Biomimetic Processing of Gel Glasses and Organic-Inorganic Hybrids

Biological hard tissues like bone and shell show combinations of strength and toughness that are hard to duplicate with synthetic materials. These properties are attained by a composite of organic and inorganic phases with very organized microstructures. The structures are hierarchical in that several different scales of organization contribute to the final properties.Biological systems form by chemical precipitation at room temperature in contrast to synthetic processing, which usually depends on thermal solidification. In principle, chemical solidification can give much more control over composition and structure but is limited by the time taken for diffusion processes in any solid component.A family of solid freeform fabrication methods have recently been developed which allow parts to be built under the direct control of a 3-dimensional CAD drawing without the need for a mold. These methods also offer a way of building composite structures, with full control of structure and composition at the scale of 100 m and up. Since this is a layerwise process, like biological growth, diffusion paths are short and so chemical processing of large parts is feasible.We have been developing an SFF system based on extrusion of a reactive slurry through a 300 m needle. The needle is moved on three axes so as to build up a part. The application of this method to the formation of components from sol-gel glasses and organic-inorganic hybrids is described.