Background: Integrated capsule systems are widely gaining momentum for analysis or drug delivery in gastrointestinal (GI) regions where alternative techniques are expensive, invasive, or inadequate. Depending on the region, there are numerous physiological considerations that must be addressed for fluid sampling with minimal human intervention. Previous passive approaches to GI sampling lack a means of knowing whether a sample has been retrieved in real-time, while active approaches suffer due to cost and complex assembly.
Goal: This project aims to develop a wireless ingestible microsystem with specialized sensors for sampling secretions throughout the GI tract and monitoring enzymes in situ for indicating pathological conditions.
Objectives: In this work, a breadboard-level circuit representative of the electronics toward full integration within the capsule are used to monitor the removal of polymer material from gratings within a 3D printed capsule. The polymers protect sensors within the capsule, only exposing them when the device has reached the GI region of interest. Different Eudragit polymers are used to target different GI regions: E PO, S 100, and L 100 dissolve respectively at the stomach, ileum, and duodenum.
Approach: The circuit setup was first characterized and signal transmission protocols (serial or wireless) were compared. Sensors are inserted into 3D-printed capsules. Once inserted, the capsules are fastened using built-in threads and sealed with epoxy, then dip-coated into a 30 w/v% solution of each polymer in methanol, each for 1-5 coats with removal for 20 min intervals between each coating. Capsule coating thicknesses were analyzed over gratings and non-grating regions for uniformity. Capsules were then immersed in a control solution (pH 3 for S/L100 and pH 7 for E PO formulations) and progressively adjusted at 30 min intervals to different test pH sequences. After coating optimization was performed for each polymer, combined coatings were tested to determine ability to tailor sampling for more complex pH sequences.
Results: Gratings resulted in a slower increase with each coating due to polymer in-fill. We obtain the sensor output and corresponding change in capacitance over the course of pH adjustments for each polymer, indicating the expected length of time for chamber filling and sampling dynamics for each coating thickness. We also obtain representative sequences of L 100 and E PO formulations, as well as a combined coating of both polymers. As expected, the capacitance increase did not occur until the respective polymers dissolved at the appropriate pH, indicative that both single and combined coating strategies can be used to protect the sensing chambers until the characteristic pH-targeted regions are reached.
Importance to public health: This work is the first demonstration of a passive pH-dependent packaging strategy for ingestible capsule technology that offers information on the package integrity at any given time, while simultaneously providing a real-time active microelectronics-based system capable of wireless retrieval of sensor data for use in GI sampling and analysis.