Preliminary Study On Tribological Behavior And Self-Repairing Mechanism Of Three Kinds Of Hard Tissue Of Biological Materials

As the three typical biological hard tissues, the fingernails, chicken claw and teeth are chosen to investigate their tribology properties and the self-healing of damages under water in this paper. Both the fingernails and chicken claw are keratin materials, which are briefly served protection, search and clutch. Teeth are the hardest tissue in human body, which are used for chewing and laniating food. Moreover, water played an important role in the self-healing of these tissues. Therefore, it is essential to research the microstructures, tribological properties and the effect of water on the self-healing of these biological materials. The results will not only enrich the biotribological theory, but also provide useful guide for designing the biomimetic composite materials.Because of their similar compositions and functions, fingernails and chicken claw were comparably studied in this paper. With a scanning electron microscopy and energy-dispersive X-ray spectroscopy, the microstructure and component of two kinds of materials were characterized. After that, the tribological behaviors and deformation recovery of fingernails and chicken claws were investigated by nano-indentation/scratch tester and Vickers hardness instrument, respectively. Finally, using NHT/NST and atomic force microscope, the micro-tribological properties of enamel and the recovery of surface damage were preliminarily investigated. The main conclusions of the research can be summarized as following:1. The tribological properties and self-repairing capability of keratin tissues are strongly depended on their microstructures. Because of the better fiber orientation, the friction coefficient on fingernail is a little lower than that on chicken claws at the same loading conditions. On the cross section of nail, even though the friction coefficient during scratching in the direction perpendicular to fibers was greater than that parallel to fibers, the residual scratch width was smaller. Moreover, due to the different structures and properties between the inner and outer of claw, the latter presented higher friction coefficient and smaller scratch width.2. Water plays a very important role in the recovery of surface damage of finger nails and chicken claw. Both the indentation and scratch deformation of nail and claw can be fully recovered after being immersed in water for5minutes and30minutes, respectively.3. Both scratching and indentation on the enamel surface can induce the occurrence of grain refinement phenomenon. With the increase in the contact pressure, the hydroxyapatite grains in enamel are crushed and the stable particles with diameter of20run are obtained.4. The recovery process of indentation deformation on enamel surface in artificial saliva may be divided into two steps. Firstly, the hydroxyapatite can aggregate together in water, which can help the small enamel grains grow up. Secondly, the irons (e.g. Ca, P, and so on) in artificial saliva deposit on the deformation area during the mineralization treatment process, which induces the further growing of the enamel grains.