Cross-section of a bioprinted vessel with epithelial cells (purple) and two types of stem cells (blue, yellow) to mimic the layers of a blood vessel wall. (Scale bar = 500 μm)
Newswise — The RMCU biofabrication lab pioneered volumetric printing in 2019, specifically for bioprinting purposes. This speedy method ensures cell viability during printing. Nevertheless, as it employs gel matrices, the resultant prints lack structural integrity. This poses a challenge for blood vessels, which require strength to endure pressure and bending. Consequently, a fusion of volumetric bioprinting and melt electrowriting was pursued.
Melt electrowriting is a precise form of 3D printing that utilizes a slender strand of liquefied (biodegradable) plastic. It excels at generating detailed scaffolds with excellent mechanical durability to withstand external forces. However, due to the elevated temperatures required, direct printing of cells within these scaffolds is not feasible. To overcome this limitation, volumetric bioprinting was employed to incorporate cell-laden gels onto the scaffolds, thereby solidifying them.
How to merge electrowriting with volumetric printing
The process commences by fabricating a cylindrical scaffold through melt electrowriting. Subsequently, the scaffold is immersed in a vial containing a photosensitive gel and positioned within the volumetric bioprinter. The printer's laser has the capability to selectively solidify the gel, both within, on, and around the scaffold. Achieving precise alignment was crucial, as emphasized by Gabriël Größbacher, the first author of the study. "To ensure accuracy, we meticulously positioned the scaffold at the center of the vial," Größbacher explained. "Any deviation from the center would result in an offset volumetric print. However, we successfully achieved perfect alignment by printing the scaffold on a mandrel specially designed to fit the vial."
In their study, Größbacher and the research team conducted experiments involving different scaffold thicknesses, yielding varying tube strengths. Additionally, they explored different placements for the bioprinted gels, including the inner side, inside, or outside of the scaffold. To demonstrate the feasibility of their approach, the team utilized two distinct types of stem cells, each labeled differently. This allowed them to successfully bioprint a prototype blood vessel comprising two layers of stem cells. Furthermore, epithelial cells were seeded in the central region to form a lining covering the vessel's lumen.
From tubes to functional vessels
Moreover, the design of the bioprinted vessels incorporated the potential for side holes, offering the opportunity for controlled permeability to facilitate the vessel's intended function in blood circulation. Furthermore, the researchers successfully fabricated more intricate structures, including forked vessels and vessels featuring functional venous valves. These valves were capable of maintaining a unidirectional flow, demonstrating the versatility and potential of the bioprinting technique for creating complex vascular structures.
Größbacher stated, "This study served as a proof of principle. Our next objective is to substitute the stem cells with functional cells that constitute an actual blood vessel, including the inclusion of muscle cells and fibrous tissue surrounding the epithelial cells. Our current aim is to bioprint a fully functional blood vessel."
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