Biomimetic model of a sponge-spicular optical fiber - mechanical properties and structure

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 mum. The spicules are composed of 2-10-mum-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.