We can’t print organs yet. The problem is that they’re just so complex, with vast networks of tiny blood vessels supplying millions of microscopic cells. Reproducing that kind of branched structure in 3D is inordinately complex. Another reason why printing artificial organs is just too difficult is that the molecular compositions and differentiation stages of the cells in an organ are never fully known and therefore never fully controllable.
What we could do, however, is create an artificial environment that is similar enough to the natural environment for the cells to retain their tissue-specific behaviour and thereby self-organise into functional tissue.
If we want to print organs in a 3D printer, the materials are of the utmost importance. They would have to be able to adapt to the properties of biological tissue and allow the machines to print them layer by layer. One institute that is currently looking into printing tissue-like structures is the Fraunhofer IGB. The inkjet printers that its researchers are using have ink cartridges and nozzles and work in much the same way as a conventional office printer. The difference, though, is in the ink: the Fraunhofer IGB uses a bio-ink that it develops especially for producing cartilage-like tissue. It is made of modified gelatine and living cartilage cells. Gelatine is derived from collagen, the main component in natural connective tissue. The researchers chemically adapt the gelatine’s gelling behaviour so that it remains fluid during printing. Once the biomolecules have been printed, they are exposed to UV light, which makes them form a stable hydrogel. Hydrogels are networks of polymer chains that contain water but don’t dissolve in water or if exposed to heat. The hydrogels can be made harder or softer, and their composition can gradually be adapted to match the typical composition of cartilage matrix. Rather than printing onto paper, the researchers print onto a hydrogel. This prevents the printed structures from drying out.
This question was answered by Kirsten Borchers of the Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB.