Hydroxyapatite, with the chemical formula Ca10(PO4)6(OH)2 and a calcium-to-phosphorus ratio of 1.67, is the inorganic scaffold of human bone and dental enamel. Because it is biocompatible, non-toxic, and non-inflammatory, and because its porous structure offers a large surface area, materials scientists have long viewed it as an ideal candidate for bone regeneration and for controlled drug delivery. An efficient delivery system, however, needs more than biocompatibility. It must load therapeutic molecules, transport them to target tissues, and release them predictably, ideally in response to physiological cues such as the acidic pH found in tumor environments, where hydroxyapatite dissolves more readily and can dump its cargo on cue.

The Mexican team added a second function to this already versatile material: light. Europium ions, Eu3+, belong to the rare-earth family and emit sharp, photostable red luminescence when excited, a property that makes them valuable for cellular imaging and diagnostic applications. The catch is that europium can be toxic at high concentrations, and too much of it in a crystal lattice causes luminescence quenching, an energy-draining conversation between neighboring dopant ions that snuffs out the very glow the dopant was added to provide. The researchers therefore kept europium levels low, testing 2, 3, and 4 molar percent relative to calcium, and relied on the nanofiber geometry to place the emitting ions near the surface, where their light is easier to harvest.

The synthesis itself is a study in efficiency. Using a microwave-assisted hydrothermal method, the team combined calcium nitrate and glutamic acid, an amino acid that steers crystal growth, with potassium phosphate and potassium hydroxide solutions. Microwave irradiation heats the reaction mixture rapidly and uniformly, and sealed vials were reacted at 170 degrees Celsius for just 45 minutes at pressures of 10 to 11 bar. For the doped samples, a third solution of europium nitrate was added at carefully calculated stoichiometries. Each synthesis yielded roughly 0.11 to 0.17 grams of product, and the researchers ran three distinct methodologies, varying precursor temperatures, pH, and the way europium entered the recipe, to map how each parameter shaped the final material.

X-ray diffraction revealed that every sample crystallized predominantly in the hexagonal hydroxyapatite phase, with sharp Bragg reflections indicating high crystallinity. More intriguing was a systematic anomaly: the standard reference pattern predicts that the (300) reflection should reach only about 62 percent of the intensity of the dominant (211) peak, yet in these samples the (300) reflection frequently matched or exceeded it. This inversion is the fingerprint of preferential crystalline orientation, a consequence of the glutamic acid and microwave method working together. Because the (100) and (300) planes that terminate the nanofibers are rich in calcium ions, they are prime real estate for europium substitution, positioning the dopant where its emission can escape the crystal most easily.

Crystallite size and lattice strain told a subtler story. Using both the Scherrer equation and the Williamson-Hall method, which accounts for strain broadening that Scherrer ignores, the team found that Methodology 1 produced the largest, most pristine crystallites, around 280 angstroms, with microstrain below 0.02 percent in doped samples. Methodology 2, with its pH manipulation, yielded smaller crystallites as low as 152 angstroms and the highest microstrain measured, 0.186 percent, signaling dense defects and lattice distortion. Methodology 3 struck a balance, and its samples grew into strikingly well-formed hexagonal nanofibers hundreds of nanometers long, with sides of about 205 nanometers and long diagonals of 390 nanometers. Electron microscopy confirmed the trend: uniform smooth fibers in Methodology 1, fragmented disordered particles in Methodology 2, and large, aligned, well-faceted fibers in Methodology 3.

Dopant concentration sculpted morphology in unexpected ways. At 2 percent europium, the fibrous habit survived intact, suggesting the ions slipped neatly into calcium sites. At 3 percent, fibers thickened and agglomerated, with irregular particles and partially fused regions appearing as the mismatch between the larger Eu3+ radius and Ca2+ disrupted the balance between nucleation and growth. At 4 percent, however, the material rebounded, producing longer, thicker, more aligned fibers, apparently because excess europium promoted directional growth along the crystallographic c-axis, though localized agglomerates hinted at europium-rich amorphous pockets. Photoluminescence spectroscopy added another layer: the splitting pattern of the 5D0 to 7F1 transition showed more lines than theory predicts for a single site, indicating that europium occupies both calcium site types, and possibly interstitial positions, simultaneously.

With 3 percent europium selected as the optimal compromise, preserving the apatite phase, fibrous morphology, and detectable red emission, the team turned to quercetin. Three formulations were prepared by stirring 0.100 grams of the doped nanofibers with 0.005, 0.010, or 0.020 grams of quercetin in ethanol for 24 hours at 30 degrees Celsius, corresponding to weight ratios of 10:0.5, 10:1, and 10:2. After centrifugation, washing, and drying, electron microscopy showed the fibrous network largely preserved but decorated with small granular deposits absent from unloaded samples, evidence that quercetin adsorbs onto the fiber surfaces, likely through hydrogen bonding and electrostatic interactions with the calcium phosphate, rather than infiltrating pores. Energy-dispersive spectroscopy detected carbon consistent with the organic molecule, though its uneven distribution across analyzed regions suggested the adsorption is patchy rather than uniform.

