Hydrogel Bioink with Multilayered Interfaces Improves Dispersibility of Encapsulated Cells in Extrusion Bioprinting

Abstract

One of the challenges for extrusion bioprinting using low-viscosity bioinks is the fast gravity-driven sedimentation of cells. Cells in a hydrogel bioink that features low viscosity tend to settle to the bottom of the bioink reservoir, and as such, their bioprintability is hindered by association with the inhomogeneous cellularized structures that are deposited. This is particularly true in cases where longer periods are required to print complex or larger tissue constructs. Increasing the bioink’s viscosity efficiently retards sedimentation but gives rise to cell membranolysis or functional disruption due to increased shear stress on the cells during the extrusion process. Inspired by the rainbow cocktail, we report the development of a multilayered modification strategy for gelatin methacryloyl (GelMA) bioink to manipulate multiple liquid interfaces, providing interfacial retention to retard cell sedimentation in the bioink reservoir. Indeed, the interfacial tension in our layer-by-layer bioink system, characterized by the pendant drop method, was found to be exponentially higher than the sedimental pull (ΔGravity‑Buoyancy = ∼10–9 N) of cells, indicating that the interfacial retention is crucial for preventing cell sedimentation across the adjacent layers. It was demonstrated that the encapsulated cells displayed better dispersibility in constructs bioprinted using the multilayered GelMA bioink system than that of pristine GelMA where the index of homogeneity of the cell distribution in the multilayered bioink was 4 times that of the latter.

Homogeneous and Reproducible Mixing of Highly Viscous Biomaterial Inks and Cell Suspensions to Create Bioinks

“…While for low viscosity bioinks, the timeframe of cell sedimentation lies within a range of a few minutes, being relevant for bioprinting; these times are significantly higher for highly viscous bioinks [ 16 ]. While there are demanding technical solutions addressing the sedimentation in low viscosity bioinks, highly viscous bioinks offer a clear advantage in this regard [ 17 ].…”

Biology and Models of the Blood–Brain Barrier

“…These bioinks integrate cells such as neurons, astrocytes, HUVECs, or glioblastoma cells (122). In order to print different types of cells, either multinozzle printers can be used simultaneously (123) or a single-nozzle printer can be employed to sequentially print multilayered bioinks in which each layer contains a different cell type (124).…”

Extrusion and Microfluidic‐Based Bioprinting to Fabricate Biomimetic Tissues and Organs

“…Nozzles with larger diameters operated with lower pressure levels were introduced as ways to reduce the shear stress. [237,239,241,242]…”