Smart Multi-Sensory Capsule for Simultaneous Location Tracking and Inflammation Detection

Inflammatory bowel disease (IBD) has gained a lot of attention in recent decades as it is increasingly prevalent in Western countries and steeply emerging in developing countries. IBD affects 7 million people worldwide and is characterized by chronic inflammation of the gastrointestinal tract (GI) which is manifested as Crohn’s disease, ulcerative colitis, and colon cancer if remained untreated. Existing methods widely used in hospitals include a combination of endoscopy, colonoscopy, and imaging studies. Endoscopy and colonoscopy are invasive and expensive and require a technician’s assistance. Similarly, MRI and CT scans require bulky equipment and manual assistance and cannot be made portable or automated.<br/><br/>To address the issues envisaged by these benchtop systems, ingestible capsules have emerged as an ideal portable wireless in-situ monitoring platform to perform around-the-clock measurements using contactless readout units. Although the existing ingestible capsules have gained popularity as miniaturized devices, the state-of-the-art active capsules are designed to sense a single parameter either for location tracking or inflammation detection but not for both parameters simultaneously. Single parameter sensing significantly limits traceability, targeted detection, and accuracy of measurements. Furthermore, the active capsules that contain electronic modules lack suitable sensor interfaces that can establish good contact with the tissues and biocompatible packaging to prevent leakage from the batteries and seepage into the electronics. To address these challenges, we report a multi-sensory smart capsule that can perform both targeted detection of inflammation using Oxidation Reduction Potential (ORP) sensing as well as location tracking of the device inside the GI tract using pH monitoring.<br/><br/>The device consists of a compartmentalized sensor interface, an electronic module, and a biocompatible encapsulation. The sensor interface consists of three compartments which include a pH sensing unit, an ORP sensing unit, and a common reference unit. The pH sensing unit is manufactured by dispensing carbon paste mixed with pH-sensitive ionophores. The ORP sensing unit is formed by dispensing carbon paste sensitive to redox reactions in the environment. The reference unit is made by mixing KCl particles, polyvinyl chloride, and cyclohexanone and is used for both pH and ORP sensors. This multi-sensory compartment is interfaced with the electronic module inside the capsule through reflow soldering. The electronic module consists of a microcontroller unit powered by batteries, separate buffer circuit boards for performing accurate potentiometric readings from the pH and ORP sensors, and an antenna to wirelessly transmit the collected data to an external reader. This heavily miniaturized electronic module of diameter 8 mm is secured inside a biocompatible 3D printed housing of outer diameter 9.5 mm and length 2.5 cm to prevent leakage and seepage.<br/><br/>To investigate the performance of the multi-sensory capsule, extensive characterizations are conducted on the pH and ORP sensors individually as well as collectively. A systematic study reveals that the sensors demonstrate the capability to detect pH within the range of 1-8 and ORP within the range of -500 mV to +500 mV. The capsule can provide successful passage through the GI tract at a polling rate of 30 min with an average power consumption of 110 µAh. As a proof-of-concept, we perform ex-vivo characterization on pig tissues to demonstrate the specificity, power consumption, and traceability of the capsule in a GI-tract surrogate environment. The multi-sensory smart capsule presented here provides a new avenue in addressing the emerging need for accurate IBD detection using a portable, wireless system and can be a successful alternative to the existing medical equipment.