3D bioprinting breakthrough: Functional heart vessels created

Biotechnologists using 3D printing technology have achieved considerable success. They have created heart blood vessels that resemble natural ones, an important step towards obtaining laboratory tissues for transplants.

Scientists from Harvard's Wyss Institute for Biologically Inspired Engineering and the John A. Paulson School of Engineering and Applied Sciences (USA) point out that cultivating functional human organs outside the body is the Holy Grail of transplant medicine. In the journal Advanced Materials, they have just reported 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 integrated with living human heart tissue.

"In prior work, we developed a new 3D bioprinting method, known as "sacrificial writing in functional tissue" (SWIFT), for patterning hollow channels within a living cellular matrix. Here, building on this method, we introduce coaxial SWIFT (co-SWIFT) that recapitulates the multilayer architecture found in native blood vessels, making it easier to form an interconnected endothelium and more robust to withstand the internal pressure of blood flow," explains one of the scientists, Paul Stankey.

One of the biggest innovations is a unique nozzle with two independently controllable "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 protrudes slightly beyond the outer sheath chamber, allowing the nozzle to fully pierce the 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 altering the printing speed or ink flow.

To confirm that the new co-SWIFT method works, the team first printed multi-layered vessels in a transparent, granular hydrogel matrix. Then, the researchers printed the 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 the next, even more complex step, the team successfully repeated the printing process using ink enriched with smooth muscle cells forming the outer layer of human blood vessels. In the final stage, the researchers tested their method in living human heart tissue.

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

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

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

"To say that engineering functional living human tissues in the lab is difficult is an understatement. I'm proud of the determination and creativity this team showed in proving that they could indeed build better blood vessels within living, beating human cardiac tissues. I look forward to their continued success on their quest to one day implant lab-grown tissue into patients," emphasizes Wyss Institute Director, Prof. Donald Ingber.