A 3D nanofibrous network of compressed chitosan in the presence of genipin as the cross-linker, carbon nanotubes and laccase constitutes a new design to enhance the stability and the biocompatibility of biocathodes. The in vitro delivered current was around À0.3 mA mL À1 for 20 days under continuous discharge. A thin film made of chitosan cross-linked with genipin was synthesized and optimized for oxygen and glucose diffusion. This film was used as a biocompatible barrier on the surface of biocathodes implanted in rats. The biocathodes remained operational after 167 days in vivo. This biocathode design minimised the inflammatory response in the first two weeks after implantation. After several months, the growth of macrophages was observed. The electrical connection and the catalytic activity of the enzyme entrapped into the biocathode were demonstrated after almost 6 months of implantation by the ex vivo measurement of the OCP (0.45 V to 0.48 V) and the delivered current (À0.6 mA mL À1) under optimal conditions. Broader context The next generation of implantable medical devices require sustainable ways to provide their energy. For an implanted energy supply, sustainability means that the device needs to be compatible with the environment inside the body, it should not cause any inammation and should be able to utilise biomolecules inside the body as a fuel to produce energy. Also, importantly, the implanted power supply should have a very long lifetime to continue to produce energy inside the body for other implanted medical devices. In this article we describe a 3D bioelectrode that continued to produce energy electrochemically for around 6 months when implanted inside a freely moving animal. This advance is based on improving the biocompatibility with an innovative design and use of biomaterials. Providing energy for such a long period of implantation, especially in a freely moving animal, is a novel result that addresses the existing issues in this eld for the future of implantable energy supplies, namely that is necessary to improve their stability and efficiency. Our results augur well for continuing improvements in the implanted lifetimes of biofuel cells, so as to enable these implantable biofuel cells to become viable and sustainable energy supplies for medical devices.