A new light-activated 3D printing technique has helped researchers to build ‘lifelike’ blood vessel networks – a major step towards synthetic organ production.

Using the new approach, the team from the University of California San Diego (UCSD) was able to print functional networks of artificial blood vessels. In animal trails, the technology was successfully introduced into living subjects.

The researchers explain in their paper, Direct 3D bioprinting of prevascularized tissue constructs with complex microarchitecture, how previous printing of blood vessels has focused on very simple structures, such as a single vessel. Now, directed by professor Shaochen Chen, the UCSD study has produced an intricate network of blood vessels branching into series of smaller vessels, similar to those found in living tissue.

The 3D printing technique involves a computer model of the desired structure, which is then transferred via 2D snapshots to a series of motorised mirrors. The mirrors are digitally controlled to project patterns of UV light in the shape of these snapshots. The UV patterns shine onto a solution containing living cells and light-sensitive polymers which then solidify on exposure to the UV light.

According to the engineers, the structure is rapidly printed one layer at a time, creating a solid 3D polymer frame around the living cells which then grows and becomes biological tissue.

‘We can directly print detailed microvasculature structures in extremely high resolution. Other 3D printing technologies produce the equivalent of ‘pixelated’ structures in comparison and usually require sacrificial materials and additional steps to create the vessels,’ noted Wei Zhu, lead researcher and co-lead author of the study.

During testing, the team created networks containing endothelial cells, which line living blood cells, and implanted them into skin wounds on mice. The researchers found that after two weeks the structures had merged with the mice’s circulatory systems and were supporting normal blood circulation.

The vessel networks are not yet able to transport nutrients or waste, said Chen. ‘We still have a lot of work to do to improve these materials. This is a promising step toward the future of tissue regeneration and repair,’ he added.

Looking forward, the team will be working on patient-specific tissues using human-induced pluripotent stem cells, preventing transplants from being attacked by a patient’s immune system. However, Chen said that the research would take at least several years to reach clinical trials.