Marios Savvakis

Organic mixed ionic-electronic conductors (OMIECs) are pivotal for next-generation organic electronics and bioelectronics. However, conventional fabrication methods such as electrochemical and chemical polymerization, and spin-coating often involve complex, multi-step processes, specialized equipment, time-consuming patterning, and significant energy input. Here, we overcome these limitations by introducing a self-driven polymerization method, in which an OMIEC precursor molecule undergoes direct oxidation on a metal electrode. This simple, equipment-free approach enables rapid, in situ formation of conducting polymer coatings on a range of noble metal surfaces, including challenging architectures. This method enables one-step formation of high-performance organic electrochemical transistors with simultaneous glucose oxidase integration, directly producing a functional glucose biosensor and highlighting its potential for multifunctional devices. Importantly, we validate the performance of these high-capacitance coatings in a soft multielectrode array cuff for sciatic nerve interfacing, achieving selective electrical stimulation and high-fidelity in vivo recording. The device supports motor-selective stimulation, ultra-low stimulation saturation thresholds (25–30 µA), and reliable detection of sensory compound action potentials across multiple plantar hind paw regions. Overall, this fast, scalable, and aqueous-based approach provides a high-throughput route for fabricating advanced bioelectronic devices.

Polymer‐based organic mixed ion‐electron conductors (OMIECs) are a class of materials offering unique coupled dual charge transport characteristics along with appealing properties including mechanical softness, biocompatibility, tunability, volumetric capacitance, and stability. These features have been exploited in devices including organic electrochemical transistors (OECTs), neuromorphic computing, energy storage, sensors, neural electrodes, and actuators. Conventionally, OMIEC polymers are prepared through chemical, vapor‐phase, electrochemical, or enzymatic polymerization, typically relying on oxidants, metal catalysts, and/or organic solvents, significantly limiting their scalability, sustainability, and biocompatibility. Here, we introduce an initiator‐free, visible‐light‐induced polymerization of water‐soluble conducting polymer precursors, enabling facile formation of high‐performance and inherently biocompatible OMIECs. This novel approach allows direct photopatterning and seamless film deposition and manufacturing of OECTs across rigid, flexible, and biological substrates, exemplified by glass, textiles, and mouse skin (in vivo). Through careful optimization of the photopolymerization process, resulting OMIECs possess state‐of‐the‐art electrical, electrochemical, and device properties along with exceptional compatibility and conformability with various flexible and biological surfaces. Finally, we demonstrate the utility of these photopatterned electrodes, manufactured directly on mouse skin in vivo, where they significantly enhance the recording efficacy and signal‐to‐noise ratio of low‐frequency brain activity in anesthetized mice.

Polymer‐based organic mixed ion‐electron conductors (OMIECs) are a class of materials offering unique coupled dual charge transport characteristics along with appealing properties including mechanical softness, biocompatibility, tunability, volumetric capacitance, and stability. These features have been exploited in devices including organic electrochemical transistors (OECTs), neuromorphic computing, energy storage, sensors, neural electrodes, and actuators. Conventionally, OMIEC polymers are prepared through chemical, vapor‐phase, electrochemical, or enzymatic polymerization, typically relying on oxidants, metal catalysts, and/or organic solvents, significantly limiting their scalability, sustainability, and biocompatibility. Here, we introduce an initiator‐free, visible‐light‐induced polymerization of water‐soluble conducting polymer precursors, enabling facile formation of high‐performance and inherently biocompatible OMIECs. This novel approach allows direct photopatterning and seamless film deposition and manufacturing of OECTs across rigid, flexible, and biological substrates, exemplified by glass, textiles, and mouse skin (in vivo). Through careful optimization of the photopolymerization process, resulting OMIECs possess state‐of‐the‐art electrical, electrochemical, and device properties along with exceptional compatibility and conformability with various flexible and biological surfaces. Finally, we demonstrate the utility of these photopatterned electrodes, manufactured directly on mouse skin in vivo, where they significantly enhance the recording efficacy and signal‐to‐noise ratio of low‐frequency brain activity in anesthetized mice.

Bioelectronics holds great potential as therapeutics, but introducing conductive structures within the body poses great challenges. While implanted rigid and substrate‐bound electrodes often result in inflammation and scarring in vivo, they outperform the in situ‐formed, more biocompatible electrodes by providing superior control over electrode geometry. For example, one of the most researched methodologies, the formation of conductive polymers through enzymatic catalysis in vivo, is governed by diffusion control due to the slow kinetics, with curing times that span several hours to days. Herein, the discovery of the formation of biocompatible conductive structures through photopolymerization in vivo, enabling spatial control of electrode patterns is reported. The process involves photopolymerizing novel photoactive monomers, 3Es (EDOT‐trimers) alone and in a mixture to cure the poly(3, 4‐ethylenedioxythiophene)butoxy‐1‐sulfonate (PEDOT‐S) derivative A5, resulting in conductive structures defined by photolithography masks. These reactions are adapted to in vivo conditions using green and red lights, with short curing times of 5–30 min. In contrast to the basic electrode structures formed through other in situ methods, the formation of specific and layered patterns is shown. This opens up the creation of more complex 3D layers‐on‐layer circuits in vivo.

Bioelectronics, a field that bridges biology and electronics, has a rich history dating back to the 18th century. The inception of bioelectronics is generally attributed to Luigi Galvani, who in th ...

Hydrogels are promising materials for medical devices interfacing with neural tissues due to their similar mechanical properties. Traditional hydrogel‐based bio‐interfaces lack sufficient electrical conductivity, relying on low ionic conductivity, which limits signal transduction distance. Conducting polymer hydrogels offer enhanced ionic and electronic conductivities and biocompatibility but often face challenges in processability and require aggressive polymerization methods. Herein, we demonstrate in situ enzymatic polymerization of π‐conjugated monomers in a hyaluronan (HA)‐based hydrogel bioink to create cell‐compatible, electrically conductive hydrogel structures. These structures were fabricated using 3D bioprinting of HA‐based bioinks loaded with conjugated monomers, followed by enzymatic polymerization via horseradish peroxidase. This process increased the hydrogels’ stiffness from about 0.6 to 1.5 kPa and modified their electroactivity. The components and polymerization process were well‐tolerated by human primary dermal fibroblasts and PC12 cells. This work presents a novel method to fabricate cytocompatible and conductive hydrogels suitable for bioprinting. These hybrid materials combine tissue‐like mechanical properties with mixed ionic and electronic conductivity, providing new ways to use electricity to influence cell behavior in a native‐like microenvironment.

Interfacing electronics with neural tissue is crucial for understanding complex biological functions, but conventional bioelectronics consist of rigid electrodes fundamentally incompatible with living systems. The difference between static solid-state electronics and dynamic biological matter makes seamless integration of the two challenging. To address this incompatibility, we developed a method to dynamically create soft substrate-free conducting materials within the biological environment. We demonstrate in vivo electrode formation in zebrafish and leech models, using endogenous metabolites to trigger enzymatic polymerization of organic precursors within an injectable gel, thereby forming conducting polymer gels with long-range conductivity. This approach can be used to target specific biological substructures and is suitable for nerve stimulation, paving the way for fully integrated, in vivo–fabricated electronics within the nervous system.