Structural and mechanical evolution of Tridacna gigas during permineralization

Mollusk shells have highly complex hierarchical structures and unique mechanical properties, which have been widely studied, especially in fresh shells. However, few studies have revealed differences in the structure-property correlations of shells during the permineralization process, which occurs after organism death. To better understand the effect of permineralization on the microstructure and mechanical properties of shells, this study investigated and compared the compositions, microstructures, and mechanical properties of Tridacna gigas and permineralized J-Tridacna gigas. The results showed that permineralized J-Tridacna gigas possessed coarsened aragonite minerals, less anisotropy and organic matter, and higher hardness and strength than Tridacna gigas. The toughening mechanisms of Tridacna gigas, including crack deflection, aragonite platelet pull-out, and mineral bridges, were discovered during Vickers hardness tests. Moreover, the permineralization mechanism comprised three main steps: organic matter dissolution, aragonite plate compaction, and recrystallization. This work further elaborates the permineralization mechanism, which can help increase the crystal size and improve the strength and hardness of materials. Moreover, this study provides valuable insights into the design of bioinspired advanced materials with outstanding hardness and strength.