Lab prints 3D capillaries under 10 micrometers

In a laboratory at the University of Notre-Dame-du-Lac, gelatin threads thinner than the finest human hairs draw paths through a soft matrix. Once the gelatin is removed, Yanliang Zhang and Yuxuan Liao’s team obtains capillary networks in which some channels measure under 10 micrometers in diameter.

The challenge lies not only in the scale, but also in the diversity of blood vessels. A natural network transitions from wider conduits to tiny capillaries. The researchers therefore print the matrix by extrusion, depositing biomaterials under pressure, then add the gelatin threads using aerosol jet printing — AJP, a technique that uses a gas flow to focus the deposition. The gelatin liquefies in hot water and leaves behind the channels.

The team adds machine-learning software to the process. It fine-tunes the ink flow and the sheath-gas flow to select parameters suited to the desired channel size, rather than relying solely on successive trial and error. The researchers thus fabricated hierarchical networks in one, two and three dimensions.

Some channels were then seeded with endothelial cells, the cells that line the inside of blood vessels. They quickly adhered to the walls and formed a monolayer comparable to that observed in living human tissues. In the reported tests, this layer reproduced a barrier function and the networks showed no leakage.

So what does this mean in practice? The method could provide vascular networks for integration into biomimetic tissues, organ-on-chip models for evaluating drugs, or regenerative medicine and organ-engineering research. It therefore tackles an essential part of bioprinting, but the result remains at the laboratory stage: no transplant or complete organ is described here.