A nozzle squeezes out a stream of molten plastic, ceramic, steel or even cells—layers and layers of which stack up, one after the other. Every layer laid down must wait for the last to dry before the next is begun. Patience is a virtue, and these machines are virtuous. 3D printers can create wildly imaginative works of art and cost-efficient products; they are only limited by the speed of research and the human mind.
3D printers have taken the world by storm. Once viewed primarily as tools for the production of low-quality prototype parts or casual artistic endeavours, 3D printing is now being used in commercial production, like resin printing for shoe soles.
Where things get even more interesting is the 3D printing of organic materials such as cells and tissues. Not only is it incredibly difficult to find organ donors, but tissue and organ transplants often fail due to a mismatch between donor and recipient, resulting in transplant rejection. Bioprinting, as this phenomenon is often called, aims to help solve these problems. In 2018 alone, over 200 people in Canada died while waiting to receive an organ transplant. As bioprinting technology continues to develop, a future without waitlists may be on the horizon.
Just as in the case of inorganic 3D printing, there are also multiple ways to approach bioprinting. One such example, and the most popular, is extrusion bioprinting.
Researchers developed a bioink made from a mixture of materials, including cells, hydrogels, and growth factors—proteins that stimulate the growth of tissues. The mixture is placed into a syringe and the bioprinter is then linked to a computer. The computer guides the movement of the nozzle, creating the desired product by extruding the ink in different shapes and concentrations to mimic different organic tissues.
Hossein Ravanbaksh, a post-doctoral researcher in McGill’s Department of Mechanical Engineering, led a research team to determine how to best store these materials and extend their shelf lives. Hydrogels, Ravanbaksh explained, are a key element in the bioprinting process.
“The hydrogels play exactly the role of a scaffold, to keep the cells in place and to keep all the nutrients in place,” Ravanbaksh said. “On the other hand, the waste materials from the cell can be washed away. The hydrogels will be degraded in the body so that the new regenerated tissue can take the place of the hydrogel after it is degraded.”
In a way, the hydrogel is the life blood of the bioink: It acts as the body before the cells are put into an actual body.
A common issue with bioprinting, however, is the shelf life of key materials—the tissue dies very rapidly after production. As most hospitals do not yet have the sophisticated machinery to 3D-print tissues on demand, organs need to be printed at another location before being shipped to where they are needed. This is where Ravanbaksh’s research into cryobioprinting comes in.
Cryobioprinting takes place at temperatures of between -15 to -20 degrees Celsius. The bioink exits the extruder, or nozzle, and touches the surface of a freezing plate, causing the bioink to freeze in a process called cryopreservation.
A primary goal of the study was to find the best cryopreservative that would ensure that the highest number of viable cells are produced and stored. According to Ravanbaksh, the bioinks are highly resistant to low temperatures and can last months in liquid nitrogen—the storage medium for these tissues. The tissues can then be transported to any hospital that needs them and thawed on site.
Much of the innovations in 3D bioprinting are still in early development; cryobioprinting, for example, is purely in its proof-of-concept stage. The possibilities are promising and could be life-changing in the near future. From mechanical Michelangelos to a new-age robotic Hippocrates, 3D printing machines have the ability to radically alter art, medicine, and industry.