A Smart Capsule With a Hydrogel-Based pH-Triggered Release Switch for GI-Tract Site-Specific Drug Delivery

In this paper, we present a smart capsule that can release its payload after a predetermined/adjustable delay subsequent to passing from the stomach into the small intestine. The described capsule (9 mm × 22 mm) comprises a pH-sensitive hydrogel-based switch, an electronic compartment containing a capacitor charged to 2.7 V, and a drug reservoir capped by a taut fusible thread intertwined with a nichrome wire. The nichrome wire, capacitor, and pH-responsive electrical switch are connected in series. The pH transition the capsule encounters when it enters the small intestine triggers controlled swelling of the pH-responsive hydrogel, which pushes a conductive elastic membrane to close an electrical switch. This initiates a sequence of events, i.e., the discharge of the capacitor, heating the nichrome wire, breakage of the fusible thread, and release of the payload stored in the capsule reservoir through the unlatched cap. The time lag between initiation of hydrogel swelling (by the near-neutral pH of the small intestine) and payload release is controlled by the deflection of the conductive elastic membrane and the gap separating the contacts. The release time can be set to within ±5 min after one hour in the small intestine (start of the swelling) increasing to ±40 min after 4 h.