Chemical, Mechanical and Structural Analysis of Evechinus chloroticus Sea Urchin Tooth

Abstract

There has been a continuous effort to understand the properties of biomaterials, especially those benefiting to the field of materials engineering. Sea urchin teeth are one of the most intriguing materials that possess the ability to self-sharpen, a feature that will surely contribute to the production of ever-sharp knifes and tools. This self-sharpening ability enables sea urchins to drill and bore through rocks that are similar in chemical composition to their teeth for food, shelter and protection. The current study is therefore based on validating present studies as well as establishing a relationship between the mechanical, structural and chemical property of sea urchin teeth. The feeding mechanism of sea urchins was examined by placing three live urchins in a tank with spirulina substrate painted on glass slides as food sources. The teeth were then extracted and analysed using a Nikon AZ100 microscope before being mounted for nanoindentation, environmental scanning electron microscopy (ESEM) and energydispersive X-ray spectroscopy (EDX) purposes. There was a total of five teeth examined using the microscope and a total of four sets (20 teeth) tested using nanoindentation, ESEM and EDX. It was found that sea urchins utilise the very tip of their teeth (chewing tip/working end of the tooth) as the primary zone for scraping against the spirulina substrate. The microscopic images further established the self-sharpening methodology for the tip of the tooth which involves shedding of softer materials surrounding the centre stone part with the highest hardness. The teeth can sharpen continuously without fracturing or ever becoming dull and it is precisely this mechanism that allows sea urchin teeth to possess such phenomenal functionality. In addition, these teeth are unique in which the growth and decay occur simultaneously and it was also found that hardness, modulus and magnesium concentration all increased towards the growing end of the teeth. Finally, the study confirmed that the mechanical property of sea urchin teeth is largely contributed to the high magnesium concentration present as well as the dispersion of nanoparticles in the stone part structure.