiffness reflects the initial rigidity of the material skeleton and responds sluggishly to pore filling, while strength depends more directly on the cementitious bonds formed by hydration products and is therefore more sensitive to accelerated hydration.

The mechanism behind the reversal at 50 degrees is a classic case of too much of a good thing. Below 40 degrees, elevated temperature accelerates cement hydration, generating more calcium silicate hydrate gel and needle-like ettringite crystals that fill pores, bind the gangue aggregate, and densify the structure. Above that threshold, hydration races ahead so quickly that products cluster unevenly, encapsulating aggregates in some regions while thermal stresses from the exothermic reaction spawn fresh microcracks. Scanning electron microscopy at 5000 times magnification made the contrast vivid: at 20 and 30 degrees the 28-day microstructure remained loose and porous, with intact spherical fly ash particles showing limited pozzolanic activity, while at 50 degrees the fly ash was tightly enveloped in a thick hydration layer that looked dense but lacked strong chemical bonding, producing what the authors call a dense-but-not-strong weak interfacial structure.

Energy analysis added a thermodynamic dimension to the picture. Applying the first law of thermodynamics, the team split the mechanical work done on each specimen into releasable elastic strain energy and dissipated energy consumed by crack growth and friction. At the peak stress point, total strain energy density peaked at 40 degrees with 36.2804 kilojoules per cubic meter, alongside 26.4641 kilojoules per cubic meter of elastic energy and 9.8163 kilojoules per cubic meter of dissipated energy. All three indices rose and then fell with temperature, confirming that the 40-degree material could both store and dissipate the most energy. Beyond that point, brittleness increased, crack propagation shifted from gradual to sudden coalescence, and the dissipated energy at the peak collapsed to 2.7745 kilojoules per cubic meter, nearly the same as the room-temperature value.

The failure modes themselves transformed with heat. At 20 degrees, specimens failed in tension along semi-penetrating axial cracks with limited secondary fracturing. At 30 and 40 degrees, the failure shifted to a tensile-shear mixed pattern with dense, interconnected crack networks that broke the material into bulking blocks. At 50 degrees the fragmentation was most severe, with pronounced lateral dilatancy and intense bulking. In practical terms, hotter-cured backfill does not merely weaken; it fails more suddenly and more violently, a distinction that matters for engineers assessing the load-bearing stability of pillars of waste backfill supporting deep mine roofs.

Perhaps the study’s most technically ambitious contribution is a new piecewise damage constitutive model. Building on the Drucker-Prager strength criterion and assuming a power-law statistical distribution of micro-element strength, the model treats the initial compaction stage as a defect-closing phase without damage propagation and captures the elastic and yield stages with a statistical damage variable corrected by a coefficient accounting for the residual load-bearing capacity of failed elements. When fitted to the experimental curves, the model tracked the pre-peak stress-strain behavior closely at all four temperatures. Its shape parameter told a striking story of its own: it stayed relatively stable from 20 to 40 degrees but jumped sharply at 50 degrees, indicating that thermal microcracks had prematurely eliminated the weakest elements and left the survivors with a homogenized strength distribution, the statistical fingerprint of thermally induced embrittlement.

For the mining industry, the implications are concrete. As backfill operations descend into hot deep seams, the ambient rock temperature becomes a design variable rather than a background detail. The study identifies 40 degrees as the optimal curing temperature for this gangue-fly ash-cement system, where a structural strengthening mechanism gives way to a thermal damage deterioration mechanism. Curing regimes and mix proportions can now be tuned to the geothermal conditions of a specific mine, and the temperature-sensitive model parameters offer a way to predict pre-peak mechanical behavior without waiting for field failures. The authors note that their model covers only the pre-peak regime, since post-peak behavior is dominated by frictional sliding along macroscopic fracture surfaces, and they plan to extend the framework with discrete element methods and acoustic emission monitoring.

There is also a broader environmental resonance. Gangue cemented backfill simultaneously disposes of coal waste and restores structural integrity to mined-out voids, making it a cornerstone of green mining initiatives. Understanding exactly how temperature governs its long-term stability means that the mountains of gangue stacked around coal mines can be converted into reliable underground support even in the hottest, deepest workings. What this study makes clear is that the relationship between heat and strength is not a straight line but a curve with a summit, and knowing where that summit lies could determine whether the backfill holding up a kilometer of rock endures or crumbles.

