Synthetic nacre by predesigned matrix-directed mineralization

Abstract

Although biomimetic designs are expected to play a key role in exploring future structural materials, facile fabrication of bulk biomimetic materials under ambient conditions remains a major challenge. Here, we describe a mesoscale "assembly-and-mineralization" approach inspired by the natural process in mollusks to fabricate bulk synthetic nacre that highly resembles both the chemical composition and the hierarchical structure of natural nacre. The milfimeter·thick synthetic nacre consists of alternating organic layers and aragonite platelet layers (91 weight percent) and exhibits good ultimate strength and fracture toughness. This predesigned matrix-directed mineralization method represents a rational strategy for the preparation of robust composite materials with hierarchically ordered structures, where various constituents are adaptable, including brittle and heat-labile materials. Biological materials are built from limited components, but their mechanical perfor mances, such as strength and toughness, are far beyond their artificial counterparts. The secret of success is their hierarchically ordered structure at multiscale levels (1 4). The most studied model among these biological rna terials is the nacreous part in some mollusk shells that oonsists of about 95 weight% (wt %) of brittle aragonitic Ca00 3 and 5 wt% of organic materials (5). Mollusks produce nacre by first generating several layers of insoluble 13 chitin matrix filled with silk fibroin gel (6). Then aragonite cores form on the surface of the matrix at the nuclea tion sites (7), followed by lateral growth in the confined space of adjacent organic layers, which finally leads to a V<.ronoi ~ (5). These arago nite platelets, despite their single crystal diffraction pattern, are not perfett single crystals but essen tially cmsist of nanograins with the same aystal lographic orientation (mesocrystals), whereby the platelets are not as fragile as perfect single crys ta1s (8). The mature nacre bas a "brick and mortar" microstructure where aragonite platelet layers are bound by an organic matrix (3). Through a number of such structural designs and toughening mech anisms at muhiscale levels (2, 9, 10), nacre ream ciles its toughness and strength, which are mutually exclusive in most artificial materials (11).In contrast to biological materials, the evolu tion of synthetic structural materials bas been achieved predominately by developing new syn thetic compounds rather than optimizing the micro/nanostructures of existing materials. (Fig. 1, A and B, and fig. Sl), a chitosan matrix with predesigned laminated structure is fubricated ( fig. S2, A, B, D, and E). Then the matrix is acetylated (Fig.lC) and transformed to 13 chitin to avoid unwanted swelling or dissolution ( fig. S2, C and E, and table Sl). The acetylated matrix is mineralized in a peristaltic pump driven circula tory system via the decomposition of Ca(H00 3 )z in the presence of polyacrylic acid (P AA) and M~· (Flg. lD). Then the final material is obtained by silk fibroin infiltration and...

High‐Performance Nanocomposites Inspired by Nature

“…For example, the synthetic nacre based on ice templating and mineralization described in this paper simulated the bioprocess, resulting in an architecture highly similar to that of natural nacre. [17] Magnetically assisted techniques, such as MASC and MM-3D printing, enable the designed orientation of building blocks to build more complex architectures mimicking lobster cuticle or compact bone. These techniques mainly focus on the construction of hierarchical architectures by mimicking the exterior structures and biological process, resulting in ceramic or ceramic-polymer nanocomposites with outstanding crack resistance or damage tolerance.…”

“…[16] Copyright 2015, American Chemical Society; Ceramic-based nanocomposite SEM image: reproduced with permission. [17] Copyright 2016, The American Association for the Advancement of Science; and Anisotropic hydrogel image: reproduced with permission. [18] Copyright 2012, Wiley-VCH.…”

“…Recently, Mao et al [17] demonstrated a synthetic nacre via ice templating and mineralization. As illustrated in Figure 4A, [54] a chitosan (CS) solution was frozen to generate a laminated [12] Copyright 2010, Nature Publishing Group.…”

“…The synthetic nacre demonstrated a laminated architecture, and the volume fraction of inorganic component was much higher than that of natural nacre. [17,54] Ice templating demonstrates a highly effective technique to design nanocomposites that mimic natural nacre's layered structure and interface interactions. Mao et al's approach demonstrates a roadmap for future research, from mimicking natural nacre's architecture to simulating its bioprocess, resulting in synthetic nacre highly similar to natural nacre.…”

“…Reproduced with permission. [17] Copyright 2016, The American Association for the Advancement of Science.…”