A Stretchable and Durable pH Sensor for In Vivo Digestive System Monitoring

Monitoring pH levels in biological systems is crucial for understanding and maintaining physiological balance. For example, in the digestive system, pH imbalances can lead to a range of issues such as peptic ulcers, indigestion, and altered gut flora. The intricate structure of the digestive tract, characterized by curves and folds, maximizes surface area for efficient digestion and nutrient absorption, necessitating precise pH monitoring across various segments. This<br/>environment features extreme pH conditions, like the highly acidic stomach necessary for protein breakdown and pathogen control.<br/><br/>However, conventional pH sensors, often based on brittle materials like iridium oxide (IrOx), struggle with durability in soft tissue environments, compromising sensor longevity and biosafety in implantable applications. To address these challenges, we developed a stretchable pH sensor capable of robust performance in complex biological environments.<br/><br/>Our approach utilizes a sandwich design that decouples the brittle IrOx interfacial layer from the soft conductive substrate by integrating a vertically conductive stretchable layer in the middle. This structure, comprising a silicone-based conductive stretchable trace sealed with a silicone-based vertically conductive layer, was fabricated through e-beam deposition of Cr/Au, followed by Pt/IrOx electrodeposition. Under strain, the brittle IrOx layer fractures, while remaining<br/>islands connect to vertical pathways in the lower stretchable traces.<br/><br/>In vitro characterization confirmed that our pH sensor maintains its sensing capabilities under strains up to 100%, essential for dynamic biological environments. Robust cycling tests demonstrated its ability to withstand active movements within the digestive system, while stability tests indicated resistance to corrosion, ensuring long-term functionality.<br/><br/>Moving forward, our next steps involve in vivo testing in a rat model to evaluate the sensor's performance for implantable pH monitoring in both the intestine and stomach. The sensor's soft and stretchable nature facilitates smooth adhesion to the intestinal wall, promising stable real-time pH recordings in the stomach over extended periods. Integration of the sensor with a wireless module will allow untethered, continuous in-vivo monitoring, enabling the unraveling of the dynamics of digestive system diseases.