Infrared spectroscopy was less conclusive. Because hydroxyapatite phosphate bands overlap with quercetin’s organic signals and the loaded amounts were small, the spectra showed only subtle changes: a phenolic OH signal near 1200 wavenumbers, aromatic CH stretches around 2959 to 2855, and weak carbon-carbon double-bond bands. The absence of new bands suggests the interaction is physical, mediated by hydrogen bonds, with no chemical reaction. Crucially, loading quercetin did not shift the positions of the characteristic europium emission transitions, meaning the optical tag survives the drug-loading process. That combination, a bone-like scaffold that glows red, carries a bioactive molecule on its surface, and keeps its luminescence intact, is precisely what a multifunctional theragnostic platform would need.

The authors are careful about limits. The physicochemical data represent single measurements without statistical replicates, the EDS technique is localized and semiquantitative, and nothing in the study establishes biological safety; cytocompatibility, ion-release, and cellular uptake experiments remain to be done before any clinical ambition can be entertained. Quantitative adsorption capacity, release kinetics, and reproducibility also await measurement. But as a proof of concept, the work demonstrates that a microwave-assisted, amino-acid-guided synthesis can deliver a luminescent calcium phosphate nanocarrier in under an hour, with morphology and dopant behavior controlled by recipe rather than chance. If the follow-up biology holds, the same mineral that builds skeletons may one day light the way for medicines traveling through the body.

Subject of Research: Europium-doped hydroxyapatite nanostructures for luminescent imaging and quercetin drug delivery

Article Title: Physicochemical and photoluminescent properties of Eu 3+ -doped hydroxyapatite nanostructures and preliminary quercetin adsorption study

Article References: Lazaro-Vidal, C., Méndez-Lozano, N., Alanis-Gómez, J. R., Hernández-Rosas, F., Rivera-Muñoz, E., & Velazquez-Castillo, R. (2026). Physicochemical and photoluminescent properties of Eu3+-doped hydroxyapatite nanostructures and preliminary quercetin adsorption study. Results in Chemistry, 31, Article 103956. https://doi.org/10.1016/j.rechem.2026.103956

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103956

Keywords: hydroxyapatite, europium doping, nanofibers, photoluminescence, quercetin, drug delivery, microwave-assisted hydrothermal synthesis, X-ray diffraction, biomedical imaging, calcium phosphate, nanomaterials, theragnostics

Cardiometabolic multimorbidity has become an increasingly urgent global public health concern. Patients rarely develop these disorders in isolation; hypertension begets atherosclerosis, diabetes accelerates vascular injury, and stroke and ischemic heart disease frequently follow. What ties this cluster together, the review emphasizes, is endothelial dysfunction, a failure of the single-cell layer that lines every blood vessel in the body. The endothelium is far more than a passive barrier. It regulates vascular tone through nitric oxide signaling, controls inflammatory adhesion of immune cells, maintains the integrity of barriers such as the blood-brain barrier, and orchestrates tissue repair. When it falters, the consequences ripple across the entire cardiovascular and metabolic system, which is why endothelial dysfunction serves both as an early warning marker and as a central driver of disease progression.

The review’s central proposition is that endothelial cells communicate their state of health, or distress, to distant tissues through extracellular vesicles, particularly exosomes. These nanoscale membrane-bound particles, typically ranging from roughly 30 to 150 nanometers in diameter, are released when multivesicular bodies within the cell fuse with the plasma membrane. Far from being cellular debris, exosomes are carefully sorted packages carrying a molecular cargo that mirrors and modulates the physiology of the parent cell. Endothelial-derived exosomes, abbreviated ECs-exo in the review, transport microRNAs, long non-coding RNAs, circular RNAs, proteins, and lipids to recipient cells, where these molecules can reprogram gene expression, alter signaling pathways, and shift cellular behavior.

The mechanistic detail assembled by the Chongqing team is considerable. Dysregulated exosomal cargos, the authors report, propagate vascular inflammation, insulin resistance, and fibrotic remodeling across cardiometabolic disease. Inflammatory cascades involving Toll-like receptor 4 signaling, adhesion molecules such as ICAM-1 and VCAM-1, and mediators like high mobility group box 3 protein and oxidized low-density lipoprotein are amplified or dampened by the exosomal payload. Signaling hubs including the MAPK and ERK pathways, protein kinase C-alpha, phosphatase and tensin homologue, forkhead box protein O1, and hypoxia-inducible factor-1alpha appear repeatedly in the regulatory networks the review describes. Hypoxia-inducible factor-1alpha in particular links oxygen deprivation, a hallmark of ischemic heart disease and stroke, to exosomal reprogramming that can either aggravate injury or, under the right conditions, promote adaptation and repair.

