Modular stimuli-responsive hydrogel sealants for early gastrointestinal leak detection and containment

Anastomotic leaks following gastrointestinal surgery are a serious complication, affecting 4-21% of patients and resulting in high mortality (6-27%). Current detection methods rely on late-stage clinical symptoms (tachycardia, hyperthermia, oliguria) and surrogate markers (C-reactive protein), which are insufficient for early intervention. Semi-permanent drains and temporary stomas are often used, highlighting the lack of effective early detection technologies. While existing surgical adhesives and sealants offer limited success, particularly fibrin-based materials like Tachosil which are susceptible to digestion, recent innovations have focused on tissue adhesion and biocompatibility but often neglect performance under active digestive conditions and lack integrated monitoring. Attempts at suture monitoring without sealant capabilities are limited by implanted electronics and bulky setups. This work addresses this unmet need by developing a novel gastrointestinal leak sensing hydrogel sealant that integrates therapeutic and monitoring elements within a modular design.

The literature extensively documents the high incidence and mortality associated with gastrointestinal anastomotic leaks following abdominal surgery. Existing detection methods based on clinical symptoms and surrogate markers are unreliable for early diagnosis. Current surgical adhesives and sealants have limitations in terms of performance under harsh digestive conditions and lack integrated monitoring capabilities. Research on tissue adhesives has largely focused on adhesion strength and biocompatibility, neglecting the crucial aspect of performance in the presence of digestive enzymes and fluids. Recent attempts to develop suture monitoring systems without sealant properties rely on implanted electronics, which are not yet clinically translatable. This study builds upon prior research on tissue adhesives and sensing technologies to create a novel solution that addresses the shortcomings of existing approaches.

This study developed a modular, layered hydrogel sealant patch for gastrointestinal leak detection and containment. The patch consists of three key layers: a non-adhesive backing (50 wt% poly(N-hydroxyethyl acrylamide) (PNHEA)), an adhesive layer (50 wt% poly(2-acrylamido-2-methyl-1-propanesulfonic acid) sodium salt (PAMPS)) containing sensing elements, and an optional therapeutic layer. Two types of sensing elements were explored: (i) enzymatically digestible gas vesicles from *Halobacterium salinarum* (TurnOFF sensing), embedded in a soft polyacrylamide matrix, and (ii) acid-reactive sodium bicarbonate (TurnON sensing) embedded in a 2 wt% agar matrix. The patch is attached to tissue using a mutually interpenetrating network (mIPN) of N-acryloyl glycinamide (NAGA) formed by visible light irradiation. The mIPN provides firm and durable tissue adhesion even under harsh digestive conditions. The study used various techniques to characterize the patch's properties, including adhesion energy measurements (T-peel setup), tensile strength testing, FTIR and Raman spectromicroscopy to confirm mIPN formation, swelling experiments in simulated intestinal fluid (SIF), simulated gastric fluid (SGF), and other biological fluids, SEM imaging, Zn²⁺ release experiments, and antimicrobial assays. *Ex vivo* and *in vivo* experiments were performed to evaluate the patch's leak sealing and detection capabilities using a handheld ultrasound probe controlled by a smartphone or tablet. *Ex vivo* tests involved sealing a perforated porcine intestine segment and monitoring ultrasound signal changes over time. The *in vivo* proof-of-concept study used a piglet model to demonstrate the patch's performance in a live setting.

The developed hydrogel sealant patch demonstrated strong adhesion to various gastrointestinal tissues (stomach, small intestine, colon) with adhesion energies comparable to first-generation mIPN adhesives. The mIPN ensured robust anchoring (>24 h contact with SIF/SGF). The patch's layered design, with a highly extensible PAMPS layer and a non-adhesive PNHEA backing, allowed for effective fluid absorption and leak containment without compromising adhesion. The TurnOFF sensing elements (gas vesicles) showed a clear signal change (disappearance of the signal) within 3 hours when exposed to SIF due to enzymatic degradation. The TurnON sensing elements (sodium bicarbonate in agar) responded to SGF within 15 minutes through CO₂ bubble formation, resulting in increased ultrasound scattering. *Ex vivo* experiments showed that the patch reliably detected leaks in both intestinal (3 hours) and gastric (15 minutes) scenarios while maintaining effective leak sealing. The *in vivo* study confirmed the patch's ability to seal a 4 mm defect in a piglet intestine and provided clear ultrasound signal changes indicating leak containment. Histological analysis showed no tissue damage. The study also showed the ability to incorporate therapeutic elements (e.g., ZnO nanoparticles) into the patch for antimicrobial properties.

This study successfully developed a novel modular hydrogel sealant patch capable of both detecting and containing gastrointestinal leaks early. The results address the critical clinical need for improved methods for detecting anastomotic leaks, as current techniques are insufficient for timely intervention. The modularity allows for customization to different gastrointestinal regions and enables the incorporation of various therapeutic agents. The use of a handheld ultrasound probe for detection makes this a cost-effective and easily accessible technology. The rapid response time of the sensing elements (3 hours for intestinal leaks, 15 minutes for gastric leaks) allows for swift clinical interventions and reduces the risk of life-threatening complications. The robust adhesion and biocompatibility of the patch ensure long-lasting efficacy and minimal adverse effects.

This research introduces a novel, modular hydrogel sealant patch for the early detection and containment of gastrointestinal anastomotic leaks. The patch's layered design, including enzyme and pH-responsive sensing elements, allows for rapid and unambiguous leak detection using point-of-need ultrasound. Successful *in vivo* proof-of-concept studies demonstrate the potential for clinical translation. Further research should focus on optimizing the long-term biocompatibility and biodegradation of the materials, exploring different therapeutic agents and conducting larger-scale animal studies before clinical trials.

The study's *in vivo* testing was limited to a piglet model. Further investigations using larger animal models and ultimately human clinical trials are needed to confirm the technology's broader applicability and efficacy. While the patch demonstrated excellent sealing and detection capabilities in the experimental settings, the long-term performance and biodegradation profile of the materials in the human body need further evaluation. The current design may need modifications for compatibility with different surgical techniques and anatomical variations.