Biomimetic crystallization of biomorphs and chemical gardens: Understanding their formation and studying their self-motion
Abiotic crystallization is typically described by classical models to form geometric shapes with flat faces, sharp edges, and well defined angles. This is in stark contrast to crystallization routes used by living systems which instead grows smoothly curved shapes such as teeth, bone, and nacre. Such morphological distinctions have been applied to determine the biogenicity of structures found in ancient rocks. However, laboratory experiments in far-from-equilibrium systems are able to precipitate similar curvilinear morphologies previously only prescribed to living organisms thus blurring the line between structures derived from biotic and abiotic origins. The first example I will discuss is the crystallization of metal carbonate and silica microstructures known as “biomorphs”. They are composed of thousands of coaligned nanorods that self-organize into larger life-like shapes such as leaf-like sheets, helices, funnels, and flowers. At the nanoscale, the growing crystallization front forms from the addition of smaller nanodot building units that merge into the elongated rod shape. At the microscale, the pseudo two-dimensional sheet shape can be simulated using reaction-diffusion equations. Finally, the hierarchical ordering is extended into the centimeter scale with the merging of neighbouring biomorphs at the air-solution interface. The second example is chemical gardens. Formed from steep chemical gradients between a metal salt and a solution of silicate, the final result is hollow tubes which resemble filaments found in many geological settings. This quick and easy production process for generating tubes can be exploited by controlling the composition of the final material to create self-moving chemical gardens.
