Free-form co-axial bioprinting of a gelatin methacryloyl bio-ink by direct in situ photo-crosslinking during extrusion

Abstract

3D bioprinting is an emerging technology for arranging cells and biomaterials in 3D, with the goal to develop functional substitutes for damaged tissue. Photo-crosslinkable hydrogels are promising materials for formulating printable bio-inks. However, owing to conflicting constraints around printability and cell survival, achieving good shape fidelity is a challenge. The typical approach to ‘post-crosslink’ a 3D bioprinted structure necessitates highly viscous bio-inks. Meanwhile ‘pre-crosslinking’ can result in the extrusion of overly gelated bio-inks, which increases shear-stresses experienced by encapsulated cells. Neither of these strategies are amenable to creating free-standing structures, or structures with overhangs, without using secondary support materials. Here, for the first time, an on board light exposure strategy is demonstrated which enables rapid (<1s) and direct crosslinking of the bio-ink as it is being extruded from the nozzle, and without the use of transparent tubing to stabilize the filament. The utilization of this technique on a manually operated device is described, allowing for free-form additive sculpting of bio-ink structures in 3D. Finally, a co-axial freeform extrusion system is demonstrated, allowing for encapsulation of a very soft, or entirely liquid, core within the rapidly photocrosslinked shell filament.