Steffi Deuerling, Sabine Kugler, Moritz Klotz, Cordt Zollfrank and Daniel Van Opdenbosch*
Deriving materials functionalities from structuring is a concept widely encountered in living nature. Living organisms are forced to create function from a hierarchical organization that balances several functional requirements. Among these requirements are the static and dynamic mechanical properties, but also active or passive actuation, and the manipulation of light and sound waves. Creating functional materials based on hierarchical structuring is therefore a generally bio-inspired approach. However, several techniques can be employed: They range from approaches not related to living nature at all, i.e. creating structural hierarchy via multiscale self-assembly, or combined bottom-up and top-down approaches. The opposite is the biotemplating technique, when carried out with nanometer-scale precision, where a biological structure is directly transformed to an engineering material.
Transferring selected structural features from biological materials to technical materials, i.e. metals or ceramics, is a well-established method. Examples range from nanoscopic structures such as tobacco mosaic viruses over microscopic structures such as photonic cuticular scales in insects to macroscale structures such as wood. The concept of transferring the entire hierarchical structure of a biological material to a technical one is, however, an accomplishment of the last decade. Materials with a multiscale hierarchical organization starting on the nanometer scale provide functionalities that are dependent on structure rather than atomic composition.
We are currently investigating a combined approach wherein hierarchical biological materials are structured on larger length scales via a contact-free method: By guiding phototactic microorganisms that excrete exopolysaccharide (EPS) with either spot- or holographic illumination, we are creating structures on length scales above the internal structuring sizes of the EPS hydrogels, which range from nanometers to the submicron size regime. In a second step, material precursors are deposited on and within the EPS to create metallic or ceramic materials which we expect can be readily purified by template removal.