A fully hydrogel implantable patch for in situ ultrasonic monitoring of gastric leakage

Gastric leakage is a common and life-threatening postoperative complication, while delayed detection often leads to severe abdominal organ damage. Current radiological imaging modalities are limited in their ability to provide timely detection of gastric leakage, while the mechanical mismatch and long-term persistence of conventional electronic sensors limit their implantable applications. In this work, we developed a fully hydrogel-based ultrasonic metagel patch (USMP) for direct, real-time monitoring of gastric leakage via ultrasound imaging. The USMP incorporates a tree-ring air cell array, in which densely distributed air cells arranged in concentric rings create a strong back-scattering effect, thereby producing distinctive and stable ultrasound imaging signatures for rapid and sensitive detection. The air cells are encapsulated within biocompatible, hydrolytically degradable pH-responsive hydrogels, forming a fully hydrogel sensing architecture. The potential of the USMP for gastric leakage monitoring up to 7 days postimplantation is validated in the live rabbit model.