An implantable glucose enzymatic biofuel cell integrated with flexible gold-coated carbon foam and carbon thread bioelectrodes grafted inside a living rat

Materials for Renewable and Sustainable Energy https://doi.org/10.1007/s40243-025-00297-8 (2025) 14:9 ORIGINAL PAPER An implantable glucose enzymatic biofuel cell integrated with flexible gold‑coated carbon foam and carbon thread bioelectrodes grafted inside a living rat S. Vanmathi1,2 · U. S. Jayapiriya1,2 · Pravesh Sharma3 · Onkar Prakash Kulkarni3 · Sanket Goel1,2 Received: 28 September 2024 / Accepted: 7 January 2025 © The Author(s) 2025 Abstract The advent of long-term implants has increased the urgent need for self-powered biomedical devices. Utilize enzymes to expedite the process of biofuel oxidation. These systems frequently make use of glucose oxidase. A possible solution involves glucose biofuel cells powered by the glucose found in physiological fluids. Biocompatible substances like carbon electrode designs help to transport electrons from the biological reactions to the external circuit as efficiently as possible while maximizing surface area. Despite advances in implantable electrodes, developing miniaturized and flexible electrodes remains challenging. In this work, a metal-coated flexible carbon thread and foam bioelectrode are fabricated and successfully implanted inside a living and freely moving rat. These electrodes are prepared using gold nanostructures as electron enhancers, a negatively charged conducting polymer, a biocompatible redox mediator, and enzymes as biocatalysts. The carbon foam-based enzymatic biofuel cell produces in vitro and in vivo settings, generates a power density of 165 µW/cm2 and 285 µW/cm2, and the carbon thread-based fuel cell produces a power density of 98 µW/cm2 and 180 µW/cm2 in vitro and in vivo environments, respectively. This work paves the way for the possible use of inexpensive electrodes for subdermal implantable microsystems. Keywords Carbon thread · Carbon foam · Gold nanostructures · Ferritin · Implants · Self-powered Introduction Implantable microelectronic devices are the weapons of growing healthcare technology that can serve as multifunctional tools for diagnostic and therapeutic purposes [1]. These micro-devices can be used for mimicking organ roles, real-time monitoring, and rapid diagnosis of patients [2]. Most of the implanted micro-devices, such as a pacemaker, insulin pumps, or brain simulators, require an external power * Sanket Goel 1 MEMS, Microfluidics and Nanoelectronics (MMNE) Lab, Birla Institute of Technology and Science (BITS) Pilani, Hyderabad Campus, Hyderabad 500078, India 2 Department of Electrical and Electronics Engineering, Birla Institute of Technology and Science (BITS) Pilani, Hyderabad Campus, Hyderabad 500078, India 3 Department of Pharmacy, Birla Institute of Technology and Science (BITS) Pilani, Hyderabad Campus, Hyderabad 500078, India supply for their continuous functioning. The replacement procedures of these batteries cost a lot of time, involve surgical procedures, and in some cases lead even to death [3, 4]. To cope with the increasing need for quality of life and scientific advancements, incorporating a bioinspired approach to developing power supply as an alternative to conventional batteries is extremely important [5]. Biofuel cells, also known as biological fuel cells, can convert chemical energy from living organisms into electrical energy. To power microscale power devices, enzymatic biofuel cells (EBFC) have been studied for more than five decades and have arguably become the best choice [6, 7]. The readily available glucose in the human bloodstream is the primary fuel of these EBFCs and produces power by redox reaction using biocatalysts [8]. The design and implementation of an EBFC for implantable applications has some challenges to overcome such as catalytic efficiency, biocompatible materials used, and biofouling due to implanted biofuel cell [9, 10]. Attempts were made to solve these problems, and biofuel cells were Vol.:(0123456789) 9 Page 2 of 11 Materials for Renewable and Sustainable Energy successfully implanted in living animals such as rat [11], rabbit [12], bird [13], snail [14] and insect [15]. Several critical factors, such as the nature of electrode materials [16], size, and architecture of EBFC, Implantable EBFCs play an important role in successful development [17]. Highly porous carbon materials such as carbon fiber [18], graphene and carbon nanotubes [19] play a major role in bioelectrode fabrication for tailored enzyme wiring and efficient biocatalysis [20]. Cinquin et al. used graphite particles for the development of EBFC to harvest the power of 6.5 µW/cm2 in a living rat as a pioneer [21]. Zebda et al. [22] improvised the bioelectrode preparation by using compacted carbon nanotube pellets and produced a high-power density of 193 µW/cm2. A flexible EBFC was developed by Fernando et al. [23] using carbon fiber microelectrodes that were capable of harvesting 95 µW/ cm2 when inserted in the jugular vein of the rat. Recently, an improvised electrode was used by the cinquin group, and the developed EBFC was connected to a transmission system for real-time monitoring of the EBFC inside the rabbit for over 2 months [12]. This work presents a flexible, highly fibrous carbon thread and carbon foam bioelectrodes-based EBFC implanted inside a living rat. The anode and cathode were coated with gold nanostructures by electrodeposition and conducting polymers were used for entrapping the enzymes. The bioelectrodes were characterized for biocatalytic efficiency, structural changes, and elemental composition using electrochemical techniques, electron microscopy, and X-ray diffractometry. The stability and biocompatibility of the biofuel cell were studied for more than 7 days with carbon thread and 12 days with carbon foam, and the results are discussed. Various biofuel cell are discussed in the literature and mentioned in Table 1. (2025) 14:9 Materials and methods Chemicals Commercially available hydrophilic carbon cloth was purchased from the fuel cell store (Texas, USA) with an electrical conductivity of 0.1 mΩ cm2 and used to prepare bioelectrodes. Carbon foam was purchased from Sigma Aldrich and had an electrical conductivity of 0.17 mΩ c m2. The carbon fibrous thread from the carbon cloth were separated, and the carbon thread and carbon foam were pre-treated with ethanol followed by distilled (DI) water and allowed to dry at room temperature. Enzymes, such as Glucose oxidase (EC 1.1.3.4, 26820 units/g solid), Catalase (5000 units/mg protein), Laccase (E.C. 1.10.3.2, 24 U/mg), and redox mediator Ferritin (Type I), Polyethyleneimine solution (PEI), were purchased from Sigma-Aldrich, India. Standard gold solution (AAS) in 0.1N HCl, Sodium phosphate (dibasic and monobasic), and sodium chloride were purchased from Sisco Research Laboratories, India. Spectra/Por® 1 dialysis membrane with a molecular weight cut-off of 6–8 kDa was obtained from Thermo Fisher, India. Phosphate buffer solutions (PBS) were made of DI water using ultrapure type I (...truncated)