Polymer Casting and Water Immersion-Based Large-Area Graphene Transfer for Flexible Electronics Fabrication

This study focuses on developing an efficient large-area graphene transfer method that combines high-throughput and precise laser engraving, simple polymer casting, and water immersion to fabricate conductive graphene and biodegradable polymer-based implantable flexible electronic devices. The low-temperature treatment of graphene sheets on a glass substrate reduced graphene sheet roughness and increased hydrophobicity, enabling facile and high-efficiency (∼100%) large-area graphene transfer to a flexible polymer substrate. This method also benefited from differences in the work of adhesion at the graphene sheet/glass substrate and the graphene sheet/flexible polymer substrate interfaces. The transferred graphene sheets showed stability, structural integrity, and high conductivity (∼40 Ω/sq sheet resistance) under in vitro and in vivo mimicking conditions. The low-temperature-treated and laser-engraved conductive graphene patterns, transferred on a flexible and biodegradable polymer substrate, demonstrated in vitro cytocompatibility on different cells. Two flexible electronic devices (1─a graphene coil-integrated electrode cuff and 2─an interdigitated graphene cuff-integrated piezoelectric device) were fabricated using the developed method, and both demonstrated functionality and proof of concept by generating output voltages that can enhance cell/tissue regeneration. In addition, the ease of handling, ex vivo implantation, and feasibility of suturing were demonstrated by performing implantation surgeries on the pudendal nerve in cadaveric rats. Overall, this promising large-area graphene transfer method can be used to fabricate biodegradable, implantable devices that can serve as interfaces to stimulate cells and tissues for regeneration and repair.