Multiscale structure of nacre biomaterial: Thermomechanical behavior and wear processes

Sheet nacre is a hybrid biocomposite with a multiscale structure, including nanograins of CaCO₃ (97% wt% - 40 nm in size) and two organic matrices: (i) the interlamellar mainly composed of β-chitin and proteins, and (ii) the intracrystalline composed by silk-fibroin-like proteins. This material is currently contemplated for the manufacture of small prostheses (e.g., rachis and dorsal vertebra prostheses) which are subjected to micro-slip or fretting motion. In this work, the tribological behavior of nacre is studied by varying the frictional dissipated power from few nW to several hundred mW, in order to assess the various responses of the different nacre's components, independently. Results reveal various dissipative mechanisms vs. dissipated frictional power: organic thin film lubrication, tablet's elastoplastic deformations, stick-slip phenomenon and/or multiscale wear processes, including various thermo-mechanical processes (i.e., mineral phase transformation, organics melting and friction-induced nanoshocks process on a large range). All these mechanisms are controlled by the multiscale and anisotropy of its structure - and especially by its both matrices and respective orientation vs. the sliding direction.