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.