Not all endothelial exosomes are harbingers of disease. The review highlights a protective side of the axis: exosomal microRNAs released by healthy endothelium support vascular repair and suppress pathological inflammation. Endothelial progenitor cells, which participate in vessel regeneration, release vesicles enriched with pro-angiogenic and anti-inflammatory microRNAs that can enhance nitric oxide production, reduce endothelin-1-driven vasoconstriction, and stabilize vulnerable plaques. Molecules such as heme oxygenase-1, Krüppel-like factor 2, and vascular endothelial growth factor feature in these restorative programs, while chemokine receptor type 4 helps guide reparative vesicles to sites of injury. In models of cerebral ischemia such as middle cerebral artery occlusion, endothelial and progenitor-derived vesicles have been shown to protect the blood-brain barrier, in part by preserving tight junction proteins like zona occludens 1 and modulating von Willebrand factor release and angiopoietin-2 signaling.

This dual nature, pathological messenger and therapeutic agent, is precisely what makes the exosomes-X axis clinically attractive. On the diagnostic front, the review catalogs circulating endothelial exosome signatures with potential utility for early detection, prognosis, and disease stratification. Because exosomes in the blood carry molecular fingerprints of their cells of origin, profiling their microRNA, protein, and lipid content offers a non-invasive window into vascular health. A blood test that reads the endothelial exosome cargo could, in principle, identify patients at risk of developing multimorbidity long before symptoms appear, distinguish between inflammatory and metabolic disease subtypes, and track response to therapy over time. The authors argue that such signatures hold genuine promise as biomarkers, though they note that standardization of isolation and analytical methods remains an obstacle to clinical deployment.

On the therapeutic side, the review evaluates an emerging strategy: engineering endothelial exosomes to deliver therapeutic cargos and thereby restore vascular homeostasis. Exosomes offer several advantages over synthetic drug carriers. They are naturally biocompatible, cross biological barriers including the blood-brain barrier, can be surface-functionalized with targeting ligands, and can be loaded with RNA therapeutics, anti-inflammatory proteins, or small molecules. The authors describe multimodal formulations and advanced bioengineering platforms designed to tune vesicle tropism, cargo loading efficiency, and release kinetics. Engineered vesicles derived from healthy endothelium or endothelial progenitor cells could, for example, deliver anti-inflammatory microRNAs to atherosclerotic plaques or insulin-sensitizing cargos to metabolically active tissues, addressing several facets of multimorbidity with a single platform.

The concept of theragnostics, the fusion of therapy and diagnostics in one system, runs throughout the review. Because the same exosomal signatures that signal disease can be engineered into delivery vehicles that report on their biodistribution, ECs-exo could enable truly individualized treatment: profile the patient’s vesicle cargo, identify the dominant pathological pathway, select or engineer a matching therapeutic vesicle, and monitor the molecular response in circulation. The authors position this integrated approach as a way to improve diagnosis, prognosis, and personalized management of cardiometabolic multimorbidity, a condition whose complexity has largely defeated single-target drugs.

The review is candid about the challenges that stand between laboratory promise and bedside impact. Isolation and characterization protocols vary widely across studies, cargo sorting mechanisms are not yet fully mapped, dose standardization for vesicle therapeutics is unresolved, and large-scale manufacturing under good manufacturing practice conditions remains a formidable engineering problem. Distinguishing protective from pathological vesicle populations within a heterogeneous circulating pool is another unsolved puzzle. Nevertheless, the convergence of mechanistic insight, biomarker discovery, and bioengineering capability documented in the review suggests that the field is approaching an inflection point.

Funded by the National Natural Science Foundation of China, the Natural Science Foundation of Chongqing, and a Chongqing medical scientific research joint project, the work reflects a broader international push to understand extracellular vesicles as the body’s intercellular internet. If the exosomes-X axis framework proves correct, the endothelium’s nanoscale messengers may soon serve simultaneously as the earliest alarm for cardiometabolic disease, the yardstick of its progression, and the vehicle that reverses it. For the millions of people living with overlapping cardiovascular and metabolic disorders, that would represent a fundamental shift from managing separate diseases to treating the vascular system as the integrated whole it truly is.

Subject of Research: Endothelial cell-derived exosomes as diagnostic biomarkers and engineered therapeutics for cardiometabolic multimorbidity

Article Title: Exosomes-X axis: endothelial-derived extracellular vesicles for precision diagnosis and therapy in cardiometabolic multimorbidity

Article References: Tang, F., Zhu, S.-C., Zhou, H.-M., Liu, M., Yuan, W.-X., & Qiu, X.-W. (2026). Exosomes-X axis: endothelial-derived extracellular vesicles for precision diagnosis and therapy in cardiometabolic multimorbidity. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-08946-w

Image Credits: AI Generated

DOI: 10.1186/s12967-026-08946-w

Keywords: exosomes, endothelial cells, extracellular vesicles, cardiometabolic multimorbidity, type 2 diabetes, hypertension, atherosclerosis, stroke, microRNAs, endothelial dysfunction, targeted therapy, theragnostics