Contactless light-based structuring approaches such as two-photon-polymerization and laser patterning are long-lasting and steadily expanding fields of research. It allows creating of 3D submicron-sized structures with complex geometries such as undercuts. However, the contactless synthesis of bio-inspired materials with more than three levels of hierarchy would be beneficial, e.g. to obtain mechanical properties that can found in biological materials such as wood. One approach is to use and shape a suitable bio template that is already hierarchically structured and transferring it to an engineering material. Besides fungus, plant or animal tissue, extracellular bio-materials such as exopolysaccharides (EPS) produced by microbes possess such structuring.
To reach ideal conditions for photosynthesis, the red alga Porphyridium purpureum, and other microbes response to light irradiation with directional motion. This so-called phototaxis is accompanied by the excretion of EPS. Under specific illumination, microbes leave tracks of EPS that can be used as biological templates due to their internal hierarchical structure. Contactless light-guidance of the microbes allows to design the EPS-tracks and thus to build an external EPS-structure, which has been demonstrated in 2D-experimental setups. To attain 3D structures, vertical movement of the microbes in a medium with raised viscosity and 3D illumination is necessary. To realise this illumination, the use of a Spatial Light Modulator (SLM) is a possible approach in addition to classical holography. This offers the possibility of creating a dynamic holographic image, providing for image adjustment or layer-by-layer application. The irradiation of SLM results in a real image that can be observed trough a screen or the semitransparent culture medium of the microbes. In this medium, the microbes are expected to move vertically and horizontally to the brightest irradiation and replicate it with EPS.
The structured EPS will be transformed into a metallic or ceramic engineering material by precursors. By this contactless approach we aim at the synthesis of delicately chiselled ceramic or metallic components that feature the structure-derived characteristics of natural materials. An example is the reproduction of small bones such as the ossicle with its complex design and its internal hierarchical structure.