Incorporating bioprinting techniques to pursue functional blood vessels

June 07, 2023

(Nanowerk News) Volumetric printing is a technique pioneered for bioprinting by the RMCU biofabrication lab in 2019. It is a fast technique, which allows cells to survive the printing process. However, because this type of printing is done in a cell-friendly gel, the resulting print is not very good structurally. This is a problem for blood vessels, which must be able to withstand high pressure and bending. For this reason, a combination of volumetric bioprinting and melt electrowriting was carried out.

Melt electrowriting is a highly accurate type of 3D printing that works by guiding thin filaments of molten (biodegradable) plastic. It is capable of producing complex scaffolds that are mechanically strong and able to handle forces. The downside here is that they can’t be printed with there cells directly, as high temperatures are involved. Therefore, volumetric bioprinting was used here to solidify the cell-laden gel onto the scaffolds.

This research was published in Advanced Materials (“Volumetric Printing on Melt-melt Electrolytic Scaffolds Creates Multi-Material Life Constructions with Tunable Architecture and Mechanics”). Strengthening effect of volumetrically printed tubes with 20, 40 or 60 layers of molten electrolytic scaffolding. (Image: LevatoLab, UMC Utrecht)

How to combine electro writing with volumetric printing

The process begins with the manufacture of tubular scaffolds using electrowriting melts. This is then immersed into a vial with photoactive gel and placed in a volumetric bioprinter. In principle, a laser printer can selectively compact gels that are in, on, and/or around the scaffold.

“To do it right, we had to place the scaffold right in the middle of the bottle,” says first author Gabriël Größbacher. “Any deviation from center means the volumetric print will be offset. But we managed to center it perfectly by scoring a scaffold on the mandrel that we attached to the vial.

In this study, Größbacher and colleagues tested various thicknesses of the scaffolds, which resulted in a more or less strong tube. Lastly, they also tested various bioprinted gel placements. This can be located on the inside of the scaffold, within the scaffold itself or outside of it. Using two differently labeled stem cells, the team was able to print a proof of principle vessel with two layers of stem cells, and seeded epithelial cells in the middle to cover the vessel lumen. Different cell layers as proof of principle of bioprinted blood vessels Cross-section of vessel bioprinted with epithelial cells (purple) and two types of stem cells (blue, yellow) to mimic the lining of the vessel wall. (Scale bar = 500 µm) (Image: LevatoLab, UMC Utrecht)

From tube to functional vessel

The design also allows for holes in the sides of the die, providing the possibility of controlled permeability of the vessel for blood to perform its functions. Finally, researchers have created more complex structures such as branching vessels, and even vessels with venous valves that function to maintain unidirectional flow.

Größbacher: “This is a proof from a study of principles. What we need to do now is replace the stem cells with functional cells that are part of the actual blood vessels. That means adding muscle cells and fibrous tissue around the epithelial cells. Our goal now is to print functional vessels.”

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