2.1. Design and printing of conductive PLA
Conductive PLA filaments (diameter: 1.75 mm) were procured from Proto-Pasta (USA), and nonconductive PLA filaments (diameter: 1.75 mm) were obtained from eSUN (China). A dual-printing-head 3D printer (Creator pro 2, Flashforge, China) was used to fabricate the electrodes and other test parts. Computer-aided design of the electrode parts was performed using Solidworks 2020 (Dassault, France) and stored as stereolithography (.stl) files, and the detail printing conditions were adjusted using FlashPrint 5 (Flashforge, China) (nozzle temperature: 215°C, bed temperature: 60°C, printing speed: 60 mm/s, moving speed: 100 mm/s).