A mist-based crosslinking technique for coaxial bioprinting of hollow hydrogel fibers

In this paper, a mist-based method for coaxial three-dimensional bioprinting of ionically crosslinking hydrogel hollow fibers is presented. Unlike current techniques of coaxial bioprinting that utilize the crosslinker in liquid or sacrificial form, the developed method introduces the core crosslinking agent in mist form. The use of mist as a core flow provides adequate pressure and sufficient crosslinking to maintain the tubular shape of a hollow fiber. Through controlled exposure of crosslinker, the developed system prevents poor resolution and layer adhesion caused by the accumulation of liquid crosslinker on the printbed. Furthermore, it eliminates additional processing steps, such as partial crosslinking of the hydrogel prior- or removal of sacrificial material post-printing. The printability and mechanical properties of hollow fiber scaffolds printed using various mist and hydrogel concentrations are studied. It is shown that mist concentration influences the gelation rate of the hollow fiber, impacting the shape fidelity, layer adhesion, and mechanical properties of the printed structures. Moreover, the effects of printing parameters, including the mist core pressure and hydrogel flowrate, on the diameter and wall thickness of the hollow fiber are investigated. Finally, scaffolds printed and crosslinked using mist exhibit over 90% cell viability. The developed mist-based coaxial system enables direct printing of continuous hollow fibers.