SAFARI Capsule for Medication Adherence
Researchers have developed Smart Adherence via FARaday cage And Resorbable Ingestible (SAFARI), a bioresorbable RFID capsule designed to confirm pill ingestion without batteries or long-term electronic waste. The capsule's temporary Faraday-cage coating dissolves in the stomach, activating a passive RFID tag to ensure signal specificity only after ingestion.
Rationale for Improved Adherence Verification
Medication non-adherence contributes to an estimated 125,000 preventable deaths and over $100 billion in costs annually in the United States. Existing adherence checks, such as self-reporting or smart bottles, can be unreliable. While ingestible electronics can confirm swallowing, many designs leave non-degradable components, raising concerns about potential gastrointestinal damage and electronic waste. The development of environmentally friendly systems for ingestion verification, without the need for batteries or retrieval, is an area of ongoing research.
Engineering of the SAFARI Capsule
The research team constructed a passive RFID tag using a thin cellulose acetate base, a polyglycol sebacate bioadhesive, patterned zinc foil antenna traces, and a small, biocompatible RFID microchip. Electrical contacts were protected with poly(lactic-co-glycolic acid). The tag was configured to fit a size-000 capsule. To create an inactive state prior to ingestion, the capsule was coated with an electromagnetic interference (EMI) shield composed of hydroxyethyl cellulose mixed with molybdenum or tungsten microparticles. This coating formed a Faraday cage that dissolved in gastric fluid, enabling temporally gated activation exclusively within the stomach. Electrical performance was assessed using a reader and panel antenna, tracking the received signal strength indicator near 915 MHz.
Shielding Effectiveness and Degradation
The SAFARI system combines a zinc-foil RFID antenna with a temporary shield, maintaining the tag's inactive status until it reaches the stomach. This design aims to reduce false positives and eliminate the need for charging, retrieval, or disposal. Bench testing indicated that the zinc tag resonated at 915 MHz and could be read at distances of approximately 10–20 centimeters. The zinc antenna and its encapsulation degraded in less than one week when immersed in simulated gastric fluid at body temperature (37 °C). The softened cellulose acetate substrate degraded over several weeks, designed to pass through the gastrointestinal tract.
Shielding Mechanism Details
A printable EMI coating was developed using hydroxyethyl cellulose and metal microparticles. Molybdenum fillers demonstrated lower sheet resistance and greater radiofrequency attenuation compared to tungsten. At 915 MHz, the molybdenum composite achieved a shielding effectiveness close to 25 decibels. The coating and tag occupied a small portion of the capsule's volume, leaving the majority available for medication.
In Vivo Testing and Safety Signals
In live swine, endoscopy and X-ray imaging confirmed capsule position and tracked dissolution. The coating swelled upon contact with gastric fluid, activating the device within approximately 0.5–3 minutes, allowing for continuous external reads of the tag’s identity and operating frequency. Signals captured in the stomach consistently remained in the ~900–925 MHz range. In vitro ion-release testing showed increasing concentrations of zinc and molybdenum over three days, peaking at approximately 5 parts per million (ppm) by day one for zinc. In vivo safety checks in swine revealed no significant increase in serum zinc or molybdenum levels after dosing, aligning with these metals being essential micronutrients.
Future Implications
The findings suggest that component-level bioresorbable RFID capsules can confirm pill ingestion and reduce electronic waste. By activating only after the Faraday-cage coating dissolves in the stomach, the system may provide specific ingestion confirmation signals. This technology could be valuable in clinical settings such as opioid stewardship and HIV therapy. Further validation regarding microchip passage, performance across different diets and mobility patterns, and real-world reader placement is necessary. Larger human trials and long-term safety observations are required before widespread adoption.