Functional Graded Materials in Locomotion Biological Surfaces

Dear Colleagues,

Functionally graded materials (FGMs) represent a category of advanced materials that display deliberate gradation and variation in both their composition and structure in relation to calibrated changes in their volume. Variation with respect to volume reflects the properties of the material and how they vary within a given domain of interest. Notably, the term material properties is not confined to traditional traits (i.e., mechanical, thermal, and physical properties). Rather, the term extends to accommodate changes in shape in response to external conditions (i.e., shape morphing). Property gradations within FGMs may be purposely induced to manifest preconceived behavioral paths in response to specific conditions.

Variation in the functional performance of FGMs depends on custom engineering of their microstructural phases. Multi-functional aspects of this class of advanced materials can therefore be implemented by inducing smooth transitions between constituent phases. Introducing such smooth transitions allows for implementing a broad domain of functional grading that meets a wide spectrum of targeted applications (e.g., targeted response to particular stimuli, such as in applications of 4D printing). They may also entail targeted by-design behavioral paths in response to shocks (mechanical, thermal, and electric). Additionally, they may also include targeted responses to thermal loads (e.g., controlled expansion, and relaxation of thermal stresses).

Currently, within the manufacturing realm, complete formulation of the exact logic of linking material properties to the desired functional response is still evolving. The relationship between the gradation of properties and desired behavior is, however, advanced in biological entities. This is especially obvious in the interaction of surface and subsurface structures during locomotion, among other examples.

Biological surfaces represent an active layer that communicates between the species and its surrounding environmental performance constraints. Surfaces in biology exchange information, accommodate functions, and contribute to the economy of effort. They also contribute to the prevention of injury, thus contributing to the survival of the species. A major contribution to the optimization of surface function in biology originates from the customization of material layers (geometry, order, and properties). This leads to optimizing the interchange between a biological system and its habitat through the tailored response of surface–subsurface materials to environmental constraints.

This Special Issue of Biomimetics aims at exploring the details of functional grading in surface–subsurface structures in biological systems. The material to be included aims to explore the building blocks of the relationship between property gradation and the dynamic response of locomotion surface systems within the biological realm. Examples of topics to be covered include (but are not limited to):

• Structural aspects of surface–subsurface systems in locomotion assemblies in biological species;
• Dynamic behavior and response of surfaces assemblies in locomotion-stress accommodation, thermal control, etc.;
• Micro-structural aspects of surface–subsurface biological materials;
• Modeling of the dynamic behavior of surfaces in relation to material micro-structure;
• Effect of surface metrological features on dynamic behavior during locomotion (e.g., accommodation of contact stresses, friction behavior, energy optimization, etc.);
• Relation between property gradients and tribological behavior;
• Bio-inspired FGM systems.

Prof. Dr. Hisham A. Abdel-Aal
Guest Editor

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• functional graded materials
• biological surfaces
• bio-inspired FGM systems