The interplay of polyphenol, amine, and metals has broad implications for surface chemistry, biomaterials, energy storage, and environmental science. Traditionally, polyphenol-amine combinations have been recognized for their ability to form adhesive, material-independent thin layers that offer a diverse range of surface functionalities. Herein, we demonstrate that a coating of tannic acid (TA) and polyethyleneimine (PEI) provides an efficient platform for capturing and monitoring metal ions in water. Unique to our PEI/TA-coated microbeads is the ‘Detection-Capture’ (Detec-Ture) mechanism. The galloyl groups in TA coordinate with Fe(III) ions (capture), initiating their oxidation to gallol-quinone. These oxidized groups subsequently react with PEI amines, leading to the formation of an Fe(II/III)-gallol-PEI network that produces a vivid purple color, thereby enabling visual detection. This mechanism couples metal capture directly with detection, distinguishing our approach from existing studies, which have either solely focused on metal removal or metal detection. The metal capture capacity of our materials stands at 0.55 mg/g, comparable to established materials like alginate and wollastonite. The detection sensitivity reaches down to 0.5 ppm. Our findings introduce a novel approach to the utility of metal-polyphenol-amine networks, presenting a new class of materials suited for simultaneous metal ion detection and capture in environmental applications.

Kappa-carrageenan (κ-CRG) forms thermo-reversible physical hydrogels via a coil–helix transition and helix bundling, but its sulfate-driven electrostatic repulsion limits mechanical robustness and control over aqueous disintegration. Here, we show that plant-derived polyphenols reprogram κ-CRG gel through sulfate-directed binding in a structure-dependent manner. Tannic acid (TA) selectively engages κ-CRG sulfate groups, yielding transparent gels and a >5-fold increase in storage modulus, whereas the same TA triggers turbidity and precipitation in sulfate-free agarose, supporting sulfate-mediated specificity. Using monomeric pyrogallol as a galloyl analogue, we demonstrate that monovalent interactions partially reinforce κ-CRG but lack cooperative stabilization. Intervention timing further separates mechanism. Pyrogallol produces pathway-dependent mechanics and gelation temperature, while TA is stage-insensitive, consistent with multivalent network annealing. In simulated gastric/intestinal fluids, pyrogallol/κ-CRG gels retain morphology longer, whereas TA/κ-CRG ones disintegrate rapidly yet exhibit strong adhesion to rough substrates and human skin. These findings provide a fully food-grade route to tune κ-CRG mechanics, thermal behavior, adhesion and programmed disintegration.

Injectable hydrogels hold promise for localized drug delivery and regenerative medicine, yet their clinical translation remains limited by reliance on backbone modification or exogenous physicochemical triggers that complicate delivery. Here, we exploit an unavoidable aspect of clinical administration, shear, which is generated during injection through catheters and needles. We introduce SIGMA (Shear-Induced Gelation by Microbead Aggregation), a system composed of gelatin microbeads that remain flowable during injection but rapidly assemble into cohesive hydrogel under confined shear, without exogenous physicochemical triggers such as temperature, pH, light, or chemical crosslinkers. Gelation was tunable by varying flow path length, mixing cycles, particle sizes, or introducing air–liquid interfaces, enabling transitions from a weak dispersion (∼11.3 Pa) to robust gels with storage moduli up to ∼5 kPa and compressive strengths approaching ∼800 kPa. Circular dichroism and gel permeation chromatography revealed shear-induced intermolecular associations without evidence of chain scissions. The platform further enabled post-encapsulation drug loading with tunable release governed by shear-programmed network density. In vitro and in vivo studies confirmed cytocompatibility, biodegradability, systemic safety, and superior submucosal lift compared with saline. Together, SIGMA establishes a mechanically actuated, clinically adaptable hydrogel platform for minimally invasive surgery and localized drug delivery.

Coupling-agent-free covalent assembly enables direct aqueous formation of polyphenol–amine materials. This process proceeds within minutes and supports liter- scale production, delivering substrate-agnostic coatings and strong wet bioadhesion.