Nanoengineers at the University of California San Diego may have found a solution to a persisting problem in tissue engineering – producing tissues and organs with the biological functions of a human body.
Blood vessels have previously been 3D printed by other scientists, but have either been singular tubes rather than a complete network, or have not been compatible with human bodily functions. In some instances, the technologies used have simply been too expensive and slow.
A 3D printed network of blood vessels, on the other hand, could have the potential to safely circulate blood, transport nutrients and other biological material if implanted inside the body, where it branches out just like its natural counterpart.
"Almost all tissues and organs need blood vessels to survive and work properly. This is a big bottleneck in making organ transplants, which are in high demand but in short supply," says Shaochen Chen, a nanoengineer at the university. "3D bioprinting organs can help bridge this gap, and our lab has taken a big step toward that goal."
The researchers created the microstructures using self-made 3D printers and UV light. A 3D model of the network was first produced on a computer before 2D snapshots were transferred to millions of miniature mirrors.
The mirrors reflect UV light patterns that solidify onto a polymer-live cell solution. These patterns are then repeatedly printed one layer at a time, creating a structure that rapidly grows into a biological tissue.
The process takes a few seconds, uses materials that are cheap and biocompatible, with the structure being as thick as a stack containing 12 strands of human hair, say the scientists.
"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," says Wei Zhu, who led the research.
The resulting tissues were implanted into skin wounds of mice, which after two weeks had grown and merged with the host blood vessel network, with a normal blood circulation. However, the implants are not yet capable of other biological functions, such as transporting nutrients and waste.
The team is now working on creating bespoke biomedical tissue implants that are specific to individual patients, using the patient’s own skin cells, preventing any rejection by their immune system.
However, they think it will be a while before they can move their work to clinical trials.
Gunther Tovar, an engineer at the University of Stuttgart who was not involved in the research but works in the same field, estimates that it might take as long as 20 years to bring such technology to hospitals. “Functional biomaterials which can be processed are the most important bottleneck, even more than the additive manufacturing machines or processes," he says.
The big breakthrough in the latest research, he adds, is the vascularisation of the tissue - the organic process whereby body tissues develop vessels and capillaries.
Vascularisation is the most challenging aspect of tissue engineering and has long been the limiting factor, says Artemis Stamboulis, a biomaterials specialist at the University of Birmingham, who didn't take part in the study either. “This somehow can be achieved now but developing stable organs for future clinical applications will require harder efforts and further research in this area,” she adds.
Last year, a different team, from China, 3D printed individual blood vessels made from stem cell-based organic material, and then implanted them into monkeys.
The University of California San Diego researchers have previously used their technology to create liver tissue and microscopic fish that can swim in the body to detect and remove toxins.
The work was published in the journal
Biomaterials.