Subject of Research: Effect of curing temperature on the mechanical properties, energy evolution, and damage behavior of gangue cemented backfill for deep coal mine backfilling

Article Title: Mechanical properties, energy evolution, damage characteristics of gangue cemented backfill under different curing temperatures

Article References: Li, T., Hou, Y., Yu, X., Xionggang, Z., Du, H., Wang, Y., & Zhang, X. Y. (2026). Mechanical properties, energy evolution, damage characteristics of gangue cemented backfill under different curing temperatures. Case Studies in Construction Materials, 25, Article e06589. https://doi.org/10.1016/j.cscm.2026.e06589

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06589

Keywords: gangue cemented backfill, curing temperature, coal mining, thermal damage, uniaxial compression, energy dissipation, damage constitutive model, hydration, fly ash, deep mines, brittle failure, elastic modulus

Mayenite owes much of its chemical personality to its architecture. It crystallizes in a cubic structure with space group I-43d, and its unit cell can be described as a positively charged framework of twelve cage-like units, [Ca24Al28O64]4+, in which two negatively charged free oxygen ions wander randomly among the cages. Because it costs only about one-third as much energy to pull one of these cage oxygens out of mayenite as it does from plain lime, the oxygen behaves almost as if it were free. Water molecules can slip through inter-cage channels into the interior of the structure, meet these quasi-free O2− ions and form hydroxyl groups — a mechanism that explains why C12A7 dissolves nearly instantaneously on contact with water. Even a dose of roughly nine percent can dramatically accelerate the setting and hardening of Portland cement, which is why mayenite sits at the heart of set regulators and spray-applied concrete accelerators.

The classic picture of mayenite hydration, established decades ago, is straightforward but troublesome. Below about 20 °C, C12A7 hydrates into metastable hexagonal phases — platy CAH10 and C2AH8. With time or heat, these convert into the thermodynamically stable cubic hydrogarnet C3AH6, releasing amorphous aluminum hydroxide. The conversion shrinks volume and raises density, enlarging the porosity of the hardened paste and degrading late-age strength. In recent years, researchers have sought to steer this pathway by doping the clinker with foreign ions. Magnesium is an obvious candidate: it enters clinker naturally from limestone raw materials, substitutes for calcium in aluminate lattices during sintering, and during hydration shifts the chemical equilibrium toward hydrotalcite, a layered double hydroxide, and magnesium-modified calcium silicate hydrate. What remained unclear was precisely how temperature modulates this magnesium intervention in mayenite.

To find out, Hu Yaru, Yang Jiahui, Wang Kai, Peng Lingwei, Song Qiang, Cheng Fuan, Chen Yanxin and Pan Zhigang synthesized magnesium-containing C12A7 from analytical-grade calcium carbonate, alumina and basic magnesium carbonate. The magnesium precursor was calcined at 900 °C into MgO powder, all raw materials were sieved to 75 micrometers, and 40 grams of MgO were added per 100 grams of C12A7, achieving a molar magnesium-to-aluminum ratio of one. Pellets were fired to 1450 °C, held for three hours and rapidly air-cooled. X-ray fluorescence showed the resulting clinker contained 43.15 percent MgO, 27.33 percent CaO and 28.86 percent Al2O3. Ground clinker was then hydrated at a water-to-solid ratio of 10:1 in nitrogen-purged sealed bottles, cured at room temperature, 50 °C or 80 °C, and halted at ages from three to twenty-eight days for XRD, FT-IR, TG-DTG and SEM-EDS analysis.

The clinker itself told the first story. Diffraction revealed two phases, C12A7 and periclase (MgO), with no free lime. Backscattered electron imaging showed clean phase separation: black granular MgO grains dispersed in a grey mayenite matrix, with trace C3A inclusions too small for diffraction to detect. Crucially, energy-dispersive spectroscopy showed the mayenite lattice had absorbed a small amount of magnesium — about 0.85 percent of calcium sites were occupied by Mg2+, nudging the Ca/Al ratio slightly below its theoretical value. Line scans across phase boundaries recorded a sharp magnesium rise within about 2.5 micrometers of the interface, evidence of genuine lattice substitution rather than mere mechanical mixing.

