The history of 3D printing can be traced back to early demonstrations in the 1970s where objects could be created by shining lasers into a liquid polymeric bath. The laser would rapidly cure and harden parts of the polymer, leading to the creation of a three-dimensional object. By the early 2000s, other advances popularized the idea of 3D printing, primarily in plastic. This was the start of additive methods for creating 3D objects.

Then a few biologists decided to see how this idea might be applied to bacteria, to human cells, to tissues. The idea of what is now called bioprinting has grown dramatically in the last ten years. Researchers have tackled the easier things first. Human bone has been successfully 3D printed. Cartilage was finally successfully done in 2018 by Swedish researchers. But none of this should obscure the incredible technical challenges still remaining for commercialization. Still, these are early success stories for what would be called structural bioprinting.

Functional bioprinting, the creation of organs, and organ-like tissues is still a long way off in the future. The early success stories are based on very small cell masses, called organoids, which demonstrate some of the functions of the original organs. Work in creating a bioprinted liver is arguably the furthest along, but still has many technical problems to solve.

The suggestion here that one should think in terms of structural versus functional bioprinting implies that this field may go down two different paths. Put simply, a bioprinted liver may not look like a normal liver but function as one nonetheless. Moreover, the ability to create a functioning liver outside the human body raises a host of other considerations. Transfections, CRISPR methods, and other types of genetic modification will likely create new types of ex vivo livers which utterly novel capabilities which will redefine what we mean by “precision medicine.”

Even while these kinds of changes are happening in research for functional bioprinting, one cannot overlook unusual developments in structural bioprinting. Two examples are the Tissue Foundry at the Advanced Regenerative Medicine Institute (Manchester, NH) and the role of engineered hydrogels in modifying how bioprinted body parts can be put to use. While still in the prototype stage as of Dec. 2019, the Tissue Foundry is making progress on automated production of combined bone-cartilage structures. As for hydrogels, there is a fair bit of research, but it is suggested here that greater understanding of the underlying chemistry of hydrogels will lead to entirely new applications.

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