Growing artificial organs might help solve the transplantation shortage, but one major hurdle still exists: it is difficult to get blood vessels to grow all the way through a large organ. A gel that allows blood vessels to grow in precise shapes and respond to human cells in a manner similar to natural vessels might help jumpstart that process.

Ying Zheng at the University of Washington in Seattle and colleagues injected human endothelial cells – which line blood vessels – into tiny channels within a collagen gel.

The endothelial cells spread throughout the channels, which were only micrometres in width, and formed hollow, three-dimensional tubes, or microvessels. When the researchers pumped blood into the system, it moved through the microvessels without sticking. It could even flow smoothly around 90 degree bends.

The researchers then added a series of proteins involved in inflammation. They found that the proteins caused the blood to clot inside the microvessels, just as it would in the body. Because the system reacted to these stimuli in the same way as a natural vascular system would, Zheng says, it might one day be useful for screening drugs.


When the group injected human brain and muscle cells into the gel, along with proteins that stimulate blood vessel growth, the microvessels showed that they could branch and integrate with the two types of tissue.

Because the channels can be directed into any shape, bioengineer Linda Griffith of Massachusetts Institute of Technology is hopeful that the system can model complex vascular systems such as the blood-brain barrier, which is difficult to study in living animals. Additionally, she adds, researchers could study how cancers metastasise by putting other cell types, such as bone or liver cells, into the channels along with cancerous cells.

Zheng says that the next step is to use the system as a starting point for an artificial organ. Drawing the channels in the right shape will allow the organ to have an adequate blood supply throughout.

Journal reference: Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1201240109