Ingestible Electronics for Diagnostics and Neuromodulation

 Designing bioelectronic devices that seamlessly integrate with the human body is a technological pursuit of great importance. Bioelectronic medical devices that reliably and chronically interface with the body can advance neuroscience, health monitoring, diagnostics, and therapeutics. Advances in materials chemistry have emerged as fundamental to the creation of the next generation of bioelectronics. Further, application-specific materials selection and process design is paramount successful bioelectronic device integration and implementation. Here, we present three unique medical applications of bioelectronic devices with individualized materials, fabrication, and characterization techniques. 

First, we explore the use of ionically conductive hydrogels as sensors for variation in strain and temperature. With a high similarity in mechanical and electrochemical nature to native biological tissue, there is strong interest in building robust sensing elements composed of ionically conductive hydrogels. However, interfacing ionic hydrogels with conventional DC voltage-based circuits produces several challenges including electrode delamination, electrochemical reaction, and drifting contact impedance. Here, we present a Poisson-Nernst-Planck theory coupled with experimental measurements to provide insights about the relationship between frequency of the applied voltage perturbation and sensitivity. 

Second, we design an ingestible sensor capable of non-invasively monitoring gastrointestinal epithelial barriers. Currently, the primary method of diagnosing and monitoring epithelial barrier integrity is via endoscopic tissue biopsies followed by histological imaging. In this work, we propose a gelatin-based ingestible electronic capsule that can monitor epithelial barriers via electrochemical impedance measurements. To do this, we develop materials-specific transfer printing methodologies to manufacture soft and edible gelatin-based electronics, validate the impedance-based sensing technique using in vitro synthetic disease models, and test the capsules ex vivo using porcine esophageal tissue. 

Lastly, we explore the fabrication of an ingestible electronic platform that can be used for non-invasive vagus nerve stimulation via the gut. Mechano- and chemosensitive vagal afferents in the gut feed into neural circuitry that control satiety, mood, and inflammatory responses. Utilizing non-invasive ingestible electronics to modulate these neural pathways holds the promise of unlocking a new class of therapies for a wide range of disorders such as obesity, diabetes, depression, and irritable bowel syndrome. Here, we design a tethered stimulator capsule with thin-film electrodes deposited on a flexible polyimide substrate that is subsequently integrated with a custom 3D printed capsule. The device was thoroughly tested and stands ready to be carried forward into preclinical in vivo studies. Alongside collaborators, the objective of this study is to stimulate different regions of the porcine GI tract with concurrent functional MRI of the central nervous system to identify specific therapeutic targets for ingestible stimulators.