Prof. Dr. Joachim P. Spatz

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Cell Biology . Material Sciences . Structural Biology

Anti-Reflection Coating like a Moth’s Eye

Living tissues possess a wealth of properties that materials scientists find fascinating – for instance, their ability to heal injuries. “With the human body, biology created a prototype that can do much more, from a materials science perspective, than we can currently achieve in our synthetic world,” explains the biophysicist. It is thus one of his dreams to employ living cells to create new, “biohybrid” materials. Such materials may be capable of regeneration. Today, research into these kinds of self-healing materials is dominated by fairly non-biological strategies, such as synthetic materials containing liquid adhesive components for cementing micro-cracks.

Joachim Spatz (right and Ralf Kemkemer, head of the Central Scientific Facility for Biomaterials, discuss how to produce intelligent materials following natural design principles. Zoom Image
Joachim Spatz (right and Ralf Kemkemer, head of the Central Scientific Facility for Biomaterials, discuss how to produce intelligent materials following natural design principles. [less]

Yet living organisms are much smarter when they have to repair injuries or need to adapt autonomously to stress. With their complex, extremely variable genetic programs, they are able to react much more flexibly to their environment than dead matter can. If it were to become possible to exploit this special biological quality to develop materials, such materials could be equipped with a completely new set of properties.

Spatz sketches out his future dream of using synthetic moth-eye structures. His team came up with this invention together with Robert Brunner from Carl Zeiss AG in Jena. One of the things that enable moths to see in the dark is a clever anti-reflection coating. On the surfaces of their multi-faceted eyes, tiny protuberances are lined up side by side like pillars. When the light hits them, they transmit the electromagnetic waves almost without loss from the optically thin air to the optically denser chitin of the lenses. On a completely smooth surface, however, such as window glass, the light comes up against an abrupt change in the material’s properties. As a result, it is partially reflected, with about 4 percent of the light being lost in the case of window panes. Moths’ eyes, on the other hand, collect almost all of the light that hits them.

The scientists in Stuttgart are experts at making these kinds of nano­structures. They developed a method that creates artificial nano-pillars on glass surfaces. These surfaces work like moths’ eyes and are more efficient than the established anti-reflection coatings on glasses, lenses and monitors. From a technical perspective, the synthetic structure of the material is in many ways superior to a real moth’s eye. “Glass can withstand higher temperatures, for example,” says Spatz. But as soon as the finely structured surface is damaged, the glass cannot repair itself. This is where bionics or biomimetics – that is, mimicking nature’s tricks through technology – reaches its limits. Hence, Joachim Spatz’s dream for the future goes much further than this. The question he wants to answer is: “Can we make living cells deposit these kinds of structures onto synthetic surfaces such as glass, and even repair specific damage there?”

This bold vision is one of the central themes in this biophysicist’s research work: “It’s all about integrating biological functions into synthetic materials.” The conceivable areas in which this concept could be applied are incredibly diverse. They range from synthetic yet biologically compatible “spare parts” for the body in a medical setting to biominerals that are as hard as tooth enamel or as tough as bones, and even to brand new magnetic materials. It may also be possible to make regenerative batteries that generate electricity with the help of microorganisms and a nutrient solution, without ever running out of power. What all applications have in common is their origin: scientists plan to make them in the biofactories of real, living cells. From magnetobacteria to mammalian cells, the researchers have a truly infinite choice of nature’s potential material-makers at their fingertips.

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