The Building Blocks of Life: Biological organisms are often limited in the resources that they can use to make structural materials. Primary building blocks may be weak or brittle materials, such as minerals and biopolymers, and processing conditions by default have to be mild. Despite this, a wide range of strong and tough structures exist, including shells, bones, quills, and fibers. Meyers et al. (p. 773 ) review a wide range of materials and architectures used in nature to make strong and tough materials and show how many of the design principles have also been used or are being considered for manmade materials and structures.

Eight structural elements in biological materials are identified as the most common amongst a variety of animal taxa. These are proposed as a new paradigm in the field of biological materials science as they can serve as a toolbox for rationalizing the complex mechanical behavior of structural biological materials and for systematizing the development of bioinspired designs for structural applications. They are employed to improve the mechanical properties, namely strength, wear resistance, stiffness, flexibility, fracture toughness, and energy absorption of different biological materials for a variety of functions (e.g., body support, joint movement, impact protection, weight reduction). The structural elements identified are: fibrous, helical, gradient, layered, tubular, cellular, suture, and overlapping. For each of the structural design elements, critical design parameters are presented along with constitutive equations with a focus on mechanical properties. Additionally, example organisms from varying biological classes are presented for each case to display the wide variety of environments where each of these elements is present. Examples of current bioinspired materials are also introduced for each element.