At room temperature, hydration followed the textbook route with a twist. After three days, the dominant product was metastable C2AH8, accompanied by traces of hydrotalcite and a diffuse halo of amorphous aluminum hydroxide. Notably, no CAH10 appeared during the first fourteen days, when laboratory temperatures averaged 30 °C — warm enough, it seems, to suppress its formation — but CAH10 precipitated between fifteen and twenty-eight days as the ambient temperature dropped to an average of 25.89 °C. This brackets the stability window of CAH10 in magnesium-bearing systems below 30 °C. Cubic C3AH6 emerged at seven days and grew steadily through the conversion reaction in which three molecules of C2AH8 yield two of C3AH6 plus aluminum hydroxide and water. The metastable hexagonal hydrates, under electron microscopy, appeared as large platy crystals, bent sheets squeezed by neighboring crystals, and multilayer stacks tens of nanometers thick.

Raising the cure to 50 °C changed the cast entirely. From day three, the products were stable C3AH6, amorphous aluminum hydroxide and hydrotalcite, with no CAH10 whatsoever. Thermogravimetric curves lost the low-temperature peaks associated with the metastable phases and gained a new peak near 229 °C, the fingerprint of water leaving hydrotalcite interlayers. By twenty-eight days, hydrotalcite accounted for 34.9 percent of the sample — a striking yield driven by the accelerating dissolution of MgO. Electron microscopy showed polyhedral hydrogarnet grains and spherical periclase particles wrapped in flaky agglomerates whose magnesium-to-aluminum ratio of about two confirmed hydrotalcite; at late ages, hydrotalcite sheets were found embedded within individual C3AH6 crystals, hinting at a direct transformation route. The analysis also revealed ternary calcium–magnesium–aluminum hydrates with an approximate stoichiometry of CaMgAl2(OH)10, an intermediate stage on the way to magnesium dominance.

At 80 °C the transformation became aggressive and visually dramatic. Hydrotalcite reached nearly a quarter of the solid mass within three days, and residual periclase was almost completely consumed by fourteen days. Because C3AH6 does not decompose below 282 °C and no CAH10 was present to feed aluminum, the observed decline of hydrogarnet could only mean one thing: magnesium ions dissolved from MgO were eroding C3AH6 itself, harvesting its aluminum to build hydrotalcite. Electron micrographs captured the aftermath — tiny hydrotalcite flakes nucleating on hydrogarnet surfaces, hollowed-out grains retaining only their outer contours like fossil shells, and finally rose-petaled hydrotalcite aggregates. The driving force is thermodynamic: hydrotalcite carries a smaller solubility product and a lower Gibbs free energy of formation than C3AH6. Broadened diffraction peaks with low-angle shoulders suggested a richer hydrotalcite family at this temperature, including compositions approximating Mg6Al2(OH)18·4.5H2O and Mg2Al(OH)7.

Synthesizing the data, the team proposes a unified pathway. Magnesium-containing mayenite first dissolves to metastable CAH10 and C2AH8, which convert with time and temperature into C3AH6. Meanwhile MgO hydrolyzes slowly, releasing Mg2+ that first reacts with calcium aluminate hydrates to form ternary Ca–Mg–Al intermediates and then fully replaces calcium to yield low-calcium hydrotalcite. Heat accelerates every step: the conversion of metastable phases, the dissolution of MgO, and the erosion of hydrogarnet. For engineers, the message is that temperature is a dial controlling not just the speed but the very destination of mayenite hydration — and that endogenous magnesium, often treated as a clinker nuisance, can be enlisted to steer cement chemistry toward thermodynamically robust, potentially more durable products.

Subject of Research: Hydration characteristics of magnesium-containing mayenite (C12A7) cured at room temperature, 50 °C and 80 °C

Article Title: Hydration characteristics of magnesium-containing C 12 A 7 cured at room temperature, 50 ℃ and 80 ℃

Article References: Hydration characteristics of magnesium-containing C 12 A 7 cured at room temperature, 50 ℃ and 80 ℃. (n.d.). https://doi.org/10.1016/j.cscm.2026.e06495

Image Credits: AI Generated

DOI: 10.1016/j.cscm.2026.e06495

Keywords: mayenite, C12A7, calcium aluminate cement, hydrotalcite, magnesium oxide, hydration, curing temperature, C3AH6, CAH10, C2AH8, XRD, SEM-EDS