Considering the number of patients with morbid obesity, some researchers have proposed digestible or implantable gastric reduction devices to facilitate weight loss. The techniques have some measure of success, but there are limitations. Intragastric balloons have been proposed reducing gastric volume. Orally administered polymer-based structures that expand in the stomach in response to changes in hydration, pH levels, etc. have also been proposed. For intragastric balloons, the techniques are invasive and thus less desirable, except in the more extreme cases. In particular, while inflatable balloons can offer internal pumping mechanisms, pressure sensors, and controlled pump release, such features make the devices overly bulky and incapable of either ingestion or passing through the intestines. For orally administered structures, digestibility requires small devices, which are typically implemented only in a solid-phase change form. Unlike implantable balloon devices, the ingestible devices are passable through the pyloric valve in the stomach, but that passing is a result of a solid phase degeneration of the device, and not actively controllable after the device has been ingested into the stomach. A few orally administrable polymer-based devices that attempt to offer some level of control functionality have been suggested. The technique is limited in a number of ways. For example, polymer release is controlled based on external conditions and not based on conditions measured within the stomach. There is no ability to dynamically control the amount of expansion of each polymer molecule, in particular to controllably reduce the volume of the carrier, for example, to induce device release.
The present application describes ingestible, biologically inert devices that can be controllably activated after the device has been ingested. The activation may be of a number of different types, but preferably at least three different activation modes may be provided. An initial activation mode is used to set the device for operation. For example, the device may be initially ingested in an inactive state, where the device is unable to expand or contract. The activation mode is then used to turn on the device for operation. Notably, this initiation does not expand or contract the device, but rather activates the device for subsequent expansion or contraction. The next activation mode may be an expansion mode, where the device is controlled to expand in volume to thereby reduce gastric volume of the stomach. As explained further herein, this mode may be achieved through wireless control of a gaseous phase device; while in other examples, this mode may be achieved by sensor devices within the device. Either control mechanism may activate a titration system within the device to release a gas mixture that expands the device. The final mode may be a contraction mode, which reduces the volume of the device using the titration system, for example, by releasing another gas agent that interacts with the gaseous medium to reduce gaseous expansion.