Bioprinting breakthrough: Scientists create human blood vessels

The cultivation of functional human organs outside the body is the Holy Grail of transplant medicine, according to scientists from Harvard's Wyss Institute for Biologically Inspired Engineering and John A. Paulson School of Engineering and Applied Science (USA). They recently reported in the journal "Advanced Materials" about a significant step towards achieving this "Grail."

Thanks to an innovative type of 3D printing, specialists have created a network of blood vessels very similar to those found in the human body. These vessels have a layer of smooth muscle and epithelium, which they integrate with living human heart tissue.

"In previous studies, we developed a new method of 3D bioprinting known as SWIFT (Sacrificial Writing Into Functional Tissue), designed to create hollow channels in a live cellular matrix. Here, building on that method, we present the coaxial SWIFT method (co-SWIFT), which recreates the multilayered architecture found in living blood vessels. This facilitates the creation of a cohesive endothelium and increases resistance to the internal pressure of flowing blood," explains one of the scientists, Paul Stankey.

One of the biggest innovations is the unique nozzle with two independently controlled "ink" channels, from which the vessels are formed: a collagen-based sheath ink and a gelatin-based core ink.

The inner chamber of the nozzle extends slightly beyond the outer sheath chamber, allowing the nozzle to completely pierce a previously printed vessel, creating interconnected branching networks that ensure sufficient oxygenation of human tissues and organs. The size of the vessels can be changed during printing by adjusting the printing speed or ink flow.

To confirm that the new co-SWIFT method works, the team first printed multilayered vessels in a transparent, granular hydrogel matrix. Then the researchers printed vessels in a new type of matrix made of a porous, collagen-based material that mimics the dense, fibrous structure of living muscle tissue.

They successfully printed branched vascular networks in both of these cell-free matrices. In a subsequent, even more complex step, the team successfully repeated the printing process using ink enriched with smooth muscle cells, which form the outer layer of human blood vessels. In the final stage, researchers tested their method in living human heart tissue.

The printed vessels not only took on the characteristic two-layer structure of human blood vessels but also, after five days of perfusion with a blood-mimicking fluid, the tissue began to contract synchronously, indicating its health and proper function. It also responded to commonly used cardiology drugs.

Additionally, the team printed a model of the branched vascular system of the left coronary artery based on the structure of a living patient's organ, demonstrating the method's potential in personalised medicine.

In the future, the team plans to develop a method for creating self-forming capillary networks and integrating them with their three-dimensionally printed networks to more fully recreate the structure of human blood vessels on a microscale and improve the function of lab-grown tissues.

"To say that creating functional living human tissues in the lab is difficult is an understatement. I am proud of the determination and creativity of this team, which has proven that it can indeed build better blood vessels in living, beating human heart tissues. I look forward to further successes in the endeavour to implant lab-grown tissues in patients," emphasizes Wyss Institute Director, Prof. Donald Ingber.