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

Nanomechanical properties, nanohardness and elastic modulus, of an Antarcti c 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 cr oss section of diameter 200-600 mum. The spicules are composed of 2-10-mum- thick layers of siliceous material that has no detectable crystallinity. Me asurements through the thickness of the spicules indicated uniform properti es regardless of layering. Both the elastic modulus and nanohardness values of the spicules are about half of that of either fused silica or commercia l glass optical fibers. The fracture strength and fracture energy of the sp icules, determined by 3-point bend tests, are several times those of silica rods of similar diameter. These sponge spicules are highly flexible and to ugh possibly because of their layered structure and hydrated nature of the silica. The spicules offer bioinspired lessons for potential biomimetic des ign of optical fibers with long-term durability that could potentially be f abricated at room temperature in aqueous solutions.