Structural Design Elements in Biological Materials: Application to Bioinspiration

Abstract

biological materials often presents similar solutions, since the number of materials available in nature is fairly limited and therefore resourceful combinations of them have to be developed to address specifi c environmental constraints. We have identifi ed these common designs and named them "structural design elements."In the emerging fi eld of biological materials science, there is a great need for systematizing these observations and to describe the underlying mechanics principles in a unifi ed manner. This is necessary as similar designs are often reported under various names. As an example, the presence of numerous interfaces within a composite that introduce a signifi cant property mismatch, which we suggest be named a "layered" structure, has been previously referred to as "lamella" in bone [ 2 ] and fi sh scales, [ 3 ] "brick and mortar" in abalone, [4][5][6] and a "laminated structure" in sea sponges [ 7 ] despite providing most if not all of the same structural advantages. We propose herein a new system of eight structural design elements that are most common amongst a wide variety of animal taxa. These structural elements have each evolved to improve the mechanical properties, namely strength, stiffness, fl exibility, fracture toughness, wear resistance, and energy absorption of different biological materials for specifi c multi-functions (e.g., body support, joint movement, impact protection, mobility, weight reduction). These structural design elements are visually displayed in Figure 1 : • Fibrous structures; offering high tensile strength when aligned in a single direction, with limited to nil compressive strength.• Helical structures; common to fi brous or composite materials, offering toughness in multiple directions and in-plane isotropy.• Gradient structures; materials and interfaces that accommodate property mismatch (e.g., elastic modulus) through a gradual transition in order to avoid interfacial mismatch stress buildup, resulting in an increased toughness.• Layered structures; complex composites that increase the toughness of (most commonly) brittle materials through the introduction of interfaces.• Tubular structures; organized porosity that allows for energy absorption and crack defl ection.• Cellular structures; lightweight porous or foam architectures that provide directed stress distribution and energy absorption.Eight structural elements in biological materials are identifi ed as the most common amongst a variety of animal taxa. These are proposed as a new paradigm in the fi eld 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, fl exibility, fracture toughness, and energy absorption of different biological materials for a variety of functions (e.g., body support, joint movement, impact protection, ...

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