Silica Biomorphs: Complex Biomimetic Hybrid Materials from “Sand and Chalk”

Abstract

Biomineralization can afford crystal frameworks of great diversity and utmost complexity, frequently featuring hierarchical structures and morphologies beyond any crystallographic restrictions. The formation of such architectures is usually directed by organic molecules or matrices, which modify crystallization in a deliberate manner. Their influence often leads to sinuous forms, which, by intuition, suggest the presence of life and distinguish these minerals from their inanimate, mostly euhedral counterparts. However, such a strict distinction does not hold. In fact, smooth curvature and higher-order structuring can occur also in purely inorganic environments: simply by precipitating alkaline earth carbonates in silica-containing media, aggregates of highly oriented carbonate nanocrystals can be obtained that display striking [a] Physical

Crystallographic orientation inhomogeneity and crystal splitting in biogenic calcite

“…In fact, the available EBSD data are qualitatively identical. A similar process was described by García-Ruiz et al [27] in the so-called witherite biomorphs, which show repeated processes of crystal splitting during growth (see also review in [28]). These authors interpreted these processes according to previous models [29], which establish that nonabsorbable polymer impurities adhering at the growth front cause the formation of new crystals which are slightly misoriented with respect to the crystalline lattice.…”

New insights into the early stages of silica-controlled barium carbonate crystallisation

“…[5][6][7] Such studies are typically inspired by natural biomineralisation, where an organic matrix controls the crystallisation of inorganic matter to produce superior hybrid structures. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] Under the influence of dissolved silicate as a crystallisation modifier, metal carbonates (usually BaCO 3 ) can indeed assemble spontaneously into a range of sinuously shaped non-crystallographic aggregates (such as regular helicoids), which mimic products from biomineralisation closely in terms of morphology and internal hierarchy, and therefore were termed "silica-carbonate biomorphs". Among these, the processes observed during precipitation of alkaline-earth carbonates into alkaline, silica-containing media are probably the most prominent and well-studied case.…”

“…Among these, the processes observed during precipitation of alkaline-earth carbonates into alkaline, silica-containing media are probably the most prominent and well-studied case. 17,24,27 After a recent surge of interest in this field, [18][19][20][21][22][23][24][25][26][27][28][29][30][31] it has been proposed that the formation of biomorphs is driven by an autocatalytic co-precipitation cycle, in which the components are alternately mineralised due to their opposite trends of solubility with pH. 16,32,33 The structural complexity of these peculiar materials relies on the fact that they are constituted of a multitude of uniform carbonate nanocrystals, which are largely co-oriented and thus generate mesoscopic order in the mature aggregates (as a third level of hierarchy in addition to molecular ordering on the nanometrescale and morphological control on the micron-scale).…”

Biological Crystallization

“…Conversely, knowledge obtained from pattern formation of self-assembled complex materials synthesized in the laboratory (for instance, inorganic biomorphs [252,253]) will be very useful to understand possible morphogenetic and textural pathways found by life. In the opinion of the authors, in the coming years there will be an increasing interest in the studying of self-organized, autocatalytic processes leading to the complex structures recently found in many organisms, including, for instance, 3D mesophases.…”