Morphology and mechanical behavior of diatoms in wet and dry states studied using nano-XCT

Background: Diatoms are widely studied biological objects because of their large variety of geometric shapes and their unique physical and chemical properties. They survive widely in nature within moisture. Imaging the diatoms three dimensionally in moisture and correlating their mechanical behavior is an interesting and challenging topic. Results: Here, the morphology and mechanical properties of diatoms were studied in wet state and then in dry state. A customized sample holder was integrated into a laboratory transmission X-ray microscope to image the morphology changes and volume shrinkage of the diatom while transitioning from the wet to the dry state. The measured volume shrinkage of a single diatom cell of Actinocyclus sp. is about 0.16. By performing an in-situ micromechanical experiment in both states, the maximal loading force of a single Actinocyclus sp. was determined until cracking appeared and compared in both states. This value is in the range of several hundred µN in the wet state and single-digit mN in the dry state. The normalized stiffness of the studied diatoms is significantly higher in the dry state than in the wet state. 2D radiograph and 3D tomography imaging of the diatoms reveal the different locations for crack propagation in both states. Conclusions: Our study supplies the important imaging method, the structure and functional information of the diatoms for future studies on diatoms in moisture but also in dry state. This information can help design bio-inspired materials and even in the development of bio-sustainable materials.