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Crystal Growing Kit
For single crystals to remain intact, there is a limit to the size and number of defects that can be included before the underlying lattice is destroyed. Biological crystals, however, are known to include large macromolecules. H. Li et al. (p. 1244; see the Perspective by Hollingsworth) used electron tomography to study the crystallization of calcium carbonate inside an agarose gel, observing that the crystals physically entrapped the agarose macromolecules. To accommodate the curvature induced by the polymer chains, both high- and low-energy facets formed at the fiber-crystal interfaces. Thus, physical interactions alone may be sufficient for the incorporation of macromolecules in biological crystals and it may be possible to grow unusually shaped single crystals.
Single crystals are usually faceted solids with homogeneous chemical compositions. Biogenic and synthetic calcite single crystals, however, have been found to incorporate macromolecules, spurring investigations of how large molecules are distributed within the crystals without substantially disrupting the crystalline lattice. Here, electron tomography reveals how random, three-dimensional networks of agarose nanofibers are incorporated into single crystals of synthetic calcite by allowing both high- and low-energy fiber/crystal interface facets to satisfy network curvatures. These results suggest that physical entrapment of polymer aggregates is a viable mechanism by which macromolecules can become incorporated inside inorganic single crystals. As such, this work has implications for understanding the structure and formation of biominerals as well as toward the development of new high–surface area, single-crystal composite materials.
↵* These authors contributed equally to this work.