What is bioprinting?

There’s been a lot of interest in the press about the concept of using 3D printing to craft living tissues, particularly transplantable organs. But how does this new technology, called ‘bioprinting’, actually work?

In simple terms, bioprinting is the practice of using 3D printing technology to generate organic cell structures rather than plastic or metal parts. This makes it possible to print functional tissue, which can then be used in medical research, or for transplant purposes. In the long-term, as the technology evolves, it could indeed be used for printing functional organs, based on transplant patients’ own cells to potentially eliminate the risk of organ rejection.

Like ‘conventional’ 3D printing, bioprinting works by building up structures layer by layer on a printing bed. However, as the process involves working with living tissue rather than metals and plastics, it is fundamentally different in a number of ways. Let’s look at it in detail…

How does it work?

All bioprinting projects begin with a 3D model of the part that needs to be created. This can be generated through a CT scan or MRI of a real body part, or created from scratch via 3D modelling. The model then needs to be translated into a form that can be successfully bioprinted, which means the architecture of the tissue must be established. The appropriate cells are therefore isolated and captured (from the original tissue, if possible) in a special solution that will keep them alive and oxygenated, ready for printing. These printable solutions are known as ‘bioinks’. As tissue regeneration requires the use of ‘scaffolds’ (the physical supports needed for cells to grow), several such inks will typically be needed for a bioprinting project, which makes multi-material printers a necessity. These scaffolds could be considered the counterpart of conventional 3D printing’s support structures.

A number of different technologies can be utilised to convert these bioinks into living tissues. The earliest bioprinting techniques utilised an inkjet-style approach (more on that later), but stereolithography and extrusion-based printers have also been utilised successfully. Regardless of the technology used, the printing process should be familiar to any AM professional: the printer builds up layers of the chosen material(s) on the printing bed until the entire 3D model has been brought to life.

Finally, once printing is complete, some post-processing is required in order to maintain the integrity of the tissue, as the newly-printed cells will not be connected straight away as they would be with printed plastic or metal. This typically involves mechanical or chemical simulations that trigger the remodelling and growth of the tissue. A more sophisticated example of this involves the use of ‘bioreactors’ to encourage the growth and vascularisation (i.e. the development of blood vessels) of tissue.

The following video provides a good overview of the bioprinting process:

Bioprinting’s pioneers and industry leaders

3D printers designed for printing tissues in this way are commonly referred to as ‘bioprinters’. The first working bioprinter was unveiled by Professor Makoto Nakamura of the University of Toyama, who showcased its capabilities by printing a biological tube, similar to a blood vessel. As mentioned above, this utilised an inkjet-based printing approach (in fact, the first prototype was based on a modified Epson printer!). Professor Nakamura has since continued his research into the potential applications of bioprinting.

Organovo are another leader in the field of bioprinting, and have worked with their partner company, Invetech, to deliver a viable commercial bioprinter: the NovoGen MMX. Organovo’s approach to printing tissue involves a specially designed multi-head printer, with separate print heads for cardiac cells, endothelial cells, and a collagen ‘biopaper’ that acts as the scaffold.

The technology has also drawn the attention of the US military, who have invested in research into whether bioprinting could be used to treat injured soldiers. The Armed Forces Institute of Regenerative Medicine (AFIRM) was established in 2008 to lead the way in this area, with universities, researchers and military scientists working together as part of a cooperative agreement.

In Germany, the Fraunhofer Institute are conducting ongoing research into the printing of whole organs, both for transplant purposes and to eliminate the need for animal testing in research environments. In particular, their researchers have made considerable strides in the vascularisation of bioprinted tissue, working closely with the ArtiVasc 3D project to create 3D printed blood vessels that will supply tissues with nutrition in the same way as a living body.

Like other 3D printing technologies, bioprinting already has its own material specialists, who focus on the development of sophisticated bioinks. Sweden’s Cellink, for example, have quickly established themselves as an industry leader in this regard by offering a comprehensive range of self-created of bioinks, along with the technology needed to make use of them.

What’s next?

While the potential benefits bioprinting can offer have certainly captured the public’s imagination, as with any new technology, it will take time to mature and establish itself. We would expect bioprinting to follow a similar path to the one taken by the nascent additive manufacturing industry. As the technology is employed more and more in ‘real world’ settings, early successes will help it establish its ideal niches. At that point, the focus will shift to establishing the processes and complementary tools that will optimise its performance.

At that point, scientists, doctors and patients (along with other industries where bioprinting has yet to reveal its potential applications) will begin to see the full benefit of the technology. The journey there will certainly be a long and complex one, but we expect the benefits to be enormous.