Biological materials have attracted widespread interests because of their exceptional properties such as lightweight, high strength, high toughness, and high stiffness. For example, a combination of 95 wt% crystalline aragonite and 5 wt% protein in nacre of red abalone leads to several orders of improvement in fracture toughness than pure aragonite. Another widely used biological material, wood, also exhibits a remarkable combination of low density, high stiffness and high strength due to the multilayered structure in wood cell walls, which contain three components: crystalline cellulose microfibrils, amorphous hemicellulose, and lignin. Recent atomistic simulation implies that the amorphous/crystalline multilayered structure may play a key role in determining the superior properties of nacre and wood (figures as shown above).
