Flaw tolerant bulk and surface nanostructures of biological systems

Bone-like biological materials have achieved superior mechanical properties through hierarchical composite structures of mineral and protein. Gecko and many insects have evolved hierarchical surface structures to achieve superior adhesion capabilities. We show that the nanometer scale plays a key role in allowing these biological systems to achieve such properties, and suggest that the principle of flaw tolerance may have had an overarching influence on the evolution of the bulk nanostructure of bone-like materials and the surface nanostructure of gecko-like animal species. We demonstrate that the nanoscale sizes allow the mineral nanoparticles in bone to achieve optimum fracture strength and the spatula nanoprotrusions in Gecko to achieve optimum adhesion strength. Strength optimization is achieved by restricting the relevant dimension to nanometer scale so that crack-like flaws do not propagate to break the desired structural link. Continuum and atomistic modeling have been conducted to verify this concept.