Structural Orientation and Anisotropy in Biological Materials: Functional Designs and Mechanics

TLDR

Biological materials are anisotropic because their constituents are anisometric and preferentially aligned, and this regulation of structural orientation underlies natural material designs that inspire engineered materials. The study revisits how structural orientation and anisotropy are engineered in biological materials to achieve diverse functions, and discusses the potential and challenges of translating these designs into synthetic systems. Using a 2D composite model of wood and bone, the authors illustrate how anisotropic architectures influence mechanical properties and enable extrinsic toughening, adhesion, programmable response, damage resistance, and simultaneous optimization through adaptive reorientation. The work highlights mechanics and design principles that can be replicated in man‑made materials, showing that translating these biological strategies can yield synthetic materials with unprecedented properties and functionalities.

Abstract

Abstract Biological materials exhibit anisotropic characteristics because of the anisometric nature of their constituents and their preferred alignment within interfacial matrices. The regulation of structural orientations is the basis for material designs in nature and may offer inspiration for man‐made materials. Here, how structural orientation and anisotropy are designed into biological materials to achieve diverse functionalities is revisited. The orientation dependencies of differing mechanical properties are introduced based on a 2D composite model with wood and bone as examples; as such, anisotropic architectures and their roles in property optimization in biological systems are elucidated. Biological structural orientations are designed to achieve extrinsic toughening via complicated cracking paths, robust and releasable adhesion from anisotropic contact, programmable dynamic response by controlled expansion, enhanced contact damage resistance from varying orientations, and simultaneous optimization of multiple properties by adaptive structural reorientation. The underlying mechanics and material‐design principles that could be reproduced in man‐made systems are highlighted. Finally, the potential and challenges in developing a better understanding to implement such natural designs of structural orientation and anisotropy are discussed in light of current advances. The translation of these biological design principles can promote the creation of new synthetic materials with unprecedented properties and functionalities.