BIOcompatible and BIOfunctional porous electrodes for miniaturized enzymatic biofuel cells – BIO3

The objective of our work is to design a fully integrated, extremely miniaturized and perfectly biocompatible glucose/O2 biofuel cell (BFC) as an in-vivo source of electricity that may power for example, a subcutaneously implanted, continuous glucose monitor for diabetes management.
However, numerous challenges have to be addressed before the implantation of such devices and they are the reason for this multidisciplinary proposal. Operating such BFC at high power density is challenging because it requires a large number of enzymes efficiently wired to the anode or the cathode and a fast enzyme turnover rate. It also requires that mass transport of products and reactants to/from the electrodes not being limited by diffusion and that the size of the BFC is small enough in order to be eventually implanted. May be the most crucial aspect in this context is to ensure also a perfect biocompatibility of such a device, thus preventing foreign body reactions or other harmful effects in the body.
Within this context, and unlike the approach of other research group, we wish to address all these issues SIMULTEANOUSLY based on the synergy between the know-how of the different partners.
The first objective of this project aims to optimize the architecture of the used electrodes by proposing a versatile coaxial design allowing the integration of anode and cathode into a single device having very small geometric dimensions. This implies increasing the active surface area of our electrodes as an imperative step to reach adequate power densities by developing highly organized porous and hierarchical structures.
The second goal is to test the in vitro toxicity of all the components of the device, in order to minimize the risks of in vivo side effects. The absence of cytotoxicity is required before any in vivo tests can be undertaken, and will be mandatory to obtain authorities’ agreement to reach the market.
The third goal is central in our project, since it aims at ensuring the in vivo long-term functionality of the device by optimizing its biocompatibility. This study implies in vivo measurement of electrode activity and analysis of tissue responses. The challenge is to identify the causes of device failure and to modify the design of the electrodes to improve its performances. It implies interactive loops between electrode designers and biologists.
As preliminary studies have shown that the electrodes trigger fibrosis, an essential fourth aspect of the project is to develop a biocompatible hydrogel, which is used to wrap the electrodes and thus prevent foreign body reactions, stabilize the enzymes immobilized in the pores and ensure longer lifetimes of the device. A key issue for the hydrogel remains the double interfaces Electrode/Hydrogel/Biological tissues. Hence, controlling the interface between biological tissues and electrodes remains an important challenge in the development of implanted devices in terms of electro-activity, biocompatibility and long-term stability. In order to engineer such a biocompatible interface a low molecular weight gel (LMWG) will be employed to wrap electrodes via a non-covalent anchoring strategy, i.e., self-assembly of the LMWG at the electrode surface. Preliminary voltammetry experiments realized with coated macroporous gold electrodes indicate that the hybrid hydrogel-based electrodes might be good candidates for the development of biocompatible electrochemical devices in general.