Modern electronics and materials science are bringing revolutionary advances to biointerface design and are shattering the limits of what is possible in the areas of biomedical diagnostics and sensing, neuroscience, and prosthetics. This special issue highlights the rapid progress in all areas of bioelectronics and includes contributions that explore the interfaces between electronics, materials science, and other engineering disciplines, as well as biochemistry, biophysics, and general biology.
Novel materials and device architectures have always been an important driver of progress in bioelectronics. This collection provides a number of examples that use nanomaterials to enable new functionality or improve the existing device performance. Curry et al.1 report the use of soft nanocomposite films as soft biocompatible implantable antennas. Terkan et al.2 embed carbon nanotubes in silicone elastomers and demonstrate that these composites can act as versatile electrodes and interconnects in peripheral nerve interfaces for neuroprosthetic applications. Wustoni et al.3 demonstrate how co-doping PEDOT:PSS with layered nanocarbides (MXenes) leads to remarkable enhancement of the volumetric capacitance and increased stability of these composite films. They also demonstrate how this material can be used to construct high performance dopamine sensors that can resist common interference agents. San Roman et al.4 review the use of graphene nanostructures and discuss the fundamental relationships between device geometries, materials properties, and performance of the next generation bioelectronic devices.
A number of new device architectures are also featured prominently in this collection. Jia et al.5 demonstrate an electrochemical device that uses Ag/AgCl contacts to achieve precise spatiotemporal control of chloride ion concentration in solution and review their recent progress on using bioelectronics to control pH. Decataldo et al.6 report an example of organic electrochemical transistors functioning as high-sensitivity oxygen sensors in realistic biological environments. With further refinement, these devices could deliver enhanced understanding of the hypoxic environments in tumors. Stanley and Pourmand7 review the evolution of nanopipettes in bioelectronics to sense analytes inside cells by puncturing the cell membrane without damaging the cell. Noy8 reviews strategies for protecting bioelectronics from non-specific binding and fouling using lipid bilayers to functionalize carbon nanotubes and nanowire transistors. Cell membranes are the connection between cells and the outside world, and Manfredi et al.9 discuss photostimulation strategies to induce changes in membrane potential using light and photosensitive electrodes.
The interface of electromagnetic probes with natural systems is an important theme of bioelectronics for sensing and stimulation. Thyagarajan et al.10 present microcoil probes that allow magnetic control of neural stimulation and discuss how device design and materials can be combined to obtain optimal results. Bruno et al.11 describe a new system-based theory to look at the coupling of the cell–electrode interface as a function of time. Bance12 and researchers model the spread of the electrical stimulus in cochlear implants using impedance spectroscopy.
Wearables that use stretchable and flexible bioelectronics integrate these devices for physiological monitoring. Zamarayeva et al.13 have developed a printed sweat sensor that is able to detect sodium, ammonium, and lactate. Novikov et al.14 have investigated conductive elastomers that are able to mitigate the challenges associated with the percolation network. Boratto et al.15 have blended PEDOT:PSS with natural rubber to increase the ability to stretch the conductive polymer. Using biomaterials, Lu et al.16 describe a method to ink-jet print films from reflectin—a protein found in squid skin. These films are able to conduct protons and are integrated in bioelectronic devices. Communication of bioelectronic devices with external electronics is important in wearables and implantables. Curry et al.1 have developed a nanocomposite that is biostable for an implantable subdermal antenna.
Finally, with sensors and actuators, control strategies for biological systems are starting to emerge. Wei and Ruder17 engineer biological circuits for molecular robots using synthetic biology. Selberg et al.18 describe how to use machine learning to expand biological control theory to increase the reach of bioelectronic devices.
Despite recent advances, many challenges still remain for the translation of bioelectronic devices from the bench to the bedside or from proofs of concept to widely used tools for research or diagnostics. Some of these challenges stem from the inherent complexity of bioelectrical and biochemical signals in our bodies and will require strong efforts in both new sensing and actuation paradigms as well as increased understanding in electrophysiology and the contribution of individual cell signaling to organ function. The advances in this collection serve to address a wide array of fundamental materials and engineering challenges toward next generation bioelectronic devices.