The transparent liquids consist of components from the natural tissue matrix and living cells.
The substance is based on a well known biological material: gelatin. Gelatin is derived from collagen, the main constituent of native tissue.
Researchers from the Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB) in Stuttgart have chemically modified the gelling behaviour of the gelatin to adapt the biological molecules for printing.
Instead of gelling like unmodified gelatin, the bio-inks remain fluid during printing. Only after they are irradiated with UV light, they crosslink and cure to form hydrogels.
These are polymers containing a huge amount of water (just like native tissue), but which are stable in aqueous environments and when being warmed up to physiological 37 degrees Celsius.
The researchers can control the chemical modification of the biological molecules so that the resulting gels have differing strengths and swelling characteristics.
The properties of natural tissue can therefore be imitated - from solid cartilage to soft adipose tissue.
In Stuttgart synthetic raw materials are printed as well that can serve as substitutes for the extracellular matrix.
For example a system that cures to a hydrogel devoid of by-products, and can be immediately populated with genuine cells.
"We are concentrating at the moment on the 'natural' variant. That way we remain very close to the original material. Even if the potential for synthetic hydrogels is big, we still need to learn a fair amount about the interactions between the artificial substances and cells or natural tissue," said Dr Kirsten Borchers.
"Our biomolecule-based variants provide the cells with a natural environment instead, and therefore can promote the self-organising behaviour of the printed cells to form a functional tissue model," said Borchers.