Forming Anisotropic Crystal Composites: Assessing the Mechanical Translation of Gel Network Anisotropy to Calcite Crystal Form

Abstract

The promise of crystal composites with direction-specific properties is an attractive prospect for diverse applications; however, synthetic strategies for realizing such composites remain elusive. Here, we demonstrate that anisotropic agarose gel networks can mechanically “mold” calcite crystal growth, yielding anisotropically structured, single-crystal composites. Drying and rehydration of agarose gel films result in the affine deformation of their fibrous networks to yield fiber alignment parallel to the drying plane. Precipitation of calcium carbonate within these anisotropic networks results in the formation of calcite crystal composite disks oriented parallel to the fibers. The morphology of the disks, revealed by nanocomputed tomography imaging, evolves with time and can be described by linear-elastic fracture mechanics theory, which depends on the ratio between the length of the crystal and the elastoadhesive length of the gel. Precipitation of calcite in uniaxially deformed agarose gel cylinders results in the formation of rice-grain-shaped crystals, suggesting the broad applicability of the approach. These results demonstrate how the anisotropy of compliant networks can translate into the desired crystal composite morphologies. This work highlights the important role organic matrices can play in mechanically “molding” biominerals and provides an exciting platform for fabricating crystal composites with direction-specific and emergent functional properties.

Exploiting and controlling gel-to-crystal transitions in multicomponent supramolecular gels

“…We have shown that the use of a magnetic field results in the alignment of the self-assembled structures formed by one of the gelators growing faster in one axis as compared to in the absence of the field. Drying of agarose gels has been shown elsewhere to be able to lead to a change in the shape of crystals grown in the network; 43 our work here opens up opportunities that do not require drying and for crystallization in multicomponent systems and could also be applicable to non-gelling components. We anticipate therefore that this will be of utility in many areas.…”

“…We have shown that the use of a magnetic field results in the alignment of the self-assembled structures formed by one of the gelators growing faster in one axis as compared to in the absence of the field. Drying of agarose gels has been shown elsewhere to be able to lead to a change in the shape of crystals grown in the network; 43 our work here opens up opportunities that do not…”

Complex morphologies of biogenic crystals emerge from anisotropic growth of symmetry-related facets

“…ontrol over nanoscale morphologies of crystalline materials is connected to their physical properties and thus their potential applications (1)(2)(3). However, the inherent thermodynamic properties of the crystalline lattice dictate a strong tendency toward specific low-energy facets, resulting in characteristic shapes (habits) (4).…”

Incorporating polymers within a single‐crystal: From heterogeneous structure to multiple functions

“…Nickl and Henisch first reported the incorporation of inorganic silica gel networks inside calcite crystals 58 . Subsequently, polymer gel networks, such as agarose (a polysaccharide), 17,27,59 polyacrylamid, 60 N‐isopropylacrylamide (NIPAM)‐based crosslinked copolymer, 61 organic silicone, 18,26 and conjugated polymer, 36 were found to be incorporated into a variety of single‐crystals including both inorganics (e.g., calcite, 16,62,63 potassium dihydrogen phosphate [KDP], 28,64 metal halides 24,34,64,65 and PbS 24 ) and organics (e.g., glycine, 25 calcium tartrate tetrahydrate, 25 polycyclic aromatic hydrocarbons, 26 fullerene, 36 and proteins 18,27,66 ). In contrast to the occlusion of isolated aggregates where guest particles distributed inside a single‐crystal individually, gel networks could retain their continuity after incorporation and, thus, create a bicontinuous structure within a crystal composite, which was illustrated by Li et al in 2009 17 .…”