Water-Reactive Printable Ga−Al−Mg Liquid Metal Alloy for Rapid Wound Hemorrhage Sensing

Owing to the high surface tension, gallium-based liquid metals are difficult to stably deposit via direct writing while maintaining high pattern fidelity, posing a challenge for their patterning into high-precision flexible conductive circuits. In this work, a Ga-Al-Mg ternary liquid metal alloy (LMA) was prepared through trace alloying with magnesium and aluminum. With the introduction of 0.6 wt % Al and 0.4 wt % Mg into liquid gallium, the resulting LMA64 achieved a favorable balance among wettability, shear-thinning behavior, low-frequency viscoelasticity, and apparent yield stress, enabling stable direct writing of conductive traces with a minimum line width of approximately 200 μm. Compared with pure gallium, LMA64 reduced the contact angle from 148.5 to 115.5°, while increasing the normalized shear-thinning factor and apparent yield stress to 2.43 and 1.77 times those of pure Ga, respectively. Furthermore, the printed LMA64 circuits exhibited chemical reactivity toward aqueous solutions and, notably, underwent rapid reaction and circuit disconnection in acidic aqueous environments. Leveraging this property, we constructed a wearable patch-type alarm sensor for wound-fluid-triggered monitoring. The integrated sensor produced an alarm response within approximately 2 s upon contact of the circuit with an aqueous solution. In addition, a multilayer moisture-buffering structure helped suppress interference from sweat and ambient humidity during routine wear, rendering the device more suitable for monitoring scenarios involving large-volume body fluid leakage. The wearable patch also features simple fabrication, replaceable sensing components, and recyclability of gallium metal, demonstrating promising potential for postoperative wound monitoring, abnormal exudate warning, and low-cost disposable wearable alarm devices.