Polymer Brushes as Ionotropic Matrices for the Directed Fabrication of Microstructured Calcite Thin Films

摘要

Many biominerals are characterized by complex, hierarchically ordered structures.[1] In nature, the formation of biominerals is guided by matrix macromolecules. For example, acidic biomacromolecules play an important role in directing the mineralization of CaCO_3, one of the most abundant biominerals.[2] In addition to the three crystalline polymorphs, biogenic CaCO_3 also occurs in two amorphous modifications: a stable hydrated form and a less stable, essentially anhydrous form, which can act as a transient precursor of the thermodynamically stable crystalline modifications.[3], [4] The formation of various complex biogenic CaCO3 structures, such as sea urchin spines, has been proposed to proceed via the second, metastable amorphous-CaCO3 (ACC) phase.[5], [6] ACC has also been exploited as a transient precursor in vitro to produce CaCO_3 crystals in constrained geometries, to fabricate microstructured calcite single crystals, and to synthesize nacre-type laminated CaCO3 coatings.[7]-[9] The advantage of the transient ACC phase is that it can be more easily molded into complex structures than the crystalline CaCO3 polymorphs. The amorphous precursor route has also been used to prepare crystalline carbonate apatite films.[10] The application of such concepts to direct the size, shape, and microstructure of synthetic inorganic materials is of great technological importance and could lead to new materials with potential applications in, for example, optical information processing, catalysis, and regenerative medicine.[11]-[14] A convenient route for the fabrication of microstructured inorganic materials is the use of self-assembled monolayers (SAMs) to create 2D spatially constrained microenvironments for crystallization.[12], [14] In this case, crystallization is limited to those regions of the substrate that present the appropriate surface chemistry. Instead of relying on specific chemical surface modification, micrometer scale patterned ceramic thin films can also be prepared by imposing physical boundaries on the crystallization.[13] These boundaries can be achieved using a variety of soft lithography techniques, including, microtransfer molding, micromolding in capillaries, and embossing.