Bioinspired Nanonetwork Hydroxyapatite from Block Copolymer Templated Synthesis for Mechanical Metamaterials.

Inspired by Mantis shrimp, this work aims to suggest a bottom-up approach for the fabrication of nanonetwork hydroxyapatite (HAp) thin film using self-assembled polystyrene--polydimethylsiloxane (PS--PDMS) block copolymer (BCP) with a diamond nanostructure as a template for templated sol-gel reaction. By introducing poly(vinylpyrrolidone) (PVP) into precursors of calcium nitrate tetrahydrate and triethyl phosphite, which limits the growth of forming HAp nanoparticles, well-ordered nanonetwork HAp thin film can be fabricated. Based on nanoindentation results, the well-ordered nanonetwork HAp shows high energy dissipation compared to the intrinsic HAp. Moreover, the uniaxial microcompression test for the nanonetwork HAp shows high energy absorption per volume and high compression strength, outperforming many cellular materials due to the topologic effect of the well-ordered network at the nanoscale. This work highlights the potential of exploiting BCP templated synthesis to fabricate ionic solid materials with a well-ordered nanonetwork monolith, giving rise to the brittle-to-ductile transition, and thus appealing mechanical properties with the character of mechanical metamaterials.