Tough Hydrogel-Based Supercapacitor Fiber Fabricated via Thermal Drawing for Long-Term and Minimally Invasive Bio-implantation

Recent advances in implantable bioelectronic devices have driven the need for biocompatible and durable energy storage solutions capable of delivering stable electrical power in vivo. However, the design of such devices faces persistent challenges in maintaining mechanical robustness, biocompatibility, and electrochemical stability under dynamic biological environments. In this study, we present the development of a novel tough hydrogel-based supercapacitor (THBS) fiber, fabricated through a thermal drawing process (TDP), which addresses these limitations by combining superior mechanical toughness, biocompatibility, and self-healing properties.

The THBS fiber consists of a polyvinyl alcohol (PVA)-based dual-network hydrogel, reinforced with polyethylene glycol (PEG) and sodium borate (SB), serving as both the electrode and electrolyte. The ionic coordination between PVA and borax significantly enhances the hydrogel’s self-healing ability, allowing the fiber to recover structural integrity after mechanical damage. This self-healing property, crucial for maintaining high electrochemical performance, is further improved by the thermal drawing process (TDP), which facilitates enhanced bonding and alignment at the electrode-electrolyte interface. The combination of the PVA-based electrolytes and the PVA-based electrodes, including activated charcoal and carbon black fillers, exhibits high electrochemical. The resulting fiber, encapsulated in poly(ethylene-co-vinyl acetate) (EVA), demonstrates exceptional mechanical and electrochemical stability under repeated deformation, with minimal capacitance degradation after 1,000 bending cycles and sustained performance over two months in simulated body fluids.

In vivo experiments demonstrated the successful implantation of THBS fibers in mice, where the fibers powered an LED for optogenetic stimulation of both the peripheral and central nervous systems. Long-term implantation tests revealed excellent biocompatibility, with minimal immune response and no significant tissue infiltration. Furthermore, the fibers retained over 99% of their capacitance after five weeks of cyclic voltammetry measurements in vivo, showcasing remarkable operational longevity.

Overall, THBS fibers hold substantial potential for a wide range of bioelectronic applications, offering a reliable, flexible, and stable energy solution. Their adaptable, one-dimensional design opens new avenues for integration into diverse medical devices, driving innovation across multiple healthcare domains.