In a sleek laboratory at New York University, researcher Parima Phowarasoontorn holds a six-petaled device no wider than a straw—the Lily stent, a breakthrough in treating one of weight-loss surgery's most devastating complications.
Each year, roughly 250,000 Americans undergo sleeve gastrectomy, one of the most common weight-loss operations in the country. For most patients, the procedure transforms their lives without incident. But for a small share—between 1% and 3% in routine cases, and as many as 1 in 10 in revision surgeries—it creates a gastric leak: fluid escapes from the stomach and forms a painful abscess. These leaks have historically meant weeks of slow, frustrating recovery.
Doctors treating gastric leaks typically thread a double-pigtail stent through the stomach wall, using what's called endoscopic internal drainage to let the fluid escape. The problem: these stents were designed for bile ducts, not the odd, irregular cavities left by gastric surgery. They slip, drain slowly, and often require repeated procedures before the leak finally closes. For roughly 2,500 Americans each year who need this treatment, the standard approach means prolonged suffering and multiple hospital visits.
Khalil Ramadi and his team at NYU—part of the Abu Dhabi and Tandon School of Engineering campuses—approached the problem from first principles. Using computer simulations and mathematical modeling, they discovered something counterintuitive: a wider tube doesn't drain better. In fact, it does the opposite. Increasing the inner diameter shrinks the gap around the stent's outside, where most fluid actually travels. The exterior shape, not the interior volume, drives drainage performance. "The key insight is that the geometry of the tube's cross-section, especially the exterior surface, fundamentally determines how fast fluid moves through and around it," Ramadi explained.
This realization became the foundation of PETALS—Personalized Endoscopic Transmural Abscess Leak Solution—a mathematical framework for optimizing drain geometry based on the viscosity and pressure of gastric fluid. By designing a six-part structure with carefully engineered exterior topography, the researchers created the Lily stent, named for its petal-like cross-section. In simulations and laboratory models, the device outperformed conventional polyethylene stents at moving fluid. It also proved significantly more flexible, a quality surgeons associate with better patient tolerance and reduced tissue damage. Early benchtop testing showed tissue surrounding the implanted material showed no significant difference from tissue around standard polyethylene—an encouraging sign for biocompatibility.
The implications extend beyond gastric surgery alone. The PETALS framework could be applied to drainage challenges throughout the body, wherever fluid needs to move through unconventional spaces. And because the Lily's constant cross-section geometry allows conventional manufacturing methods rather than specialized 3D printing, hospitals won't need new infrastructure to adopt it.
The device remains early in development—still in the simulation and benchtop testing phase, with animal studies ahead before human trials. Yet if the results hold up beyond the lab, the payoff could be substantial: faster drainage, shorter recovery times, and fewer repeat procedures for thousands of patients each year. "Instead of simple tubes," as first author Phowarasoontorn put it, "we introduce cross-sectional design that fundamentally changes how the device functions." In weight-loss surgery, where complications ripple through months of a patient's recovery, that shift in thinking could make all the difference.