Korean researchers have developed an implantable supercapacitor that could be used to power future medical devices

Implantable devices aren’t new – pacemakers, which use electrical impulses to regulate the beating of a heart – have improved the quality of life for millions of people since the 1960s. But they can be rejected by a patient’s immune system, and their battery needs to be replaced every 6-10 years. With people living longer than ever, there’s a growing need for reliable, low-cost implantable devices. In particular, the race is on to improve their biocompatibility and to find a way to power them. In both cases, a Korean-UK collaboration may already be a step ahead.

Writing in a recent issue of Nano Energy [DOI: 10.1016/j.nanoen.2017.02.018], they report on the development of a novel energy storage device that operates in-vivo, and makes use of the ions naturally present in the body. Rather than batteries or fuel cells, they looked at supercapacitors. But unlike the architecture used in a traditional capacitor, here the electrolyte is not packaged between the electrodes. Rather, body fluids that contain various ions – like Na+, K+, Ca2+, Cl-, and HCO3- – act as an aqueous electrolyte.

This choice could limit the operating voltage of the capacitor, so to improve the device’s energy density, the team tested different combinations of positive and negative electrode materials. The toxicity of MnO2 – a well-established anode material – was found to be too high for use in this implantable device. But when tested in vitro with two types of fibroblast-like cells, a composite of MnO2 nanoparticles, embedded in multi-walled carbon nanotubes (MWCNTs), had a much lower toxicity, and so was used to form the anode. For the cathode, they used phosphidated activated carbon (pAC), which displayed excellent cell viability in toxicity tests.

These active materials were deposited onto a flexible tantalum substrate, and surgically implanted into the hypodermis of a rodent. A small solar panel was used to supply energy to the implanted capacitor. The electrical characteristics of this MnO2-MWCNT/body fluid/ pAC capacitor were impressive too – after 1000 charge-discharge cycles, the device retained 99% of its initial capacitance, suggesting it could be suitable for long-term use.

The authors believe that this study “…is the first to describe an implanted electrode that delivers stored electricity to the interior of a mammal.”  If so, it could be a step on the way to designing an energy storage system for use in implantable medical devices for humans.


J. S. Chae, N-S Heo, C. H. Kwak, W-S Cho, G. H. Seol, W-S Yoon, H-K Kim, D. J. Fray, A.T. Ezhil Vilian, Y-K Han, Y. S. Huh, K. C. Roh. “A biocompatible implant electrode capable of operating in body fluids for energy storage devices” Nano Energy 34 (2017) 86–92. DOI: 10.1016/j.nanoen.2017.02.018