It sounds dystopian: as the world runs out of coral, scientists 3D print imitations. However, the purpose isn't to fool tourists but to grow algae biofuels, addressing a major cause of coral loss and improving our understanding of natural reefs in the process.
Tropical corals depend on a symbiotic relationship with photosynthesizing microalgae that feed them sugars, and their shapes are adapted to increase the amount of algae they can support. Nevertheless, Dr Daniel Wangpraseurt of Cambridge University found this is one area nature can be improved upon.
"Corals are one of the most efficient organisms at using, capturing and converting light to generate energy. And they do so in extreme environments, where light is highly fluctuating and there's limited space to grow,” Wangpraseurt said in a statement.
Wangpraseurt wants to maximize the growth of the microalgae Marinichlorella kaistiae, which produces fatty acids suitable for use as biofuels. He scanned fast-growing Pocilloporidae corals to learn their structure and used this to create instructions for 3D printing surfaces formed of tiny cuplike shapes. These features’ width makes them perfect to hold onto light of blue to orange wavelengths, maximizing the chance each photon will be captured by an algal cell.
"We developed an artificial coral tissue and skeleton with a combination of polymer gels and hydrogels doped with cellulose nanomaterials to mimic the optical properties of living corals," said team leader Dr Silvia Vignolini, also of Cambridge.
However, the Marinichlorella die quickly when separated from the medium in which they are cultured and Wangpraseurt found traditional manufacturing techniques are too slow. Professor Shaochen Chen of the University of California, San Diego, was able to offer a 3D bioprinting technology swift enough to keep the algal cells alive while the artificial corals were printed.
Wangpraseurt and Chen found they could make imitation corals that scatter light more efficiently than the real thing, offering the algae living on the surface the maximum energy with which to grow. The results are described in Nature Communications.
Besides outdoing natural corals' light scattering, the authors claim they have created an environment in which microalgae grow 100 times faster than liquid growth mediums, packing 800 million cells into a milliliter of hydrogel – 10 times more than has been achieved in flasks.
At the moment, the team lack the capacity to scale their printing up to compete with commercial algal production. As 3D printing develops, however, the authors think their bionic structures could be ideal for growing algae where space is short, including on spaceflights or in urban environments.
The team also grew symbiotic algae from real reefs on their structures and hope that by removing some of the complexity of living coral, they will improve understanding of the relationship, which may assist reef protection and repair.