Notre Dame Researchers 3D Print Blood Capillary Networks

Printing vessels smaller than a hair

Researchers at the University of Notre Dame have developed a hybrid bioprinting method that can produce blood capillary networks with channel diameters under 10 micrometers. That's thinner than a human hair, and getting vessels that small to remain stable and functional has been one of the hardest problems in tissue engineering.

The team, led by Yanliang Zhang, Advanced Materials and Manufacturing Collegiate Professor, combined extrusion printing with aerosol jet printing in a single process. First, the printer extrudes a soft, gel-like scaffold that mimics human tissue. Then, once a section is laid down, an aerosol jet deposits fine threads of gelatin onto the surface. Those threads are later removed, leaving behind hollow channels embedded in the matrix. The researchers used machine learning to autonomously tune print parameters for different vascular configurations.

Living cells line the channels

In tests, the method produced stable one-dimensional, two-dimensional, and three-dimensional vascular structures. Selected channels in each structure were successfully lined with living cells, a key step toward functional tissue. The results appeared on the cover of Nature Chemical Engineering earlier this year.

Yanliang Zhang developed the approach in collaboration with Y. Shrike Zhang, associate professor of medicine at Harvard Medical School and Brigham and Women's Hospital. The long-term goal is an intelligent, autonomous bioprinter capable of fabricating complete tissues and organs: livers, kidneys, even hearts. If the technology scales, it could reduce reliance on organ transplants and eliminate the need for patients to take immunosuppressive drugs for the rest of their lives.

Why capillaries matter

Capillaries do the actual exchange of oxygen and nutrients between blood and tissue. Without a network of tiny vessels, any bioprinted organ larger than a few millimeters will die from the inside out. Most existing bioprinting methods can produce larger blood vessels, but they struggle at the capillary scale where diffusion alone isn't enough to keep cells alive. The Notre Dame approach addresses that bottleneck directly by integrating two printing techniques rather than trying to force one method to do everything.

The research doesn't mean 3D printed organs are around the corner. Functional livers and hearts require far more than working capillaries. But clearing the vascularization hurdle is a necessary step, and this method gives researchers a reproducible way to build the microscopic plumbing those future organs will need.