Cryo-Electrohydrodynamic Jetting of Aqueous Silk Fibroin Solutions

The incorporation of 3D-printing principles with electrohydrodynamic (EHD) jetting provides a harmonious balance between resolution and processing speed, allowing for the creation of high-resolution centimeter-scale constructs. Typically, EHD jetting of polymer melts offers the advantage of rapid solidification, while processing polymer solutions requires solvent evaporation to transition into solid fibers, creating challenges for reliable printing. This study navigates a hybrid approach aimed at minimizing printing instabilities by combining viscous solutions and achieving rapid solidification through freezing. Our method introduces and fully describes a modified open-source 3D printer equipped with a frozen collector that operates at -35 °C. As a proof of concept, highly concentrated silk fibroin aqueous solutions are processed into stable micrometer scale jets, which rapidly solidify upon contact with the frozen collector. This results in the formation of uniform microfibers characterized by an average diameter of 27 ± 5 μm, a textured surface, and porous internal channels. The absence of instabilities and the notably fast direct writing speed of 42 mm·s^-1 enable precise, fast, and reliable deposition of these fibers into porous constructs spanning several centimeters. The effectiveness of this approach is demonstrated by the consistent production of biologically relevant scaffolds that can be customized with varying pore sizes and shapes. The achieved degree of control over micrometric jet solidification and deposition dynamics represents a significant advancement in EHD jetting, particularly within the domain of aqueous polymer solutions, offering new opportunities for the development of intricate and functional biological structures.