Rheological Analysis of Bio-ink for 3D Bio-printing Processes.

3D bio-printing is an emerging technology to fabricate tissue scaffold in-vitro through the controlled allocation of biomaterial and cells, which can mimic the in-vivo counterpart of living tissue. Live cells are often encapsulated into the biomaterials (i.e., bio-ink) and extruded by controlling the printing parameters. The functionality of the bioink depends upon three factors: (a) printability, (b) shape fidelity, and (c) bio-compatibility. Increasing viscosity will improve the printability and the shape fidelity but require higher applied extrusion pressure, which is detrimental to the living cell dwelling in the bio-ink, which is often ignored in the bio-ink optimization process. This paper demonstrates a roadmap to develop and optimize bio-inks, ensuring printability, shape fidelity, and cell survivability. The pressure exerted on the bio-ink during extrusion processes is measured analytically, and the information is incorporated in the bio-ink's rheology design. Cell-laden filaments are fabricated with multiple cell lines, i.e., Human Embryonic Kidney (HEK 293), BxPC3, and prostate cancer cells which are analyzed for cell viability. The cross-sectional live-dead assay of the extruded filament demonstrates a spatial pattern for HEK 293 cell viability, which correlates with our analytical finding of the shear stress at the nozzle tip. All three cell lines were able to sustain a transient shear stress of 3.7 kPa and demonstrate 90% viability with our designed bio-ink after 15 days of incubation. Simultaneously, the shape fidelity and printability matrices show its suitability for 3D bio-printing process.