Notre Dame and Harvard Print Blood Vessels Smaller Than 10 Microns

The capillary problem

More than 100,000 people in the United States are waiting for an organ transplant, and a new name joins the list every ten minutes. Lab-grown organs built from a patient's own cells could sidestep rejection and the lifelong drugs that follow, but first researchers need to copy the tiny blood vessels that keep real organs alive. Capillaries are the bottleneck: they are thinner than the finest human hair and must form a complete network before tissue can survive.

A hybrid workaround

Researchers at the University of Notre Dame, working with collaborators at Harvard Medical School and Brigham and Women's Hospital, have reported a new approach that reaches capillary scale. The team, led by Yanliang Zhang at Notre Dame and Y. Shrike Zhang at Harvard, combines two very different printing methods in one platform. The soft tissue-like scaffold is laid down by extrusion bioprinting, the familiar pressure-driven process that builds one layer at a time. Once a section is in place, an aerosol jet deposits thin gelatin threads inside the matrix. Those threads are removed later, leaving hollow channels behind.

Why aerosol jet matters

The aerosol jet uses a sheath flow to focus the material aerodynamically, which lets the nozzle print channels from hundreds of micrometers down to below ten micrometers. That range matches the natural variation in real blood vessels. The catch is that small changes in ink flow or sheath gas flow shift the channel size, so the team added a machine-learning controller to find the right settings for each geometry instead of tuning by hand.

Living cells followed the blueprint

The printed vascular networks held their shape in one, two, and three dimensions. When the researchers seeded selected channels with endothelial cells, the cells spread along the inner walls and formed single-cell linings similar to those in living tissue. The barrier function was intact, with no leakage across the printed capillaries.

What comes next

The group has secured new National Institutes of Health funding to build a more powerful version of the hybrid bioprinter and push toward lab-grown organs. Organ-on-a-chip drug testing and personalized medicine are nearer-term targets. For now, the work shows that combining old and new printing tools, guided by machine learning, can reach a scale that neither method could manage alone.