Advances that have been made in understanding the mechanisms underlying the mechanical behavior of a number of biological materials (namely mollusk shells and sponge spicules) are discussed here. Attempts at biomimicry of the structure of a nacreous layer of a mollusk shell have shown reasonable success. However, they have revealed additional issues that must be addressed if new synthetic composite materials that are based on natural systems are to be constructed. Some of the important advantages and limitations of copying from nature are also described here.

No abstract

Nanomechanical properties, nanohardness and elastic modulus, of an Antarctic sponge Rosella racovitzea were determined by using a vertical indentation system attached to an atomic force microscope. The Rosella spicules, known to have optical waveguide properties, are 10–20 cm long with a circular cross section of diameter 200–600 μm. The spicules are composed of 2–10-μm-thick layers of siliceous material that has no detectable crystallinity. Measurements through the thickness of the spicules indicated uniform properties regardless of layering. Both the elastic modulus and nanohardness values of the spicules are about half of that of either fused silica or commercial glass optical fibers. The fracture strength and fracture energy of the spicules, determined by 3-point bend tests, are several times those of silica rods of similar diameter. These sponge spicules are highly flexible and tough possibly because of their layered structure and hydrated nature of the silica. The spicules offer bioinspired lessons for potential biomimetic design of optical fibers with long-term durability that could potentially be fabricated at room temperature in aqueous solutions.

No abstract

ABSTRACT--Biological hard tissues are composites of inorganics and biopolymers, and, therefore, represent hybrid systems. The inorganic components may be oxides (e.g., SiO2, Fe304), carbonates (e.g., CaCO3) sulfides (e.g., FeS, CdS), or others, mostly in crystalline forms but also occasionally in glassy forms. The biopolymer is often proteinaceous, but can also involve lipids and especially polysaccharides (e.g., chitin). These hybrid materials can be found in single celled organisms (such as bacteria and protozoa), invertebrates (such as mollusks), insects (such as beetles), and vertebrates (such as mammals). A common denominator of all hard tissues is that they are hierarchically structured from the nanometer scale to the microscale and the macroscale. It is these controlled structures that give biological hard tissues their unique and highly evolved functional properties. The engineering properties include mechanical, piezoelectric, optical, and magnetic. The hard tissues can be in the form of nanoparticles, spines, spicules, skeletons, and shells. The objective of this paper is to demonstrate mechanical aspects of some of these hard tissues, to discuss their structure-function relationships (with examples from the literature as well as from our research), and to reveal their potential utility in materials science and engineering applications.