Small structures fabricated using ash-forming biological materials as templates

Different ash-forming biological materials such as gills of mushrooms, cotton wool, silk fiber, spider silk, dog's hair, and human hair were examined as templates to fabricate small structures. Ashes obtained from gills of mushrooms, silk fiber, and spider silk were miniaturized replicas of the original materials, whereas ashes from dog's hair and human hair were tubes. These materials were successfully coated with different inorganic materials by interface-selective sol-gel polymerization. Calcining coated materials yielded structures composed of ash and coated inorganic materials such as silica, titania, copper oxide, aluminum oxide, and iron oxide. Fully calcined ashes from native materials and materials coated with silica were usually 1/3 and 1/5 as large as their original materials, respectively. Silica-ash hybrid materials were much more rigid than ash materials. Incompletely calcined human hairs formed tubes with thick carbonized walls, and their inside morphologies suggested that medulla in human hairs might be responsible for tube formation. Preparation of complex tubular structures was possible as tied hairs did not break during calcination. Results in this study showed biological materials were useful as templates for fabricating inorganic structures regardless of ash formation.