Nature's hierarchical materials

Many biological tissues, such as wood and bone, are fiber composites with a hierarchical structure. Their exceptional mechanical properties are believed to be due to a functional adaptation of the structure at all levels of hierarchy. This article reviews the basic principles involved in designing hierarchical biological materials, such as cellular and composite architectures, adapative growth and as well as remodeling. Some examples that are found to utilize these strategies include wood, bone, tendon, and glass sponges - all of which are discussed. (C) 2007 Elsevier Ltd. All rights reserved.