Multidirectional alignment of collagen fibers to guide cell orientation in 3D-printed tissue
Natural tissue comprises fibrous proteins with complex fiber alignment patterns. Here, we develop a reproducible method to fabricate biomimetic scaffolds with patterned fiber alignment along multiple orientations. While extrusion-based approaches are commonly used to align fibrous polymers in a single orientation parallel to the direction of flow, we hypothesized that extrusion-based 3D printing could be utilized to achieve more complex patterns of fiber alignment. Specifically, we show control of lateral spreading of a printed filament can induce fiber alignment that is either parallel or perpendicular to the flow direction. Theoretical prediction of the printing parameters that control fiber orientation was experimentally validated using a collagen biomaterial ink. The velocity ratio of the printhead movement relative to the ink extrusion rate was found to dictate collagen fiber alignment, allowing for the informed fabrication of collagen scaffolds with prescribed patterns of fiber alignment. For example, controlled variation of the ink extrusion rate during a single print resulted in scaffolds with specified regions of both parallel and perpendicular collagen fiber alignment. Human corneal mesenchymal stromal cells seeded onto the printed scaffolds adopted a spread morphology that aligned with the underlying collagen fiber patterns. This technique worked well for filaments either printed into air or extruded within a support bath using embedded 3D printing, enabling the fabrication of 3D structures with aligned collagen fibers. Taken together, this work demonstrates a theoretical and experimental framework to achieve the reproducible fabrication of 3D printed structures with controlled collagen fiber patterns that guide cellular alignment.