Structure-property relationships in Arapaima Gigas scales revealed by nanoindentation tests

Fish scales from Arapaima Gigas have been studied in terms of their structure (morphology, collagen content) and mechanical properties. A strong mechanical gradient was revealed in the scale, hardness and reduced modulus being reduced by a factor of three. Correlations between the hardness and reduced modulus and the mineral content have been found. The external mineral rich layers were determined to be hard and stiff while the inner surface, being collagen rich, was less hard and less stiff. The inside of the scales showed a progressive decrease of mechanical properties, with variations attributed to the plywood-like structure of the scale.