New technique advances rapid bioprinting

This new technique is claimed to improve the precision and scalability of tissue fabrication, producing tissue 10-times faster than existing methods. It further opens the door to developing functional tissues and organs and progress in the field of regenerative medicine, the researchers said. Their findings are detailed in Nature Communications.

“This technique is a significant advancement in rapid bioprinting of spheroids,” said Professor Ibrahim T. Ozbolat, Dorothy Foehr Huck and J. Lloyd Huck Chair in 3D Bioprinting and Regenerative Medicine at Penn State. “It enables the bioprinting of tissues in a high-throughput manner at a speed much faster than existing techniques with high cell viability.”

Bioprinting allows researchers to build 3D structures from living cells and other biomaterials. Living cells are encapsulated in a substrate like a hydrogel to make a bioink, which is printed in layers using a specialised printer. These cells grow and proliferate, eventually maturing into 3D tissue over the course of several weeks.

Ozbolat said it is difficult to achieve the same cell density as found in the human body with this standard approach. That cell density is essential for developing tissue that is functional and can be used in a clinical setting. Spheroids offer a promising alternative for tissue bioprinting because they have a cell density similar to human tissue.

While 3D printing spheroids offers a viable solution to producing the necessary density, researchers have been limited by the lack of scalable techniques. Existing bioprinting methods can damage the delicate cellular structures during the printing process, killing some of the cells. Other technologies are cumbersome and do not offer precise control of the movement and placement of the spheroids needed to create replicas of human tissue.

In previously published research, Ozbolat and his colleagues developed an aspiration-assisted bioprinting system. Using a pipette tip, the researchers could pick up balls of cells and place them precisely where they self-assemble and create a solid tissue. However, since the technique involves moving spheroids one at a time, it could take days to build a 1cm³ structure.

To address these issues, the team developed High-throughput Integrated Tissue Fabrication System for Bioprinting (HITS-Bio). HITS-Bio uses a digitally controlled nozzle array, an arrangement of multiple nozzles that moves in three dimensions and allows researchers to manipulate several spheroids simultaneously.

The team organised the nozzles in a four-by-four array, which can pick up 16 spheroids concurrently and place them on a bioink substrate quickly and precisely. The nozzle array can also pick up spheroids in customised patterns, which can then be repeated to create the architecture found in complex tissue.

“We can then build scalable structures very fast,” Ozbolat said in a statement. “It’s 10-times faster than existing techniques and maintains more than 90 per cent high cell viability.”

To test the platform, the team set out to fabricate cartilage tissue. They created a 1cm³ structure, containing approximately 600 spheroids made of cells capable of forming cartilage. The process took under 40 minutes, surpassing the capacity of existing bioprinting technologies.

The team then showed that the bioprinting technique can be used for on-demand tissue repair in a surgical setting in a rat model. They printed spheroids directly into a wound site in the skull during surgery, which was the first time spheroids have been printed intraoperatively. The researchers programmed the spheroids to transform into bone using microRNA technology, which helps control gene expression in cells, including how cells differentiate into specific types.

“Since we delivered the cells in high dosages with this technique, it actually sped up the bone repair,” said Ozbolat. After three weeks, the wound was 91 per cent healed after three weeks and 96 per cent healed after six weeks.

The HITS-Bio technique offers an opportunity to create complex and functional tissue in a scalable manner, Ozbolat said. Expanding the number of nozzles could lead to production of larger and more intricate tissues, such as organs and organ tissue like the liver.

Ozbolat said that the team is also working on techniques to incorporate blood vessels into the fabricated tissue, a necessary step for producing more types of tissues that can be used clinically or for transplantation.