Bio-inspired material design and optimization

Natural materials such as bone, tooth, and nacre are nano-composites of proteins and minerals with superior stiffness and toughness. At the most elementary structure level, bio-composites exhibit a generic microstructure consisting of staggered mineral bricks wrapped by soft protein in nanoscale. Why does nature design building blocks of biological materials in this form? Can we reproduce this kind of structure from the structural optimization point of view? We believe that biological materials are designed with simultaneous optimization of stiffness and toughness for maximum structural support and flaw tolerance. With this philosophy, an optimization problem is formulated under the assumption of appropriate material constitutive models and failure criteria. It is shown that, within this optimization framework, the staggered microstructure of biological materials can be successfully reproduced at the nanometer length scale. This study may have at least partially provided an answer to the question whether the nanostructure of biological materials is an optimized structure and what is being optimized. The results suggest that we can draw lessons from the nature in designing nanoscale and hierarchically structured materials.