Algae used to give bioprinted tissue an oxygenated boost
One of the challenges in 3D printing biological tissue lies in the fact that the cells may die before oxygen-delivering blood vessels grow into the material. Harvard scientists are addressing that issue, by adding algae to the mix.
Led by Asst. Prof. Y. Shrike Zhang, the researchers started by encapsulating photosynthetic Chlamydomonas reinhardtii algae within a cellulose-based bioink. Both the algae-laden bioink and human-liver-derived cells were then extruded from a needle into a 3D hydrogel matrix. They were deposited in honeycomb-shaped patterns, similar to the lobule structures that make up the liver.
Exposed to light, the algae proceeded to produce oxygen, keeping the cells alive and even prompting them to reproduce and produce liver-specific proteins. At the same time, carbon dioxide released by the cells allowed the algae to thrive.
Once the cells had grown and "taken over" to a sufficient point, the bioink (including the algae within it) was removed by introducing an enzyme known as cellulase. This left empty microchannels where the bioink had been, which were subsequently filled with human vascular cells. As a result, those channels formed into blood vessels.
It is hoped that once developed further, the technology could ultimately allow human biological tissue to be produced for purposes such as research and drug testing, or even for the replacement of organs or other body parts.
"Development of such a fugitive bioink that allows initial oxygenation and subsequent vessel formation within a single tissue construct has not been reported before," says Zhang. "This a critical step toward successful engineering of viable and functional tissues."
A paper on the research was recently published in the journal Matter.