LAUSR

Abstract Implantable medical electronic devices are usually powered by batteries or capacitors, which have to be removed from the body after completing their function due to their non‐biodegradable property. Here, a fully bioabsorbable capacitor (BC) is developed for life‐time implantation. The BC has a symmetrical layer‐by‐layer structure, including polylactic acid (PLA) supporting substrate, PLA nanopillar arrays, self‐assembled zinc oxide nanoporous layer, and polyvinyl alcohol/phosphate buffer solution (PVA/PBS) hydrogel. The as‐fabricated BC can not only work normally in air but also in a liquid environment, including PBS and the animal body. Long‐term normal work time is achieved to 30 days in PBS and 50 days in Sprague–Dawley (SD) rats. The work time of BC in the liquid environment is tunable from days to weeks by adopting different encapsulations along BC edges. Capacitance retention of 70% is achieved after 3000 cycles. Three BCs in series can light up 15 green light‐emitting diodes (LEDs) in vivo. Additionally, after completing its mission, the BC can be fully degraded in vivo and reabsorbed by a SD rat. Considering its performance, the developed BC has a great potential as a fully bioabsorbable power source for transient electronics and implantable medical devices.