A hollow microcavity enzymatic fuel cell for in vivo energy harvesting

Enzymatic fuel cells (EFCs) have emerged in recent years as a promising power source for wearable and implantable electronic devices. Here, successful in vivo implantation of a glucose/O₂ EFC beyond 70 days is reported that exploits an innovative “cavity electrode” concept for biocatalyst entrapment to address lifetime and biocompatibility issues. The hollow bioanode shows long-term in vitro bioelectrocatalytic storage stability of >25 days. The hollow buckypaper-based EFC exhibits attractive maximum voltage and power outputs of 0.62 V and 0.79 mW cm⁻², respectively, and high storage stability of ∼80% after 19 days. The maximum in vivo performance outputs are 0.34 ± 0.05 V and 38.7 ± 4.7 μW. After 74 days in Sprague-Dawley rats, the hollow EFC continues to present a stable 0.59 V. Postmortem analysis confirms high-level robustness and operational performance. Autopsy findings reveal no signs of rejection and demonstrate effective biocompatibility.